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First published online 13 August 2008
doi: 10.1242/dev.020800
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1 Program in Cell, Molecular and Developmental Biology, 150 Harrison Avenue,
Boston, MA 02111, USA.
2 Program in Genetics, Tufts University School of Medicine, Department of
Anatomy and Cellular Biology, 150 Harrison Avenue, Boston, MA 02111,
USA.
* Author for correspondence (e-mail: victor.hatini{at}tufts.edu)
Accepted 9 July 2008
 |
SUMMARY |
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 TOP SUMMARY INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Key words: Wing imaginal disc, Peripodial epithelium, Proximo-distal patterning, odd-skipped genes
|
INTRODUCTION |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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;
Fristrom and Fristrom, 1993;
Milner, 1984). Despite the
central role of this symmetry-breaking event in setting up two fields of cells
with distinct morphologies and developmental potentials, the mechanisms that
generate this major asymmetry remain poorly understood.
The formation of the wing appendage depends on the establishment of the
anteroposterior (AP), dorsoventral (DV) and proximodistal (PD) axes within the
DP (reviewed by Blair, 1995;
Dahmann and Basler, 1999;
Klein, 2001;
Lawrence et al., 1996;
Mann and Morata, 2000). The AP
and DV subdivisions are established by the transcription factors
engrailed (en) and apterous (ap)
(Blair et al., 1994;
Diaz-Benjumea and Cohen, 1993;
Lawrence and Morata, 1976;
Morata and Lawrence, 1975),
which program their respective compartment to induce expression of the
Decapentaplegic (Dpp) and Wingless (Wg) morphogens adjacent to the AP and DV
compartment boundaries (Basler and Struhl,
1994; Diaz-Benjumea and Cohen,
1995; Fleming et al.,
1997; Panin et al.,
1997; Tabata and Kornberg,
1994; Williams et al.,
1994; Zecca et al.,
1995). Dpp and Wg, in turn, induce expression of target genes to
pattern the AP and DV axes in a concentration-dependent manner
(Lecuit et al., 1996;
Nellen et al., 1996;
Neumann and Cohen, 1996;
Zecca et al., 1996). During
the second instar, the wing undergoes a third major subdivision along the PD
axis to form the wing distally and the notum proximally; this subdivision is
mediated by the secreted Wg ligand and the Epidermal Growth Factor (EGF)
receptor ligand, Vein. Wg is expressed in a wedge of ventroanterior cells
(Couso et al., 1993;
Klein and Arias, 1998;
Ng et al., 1996;
Williams et al., 1993), and
induces the expression of the pdm1 homolog nubbin
(nub) to initiate wing formation
(Cifuentes and Garcia-Bellido,
1997; Ng et al.,
1995; Ng et al.,
1996). Vein emanates from a patch of proximal cells to induce
expression of pannier and members of the Iroquois-C gene
complex to specify the medial and lateral parts of the notum
(Simcox et al., 1996;
Wang et al., 2000;
Zecca and Struhl, 2002a;
Zecca and Struhl, 2002b). As
development proceeds, the wing field is further subdivided into the pouch
distally, and the hinge proximally. The transcription factors
vestigial (vg) and homothorax (hth),
teashirt (tsh) and zfh2 are expressed in discrete
subregions of the wing pouch and hinge, respectively, and control the identity
of these subregions. (Mann and Morata,
2000; Kim et al.,
1996; Williams et al.,
1991; Azpiazu and Morata,
2000; Casares and Mann,
2000; Whitworth and Russell,
2003; Wu and Cohen,
2002).
The contribution of the PE to wing growth and patterning has received far
less attention. The PE has been implicated in disc eversion and fusion of
adjacent discs to form a continuous adult cuticle during metamorphosis
(Agnes et al., 1999;
Fristrom and Fristrom, 1993;
Milner et al., 1984;
Pastor-Pareja et al., 2004;
Usui and Simpson, 2000;
Zeitlinger and Bohmann, 1999).
