|
|
|
|
|
|
|
||||
| Home Help Feedback Subscriptions Archive Search Table of Contents | ||||
First published online 23 January 2008
doi: 10.1242/dev.015529
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Centro de Biología Molecular Severo Ochoa, CSIC and UAM, Universidad Autónoma de Madrid, 28049, Madrid, Spain.
* Author for correspondence (e-mail: mruiz{at}cbm.uam.es)
Accepted 17 December 2007
 |
SUMMARY |
|---|
 TOP SUMMARY INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Key words: mind bomb 2, Drosophila, Founder myoblasts, Myoblast fusion, Myofibrillogenesis
|
INTRODUCTION |
|---|
|
TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
; Ruiz-Gómez and
Bate, 1997), whereas the unselected mesodermal cells become
fusion-competent myoblasts (FCMs) (Bate,
1993; Baylies et al.,
1998). The activation of lame duck (lmd) in FCMs
initiates the expression of genes exclusive to the FCM population, such as
sticks and stones (sns), and maintains the expression of the
myogenic differentiation gene Drosophila Myocyte enhancing factor 2
(Mef2) (Duan et al.,
2001; Ruiz-Gómez et
al., 2002).
Individual muscle identity is defined very early during myogenesis in
progenitors by specific combinations of transcriptional factors and other
proteins that are inherited by FMs (Baylies
et al., 1998). Thus, as FCMs fuse to FMs to generate myotubes,
FCMs are reprogrammed to the exclusive genetic programme of the FM, which
defines the characteristics of the final muscle, including size, choice of
tendon sites and distinctive pattern of innervation. Under mutant conditions
that block fusion, FMs are the sole myoblasts able to complete myogenesis,
giving rise to mononucleated fibres that, otherwise, exhibit the same
properties as the wild-type muscles. By contrast, FCMs initiate the expression
of differentiation genes, such as Mef2 and Myosin heavy
chain (Mhc), but they fail to exhibit contractile capability,
are unable to contact tendon cells or to be recognised as targets for
innervation. FCMs die before the end of embryogenesis without completing the
muscle terminal differentiation programme
(Rushton et al., 1995).
All FMs share the expression of a set of genes that confer to them the
general properties of this population. For example, dumbfounded
(duf; also known as kin of irre - FlyBase), a member of the
immunoglobulin superfamily, enables FMs to attract FCMs to their vicinity and
thus nucleate the fusion process
(Ruiz-Gómez et al.,
2000; Strunkelnberg et al.,
2001). The cytoplasmic protein Rolling pebbles (Rols), which is
recruited to the membrane by interaction with Duf, acts as an adaptor between
events taking place at the membrane during the fusion process and the
cytoskeleton, through its interaction with two other proteins, Myoblast city
(Mbc) and Sallimus (Sls; also known as D-titin)
(Chen and Olson, 2001;
Menon and Chia, 2001).
Similarly, all founders express the 
2 position-specific Integrin
subunit PS2, which is required to maintain the integrity of apodemes and
stabilise the binding of muscles to tendon cells via the extracellular matrix
(Brown, 1994). However, the
genes that control other properties of FMs, such as their unique ability to
complete myogenesis in the absence of fusion, are unknown. For instance,
although all myoblasts express genes encoding myofibrillar proteins [i.e.
Myosin, Kettin (also known as Sallimus - FlyBase), Tropomyosin], only FMs are
capable to build functional sarcomeres.
To identify additional genes conferring FM-specific characteristics, we searched for genes with expression restricted to the founder population. Here we describe mind bomb 2 (mib2), a gene that encodes a founder-specific modular protein containing two RING-finger domains with putative E3 ubiquitin ligase activity. Mib2 performs separable functions during myogenesis. Thus, Mib2 is necessary to complete myoblast fusion, a function that requires the E3-RING-finger domain. Mib2 is also required to maintain muscle integrity, as its absence leads to loss of sarcomeric structure, in both larval and adult muscles, and muscle detachment from tendons.
|
MATERIALS AND METHODS |
|---|
|
TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
-GFP, kettin-GFP, UAS-Dmib
(Le Borgne et al., 2005),
rP298, 24B-GAL4, Mef2-GAL4, 1151-GAL4
(Dutta et al., 2004),
duf-GAL4 and sns-GAL4
(Stute et al., 2006).
Df(2L)mib2r14 was obtained as an
imprecise excision of the P element in
CG17492KG10508
(Hamilton and Zinn, 1994).
