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First published online January 23, 2009
doi: 10.1242/10.1242/dev.016816
1 Department of Biology, Trinity Western University, 7600 Glover Road, Langley,
BC V2Y 1Y1, Canada.
2 Department of Molecular Biology and Biochemistry, 8888 University Drive, Simon
Fraser University, Burnaby, BC V5A 1S6, Canada.
* Author for correspondence (e-mail: stringha{at}twu.ca)
Accepted 9 December 2008
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SUMMARY |
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TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
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Key words: Cell migration, Axonal guidance, Cytoskeleton, ARP2/3 complex, C. elegans
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INTRODUCTION |
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TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
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;
Ishii et al., 1992), the
SLT-1/SLIT cue (Hao et al.,
2001) and its multifunctional receptor SAX-3/ROBO
(Ghenea et al., 2005;
Levy-Strumpf and Culotti,
2007; Zallen et al.,
1998), WNTs and their associated FZ receptors
(Pan et al., 2006), and growth
factors such as EGL-17/FGF (Burdine et al.,
1997) and its receptor EGL-15/FGFR
(Birnbaum et al., 2005;
Bulow et al., 2004;
DeVore et al., 1995). Besides
the identification of the signaling cues and their receptors, the machinery
required for the subcellular positioning of receptors is also being uncovered.
For example, recent evidence suggests that the kinesin-like molecule VAB-8
localizes SAX-3/ROBO to the cell surface to modulate the response to SLT-1
guidance cues (Watari-Goshima et al.,
2007), and that both MIG-2/RhoGTPase and VAB-8 are required for
the localization of the UNC-40 receptor
(Levy-Strumpf and Culotti,
2007).
At the leading edge of motile cells, local reorganization of the actin
cytoskeleton is mediated by the ARP2/3 complex, which nucleates the assembly
of branched actin filaments (Higgs and
Pollard, 2000; Volkmann et
al., 2001). Potential regulators of ARP2/3 include the ABI
proteins, initially discovered to function as downstream targets of ABL
non-receptor tyrosine kinases implicated in RAC-dependent cytoskeletal
organization and remodeling (Courtney et
al., 2000; Funato et al.,
2004; Jenei et al.,
2005; Stradal et al.,
2001), in addition to processes such as cell migration, neuronal
development, growth cone pathfinding and endocytosis
(Courtney et al., 2000;
Grove et al., 2004;
Ibarra et al., 2005;
So et al., 2000). ABI family
members localize to the actin-rich tips of lamellipodia and filopodia, and are
widely expressed in the developing murine nervous system
(Courtney et al., 2000;
Stradal et al., 2001). ABI
forms part of the pentameric WAVE complex together with NAP-1, PIR121/SRA-1,
HSPC300 and WAVE, which has been shown to mediate actin remodeling through
ARP2/3 (Bompard and Caron,
2004; Takenawa and Suetsugu,
2007). The WAVE complex members WVE-1, GEX-2 (SRA-1) and GEX-3
(NAP-1) have been characterized in C. elegans. GEX-2 and GEX-3
colocalize to cell boundaries during embryogenesis and interact physically
(Soto et al., 2002), and loss
of WVE-1 or the GEXs results in defective hypodermal cell migration,
incomplete ventral enclosure during morphogenesis, and embryonic lethality
(Soto et al., 2002;
Withee et al., 2004).
Additionally, ventral enclosure defects in WVE-1 and GEX mutants are
reminiscent of those found in RAC and ARP2/3 mutant animals, suggesting that a
conserved pathway involving RAC, the WAVE complex and ARP2/3 is maintained
during embryogenesis in C. elegans
(Sawa and Takenawa, 2006;
Soto et al., 2002;
Withee et al., 2004).
While much has been uncovered with respect to the signaling events at the
cell surface and the mechanics of actin filament assembly, relatively little
is known about the proteins that integrate guidance information to instruct
cytoskeletal reorganization. One candidate is UNC-53, initially discovered to
control the migration of a subset of cells and cellular extensions along the
anterior to posterior axis in C. elegans. Hypomorphic alleles of
unc-53 display reduced extension and guidance defects in the
outgrowth of the mechanosensory neurons
(Hekimi and Kershaw, 1993),
the excretory canals (Hedgecock et al.,
1990; Stringham et al.,
2002) and the sex muscles, the latter resulting in an egg-laying
defective phenotype in hermaphrodites
(Stringham et al., 2002). By
contrast, overexpression of UNC-53 in muscle cells results in exaggerated
outgrowth during embryogenesis (Stringham
et al., 2002). UNC-53 interacts genetically and physically with
the SH2-SH3 adaptor protein SEM-5 (GRB-2), a mediator of EGL-15/FGFR signaling
in sex myoblast migration in C. elegans
(Chen et al., 1997;
Stringham et al., 2002),
suggesting a role for UNC-53 in signal transduction. UNC-53 also contains
several domains observed in actin-binding proteins, suggesting a possible
function in actin cytoskeleton dynamics
(Stringham et al., 2002).
Roles in cell migration have also been documented for the vertebrate
homologs of UNC-53. Three human UNC-53 homologs (NAV1, NAV2 and NAV3; Neuron
Navigator 1, 2 and 3) have been identified
(Maes et al., 2002;
Merrill et al., 2002). The
most similar homolog to UNC-53, NAV2, is retinoic acid inducible in the
developing nervous system (Merrill et al.,
2002), and hypomorphic mice have sensory deficits subsequent to
morphological defects that are consistent with a role for NAV2 in neuron
outgrowth (Peeters et al.,
2004). NAV1 associates with microtubule plus-ends on developing
neuronal growth cones and is required for netrin-induced directionality in
pontine neurons (Martinez-Lopez et al.,
2005). The NAV proteins are also expressed in a range of adult
tissues, including brain, heart and kidney, in both mice and humans following
outgrowth (Maes et al., 2002;
Martinez-Lopez et al., 2005;
Peeters et al., 2004), and
Nav3 mRNA is localized to synapses at neuromuscular junctions
(Kishi et al., 2005).
In this study, we show that the largest UNC-53 isoforms are expressed in several migrating cells in which UNC-53 is required, as well as in adult cells. Additionally, we show that UNC-53 binds the C. elegans ABI-1 homolog, and that loss of ABI-1 leads to migration defects similar to those found when unc-53, wve-1, nck-1 and arx-2 (arp2) are removed. We find that UNC-53 and ABI-1 have an overlapping pattern of expression, and that disruption of the interaction between UNC-53 and ABI-1 impairs longitudinal guidance. Finally, we propose a model for how UNC-53 might function with ABI-1 and the ARP2/3 complex in cytoskeletal remodeling.
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MATERIALS AND METHODS |
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SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
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). Strains used in this study include: )]; )]; )];
Yeast two-hybrid assays
A NdeI-NcoI fragment of the unc-53 cDNA
(nucleotides 64-480 corresponding to amino acids 1 to 139) was subcloned into
pAS2 (Matchmaker, Clontech Laboratories) to generate pVA200. Using pVA200 as
bait and a mixed stage C. elegans cDNA library as prey (gift of Bob
Barstead, Oklahoma Medical Research Foundation, Oklahoma, USA) candidate
binding partners were identified in a yeast two-hybrid screen by assaying for
growth on triple drop-out media (-Trp-Leu-His) and the β-galactosidase
activity of doubly transformed yeast Y190 cells as described
(Aspenstrom and Olson, 1995).