Selective ablation of the PE resulted in smaller and malformed wings
(Gibson and Schubiger, 2000),
and inhibition of specific signaling pathways in the eye and wing PE resulted
in patterning abnormalities and a reduction in disc size
(Cho et al., 2000;
Gibson and Schubiger, 2000;
Pallavi and Shashidhara,
2003), suggesting earlier roles for the PE in signaling to the DP
to control its growth and patterning (reviewed by
Gibson and Schubiger, 2001).
Lineage analysis have suggested that peripodial cells stream laterally to
populate the DP (McClure and Schubiger,
2005; Pallavi and Shashidhara,
2003). Despite these intriguing results, little is known about how
the PE and the DP are specified or how they interact with each other.
Drumstick (Drm), Odd-skipped (Odd), Bowl, and Sister of Odd and Bowl (Sob)
share a conserved Cys2His2 zinc-finger domain, and play
diverse roles in patterning ectodermal structures. Bowl is a putative
transcription factor (Wang and Coulter,
1996). During embryogenesis, the protein Lines binds to and
destabilizes Bowl (Hatini et al.,
2005). Drm is a small peptide that binds to Lines and localizes it
to the cytoplasm, permitting stabilization of Bowl in restricted domains (see
Fig. 1L for the regulatory
interactions connecting drm, lines and bowl)
(Green et al., 2002;
Hatini et al., 2005). During
larval development, bowl contributes to leg and eye development
(Bras-Pereira et al., 2006;
de Celis Ibeas and Bray, 2003;
Hao et al., 2003).
drm mutants, however, do not display phenotypes in these tissues,
suggesting that odd and/or sob, which are related to
drm in structure and pattern of gene expression, may sometimes act
redundantly with drm
(Bras-Pereira et al., 2006;
Hao et al., 2003). Although
gain-of-function experiments support this hypothesis, loss-of-function and
biochemical evidence are still lacking. Lines, however, destabilizes Bowl in
all tissues examined (Green et al.,
2002; Hatini et al.,
2005; Iwaki et al.,
2001; Johansen et al.,
2003; Bras-Pereira et al.,
2006; Hao et al.,
2003).
We now report that lines and bowl specify alternative DP and PE fates during early stages of wing development. By blocking the specification of the PE, we were further able to provide definitive evidence that the PE is not required for the establishment of the AP, DV or PD patterning systems. The PE is instead required to support the growth and survival of the DP and the formation of the notum. Overall, our work elucidates a mechanism that generates a major asymmetry across the wing primordium and reveals crucial roles for this asymmetry in wing growth and patterning.
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MATERIALS AND METHODS |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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;
Xu and Rubin, 1993) and the
MARCM techniques (Lee and Luo,
2001) at 24-36, 36-48, 48-72, 72-96 and 96-120 hours AEL, which
correspond to early first, late first, second, early third and mid third
instar. Flies of the genotype y w hs-FLP; FRT42D Ubi-GFP and y w
hs-FLP; Ubi-GFP FRT40A (B. Edgar) were used to induce FLP/FRT clones and
y w hs-FLP Tub-GAL4 UAS-GFP-6Xmyc-NLS; FRT42D Tub-Gal80 hs-CD2,
y+ (gift of G. Struhl) to induce MARCM clones. The
linesG2 (Bokor and
DiNardo, 1996), lines2f
(Nusslein-Volhard et al.,
1984), bowl1
(Wang and Coulter, 1996) and
drm3 (Green et al.,
2002) alleles were used to generate mutant clones.
wg-lacZ (Kassis et al.,
1992) and P{lacZ}oddrk111 were used to map
domains of gene expression. UAS-Lines (9.2), UAS-Myc-Lines
(8), UAS-Flag-Bowl (28)
(Hatini et al., 2005),
UAS-Drm (2.1) (Green et al.,
2002), UAS-LinesRNAi (VDRC), were expressed in clones
using y w hs-FLP; act5C>y+>GAL4 UAS-GFP
(Pignoni and Zipursky, 1997),
and in the PE using Ubx-GAL4
(Pallavi and Shashidhara,
2003).