UAS-SKE and UAS-mib2 were obtained after insertion of human
SKE cDNA (Takeuchi et al.,
2005) and a synthetic mib2 cDNA, respectively (details
will be provided under request), into pUAST and transformation into
yw embryos. To generate the UAS-RNAi-mib2 construct a
fragment of 503 bp obtained by PCR on mib2 cDNA using primers
5'-CAACGATGCCAACAAAGTGC and 5'-GCAGAGCTGAATCACCTTCC was used to
make intron-spliced hairpin RNA according to Nagel et al.
(Nagel et al., 2002).
UAS-mib2-C935S-C1020S was generated by replacement of cysteines C935
and C1020 for serines (performed according to a modification of the Quick
Change Mutagenesis method, Stratagene). Mutants were identified by the absence
of embryonic lacZ expression or GFP fluorescence.
|
In situ hybridisation and immunohistochemistry
Whole-mount in situ hybridisation with digoxigenin-labelled EST LD36078 RNA
probe and immunocytochemistry were performed as described previously
(San-Martín et al.,
2001). The following primary antibodies were used: anti-muscle
Myosin (Kiehart and Feghali,
1986), anti-Eve, anti-Runt
(Kosman et al., 1998),
anti-Rols (Menon and Chia,
2001), anti-Kz (Machado and
Andrew, 2000), anti-Connectin
(Meadows et al., 1994),
anti-Lmd (Duan et al., 2001),
anti-Tm (MAC141, Babraham Tech), anti-cleaved Caspase 3 (also known as Decay -
FlyBase) (Cell signaling Tech), anti-GFP (Molecular Probes) and
anti-β-galactosidase (Cappel).
Electron and confocal microscopic analysis
Electron microscopic analyses were carried out according to
Beall and Fyrberg, 1991
(Beall and Fyrberg, 1991).
Samples were observed in a Jem1010 (JEOL) instrument working at 80 kV.
Fluorescent preparations were scanned using confocal microscopes MicroRadiance
(BioRad) and LSM510 META (Zeiss) and images were analysed using the software
Zeiss LSM Image or LaserSharp and Adobe Photoshop 7.0. In most cases the
images correspond to z-projections of series of confocal
sections.
Protein blot and co-immunoprecipitation
Protein extracts from adult thoraces and co-immunoprecipitations with
anti-Mib2 and anti-GFP (using 300-500 µg of protein) were performed
following standard protocols with minor modifications
(Sambrook et al., 1989).
Primary antibodies used for immunoblots were anti-nonmuscle myosin
(Kiehart and Feghali, 1986)
and anti-GFP (clones 7.1 and 13.1, Roche).
|
RESULTS |
|---|
|
TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
We generated a specific antibody against the Mib2 protein (Fig. 1E). Using the duf-lacZ line rP298 as a nuclear marker for FMs, we observed co-expression in all FMs of the somatic and visceral mesoderm (Fig. 1F,G). Double stainings with antibodies to Connectin and Kettin (used to reveal myotube membranes and muscle attachments sites, respectively), showed that Mib2 accumulates in the cytoplasm (Fig. 1H-H'') and that it is not concentrated at the attachment sites (Fig. 1I-I''). We did not detect Mib2 in FCMs by double staining with the Sns marker (not shown).
Physical organisation of the mib2 locus
mib2 encodes a modular protein that contains, at the
amino-terminus, a `ZZ-zinc-binding' domain
(Ponting et al., 1996), which
is flanked on either side by a `mib/herc2' domain
(Fig. 2A). At the
carboxy-terminus, Mib2 has two `RING-finger' motifs that fulfil the consensus
for RING domains with catalytic E3 ubiquitin ligase activity
(Fig. 2B)
(Joazeiro and Weissman, 2000).
The central part of the protein bears seven `ankyrin repeats', normally
implicated in protein-protein interactions. This molecular organisation is
similar to that of two E3 ubiquitin ligases that regulate Notch signalling:
namely, Drosophila Mind bomb (Mib1) and human skeletrophin (SKE; also
known as MIB2 - Human Gene Nomenclature Database)
(Lai et al., 2005;
Le Borgne et al., 2005;
Takeuchi et al., 2005). The
similarity of the conserved domains is higher with SKE (51%) than with Mib1
(44%, Fig. 2B).
|
) that
maps at 37B10-11
(http://www.flybase.org;
Fig. 2A), indicated that
mib2 and l(2)37Be were the same gene.