Six of the positives corresponded to the B0336.6/abi-1 locus. pVA305
corresponds to the shortest abi-1 cDNA isolated in the screen cloned
into the pSE1107 vector, coding for amino acids 12 to 427 of ABI-1, and was
used for subsequent biochemical studies.
In vitro binding assays
ABI-1::GST and UNC-53N::6xHis protein were purified from BL21(DE3)
E. coli harboring pVA600 and pVA63, respectively. pVA600 was
generated by inserting a 1.3-kb XhoI fragment from pVA305 into
pGEX4T2 (Invitrogen). Recombinant proteins ABI-1::GST or GST were expressed
and purified according to the manufacturer's instructions (Invitrogen), with
modifications (Frangioni and Neel,
1993). Ten micrograms of ABI-1::GST or GST were applied to
glutathione resin for pull-down experiments. Total UNC-53N::6xHis
lysates (25 µg) were applied to ABI-1::GST or GST glutathione resin and
incubated at 4°C for 3 hours. Following incubation, beads were washed four
times with 20 mM Tris pH 7.4, 0.1 mM EDTA, 300 mM NaCl and 0.1% Triton X-100,
and bound proteins were extracted and analyzed by SDS-PAGE and western
blotting.
RNA interference and mutant analysis
RNAi experiments were performed by feeding
(Kamath et al., 2001), using
RNAi clones obtained from Geneservice, with the exception of the
unc-53L RNAi clone pVA504, which was generated by cloning a 0.3-kb
XhoI-NcoI PCR fragment corresponding to nucleotides 1 to 280
(exons 1-4) of the unc-53 cDNA from pTB113
(Stringham et al., 2002) in
tandem into pPD129.36 (gift of Andrew Fire, Stanford University School of
Medicine, Stanford, USA). Animals carrying the ppgp-12::gfp reporter
were scored for excretory canal outgrowth with respect to the position of the
gonad arms, the vulva and the anus. Neuronal RNAi was carried out using either
the neuronal enhanced sensitive strain eri-1(mg366); pmec-4::gfp for
mechanosensory neurons (Kennedy et al.,
2004), or nre-1(hd20); lin15b(hd126) for motoneurons. The
anterior process of the PLM neuron was scored as abnormal if the stop point
was posterior to the wild-type position at the mid-body. Ventral cord
motoneurons commissures were determined to have defects if two or more axons
exhibited ectopic lateral branching or stalling and were unable to reach the
dorsal cord.
Preparation of UNC-53 and ABI-1 polyclonal antisera
A SacI-NcoI fragment of the unc-53 cDNA
(nucleotides 64-480) that corresponds to amino acids 1 to 139 was subcloned
into the expression vector pRSET (Amersham Pharmacia) to generate pVA63, which
was then expressed in E. coli BL21 cells according to manufacturer's
protocols (Invitrogen). Purified protein was emulsified in Titre Max Gold and
injected into a female New Zealand white rabbit. The antiserum collected was
active at titers of 1:30,000 on western blots of recombinant fusion protein.
The specificity of PAb-UNC-53N was confirmed by staining animals that
ectopically express UNC-53 in the intestine under control of the
hsp-16 promoter (Stringham et
al., 1992). Whereas no staining was observed in control animals,
strong staining in the cytoplasm of intestinal cells was observed after heat
shock. For the generation of ABI-1 polyclonal antibody (PAb-ABI-1), a
synthesized peptide (DYNSIYQPDRYGTIRAGGR) containing amino acids 256-274 from
ABI-1 was coupled to keyhole limpet hemocyanin (KLH) and used to immunize
guinea pigs (Open Biosystems). Anti-sera were affinity purified towards the
ABI-1 peptide and were active at a dilution of 1:10,000 on western blots of
recombinant protein.
|
). PAb-UNC-53N was used at 1:500 dilution and
PAb-ABI-1 antibody at 1:100, with secondary anti-Rabbit IgG
(Invitrogen Molecular Probes) and anti-Guinea Pig IgG (Open Biosystems) used
at 1:500 and 1:400, respectively. Anti-GFP immunostaining was performed using
chick anti-GFP primary at 1:100 with secondary rabbit anti-Chick IgG at 1:400
(Millipore, USA), directed towards the VA97 strain. VA97 contains the
extrachromosomal array pmEx97 generated by co-injecting 1 ng/µl of
the pabi-1::abi-1::gfp, containing 0.5 kb upstream of abi-1
and the entire abi-1 locus fused to GFP with the pRF4 co-injection
marker at 100 ng/µl. Expression of abi-1 and unc-53L were
also determined using promoter GFP transcriptional fusions. The
pabi-1::gfp fusion (BC10129) included 275 bp upstream of
abi-1 fused to GFP, whereas 2.9 kb upstream of unc-53 was
fused to GFP to generate BC14371 (McKay et
al., 2003). Specimens were viewed with Olympus IX81 or Leica DMLB
fluorescence microscopes using appropriate filter sets.
Cell autonomy and overexpression experiments
Rescue of the abi-1(tm494) posterior canal defects was achieved by
co-injecting 10 ng/µl of the PCR fusion ppgp12::abi-1, containing
the pgp-12 promoter (Zhao et al.,
2005) fused to full-length abi-1, with 100 ng/µl of
the plasmid pDPY-30::NLS::DSRED2 (Cordes
et al., 2006) into the strain VA74 to create vaEx91 and
vaEx92. unc-53(n152) posterior canal defects were rescued by
co-injecting the PCR fusion ppgp12::unc-53L (100 ng) with
pDPY-30::NLS::DSRED2 into VA106 and scoring transgenic unc-53(n152)
homozygous animals as described. UNC-53CH-expressing arrays
vaEx93-vaEx96 were generated by co-injecting
ppgp-12::unc-53CH::gfp containing the pgp-12 promoter fused
to the first 422 nucleotides of unc-53 cDNA from pVA63 and GFP at 100
ng/µl, along with 100 ng/µl of the plasmid pDPY-30::NLS::DSRED2
(Cordes et al., 2006) into the
strain BC06288. Excretory canal morphology was scored in young adult animals
co-expressing GFP and dsRED from all lines for general defects and for
posterior canal migration position, as described above.
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RESULTS |
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SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
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).