Immunofluorescence and microscopy
Staining protocols have been described elsewhere
(Hatini et al., 2005). Primary
antibodies used were: rabbit anti-Vg (Kim
et al., 1996), mouse anti-Nub
(Ng et al., 1996), mouse
anti-Dll (Vachon et al.,
1992), mouse anti-Sal (gift of S. Cohen), rabbit anti-Tsh
(Wu and Cohen, 2000), rat
anti-Zfh2 (gift of M. Lundell), rabbit anti-β-galactosidase (Cappel),
mouse anti-Wg (4D4, DSHB) (Brook and
Cohen, 1996), rabbit anti-Bowl
(de Celis Ibeas and Bray,
2003), mouse anti-Ubx (White
and Wilcox, 1984), rabbit anti-Hth
(Pai et al., 1998), guinea pig
anti-Hth (Casares and Mann,
1998), rabbit anti-Al (gift of G. Campbell), rabbit anti-activated
caspase 3 (Cell Signaling Technology), mouse anti-Arm (7A1, DSHB) and rabbit
anti-phospho Histone H3 (Upstate Signaling). Confocal images were scanned
using a Zeiss LSM510 in multi-tracking mode. β-Galactosidase activity
stains are described elsewhere (Patel et
al., 1989).
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RESULTS |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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;
Ng et al., 1996;
Williams et al., 1993). At
this stage, Bowl accumulated only in peripodial cells
(Fig. 1A), and not in DP cells
(Fig. 1B). At the early to mid
third instar, Wg was upregulated along the DV compartment boundary
(Fig. 1D,F, arrows). Bowl,
however, was detected in the PE (Fig.
1C,E) and in the lateral margins of the notum (arrowheads in
Fig. 1D,F). At the completion
of larval development, Bowl was upregulated along the lateral margins of the
notum (arrowheads in Fig. 1H)
and the ventro-anterior margin of the PE (asterisks in
Fig. 1G,H). However, Bowl was
downregulated in the medial region of the PE and absent from its posterior
margin. After pupariation, Bowl was detected at high levels in both the
ventro-anterior hinge (asterisk in Fig.
1I) and the lateral margins of the notum (data not shown). An
odd-lacZ reporter that is expressed similarly to Bowl
(Fig. 1J) was detected in the
axillary region and in a subset of proximal hinge derivatives in ventral
nuclei in adult wings (Fig.
1K), suggesting that a subset of odd-lacZ- and
Bowl-expressing cells are fated to contribute to the ventral hinge.
Lines accumulates in nuclei in the DP and in the cytoplasm in the PE
drm is expressed in restricted domains, where it inhibits Lines,
in part, by localizing it to the cytoplasm
(Hatini et al., 2005). To
probe the pattern of Lines activity in the wing imaginal disc, we induced
expression of a `weak' Myc-Lines transgene that minimally affects wing
development (UAS-Myc-Lines 8) in `FLP-out' cell clones using a combination of
the FLP/FRT and the GAL4/UAS techniques
(Pignoni and Zipursky, 1997).
Myc-Lines accumulated in the cytoplasm in clones in the lateral margins and
the medial region of the PE (Fig.
2A,B, respectively). However, Myc-Lines accumulated in nuclei in
the DP (Fig. 2C). Thus, the
distribution of Lines and Bowl in the PE and the DP was reciprocal. In the PE
where Bowl accumulates, Lines was cytoplasmic and inactive. Reciprocally, in
the DP where Bowl was absent, Lines was nuclear and active.
Lines inhibits Bowl accumulation in the DP
We also expressed a Flag-Bowl transgene in Flp-out clones to
determine whether Bowl was destabilized in the DP. Indeed, Flag-Bowl
accumulated only in cell clones that were generated in the medial and
ventro-anterior margin of the PE where Bowl is normally detected
(Fig. 2D-D'; arrow and
arrowhead in D', respectively). However, Flag-Bowl was not detected in
DP clones, suggesting that endogenous Lines destabilized Bowl in this region.