Therefore, we renamed the l(2)37Be1 as
mib21. Molecular analysis of mib21
revealed a C-to-T transition that changes residue Gln377 to an amber nonsense
codon that should eliminate the ankyrin repeats and the catalytic RING-finger
motifs. Comparison of the phenotypes of embryos homozygous for
Df(2L)Exel8039 (that removes mib2 and
adjacent genes), mib21 and
Df(2L)mib2r14, and in pair-wise
combinations between them and Df(2L)Exel8039,
suggested that all were null alleles, as their phenotypes were
indistinguishable. Congruently, we failed to detect Mib2 protein in mutant
embryos homozygous for each of these mib2 alleles (not shown).
mib2 is required for proper myoblast fusion and muscle stability
We first analysed the specification of FMs by comparing the distinct
patterns of expression of markers like eve
(Fig. 3D,E; for three
additional markers, see Fig. S1 in the supplementary material) in the
individually identifiable nascent muscles of wild-type and
mib21 embryos. No differences were observed (except in the
number of nuclei present in the muscles), which indicated that all FMs
segregated and were correctly specified. Numbers of FCMs, as determined by
expression of sns, were essentially unmodified (see Fig. S1 in the
supplementary material). All adult muscle precursors were also present (for
expression of twist, see Fig. S1 in the supplementary material).
By contrast, myoblast fusion was clearly affected in mutant embryos. Muscles were smaller, and unfused myoblasts were still present at stage 16, when fusion should be completed (analysed by myosin staining; arrowheads, Fig. 3A-C). Quantification of the number of eve-expressing nuclei incorporated into the dorsal acute 1 (DA1) muscle at stages 14 and 15 showed a 31% and 40% decrease, respectively, under several mib2 mutant conditions (Fig. 3D-F).
In stage 16 embryos, myosin staining also revealed other phenotypes:
namely, the lack of gut constrictions, probably caused by defects in the
visceral muscles, and the absence of some muscles, which was usually
associated with the presence of myospheres (arrows in
Fig. 3B; see Fig. S2B in the
supplementary material) (Estrada et al.,
2006). As this defect suggested muscle detachment, we examined
muscle development in living embryos. To visualise muscles, the
Mhc--GFP chromosome was introduced into
mib21 embryos. Initially, all muscles were present and
made correct contacts with tendons (Fig.
3H, compare with
3G). However, when contractions
started (stage 16) (Broadie and Bate,
1993), muscles begun to detach and form myospheres
(Fig. 3I arrow and arrowhead).
Subsequently, most muscles were affected, although some of them were most
resistant to detachment (Fig.
3K). Approximately one-third of individuals died before hatching,
while the remaining ones reached first larval instar. These died shortly
afterwards with most of the muscles missing
(Fig. 3J and see Fig. S3A,B in
the supplementary material). Essentially the same phenotype was observed in
mutant embryos derived from mib21 germline clones
(Fig. 3C), which indicated that
there is no major contribution of maternally delivered Mib2 to the zygotic
function.
|
Rescue of the mib21 phenotype
Forced expression of UAS-mib2 in the mesoderm (24B-GAL4
driver) or exclusively in FMs (duf-GAL4 driver) rescued the somatic
and visceral mesodermal defects of mib21 embryos
(Fig. 4D,D' and see Fig.
S2A-SA'' in the supplementary material). (Similar overexpression in a
wild-type background did not produce obvious defects and individuals survived
up to pupal stages.) Neither UAS-SKE nor UAS-mib1 was able
to rescue any aspect of the mib21 embryonic phenotype (not
shown), which suggested that the closely related E3 ubiquitin ligases Mib1 and
SKE are not functional homologues of Mib2.
The Mib2 RING-finger domains are required for myoblast fusion and are dispensable for muscle integrity
We next examined whether the RING-finger domains of Mib2, putatively
responsible for an E3 ubiquitin ligase activity, were necessary for the
function of this protein in myogenesis. We prepared
UAS-mib2-C935S-C1020S by replacing the third conserved cysteine in
each Mib2 RING domain by serine, a substitution shown to abrogate ubiquitin
ligase activity in other RING-finger E3 proteins with minimal modification of
tertiary structure (Takeuchi et al.,
2005). UAS-mib2-C935S-C1020S did not rescue the fusion
defect of mib21 embryos, as they displayed unfused
myoblasts (black arrowhead, Fig.