Several protein motifs are shared between UNC-53 and its orthologs, including
a calponin homology (CH) domain, two putative actin-binding sites of the LKK
motif, two coiled-coil regions, two polyproline-rich SH3-binding motifs, and
an AAA (ATPases associated with diverse cellular activities) domain
(Stringham et al., 2002). A
combination of alternative trans-splicing and cis-splicing events and the
presence of two intronic promoters gives rise to four large isoforms of UNC-53
(LA, LB, LC and LD), collectively referred to as UNC-53L, and two small
isoforms of UNC-53 (SA and SB), referred to as UNC-53S. Previous studies
indicate that the intronic promoters that transcribe UNC-53SA and UNC-53SB
have complementary non-overlapping expression patterns
(Stringham et al., 2002). To
characterize the expression of the UNC-53L isoforms, a promoter region 2.9-kb
upstream of the most 5' SL1 splice site of unc-53 was used, and
strong GFP expression was observed in the excretory cell, in neurons in head
and tail ganglia, and in several classes of ventral cord motoneuron
(Fig. 1C), as well as in the
sex myoblasts (Fig. 1D).
Immunostaining with an antibody raised against the translated product of the
first 5 exons of unc-53 (Fig.
1B) revealed UNC-53L protein localized in the cytoplasm of the
excretory cell (Fig. 1E), the
sex myoblasts, the anal muscles, the head neurons and the coelomocytes
(Fig. 1F). Expression was
detected at all developmental stages, including adults.
UNC-53L interacts with Abelson Interactor-1 (ABI-1)
Previous studies suggest that UNC-53 functions in signal transduction
during migration (Stringham et al.,
2002), yet few molecules known to interact directly with UNC-53
have been identified. Moreover, a phage cDNA devoid of the first four exons
was sufficient to partially rescue the Unc and Egl phenotypes of
unc-53 mutants (Stringham et al.,
2002). Therefore, we wondered what molecules might interact with
the N-terminal of UNC-53, as this region is conserved in NAV2 and NAV3. To
answer this question, we screened for interactors in a C. elegans
yeast two-hybrid library, using the N terminus (UNC-53N) as bait
(Fig. 1B). Of the candidates
isolated, six corresponded to the B0336.6 genomic locus, the C. elegans
abi-1 (Abelson Interactor-1) homolog
(Fig. 2A). Of the
abi-1 clones isolated, the smallest cDNA encoded amino acids 12-427,
thereby excluding the SH3 region of ABI-1 as a required domain for UNC-53
binding. Moreover, the UNC-53 bait contained only the first 139 amino acids of
UNC-53L, and thus was devoid of the polyproline repeats that are typical of
SH3-binding domains. Therefore, the interaction between ABI-1 and UNC-53 does
not appear to be mediated by SH3 binding. The yeast two-hybrid data was
further confirmed by GST pull down (Fig.
2B), demonstrating that the interaction between ABI-1 and UNC-53
is direct.
Characterization of abi-1
BLAST analysis revealed the presence of a single abi-1 gene in
C. elegans. The abi-1 genomic locus spans 2624 bp and
contains five exons encoding a predicted polypeptide of 469 amino acids
(Fig. 3). C. elegans
ABI-1 is a conserved protein that is homologous to ABI-1 of C.
briggsae (CAE64316), Homo sapiens (NP_005461), Mus
musculus (Q3TJ64) and Drosophila melanogaster (NP_477263). The
highest degree of homology resides within several recognizable protein domains
suggestive of function. Near the N terminus is a Q-SNARE motif
(Echarri et al., 2004), which
in the case of mammalian ABI-1, has been shown to be involved in growth factor
receptor endocytosis and to bind Syntaxin 1
(Echarri et al., 2004;
Tanos and Pendergast, 2007).
Partially overlapping with the Q-SNARE motif is an ABL-homeodomain homologous
region that is similar to the DNA-binding region of homeodomain proteins, and
which is found exclusively in adaptor proteins that interact with Abl-family
tyrosine kinases (Dai and Pendergast,
1995). Additionally, C. elegans ABI-1 contains a
serine-rich region and multiple polyproline-rich putative SH3-binding motifs.
A single SH3 domain is located at the C terminus of C. elegans ABI-1
and this domain has been shown to mediate the interaction of ABI-1 with
Abelson tyrosine kinases (Shi et al.,
1995), and to control the ability of ABL to phosphorylate
downstream targets, including mammalian enabled (Mena)
(Tani et al., 2003). The
abi-1(tm494) allele (Mitani Laboratory, National Bioresource Project)
carries a 684-bp deletion beginning at nucleotide 1659 in exon 4
(Fig. 3A), and encodes a
predicted truncated product ending at proline 350 followed by TGPVRL and a
premature stop codon, resulting in a 356 amino acid product
(Fig. 3C).
|
), the
ALN/PLN and ALM/PLM axons, and the excretory cell
(Stringham et al., 2002). To
determine whether the observed interaction between ABI-1 and UNC-53 is
relevant in vivo, the migration phenotypes of abi-1 were
characterized. The migration and outgrowth of both the anterior and posterior
excretory canal processes were visualized using the transgenic reporter
ppgp-12::gfp, which is expressed exclusively in the
excretory cell from the 3-fold embryonic stage onwards
(Zhao et al., 2005). The
excretory cell (EC) is a large H-shaped cell in C. elegans and
represents an excellent cell type for the study of both dorsoventral and
anteroposterior migrations. During its outgrowth, two processes emerge from
the EC body and migrate dorsolaterally from the ventral side of the terminal
pharyngeal bulb towards the lateral hypodermis. In wild-type animals, when the
canals reach the lateral hypodermis they cross the hypodermal basement
membrane and bifurcate, sending processes anteriorly to the head and
posteriorly to the tail (Nelson et al.,
1983) (Fig.
4A).
By contrast, although the excretory cell body is positioned normally in
unc-53(n166) animals, both the anterior and posterior canals are
severely truncated. In the case of the anterior processes, they terminate
close to the excretory cell body, often not extending further than the
anterior pharyngeal bulb, while the majority of posterior canals grow out
approximately half way, terminating at the level of the vulva
(Fig. 4B). These phenotypes
were also observed by unc-53(rnai) and in unc-53(n152)
mutants (Fig. 4C,H). Notably,
defects in the posterior migrations of the excretory canals in
unc-53(n166) animals were equally as strong as in heterozygous
n166/mnDf87 worms (Fig.
4H), suggesting that unc-53(n166), which removes a
coiled-coil domain, an LKK motif and the AAA cassette from all isoforms
(Fig. 1B), is a null allele for
this phenotype. To determine the role of abi-1 in excretory cell
migration, we examined the length of canals in abi-1(tm494) and by
RNAi. Animals carrying the abi-1(tm494) deletion are superficially
wild type, with the exception of a mild uncoordination defect, characterized
by an increased frequency of backing. Although the cell body of the excretory
cell in abi-1(tm494) is positioned normally, examination of the
posterior excretory canals of tm494 revealed a failure of the
majority to exit the gonad region (Fig.
4E,H). The position of the excretory cell body was also normal in
abi-1(rnai) animals, but a range of migration defects were observed,
including truncated anterior and posterior excretory canals
(Fig. 4C,H), which is
reminiscent of unc-53 loss-of-function alleles, in addition to
dorsoventral defects not observed in unc-53 mutants (data not shown)
and excretory cell cysts (Fig.
4G). Notably, excretory canal defects were observed to be no more
severe in unc-53(n166); abi-1(tm494) double mutants than in
unc-53(n166) (Fig.