To test this idea, we examined Bowl accumulation in lines mutant
clones and in drm-expressing clones and detected a stabilization of
Bowl in these clones (Fig.
2E,F, respectively). Reciprocally, Bowl was destabilized in
lines-expressing cell clones generated in the PE
(Fig. 2G). However, Bowl
accumulation was unaffected in drm mutant clones generated in the PE
(data not shown), consistent with the proposal that odd and/or
sob may sometimes act redundantly with drm to stabilize Bowl
(Bras-Pereira et al., 2006;
Hao et al., 2003). We were
unable to test sob function as sob mutant alleles are not
available. However, Bowl accumulation was unaffected in odd mutant
clones. We also attempted to induce homozygous clones for the drm(P2)
deficiency to generate drm odd sob triple mutant clones but failed to
recover these clones. Therefore, additional studies will be necessary to
define the multiple inputs necessary to stabilize Bowl in the PE.
|
) to broadly destabilize Bowl in the PE using the GAL4/UAS
technique (Brand and Perrimon,
1993). We found that the flattened morphology of wild-type wing
discs (Fig. 3A) was replaced
with a spherical morphology (Fig.
3B), in which the thin PE (Fig.
3A',C,D'-D''') was replaced with the thickened
pseudostratified CE that forms the DP (Fig.
3B',E'-E'''). Coincidentally, the expression of
the peripodial markers Bowl, Ubx and Eya was lost in these discs
(Fig. 4B,C; data not shown).
Conversely, Lines was broadly nuclear (Fig.
4D), indicating that the PE (where Lines is enriched in the
cytoplasm) was replaced with the DP (where Lines is enriched in nuclei). The
Ubx>Lines wing discs were also roughly 10-30% the size of
wild-type wing discs (compare Fig.
3A with
3B; experimental discs, 39
mm2, n=7, s.d.=18 mm2; wild type, 147
mm2, n=7, s.d.=21 mm2). These discs survived
beyond the larval stages and elongated during metamorphosis (see Fig. S1 in
the supplementary material) but failed to contribute to adult structures. We
obtained similar phenotypes by driving expression of UAS-Lines with
C311-GAL4 and Tsh-GAL4 (see Fig. S2 in the supplementary
material).
Organ growth depends largely on a balance between cell proliferation and
cell death. Therefore, to determine the reason for the reduction in wing size,
we examined the expression of Phospho-Histone H3 (PH3) and activated caspase 3
(Ice) in Ubx>Lines discs to detect dividing and apoptotic
cells, respectively (Ryoo et al.,
2002). We detected similar levels of proliferating cells
(Fig. 3G), but elevated levels
of apoptotic cells in these discs (Fig.
3F) compared with age-matched controls (not shown). We therefore
propose that the PE supports wing growth by promoting cell survival in the
DP.
The AP, DV and PD patterning systems are established and maintained in the absence of the PE
We considered the possibility that the reduction in wing size resulted from
the loss of positional identities along the wing PD axis. We therefore
analyzed Vg (Kim et al., 1996;
Williams et al., 1991), Nub
(Cifuentes and Garcia-Bellido,
1997; Ng et al.,
1995; Ng et al.,
1996) and Zfh2 expression
(Whitworth and Russell, 2003)
to determine whether the pouch, the hinge or the notum were affected. In wild
type, Vg is restricted to the distal pouch, whereas Zfh2 is restricted to the
hinge (Fig. 4E). Nub is
detected in the pouch and in part of the dorsal hinge
(Fig. 3D,D'',D''').
In experimental discs, Nub (Fig.
3E,E''-E'''), Vg and Zfh2
(Fig. 4F,J) were detected in
both layers of the disc epithelium, indicating that the PE was replaced with a
mirror image duplication of the DP. Only a small region near the disc stalk
did not express Zfh2 (arrowhead in Fig.