4E'). Moreover, the number of eve-expressing nuclei
in DA1 of the rescued embryos was the same as in mib2 mutant embryos
(Fig. 3F). However, this Mib2
variant completely rescued the detachment phenotype
(Fig. 4E'), the
sarcomeric organisation (Fig.
4C) and, to a large extent, the visceral mesoderm defects, as all
but the first gut constriction were formed
(Fig. 4E). Hence, the
RING-finger domains, and consequently the putative ubiquitin ligase activity
of Mib2, appear essential for myoblast fusion, but they are largely
dispensable for other functions of Mib2.
|
). As the
above experiments suggested that the putative E3 ligase activity of Mib2 is
important for myoblast fusion, we explored whether the fusion phenotypes
associated with the absence of Mib2 were related to modifications in the
accumulation of proteins required for fusion. Two obvious founder-specific
candidates were Duf and Rols (Chen and
Olson, 2001; Menon and Chia,
2001; Rau et al.,
2001; Ruiz-Gómez et
al., 2000). However, we did not detect changes in the accumulation
or subcellular localisation of either of them in mib21
embryos (not shown). Next, we overexpressed two copies of UAS-mib2 in
the mesoderm using a strong GAL4 line, Mef2-GAL4. This caused a
severe defect in myoblast fusion (compare
Fig. 3A with
Fig. 5A,A') that required
the presence of intact RING domains (Fig.
5C,C') but was not associated with changes in the membrane
localisation of Duf and Rols in FMs (Fig.
5D). Furthermore, the resulting mini-myotubes elongated properly
and were able to contract under these conditions (not shown).
By contrast, this overexpression of UAS-mib2 induced early massive
death of FCMs (Fig. 5E,F). This
suggested that the failure to fuse was due to a deleterious effect of Mib2 on
FCMs. To verify this, we overexpressed Mib2 exclusively in FMs
(duf-GAL4) or FCMs (sns-GAL4). Interference with fusion was
associated only with overexpression in FCMs
(Fig. 5B,B'). This
suggested an interference with an FCM-specific factor. Lmd was an obvious
candidate as it is a regulator of the FCMs differentiation programme. We
reasoned that Mib2 might be important in FMs to keep Lmd inoperative after
fusion, when muscle precursors are loaded with Lmd brought in as FCMs fuse
with founders. We explored this by examining the distribution of Lmd in
wild-type and mib21 embryos. Lmd was absent from wild-type
muscle precursors (Fig. 5G,J),
but it was present in precursors (Fig.
5H) and mature muscles (Fig.
5K) of mutant embryos. Thus, Mib2 is required to remove Lmd from
developing myotubes. The persistence of Lmd could be the basis of the fusion
defects observed in mib2 mutants, as forced expression of Lmd in FMs
interferes with fusion (Duan and Nguyen,
2006).
Mib2 accumulates in sarcomeres and is required for their stability
The dispensability of the Mib2 RING-finger domains for muscle stability
points to a possible structural role of Mib2 in regulating muscle integrity.
Due to the difficulty in performing structural analysis on mib2
larval muscles, we turned our attention to adult muscles. Mib2 was present in
myofibrils isolated from thoracic muscles. It accumulated preferentially in
the Z bands (co-expression with Kettin,
Fig. 6A,A''') and at lower
levels in the M bands (absence of phalloidin
Fig. 6A,A''). Next, we
examined the requirement for Mib2 during adult myogenesis by using a
UAS-RNAi-mib2 transgene. After confirmation of its ability to
attenuate mib2 function (see Fig. S3A-C,E in the supplementary
material), we expressed two copies of UAS-RNAi-mib2 in the precursors
of adult muscles (1151-GAL4, see Fig. S3D-D'' in the
supplementary material). The indirect flight muscles (IFM) of newly emerged
flies (before acquisition of flight ability) presented poorly defined M bands,
and the Z bands were less dense than those of the wild type and, occasionally,
of zigzagging shape (Fig.
6B-C'). Flies 2-3 days old remained flightless and unable to
jump, and their thoraces displayed empty cavities (see Fig. S3G in the
supplementary material) due to loss of muscle mass. Their remaining IFMs
lacked myofibrils (although both thick and thin filaments were present) and
only possessed remnants of electron-dense material, which resembled Z bands
(Fig. 6D,D'). The tergal
depressor muscles of the trochanter (TDT) were similarly affected (M.