4H). Although the deletion in abi-1(tm494) results in a
truncated protein, the abi-1(tm494) allele behaves as a hypomorph, as
abi-1(rnai) exacerbates excretory canal defects in an
abi-1(tm494) background (data not shown). As is the case for the
abi-1(tm494); unc-53(n166) double mutant,
abi-1(rnai) in an unc-53(n166) background does not reduce
the extension of the posterior excretory canals beyond that of
unc-53(n166) alone (Fig.
4H), suggesting that these genes function within the same pathway
to control outgrowth of the posterior excretory canals. Previous work suggests
that unc-53 may function cell autonomously
(Stringham et al., 2002), so
given the physical interaction observed between UNC-53 and ABI-1, we
hypothesized that ABI-1 and UNC-53 may both function within the excretory
canals. Consistent with this prediction, full-length abi-1 and
unc-53 cDNA driven by the ppgp-12 excretory cell-specific
promoter was sufficient to rescue the canal outgrowth defects of
abi-1(tm494) and unc-53(n152) mutants, respectively
(Fig. 4H).
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ABI-1 and UNC-53 have overlapping expression patterns
Given the physical interaction between UNC-53 and ABI-1, the shared
phenotypes, and because UNC-53 has been shown to function cell autonomously
(Stringham et al., 2002), we
expected that ABI-1 would be found in the same cells as UNC-53. To determine
the expression pattern of ABI-1, we generated transcriptional and
translational GFP-reporter fusions of abi-1 and raised a polyclonal
antibody towards a peptide corresponding to amino acids 256 to 274 of ABI-1.
Collectively, these approaches revealed that ABI-1 is expressed in a number of
neurons within the nerve ring and head, including the amphid interneurons
AIYL/R (Fig. 6A), the RMEL/R
motoneurons (Fig. 6B),
coelomocytes (Fig. 6D), and
several classes of ventral cord motoneuron, where it is localized throughout
the cell bodies, dendrites and commissural axons extending to the dorsal cord
(Fig. 6C), similar to the
pattern of expression observed for UNC-53L transcripts
(Fig. 1C).
ABI-1 and UNC-53 control dorsoventral migrations of the motoneurons
The expression of both UNC-53 and ABI-1 in motoneurons suggests that both
genes may have a role in the guidance and outgrowth of these cells. Consistent
with this, RNAi of abi-1 revealed multiple defects in motoneurons,
including the presence of ectopic branches in commissures, giving rise to
disorganized neural networks (Fig.
6F,G). Frequently, dorsally directed axons were unable to complete
their migration to the dorsal cord (32%, n=90) and either bifurcated
prematurely, extending lateral processes anteriorly and posteriorly, or
produced several knob-like structures in disoriented processes, which was
suggestive of growth cone stalling (Fig.
6F). Defasciculation of the ventral cord was also frequently
observed (13%, n=90; Fig.
6H). Similar phenotypes have been reported in unc-53,
where approximately 13% of motoneuron commissures are abnormal and fail to
reach the dorsal cord (Stringham et al.,
2002).
|
). To
determine whether the long-isoform of UNC-53 is required for posterior EC
migration, we directed RNAi toward exons 1-4 of UNC-53 and found that
knockdown of UNC-53L is sufficient to impair longitudinal guidance even with
the short isoforms present (Fig.
7A), a finding that is consistent with UNC-53L function and
expression in the EC. To test further whether the interaction between UNC-53
and ABI-1 is functionally important, we overexpressed the CH domain of UNC-53L
in the excretory cell. At a low frequency, various canal defects were
observed, including ectopic outgrowths, cysts and the truncation of posterior
canals (Fig. 7B-D), phenotypes
that are reminiscent of abi-1 knockdown. This suggests that
expression of the CH domain alone may act in a dominant-negative fashion to
sequester endogenous ABI-1 and prevent functional interaction with wild-type
UNC-53 in vivo.
Mutations in actin-polymerization proteins disrupt longitudinal migration
The extension of cellular processes is mediated primarily through the
extension of growth cones, highly motile ends at cell tips that are undergoing
constant cytoskeletal reorganization. ABI-1 functions in cytoskeletal
organization through its ability to regulate the ARP2/3 complex to induce
actin polymerization. Evidence suggests that ABI-1 may regulate ARP2/3 through
a complex with WAVE in response to RAC
(Bompard and Caron, 2004;
Stradal et al., 2004) or by
binding WASP (Innocenti et al.,
2002). To test whether these and other proteins known to function
with ABI-1 are involved in longitudinal migration in C. elegans, we
analyzed the excretory canal phenotypes of mutant and RNAi-treated animals. Of
the genes tested, wve-1(rnai), nck-1(ok694) and arx-2(rnai)
produced excretory canal migration phenotypes reminiscent of unc-53
and abi-1 mutants (Fig.
8), while wsp-1 and abl-1 did not. Notably, none
of the genes tested had more severe phenotypes either alone or in the
background of the null unc-53 allele (n166), suggesting that
the initial trajectory of the posterior excretory canals to the anterior gonad
arm is unaffected by loss of unc-53, abi-1 or known abi-1
interactors. Interestingly, nck-1 is expressed in the excretory cell
and ventral cord motoneurons (Fig.
9), two cell types affected in unc-53 and abi-1
mutant backgrounds. We also examined the potential role of these proteins in
the migration of PLM axons and found that RNAi had modest effects
(Table 1).
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DISCUSSION |
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TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
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;
Grove et al., 2004). ABI-1
localizes to the motile tips of lamellipodia and filopodia, which is
consistent with a role for ABI-1 in actin-polymerization events
(Echarri et al., 2004;
Stradal et al., 2001).
Surprisingly, ABI-1 expression was not seen in the excretory cell as had been
expected given the physical interaction between UNC-53 and ABI-1, and because
UNC-53 is expressed in the EC (Stringham
et al., 2002). It is possible that endogenous levels of ABI-1 are
very low and/or that sequences required for expression in these cells were
absent in the reporter fusions. Nonetheless, the ability of both ABI-1 and
UNC-53 to rescue outgrowth when expressed specifically in the excretory cell,
coupled with the finding that disruption of the UNC-53-ABI-1 interaction
interfered with canal outgrowth, strongly suggest that ABI-1 and UNC-53
function together in the excretory cell.
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). Circumferential guidance of growth cones in C.
elegans is controlled by multiple guidance cues, including UNC-6/netrin,
which is expressed ventrally, where it attracts UNC-40/DCC-expressing growth
cones and repels those expressing both UNC-40 and UNC-5
(Wadsworth, 2002).
Interestingly, UNC-34/Ena, which controls multiple aspects of cell migration
and guidance (Gitai et al.,
2003; Shakir et al.,
2006; Withee et al.,
2004; Yu et al.,
2002), can suppress ectopic UNC-5 expression, placing UNC-34
downstream of UNC-5 in circumferential guidance
(Colavita and Culotti, 1998).
Mammalian Ena function is partially dependent on ABI proteins, and could
suggest a role for ABI-1 in circumferential guidance in worms.
(Comer et al., 1998;
Juang and Hoffmann, 1999;
Tani et al., 2003).