4F), indicating that the notum, which is Zfh2 negative, was nearly
lost. The reduction in notal growth could partially account for the reduction
in overall wing size.
|
|
;
Nellen et al., 1996;
Neumann and Cohen, 1996;
Zecca et al., 1996). In
experimental discs, Wg was detected in both layers of the disc epithelium, in
ring-like structures that encircled the pouch (short arrow) and the hinge
(long arrows) (Fig. 4H).
dpp was expressed orthogonally to Wg (see Fig. S3 in the
supplementary material). Dll and Sal were also detected in both layers of
these discs (Fig. 4J,L,
respectively), indicating that the Wg and Dpp morphogens were able to signal
broadly to induce their targets. We thus conclude that at least part of the
AP, DV and PD axes are established independently of the PE. These findings
imply that the PE supports wing growth in parallel to these systems, and plays
a crucial role in promoting the growth of the notum.
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26%
of the surface area of the entire wing (n=9, s.d.=5%) and roughly 50%
of the surface area of the secondary wing fields. To further clarify the
origin of clones that permitted induction of secondary wings, we expressed
UAS-Lines with Ptc-GAL4 in both the DP and the PE (marked by
apposing arrowheads) along the AP compartment boundary. The
Ptc>Lines-expressing cells in the PE adopted DP fate and permitted
the induction of secondary wing (Fig.
5H). We conclude that smaller patches of lines-expressing
clones generated in the PE adopted DP fate, and subsequently acquired the
competence to respond to wing inducing signals. Clones that did not disrupt
wing development localized to the DP even when they formed large confluent
patches (Fig. 5C). Taken
together, we interpret these results as evidence that lines can
reprogram the PE to adopt DP fate during early stages of wing development.
Reciprocal roles for lines and bowl in promoting cell survival in the DP and the PE
To investigate the contribution of bowl to wing development, we
induced marked bowl mutant clones and examined clone recovery
relative to wild-type twin spots generated by the same mitotic recombination
event. Control clones and their twin clones survived in both the PE and the DP
(Fig. 6A; PE nuclei are spread
out; DP nuclei are densely packed). Most of the bowl mutant clones
generated at the early first instar survived in the DP. However, only 50% of
clones survived in the PE mostly near the disc stalk
(Fig. 6F, arrow indicates a
stalk clone) indicating that the bowl mutant clones were either dying
or sorting out from the PE at early stages. bowl mutant clones
generated at the second instar survived in the PE
(Fig. 6G) and adopted PE fate,
suggesting that the maintenance of PE fate depends on additional
mechanisms.
|
We also examined the recovery of lines mutant clones induced at the first instar. lines mutant and wild-type twin spots survived in the PE (Fig. 6B). However, mostly wild-type twin spots survived in the DP (Fig. 6C), and were much smaller than respective wild-type twin spots. Similar to the lines mutant clones, drm-expressing clones generated at the first instar survived in the PE but not in the DP (Fig. 6E). We therefore conclude that at early stages of wing development bowl promotes cell survival in the PE, whereas lines promotes cell survival in the DP. The quantitative analysis is presented in Fig. 6G.
|
;
Pallavi and Shashidhara,
2003). Tsh and Hth, which are expressed in the PE as well as in
the notum and hinge, but are excluded from the pouch, were also ectopically
expressed in the clones (Fig.
7E-F). We conclude that lines is necessary to specify DP
fate and to inhibit the specification of PE fate at early stages of wing
development.
lines maintains distal pouch identities and inhibits proximal hinge identities at later stages of wing development
lines could be needed either continuously or transiently in the DP
to specify DP fate and to inhibit PE fate. Moreover, lines could play
yet another role at later stages of wing development. To address these issues,
we examined the behavior of lines mutant clones and
drm-expressing clones that were generated at the mid to late third
instar following the formation of the PE and the DP. Most of the clones
generated in the DP and the posterior lateral margin of the hinge minimized
contact with their wild-type neighbors and formed round vesicles that extruded
basally (Fig.