Carrasco-Rando, PhD thesis, Universidad Autónoma de Madrid, 2005). We
conclude that depletion of Mib2 disrupts myofibrillar organisation and affects
sarcomere assembly to some an extent. Similarly to embryonic muscles, the
defects worsen with age and probably with muscle use. This structural role of
Mib2 was further evidenced by the ability of this protein to interact with
Spaghetti-squash (Sqh) and Zipper, the regulatory light chain and the heavy
chain of nonmuscle myosin (Fig.
6E-G), a component of muscle sarcomeres that plays a fundamental
role in myofibrillogenesis during embryogenesis
(Bloor and Kiehart, 2001).
|
|
DISCUSSION |
|---|
|
TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
). The nature of the genes responsible for regulating
many of the properties exclusive to founders has remained elusive, in
particular those necessary to implement the terminal differentiation
programme. We searched for these genes using the criterion of FM-restricted
expression, and identified and characterised mib2 as such a candidate
gene. Two recent genome-wide analyses have also found mib2 expression
enriched in the FM population (Artero et
al., 2003; Estrada et al.,
2006).
mib2 encodes a modular protein very similar to human SKE and
Drosophila Mib1, two ubiquitin ligases that act as positive
regulators of the N signalling pathway by targeting N ligands for degradation
(Lai et al., 2005;
Le Borgne et al., 2005;
Takeuchi et al., 2005). Our
results, however, ruled out a role for Mib2 in regulating N during myogenesis,
as the processes of progenitor segregation and their subsequent asymmetric
division, both dependent on N signalling
(Corbin et al., 1991;
Ruiz-Gómez and Bate,
1997), were not affected in mib21 mutants.
Moreover, the failure to rescue mib21 phenotypes with SKE
or Mib1 indicated that they were not functional homologues.
|
Mib2 RING fingers are necessary for correct myoblast fusion
To study the contribution of the putative E3 ubiquitin ligase activity of
Mib2 to its function we prepared the modified variant
UAS-mib2-C935S-C1020S, which should lack ligase activity because two
conserved cysteines that bind the Zn2+ ions in the putative
catalytic centre were replaced by serine
(Lorick et al., 1999). Its
mesodermal expression in mib21 mutant embryos rescued the
detachment phenotype and the sarcomeric defects, but not the myoblast fusion
problem. This suggested that the RING-finger domains actually have enzymatic
activity.
As Mib2 is an FM-restricted protein, the requirement of its RING domains
for fusion pointed to Duf and Rols as targets for Mib2, as they are exclusive
to FMs and are implicated in myoblast fusion. However, we failed to detect an
effect on the stability or subcellular localisation of these crucial proteins,
both in mib21 mutants and under overexpression conditions
that compromise fusion. Moreover, by means of overexpressions directed at
either FMs or FCMs, we found that these overexpressions induced damage,
including cell death, only in FCMs, but did not interfere with the survival or
contractile capability of the FM-derived mini-myotubes. Based on these
results, and on our finding that Lmd accumulates in mib21
muscle precursors, we suggest that Mib2 is required in FMs to eliminate
Minc/Lmd provided to nascent muscles by the fusing FCMs. The presence of the
FCM-specific factor Lmd in FMs would interfere with normal myotube
development, in agreement with a recent report showing that forced expression
of Lmd in FMs induces fusion defects (Duan
and Nguyen, 2006) similar to those observed in
mib21 mutant embryos.
Mib2 plays a structural role in muscle stability
As the presumed ligase activity of the RING-finger domains appear
dispensable for the Mib2 functions related to muscle stability, we inferred
that Mib2 might have a structural role in maintaining muscle attachments and
sarcomeric stability. In the light of the similarity of the mib2
detachment phenotype to that produced by the loss-of-function of Integrins
(Brown, 1994), and the presence
of ankyrin repeats in Mib2, we reasoned that Mib2 might mediate interactions
with proteins involved in stabilising muscle attachments, such as Inflated,
Integrin-linked kinase (Ilk) and Tensin (also known as Blistery - FlyBase).
However, the absence of Mib2 did not influence their cellular localisations.
Similarly, we did not detect changes in the expression or localisation of
Alien and Stripe, two markers for tendon cells (M. Carrasco-Rando, PhD thesis,
Universidad Autónoma de Madrid, 2005). By contrast, mib2
mutant embryos showed extensively disrupted myofibrillar organisation at the
ultrastructural level. In vivo observations (Kettin-GFP) revealed that
sarcomeric assembly proceeded almost normally, as imperfect Z bands were
evident in stage 17 mutant muscles. These muscles could contract, but
progressively the Z bands broke. The splitting of the Z bands was concomitant
with a decrease of contraction frequency and ended up with the loss of
contractile ability.