ABI-1 interactors and ARP2/3 control longitudinal migration
The migration defects observed in both abi-1 and unc-53
mutants is consistent with the biochemical interaction observed between them.
Moreover, the phenotype of the ABI-1 interactor nck-1 in the
excretory cell suggests a similar role for nck-1. The adaptor NCK-1
exerts its influence in part through the modulation of WVE-1, as NCK-1 and/or
RAC activation is able to release SCAR-1 from an inhibitory complex containing
ABI-2 to activate the ARP2/3 complex (Eden
et al., 2002). Therefore, it was not surprising that similar
longitudinal guidance phenotypes were also observed in wve-1 and
arx-2, suggesting that the primary mode of unc-53 action in
these migrations is mediated through conserved interactions. Consistent with
this view, both UNC-53 and the RAC activator UNC-73/TRIO have been implicated
in an EGL-17/FGF-independent signaling mechanism controlling sex myoblast
migration (Chen et al., 1997),
suggesting that modulation of the ARP2/3 complex may be the crucial
determinant of actin filament assembly in this migration as well.
Interestingly, the first part of the posteriorly directed migration of the
excretory canals to the anterior gonad arm was intact for all genes tested,
suggesting that another mechanism independent of unc-53, abi-1 and
the ARP2/3 complex might be driving the initial posterior outgrowth of the
canals.
Experiments in both cell culture and model systems reveal that cell shape
changes, and the extension of cellular processes are mediated through GTPases
of the RHO family, including CDC42 and RAC, which induce the formation of
lamellipodia and filopodia by interacting directly or indirectly with the WASP
family of proteins, resulting in the activation of the ARP2/3 complex and
directed actin nucleation (Bompard and
Caron, 2004; Stradal et al.,
2004; Takenawa and Suetsugu,
2007). For example, in C. elegans, loss of WSP-1 or WVE-1
disrupts hypodermal cell migration and ventral enclosure during embryogenesis,
phenotypes that are also characteristic of CED-10/RAC-1 mutants
(Lundquist et al., 2001) and
ARP2/3-complex knockdown (Sawa et al.,
2003). Moreover, the motoneuron guidance defects observed in
unc-53 and abi-1 animals are similar to those observed in
ced-10 and wve-1
(Lundquist et al., 2001;
Lundquist, 2003;
Withee et al., 2004),
consistent with a model in which these proteins operate together in
cytoskeletal remodelling. ABI-1 is a member of a complex consisting of WAVE-1
(WVE-1), GEX-2, GEX-3 and HSPC300 that promotes actin nucleation
(Innocenti et al., 2004;
Stroschein-Stevenson et al.,
2006). The defects in cell movements during morphogenesis reported
for gex-2 and gex-3
(Soto et al., 2002), and the
similarities in the phenotypes of abi-1 and wve-1 reported
here are consistent with a model in which these proteins form a similar
complex in C. elegans.
|
|
;
Stradal et al., 2004). ABI-1
seems to participate in both, binding through its N terminus to WAVE to
regulate membrane protrusion and macropinocytosis, and through its SH3 domain
to N-WASP to stimulate actin-dependent vesicular transport and endocytosis
(Innocenti et al., 2005). Thus
ABI-1 may be a central figure that regulates the proportion of actin filament
nucleation designated for particular processes by partitioning WASP versus
WAVE activation (Innocenti et al.,
2005). Our results indicate an essential role for WAVE as opposed
to WASP in longitudinal outgrowth in C. elegans.
A model for UNC-53-ABI-1 action
Previously, it was shown that UNC-53 interacts physically with SEM-5/GRB2
(Stringham et al., 2002), a
SH2-SH3 adapter involved in multiple RTK pathways, including FGFR
(Dixon et al., 2006), EGFR
(Moghal and Sternberg, 2003),
and IR (Hopper, 2006)
signaling. At present, it is unclear whether UNC-53 is a participant in one or
several signaling cascades. For example, whereas both unc-53 and
egl-15/FGFR are expressed in the migrating sex myoblasts
(Goodman et al., 2003),
egl-15 is not expressed in axons (where it regulates outgrowth) but
instead exerts its effect through the underlying hypodermis on which they
migrate (Bulow et al., 2004).
As UNC-53 is a cytoplasmic protein that functions cell autonomously, this
suggests that it does not act directly downstream of EGL-15/FGFR signaling in
neuronal cell migrations, but that it might be recruited by a different
receptor upstream of SEM-5/GRB2. Moreover, UNC-53, the cell-adhesion molecule
UNC-71/ADAM and UNC-73/TRIO, have all been implicated in a
EGL-17/FGF-independent signaling mechanism controlling sex myoblast migrations
(Chen et al., 1997), suggesting
non-FGFR signaling is involved in this pathway as well. Therefore the identity
of ligands and receptors upstream of the SEM-5/UNC-53 interaction in cell
migration remain elusive.
In this study, we found that a restricted region of the N terminus of
UNC-53 containing a CH domain was sufficient to bind ABI-1 in vitro, and that
the UNC-53-ABI-1 interaction mediated by this domain is required for
longitudinal cell outgrowth in vivo. CH domains are commonly found in proteins
involved in signal transduction and actin binding, and are classified by the
number and position of CH domains they contain
(Korenbaum and Rivero, 2002).
Type 1/2 CH domain proteins, such as 
-actinin, β-spectrin and
dystrophin, which function in actin bundling and membrane anchoring
(Broderick and Winder, 2005),
possess two N-terminal CH domains in tandem. The first Type 1 CH domain
mediates actin binding, whereas the second Type 2 CH domain may (1) stabilize
the actin interaction of the Type I domain, (2) localize the actin-binding
protein to the cytoskeleton, or (3) act as a scaffold for signal transduction
(Gimona et al., 2002). By
contrast, UNC-53 possesses a single N-terminal CH domain, and in this respect
is more closely related to Type 3 CH domain-containing proteins, such as VAV,
IQGAP, PIX and SM22 (Gimona et al.,
2002; Stradal et al.,
1998). Type 3 CH domains function like Type 2 CH domains in that
they act as scaffolds that bind proteins involved in the control of
cytoskeletal change and signal transduction
(Galkin et al., 2006;
Gimona and Mital, 1998;
Korenbaum and Rivero, 2002;
Leinweber et al., 1999). In
such a model, UNC-53 may be a scaffold that coordinates upstream signals
transduced through SEM-5/GRB2 to ABI-1 and the actin cytoskeleton.
The complexity of the unc-53 locus gives rise to several protein
isoforms that are regulated by different promoters and that display
non-overlapping tissue-specific expression patterns
(Choi and Newman, 2006;
Stringham et al., 2002). The
smaller isoforms are under the control of intronic promoters, producing
polypeptides that lack CH domains, which might limit their ability to interact
with ABI-1 and significantly alter their function. Interestingly, both murine
and human NAV1 also lack CH domains (unlike mouse and human NAV2 and NAV3),
and are the only NAV genes downregulated in brain following development
(Maes et al., 2002;
Peeters et al., 2004),
suggesting a possible post-developmental role for the NAVs possessing CH
domains. Understanding the relationship between the tissue specificity and the
domain organization of the various isoforms of UNC-53 and the vertebrate NAVs
should shed light on the importance of the CH domains in these proteins and
how they operate.
|
Footnotes |
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REFERENCES |
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TOP
SUMMARY
INTRODUCTION
MATERIALS AND METHODS
RESULTS
DISCUSSION
REFERENCES |
|---|
Aspenstrom, P. and Olson, M. F. (1995). Yeast
two-hybrid system to detect protein-protein interactions with Rho GTPases.
Methods Enzymol. 256,228
-241.[Medline]
Bettinger, J. C., Lee, K. and Rougvie, A. E.
(1996). Stage-specific accumulation of the terminal
differentiation factor LIN-29 during Caenorhabditis elegans
development. Development
122,2517
-2527.[Abstract]
Birnbaum, D., Popovici, C. and Roubin, R.
(2005). A pair as a minimum: the two fibroblast growth factors of
the nematode Caenorhabditis elegans. Dev.
Dyn. 232,247
-255.[CrossRef][Medline]
Bompard, G. and Caron, E. (2004). Regulation of
WASP/WAVE proteins: making a long story short. J. Cell
Biol. 166,957
-962.
Brenner, S. (1974). The genetics of
Caenorhabditis elegans. Genetics
77, 71-94.
Broderick, M. J. and Winder, S. J. (2005).
Spectrin, alpha-actinin, and dystrophin. Adv. Protein
Chem. 70,203
-246.[CrossRef][Medline]
Bulow, H. E., Boulin, T. and Hobert, O. (2004).
Differential functions of the C. elegans FGF receptor in axon
outgrowth and maintenance of axon position. Neuron
42,367
-374.[CrossRef][Medline]
Burdine, R. D., Chen, E. B., Kwok, S. F. and Stern, M. J.
(1997). egl-17 encodes an invertebrate fibroblast growth
factor family member required specifically for sex myoblast migration in
Caenorhabditis elegans. Proc. Natl. Acad. Sci.
USA 94,2433
-2437.
Chen, E. B., Branda, C. S. and Stern, M. J.
(1997). Genetic enhancers of sem-5 define components of
the gonad-independent guidance mechanism controlling sex myoblast migration in
Caenorhabditis elegans hermaphrodites. Dev.
Biol. 182,88
-100.[CrossRef][Medline]
Choi, J. and Newman, A. P. (2006). A
two-promoter system of gene expression in C. elegans. Dev.
Biol. 296,537
-544.[CrossRef][Medline]
Colavita, A. and Culotti, J. G. (1998).
Suppressors of ectopic UNC-5 growth cone steering identify eight genes
involved in axon guidance in Caenorhabditis elegans. Dev.
Biol. 194,72
-85.[CrossRef][Medline]
Comer, A. R., Ahern-Djamali, S. M., Juang, J. L., Jackson, P. D.
and Hoffmann, F. M. (1998). Phosphorylation of Enabled by the
Drosophila Abelson tyrosine kinase regulates the in vivo
function and protein-protein interactions of Enabled. Mol. Cell.
Biol. 18,152
-160.
Cordes, S., Frank, C. A. and Garriga, G.
(2006). The C. elegans MELK ortholog PIG-1 regulates
cell size asymmetry and daughter cell fate in asymmetric neuroblast divisions.
Development 133,2747
-2756.
Courtney, K. D., Grove, M., Vandongen, H., Vandongen, A.,
LaMantia, A. S. and Pendergast, A. M. (2000). Localization
and phosphorylation of Abl-interactor proteins, abi-1 and
abi-2, in the developing nervous system. Mol. Cell.
Neurosci. 16,244
-257.[CrossRef][Medline]
Dai, Z. and Pendergast, A. M. (1995). Abi-2, a
novel SH3-containing protein interacts with the c-Abl tyrosine kinase and
modulates c-Abl transforming activity. Genes Dev.
9,2569
-2582.
DeVore, D. L., Horvitz, H. R. and Stern, M. J.
(1995). An FGF receptor signaling pathway is required for the
normal cell migrations of the sex myoblasts in C. elegans
hermaphrodites. Cell 83,611
-620.[CrossRef][Medline]
Dixon, S. J., Alexander, M., Fernandes, R., Ricker, N. and Roy,
P. J. (2006). FGF negatively regulates muscle membrane
extension in Caenorhabditis elegans.
Development 133,1263
-1275.
Echarri, A., Lai, M. J., Robinson, M. R. and Pendergast, A.
M. (2004). Abl interactor 1 (abi-1) Wave-binding and
SNARE domains regulate its nucleocytoplasmic shuttling, lamellipodium
localization, and Wave-1 levels. Mol. Cell. Biol.
24,4979
-4993.
Eden, S., Rohatgi, R., Podtelejnikov, A. V., Mann, M. and
Kirschner, M. W. (2002). Mechanism of regulation of
WAVE1-induced actin nucleation by Rac1 and Nck. Nature
418,790
-793.[CrossRef][Medline]
Frangioni, J. V. and Neel, B. G. (1993).
Solubilization and purification of enzymatically active glutathione
S-transferase (pGEX) fusion proteins. Anal. Biochem.
210,179
-187.[CrossRef][Medline]
Funato, Y., Terabayashi, T., Suenaga, N., Seiki, M., Takenawa,
T. and Miki, H. (2004). IRSp53/Eps8 complex is important for
positive regulation of Rac and cancer cell motility/invasiveness.
Cancer Res. 64,5237
-5244.
Galkin, V. E., Orlova, A., Fattoum, A., Walsh, M. P. and
Egelman, E. H. (2006). The CH-domain of calponin does not
determine the modes of calponin binding to F-actin. J. Mol.
Biol. 359,478
-485.[CrossRef][Medline]
Ghenea, S., Boudreau, J. R., Lague, N. P. and Chin-Sang, I.
D. (2005). The VAB-1 Eph receptor tyrosine kinase and
SAX-3/Robo neuronal receptors function together during C. elegans
embryonic morphogenesis. Development
132,3679
-3690.
Gimona, M. and Mital, R. (1998). The single CH
domain of calponin is neither sufficient nor necessary for F-actin binding.
J. Cell. Sci. 111,1813
-1821.[Abstract]
Gimona, M., Djinovic-Carugo, K., Kranewitter, W. J. and Winder,
S. J. (2002). Functional plasticity of CH domains.
FEBS Lett. 513,98
-106.[CrossRef][Medline]
Gitai, Z., Yu, T. W., Lundquist, E. A., Tessier-Lavigne, M. and
Bargmann, C. I. (2003). The Netrin receptor UNC-40/DCC
stimulates axon attraction and outgrowth through Enabled and, in parallel, Rac
and UNC-115/AbLIM. Neuron
37, 53-65.[CrossRef][Medline]
Goodman, S. J., Branda, C. S., Robinson, M. K., Burdine, R. D.
and Stern, M. J. (2003). Alternative splicing affecting a
novel domain in the C. elegans EGL-15 FGF receptor confers functional
specificity. Development
130,3757
-3766.