These observations are consistent with ultrastructural data obtained in adult muscles. Here again, the slight defects observed in muscles of newborn adults, before acquisition of flight ability, suggested that muscle assembly did not require Mib2; but the absence of striated myofibrils in older muscles points to a structural role of Mib2 in maintenance of muscle integrity. To our knowledge, this is the first phenotype of muscle decay described in Drosophila. It is noteworthy that Mib2-deficient muscles display signs of faulty differentiation when they still can contract, which suggests that muscle decay is a consequence of loss of sarcomeric integrity.
Mib2 localises to the sarcomeres of adult muscles and accumulates at the Z
bands and, at lower levels, at the M bands. Furthermore, during embryogenesis
it does not co-localise with Integrins at the muscle termini. Thus,
detachments are probably a consequence of loss of sarcomeric structure. In
this line of thinking, it should be stressed that Z bands and muscle termini
function as transmitters of muscle tension during contraction. The
mib2 phenotypes and Mib2 localisation suggest a role of this protein
as a cross-linker that helps to maintain Z band and muscle termini integrity.
Many proteins have been identified at Z bands, alpha-actinin being one of the
major components (reviewed by Sanger et
al., 2005). So far, we have not found evidence for a physical
interaction between Mib2 and alpha-actinin. However, we show an interaction in
adults with nonmuscle myosin, recently identified as another component of
embryonic Z bands (Bloor and Kiehart,
2001). This interaction is of interest, as it might be related to
the unique ability of FMs, as opposed to FCMs, to synthesise stable
sarcomeres, as nonmuscle myosin is required for the formation of striated
myofibrils (Bloor and Kiehart,
2001). Moreover, during embryogenesis, the genes encoding two of
the nonmuscle myosin chains (zipper and spaghetti squash)
are in the fraction of genes with expression that is strongly enriched in FMs
versus FCMs, similarly to duf and rols, two FM-specific
genes (Estrada et al., 2006).
These data support the idea that sarcomeres are synthesised only in FMs. In
addition, the restricted localisation of Mib2 to FMs favours the idea that
stabilisation of the assembled sarcomeres occurs exclusively in muscle
precursors and myotubes. In this context, it is worth mentioning that although
the closest human structural homologue of Mib2, skeletrophin, does not seem to
play the same role during myogenesis, there is another E3 ubiquitin ligase,
TRIM32, that has been linked to two forms of progressive skeletal
muscle-wasting dystrophies (Kudryashova et
al., 2005). TRIM32 binds to muscle myosin and is able to
ubiquitinate actin. Although the molecular bases for these dystrophies are
unknown, our findings highlight the importance that bifunctional ubiquitin
ligases may have in the control of sarcomeric stability in both systems.
Supplementary material
Supplementary material for this article is available at
http://dev.biologists.org/cgi/content/full/135/5/849/DC1
Note added in proof
After submission of this work, Nguyen et al.
(Nguyen et al., 2007) reported
a requirement of Drosophila mib2 for embryonic muscle integrity and
survival.
|
ACKNOWLEDGMENTS |
|---|
|
REFERENCES |
|---|
|
TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
Artero, R., Furlong, E. E., Beckett, K., Scott, M. P. and
Baylies, M. (2003). Notch and Ras signaling pathway effector
genes expressed in fusion competent and founder cells during Drosophila
myogenesis. Development
130,6257
-6272.
Bate, M. (1993). The mesoderm and its derivatives. In The Development of Drosophila melanogaster (ed. M. Bate and A. Martinez Arias), pp.1013 -1090. Cold Spring Harbor: CHS Laboratory Press.
Baylies, M. K., Bate, M. and Ruiz-Gómez, M. (1998). Myogenesis: a view from Drosophila. Cell 93,921 -927.[CrossRef][Medline]
Beall, C. J. and Fyrberg, E. (1991). Muscle
abnormalities in Drosophila melanogaster heldup mutants are caused by missing
or aberrant troponin-I isoforms. J. Cell Biol.
114,941
-951.