Grove, M., Demyanenko, G., Echarri, A., Zipfel, P. A., Quiroz,
M. E., Rodriguiz, R. M., Playford, M., Martensen, S. A., Robinson, M. R.,
Wetsel, W. C. et al. (2004). ABI2-deficient mice exhibit
defective cell migration, aberrant dendritic spine morphogenesis, and deficits
in learning and memory. Mol. Cell. Biol.
24,10905
-10922.
Hao, J. C., Yu, T. W., Fujisawa, K., Culotti, J. G.,
Gengyo-Ando, K., Mitani, S., Moulder, G., Barstead, R., Tessier-Lavigne, M.
and Bargmann, C. I. (2001). C. elegans Slit acts in
midline, dorsal-ventral, and anterior-posterior guidance via the SAX-3/Robo
receptor. Neuron 32,25
-38.[CrossRef][Medline]
Hedgecock, E. M., Culotti, J. G. and Hall, D. H.
(1990). The unc-5, unc-6, and unc-40 genes
guide circumferential migrations of pioneer axons and mesodermal cells on the
epidermis in C. elegans. Neuron
4, 61-85.[Medline]
Hekimi, S. and Kershaw, D. (1993). Axonal
guidance defects in a Caenorhabditis elegans mutant reveal
cell-extrinsic determinants of neuronal morphology. J.
Neurosci. 13,4254
-4271.[Abstract]
Higgs, H. N. and Pollard, T. D. (2000).
Activation by Cdc42 and PIP(2) of Wiskott-Aldrich syndrome protein (WASp)
stimulates actin nucleation by Arp2/3 complex. J. Cell
Biol. 150,1311
-1320.
Hopper, N. A. (2006). The adaptor protein
Soc-1/Gab1 modifies growth factor receptor output in Caenorhabditis
elegans. Genetics
173,163
-175.
Ibarra, N., Pollitt, A. and Insall, R. H.
(2005). Regulation of actin assembly by SCAR/WAVE proteins.
Biochem. Soc. Trans. 33,1243
-1246.[CrossRef][Medline]
Innocenti, M., Tenca, P., Frittoli, E., Faretta, M., Tocchetti,
A., Di Fiore, P. P. and Scita, G. (2002). Mechanisms through
which Sos-1 coordinates the activation of Ras and Rac. J. Cell
Biol. 156,125
-136.
Innocenti, M., Zucconi, A., Disanza, A., Frittoli, E., Areces,
L. B., Steffen, A., Stradal, T. E., Di Fiore, P. P., Carlier, M. F. and Scita,
G. (2004). Abi-1 is essential for the formation and
activation of a WAVE2 signaling complex. Nat. Cell
Biol. 6,319
-327.[CrossRef][Medline]
Innocenti, M., Gerboth, S., Rottner, K., Lai, F. P., Hertzog,
M., Stradal, T. E., Frittoli, E., Didry, D., Polo, S., Disanza, A. et al.
(2005). Abi-1 regulates the activity of N-WASP and WAVE in
distinct actin-based processes. Nat. Cell Biol.
7, 969-976.[CrossRef][Medline]
Ishii, N., Wadsworth, W. G., Stern, B. D., Culotti, J. G. and
Hedgecock, E. M. (1992). UNC-6, a laminin-related protein,
guides cell and pioneer axon migrations in C. elegans.
Neuron 9,873
-881.[CrossRef][Medline]
Jenei, V., Andersson, T., Jakus, J. and Dib, K.
(2005). E3B1, a human homologue of the mouse gene product
abi-1, sensitizes activation of Rap1 in response to epidermal growth
factor. Exp. Cell Res.
310,463
-473.[CrossRef][Medline]
Juang, J. L. and Hoffmann, F. M. (1999).
Drosophila Abelson interacting protein (dAbi) is a positive regulator
of Abelson tyrosine kinase activity. Oncogene
18,5138
-5147.[CrossRef][Medline]
Kamath, R. S., Martinez-Campos, M., Zipperlen, P., Fraser, A. G.
and Ahringer, J. (2001). Effectiveness of specific
RNA-mediated interference through ingested double-stranded RNA in
Caenorhabditis elegans. Genome Biol.
2, RESEARCH0002.
Kennedy, S., Wang, D. and Ruvkun, G. (2004). A
conserved siRNA-degrading RNase negatively regulates RNA interference in
C. elegans. Nature
427,645
-649.[CrossRef][Medline]
Kishi, M., Kummer, T. T., Eglen, S. J. and Sanes, J. R.
(2005). LL5beta: a regulator of postsynaptic differentiation
identified in a screen for synaptically enriched transcripts at the
neuromuscular junction. J. Cell Biol.
169,355
-366.
Korenbaum, E. and Rivero, F. (2002). Calponin
homology domains at a glance. J. Cell. Sci.
115,3543
-3545.
Leinweber, B. D., Leavis, P. C., Grabarek, Z., Wang, C. L. and
Morgan, K. G. (1999). Extracellular regulated kinase (ERK)
interaction with actin and the calponin homology (CH) domain of actin-binding
proteins. Biochem. J.
344,117
-123.[CrossRef][Medline]
Levy-Strumpf, N. and Culotti, J. G. (2007).
VAB-8, UNC-73 and MIG-2 regulate axon polarity and cell migration functions of
UNC-40 in C. elegans. Nat. Neurosci.
10,161
-168.[CrossRef][Medline]
Lundquist, E. A. (2003). Rac proteins and the
control of axon development. Curr. Opin. Neurobiol.
13,384
-390.[CrossRef][Medline]
Lundquist, E. A., Reddien, P. W., Hartwieg, E., Horvitz, H. R.
and Bargmann, C. I. (2001). Three C. elegans Rac
proteins and several alternative Rac regulators control axon guidance, cell
migration and apoptotic cell phagocytosis. Development
128,4475
-4488.
Maes, T., Barcelo, A. and Buesa, C. (2002).
Neuron navigator: a human gene family with homology to unc-53, a cell
guidance gene from Caenorhabditis elegans.
Genomics 80,21
-30.[CrossRef][Medline]
Martinez-Lopez, M. J., Alcantara, S., Mascaro, C.,
Perez-Branguli, F., Ruiz-Lozano, P., Maes, T., Soriano, E. and Buesa, C.
(2005). Mouse Neuron Navigator 1, a novel microtubule-associated
protein involved in neuronal migration. Mol. Cell.
Neurosci. 28,599
-612.[CrossRef][Medline]
McKay, S. J., Johnsen, R., Khattra, J., Asano, J., Baillie, D.
L., Chan, S., Dube, N., Fang, L., Goszczynski, B., Ha, E. et al.
(2003). Gene expression profiling of cells, tissues, and
developmental stages of the nematode C. elegans. Cold
Spring Harb. Symp. Quant. Biol. 68,159
-169.
Merrill, R. A., Plum, L. A., Kaiser, M. E. and Clagett-Dame,
M. (2002). A mammalian homolog of unc-53 is
regulated by all-trans retinoic acid in neuroblastoma cells and embryos.
Proc. Natl. Acad. Sci. USA
99,3422
-3427.