Bloor, J. W. and Kiehart, D. P. (2001). zipper Nonmuscle myosin-II functions downstream of PS2 integrin in Drosophila myogenesis and is necessary for myofibril formation. Dev. Biol. 239,215 -228.[CrossRef][Medline]
Broadie, K. S. and Bate, M. (1993). Development of the embryonic neuromuscular synapse of Drosophila melanogaster. J. Neurosci. 13,144 -166.[Abstract]
Brown, N. H. (1994). Null mutations in the alpha PS2 and beta PS integrin subunit genes have distinct phenotypes. Development 120,1221 -1231.[Abstract]
Carmena, A., Murugasu-Oei, B., Menon, D., Jimenez, F. and Chia,
W. (1998). Inscuteable and numb mediate asymmetric muscle
progenitor cell divisions during Drosophila myogenesis. Genes
Dev. 12,304
-315.
Chen, E. H. and Olson, E. N. (2001). Antisocial, an intracellular adaptor protein, is required for myoblast fusion in Drosophila. Dev. Cell 1, 705-715.[CrossRef][Medline]
Corbin, V., Michelson, A. M., Abmayr, S. M., Neel, V., Alcamo, E., Maniatis, T. and Young, M. W. (1991). A role for the Drosophila neurogenic genes in mesoderm differentiation. Cell 67,311 -323.[CrossRef][Medline]
Duan, H. and Nguyen, H. T. (2006). Distinct
posttranscriptional mechanisms regulate the activity of the Zn finger
transcription factor lame duck during Drosophila myogenesis. Mol.
Cell. Biol. 26,1414
-1423.
Duan, H., Skeath, J. B. and Nguyen, H. T. (2001). Drosophila Lame duck, a novel member of the Gli superfamily, acts as a key regulator of myogenesis by controlling fusion-competent myoblast development. Development 128,4489 -4500.[Medline]
Dutta, D., Anant, S., Ruiz-Gómez, M., Bate, M. and
VijayRaghavan, K. (2004). Founder myoblasts and fibre number
during adult myogenesis in Drosophila. Development
131,3761
-3772.
Estrada, B., Choe, S. E., Gisselbrecht, S. S., Michaud, S., Raj, L., Busser, B. W., Halfon, M. S., Church, G. M. and Michelson, A. M. (2006). An integrated strategy for analyzing the unique developmental programs of different myoblast subtypes. PLoS Genet. 2,e16 .[CrossRef][Medline]
Hamilton, B. A. and Zinn, K. (1994). From clone to mutant gene. Methods Cell Biol. 44, 81-94.[Medline]
Joazeiro, C. A. and Weissman, A. M. (2000). RING finger proteins: mediators of ubiquitin ligase activity. Cell 102,549 -552.[CrossRef][Medline]
Kiehart, D. P. and Feghali, R. (1986).
Cytoplasmic myosin from Drosophila melanogaster. J. Cell
Biol. 103,1517
-1525.
Kosman, D., Small, S. and Reinitz, J. (1998). Rapid preparation of a panel of polyclonal antibodies to Drosophila segmentation proteins. Dev. Genes Evol. 208,290 -294.[CrossRef][Medline]
Kudryashova, E., Kudryashov, D., Kramerova, I. and Spencer, M. J. (2005). Trim32 is a ubiquitin ligase mutated in limb girdle muscular dystrophy type 2H that binds to skeletal muscle myosin and ubiquitinates actin. J. Mol. Biol. 354,413 -424.[CrossRef][Medline]
Lai, E. C., Roegiers, F., Qin, X., Jan, Y. N. and Rubin, G.
M. (2005). The ubiquitin ligase Drosophila Mind bomb promotes
Notch signaling by regulating the localization and activity of Serrate and
Delta. Development 132,2319
-2332.
Le Borgne, R., Remaud, S., Hamel, S. and Schweisguth, F. (2005). Two distinct E3 ubiquitin ligases have complementary functions in the regulation of delta and serrate signaling in Drosophila. PLoS Biol. 3,e96 .[CrossRef][Medline]
Lorick, K. L., Jensen, J. P., Fang, S., Ong, A. M., Hatakeyama,
S. and Weissman, A. M. (1999). RING fingers mediate
ubiquitin-conjugating enzyme (E2)-dependent ubiquitination. Proc.
Natl. Acad. Sci. USA 96,11364
-11369.
Machado, C. and Andrew, D. J. (2000). D-Titin:
a giant protein with dual roles in chromosomes and muscles. J. Cell
Biol. 151,639
-652.