Moghal, N. and Sternberg, P. W. (2003). The
epidermal growth factor system in Caenorhabditis elegans.
Exp. Cell Res. 284,150
-159.[CrossRef][Medline]
Nelson, F. K., Albert, P. S. and Riddle, D. L.
(1983). Fine structure of the Caenorhabditis elegans
secretory-excretory system. J. Ultrastruct. Res.
82,156
-171.[CrossRef][Medline]
Pan, C. L., Howell, J. E., Clark, S. G., Hilliard, M., Cordes,
S., Bargmann, C. I. and Garriga, G. (2006). Multiple Wnts and
Frizzled receptors regulate anteriorly directed cell and growth cone
migrations in Caenorhabditis elegans. Dev.
Cell. 10,367
-377.[CrossRef][Medline]
Peeters, P. J., Baker, A., Goris, I., Daneels, G., Verhasselt,
P., Luyten, W. H., Geysen, J. J., Kass, S. U. and Moechars, D. W.
(2004). Sensory deficits in mice hypomorphic for a mammalian
homologue of unc-53. Brain Res. Dev. Brain
Res. 150,89
-101.[CrossRef][Medline]
Sawa, M. and Takenawa, T. (2006).
Caenorhabditis elegans WASP-interacting protein homologue WIP-1 is
involved in morphogenesis through maintenance of WSP-1 protein levels.
Biochem. Biophys. Res. Commun.
340,709
-717.[CrossRef][Medline]
Sawa, M., Suetsugu, S., Sugimoto, A., Miki, H., Yamamoto, M. and
Takenawa, T. (2003). Essential role of the C.
elegans Arp2/3 complex in cell migration during ventral enclosure.
J. Cell. Sci. 116,1505
-1518.
Shakir, M. A., Gill, J. S. and Lundquist, E. A.
(2006). Interactions of UNC-34 Enabled with Rac GTPases and the
NIK kinase MIG-15 in Caenorhabditis elegans axon pathfinding and
neuronal migration. Genetics
172,893
-913.
Shi, Y., Alin, K. and Goff, S. P. (1995).
Abl-interactor-1, a novel SH3 protein binding to the carboxy-terminal portion
of the Abl protein, suppresses v-Abl transforming activity. Genes
Dev. 9,2583
-2597.
So, C. W., So, C. K., Cheung, N., Chew, S. L., Sham, M. H. and
Chan, L. C. (2000). The interaction between EEN and
abi-1, two MLL fusion partners, and Synaptojanin and Dynamin:
implications for leukaemogenesis. Leukemia
14,594
-601.[CrossRef][Medline]
Soto, M. C., Qadota, H., Kasuya, K., Inoue, M., Tsuboi, D.,
Mello, C. C. and Kaibuchi, K. (2002). The GEX-2 and GEX-3
proteins are required for tissue morphogenesis and cell migrations in C.
elegans. Genes Dev.
16,620
-632.
Stradal, T., Kranewitter, W., Winder, S. J. and Gimona, M.
(1998). CH domains revisited. FEBS Lett.
431,134
-137.[CrossRef][Medline]
Stradal, T., Courtney, K. D., Rottner, K., Hahne, P., Small, J.
V. and Pendergast, A. M. (2001). The Abl interactor proteins
localize to sites of actin polymerization at the tips of lamellipodia and
filopodia. Curr. Biol.
11,891
-895.[CrossRef][Medline]
Stradal, T. E., Rottner, K., Disanza, A., Confalonieri, S.,
Innocenti, M. and Scita, G. (2004). Regulation of actin
dynamics by WASP and WAVE family proteins. Trends Cell
Biol. 14,303
-311.[CrossRef][Medline]
Stringham, E. G., Dixon, D. K., Jones, D. and Candido, E. P.
(1992). Temporal and spatial expression patterns of the small
heat shock (hsp16) genes in transgenic Caenorhabditis elegans.
Mol. Biol. Cell 3,221
-233.[Abstract]
Stringham, E., Pujol, N., Vandekerckhove, J. and Bogaert, T.
(2002). unc-53 controls longitudinal migration in C.
elegans. Development
129,3367
-3379.[Medline]
Stroschein-Stevenson, S. L., Foley, E., O'Farrell, P. H. and
Johnson, A. D. (2006). Identification of Drosophila
gene products required for phagocytosis of Candida Albicans.
PLoS Biol. 4,e4
.[CrossRef][Medline]
Takenawa, T. and Suetsugu, S. (2007). The
WASP-WAVE protein network: connecting the membrane to the cytoskeleton.
Nat. Rev. Mol. Cell. Biol.
8, 37-48.[CrossRef][Medline]
Tani, K., Sato, S., Sukezane, T., Kojima, H., Hirose, H.,
Hanafusa, H. and Shishido, T. (2003). Abl interactor 1
promotes tyrosine 296 phosphorylation of mammalian Enabled (Mena) by c-Abl
kinase. J. Biol. Chem.
278,21685
-21692.
Tanos, B. E. and Pendergast, A. M. (2007).
Abi-1 forms an epidermal growth factor-inducible complex with Cbl: role in
receptor endocytosis. Cell. Signal.
19,1602
-1609.[CrossRef][Medline]
Volkmann, N., Amann, K. J., Stoilova-McPhie, S., Egile, C.,
Winter, D. C., Hazelwood, L., Heuser, J. E., Li, R., Pollard, T. D. and
Hanein, D. (2001). Structure of Arp2/3 complex in its
activated state and in actin filament branch junctions.
Science 293,2456
-2459.
Wadsworth, W. G. (2002). Moving around in a
worm: Netrin UNC-6 and circumferential axon guidance in C. elegans.
Trends Neurosci. 25,423
-429.[CrossRef][Medline]
Watari-Goshima, N., Ogura, K., Wolf, F. W., Goshima, Y. and
Garriga, G. (2007). C. elegans VAB-8 and UNC-73
regulate the SAX-3 receptor to direct cell and growth-cone migrations.
Nat. Neurosci. 10,169
-176.[CrossRef][Medline]
Withee, J., Galligan, B., Hawkins, N. and Garriga, G.
(2004). Caenorhabditis elegans WASP and Ena/VASP
proteins play compensatory roles in morphogenesis and neuronal cell migration.
Genetics 167,1165
-1176.
Yu, T. W., Hao, J. C., Lim, W., Tessier-Lavigne, M. and
Bargmann, C. I. (2002). Shared receptors in axon guidance:
SAX-3/Robo signals via UNC-34/Enabled and a Netrin-independent UNC-40/DCC
function. Nat. Neurosci.
5,1147
-1154.[CrossRef][Medline]
Zallen, J. A., Yi, B. A. and Bargmann, C. I.
(1998). The conserved immunoglobulin superfamily member
SAX-3/Robo directs multiple aspects of axon guidance in C. elegans.
Cell 92,217
-227.[CrossRef][Medline]
Zhao, Z., Fang, L., Chen, N., Johnsen, R. C., Stein, L. and
Baillie, D. L. (2005). Distinct regulatory elements mediate
similar expression patterns in the excretory cell of Caenorhabditis
elegans. J. Biol. Chem.
280,38787
-38794.
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