Meadows, L. A., Gell, D., Broadie, K., Gould, A. P. and White, R. A. (1994). The cell adhesion molecule, connectin, and the development of the Drosophila neuromuscular system. J. Cell Sci. 107,321 -328.[Abstract]
Menon, S. D. and Chia, W. (2001). Drosophila rolling pebbles: a multidomain protein required for myoblast fusion that recruits D-Titin in response to the myoblast attractant Dumbfounded. Dev. Cell 1,691 -703.[CrossRef][Medline]
Nagel, A. C., Maier, D. and Preiss, A. (2002). Green fluorescent protein as a convenient and versatile marker for studies on functional genomics in Drosophila. Dev. Genes Evol. 212, 93-98.[CrossRef][Medline]
Nguyen, H. T., Voza, F., Ezzeddine, N. and Frasch, M.
(2007). Drosophila mind bomb2 is required for
maintaining muscle integrity and survival. J. Cell
Biol. 179,219
-227.
Ponting, C. P., Blake, D. J., Davies, K. E., Kendrick-Jones, J. and Winder, S. J. (1996). ZZ and TAZ: new putative zinc fingers in dystrophin and other proteins. Trends Biochem. Sci. 21,11 -13.[CrossRef][Medline]
Rau, A., Buttgereit, D., Holz, A., Fetter, R., Doberstein, S. K., Paululat, A., Staudt, N., Skeath, J., Michelson, A. M. and Renkawitz-Pohl, R. (2001). rolling pebbles (rols) is required in Drosophila muscle precursors for recruitment of myoblasts for fusion. Development 128,5061 -5073.[Medline]
Ruiz-Gómez, M. and Bate, M. (1997). Segregation of myogenic lineages in Drosophila requires numb. Development 124,4857 -4866.[Abstract]
Ruiz-Gómez, M., Coutts, N., Price, A., Taylor, M. V. and Bate, M. (2000). Drosophila dumbfounded: a myoblast attractant essential for fusion. Cell 102,189 -198.[CrossRef][Medline]
Ruiz-Gómez, M., Coutts, N., Suster, M. L., Landgraf, M.
and Bate, M. (2002). myoblasts incompetent encodes a zinc
finger transcription factor required to specify fusion-competent myoblasts in
Drosophila. Development
129,133
-141.
Rushton, E., Drysdale, R., Abmayr, S. M., Michelson, A. M. and Bate, M. (1995). Mutations in a novel gene, myoblast city, provide evidence in support of the founder cell hypothesis for Drosophila muscle development. Development 121,1979 -1988.[Abstract]
Sambrook, J., Fritsch, E. F. and Maniatis, T. (1989). Molecular Cloning. Cold Spring Harbor: Cold Spring Harbor Laboratory Press.
San-Martín, B., Ruiz-Gómez, M., Landgraf, M. and
Bate, M. (2001). A distinct set of founders and
fusion-competent myoblasts make visceral muscles in the Drosophila embryo.
Development 128,3331
-3338.
Sanger, J. W., Kang, S., Siebrands, C. C., Freeman, N., Du, A., Wang, J., Stout, A. L. and Sanger, J. M. (2005). How to build a myofibril. J. Muscle Res. Cell Motil. 26,343 -354.[CrossRef][Medline]
Stathakis, D. G., Pentz, E. S., Freeman, M. E., Kullman, J., Hankins, G. R., Pearlson, N. J. and Wright, T. R. (1995). The genetic and molecular organization of the Dopa decarboxylase gene cluster of Drosophila melanogaster. Genetics 141,629 -655.[Abstract]
Strunkelnberg, M., Bonengel, B., Moda, L. M., Hertenstein, A.,
de Couet, H. G., Ramos, R. G. and Fischbach, K. F. (2001).
rst and its paralogue kirre act redundantly during embryonic muscle
development in Drosophila. Development
128,4229
-4239.
Stute, C., Kesper, D., Holz, A., Buttgereit, D. and Renkawitz-Pohl, R. (2006). Establishment of cell type specific Gal4-driver lines for the mesoderm of Drosophila. Drosoph. Inf. Serv. 89,111 -115.
Takeuchi, T., Adachi, Y. and Ohtsuki, Y.
(2005). Skeletrophin, a novel ubiquitin ligase to the
intracellular region of Jagged-2, is aberrantly expressed in multiple myeloma.
Am. J. Pathol. 166,1817
-1826.
Welchman, R. L., Gordon, C. and Mayer, R. J. (2005). Ubiquitin and ubiquitin-like proteins as multifunctional signals. Nat. Rev. Mol. Cell Biol. 6, 599-609.[CrossRef][Medline]
CiteULike 
Complore 
Connotea 
Del.icio.us 
Digg 
Reddit 
Technorati 
Twitter What's this?
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