8A-A'',B',C-H). We examined the positional identity of
these clones with molecular markers to determine whether the clones assumed an
alternative cell fate. The peripodial markers Ubx and Eya were not detected in
the clones, indicating the clones did not assume PE fate (data not shown).
However, the Tsh, Hth, Wg and Zfh2 proteins, which localize to the hinge and
control hinge formation, were ectopically expressed in the clones
(Fig. 8C-E; data not shown).
Expression of these markers was lower near the AP compartment boundary and
increased at a distance from this boundary, suggesting that Dpp signaling
antagonized this fate transformation in a graded manner, as previously
proposed (Azpiazu and Morata,
2000; Casares and Mann,
2000). Hinge-specific markers were also induced in
linesRNAi clones generated in the pouch, but were either
downregulated or lost in linesRNAi clones lacking bowl
function, indicating that the lines clonal phenotypes were due to the
stabilization of Bowl (see Fig. S4 in the supplementary material).
nub, which localizes to both the pouch and the distal hinge, was
maintained in these clones (Fig.
8F). Reciprocally, the pouch specific proteins Dll and Sal were
lost in lines mutant clones generated in the pouch in both distal and
proximal positions (Fig. 8G,H,
respectively). Overall, these results indicate that lines and
bowl are required at early stages to specify the DP and the PE,
suggesting that the maintenance of these fates depends on additional
mechanisms. However, they reveal a later role for lines in
maintaining distal pouch identities and in inhibiting the specification of
proximal hinge identities.
|
DISCUSSION |
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|
TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
|---|
|
;
Cho et al., 2000;
Gibson and Schubiger, 2000;
McClure and Schubiger, 2005;
Pallavi and Shashidhara,
2003). Our mapping studies show that the distribution of Bowl and
Lines correlates with the establishment of this asymmetry (Figs
1,
2). The wing primordium
inherits its subdivision into en-expressing cells that form the
posterior compartment and adjacent anterior compartment cells from the
embryonic epidermis (Cohen et al.,
1991; Cohen,
1990). Bowl accumulates in the posterior en-expressing
cells in the embryonic epidermis (Hatini
et al., 2005), suggesting that the wing primordium also inherits
the PE/DP subdivisions from pre-existing asymmetries across this tissue.
Reciprocal roles for lines and bowl in specifying alternative cell fates across the wing imaginal disc
lines and odd-skipped genes act as a switch to specify
alternative cell fates across fields of cells
(Fig. 1L). bowl and
lines specify the alternative 1°-3° and 4° cell fate
across the dorsal embryonic epidermis
(Bokor and DiNardo, 1996;
Hatini et al., 2000;
Hatini et al., 2005).
bowl and lines also specify alternative cell fates in the
developing gut, leg and eye imaginal discs
(Iwaki et al., 2001;
Johansen et al., 2003;
Bras-Pereira et al., 2006;
de Celis Ibeas and Bray, 2003;
Hatini et al., 2005). The
asymmetric distributions of Bowl and odd-skipped genes, and the
reciprocal distribution of Lines in the wing primordium are also used to
specify the alternative PE and DP fates. Indeed, our functional studies show
that ectopic lines expression or the inhibition of bowl
function in the PE transforms PE into DP fate. Reciprocally, the removal of
lines function from the DP transforms DP into PE fate. Our data
further suggest that lines exerts its function by controlling the
stability of the Bowl protein (see Fig. S4 in the supplementary material).
Thus, lines and bowl act as a switch to specify alternative
DP and PE fates across the wing primordium. The distribution of Lines and Bowl
correlates with the subdivision of the wing primordium into a thin squamous
and a thickened columnar epithelial sheet. The activation of EGF receptor and
Wg signaling in the DP may specify the formation of a columnar epithelial
morphology (Baena-Lopez et al.,
2003). The pathways that specify the squamous morphology of the PE
downstream to bowl remain to be elucidated.
The subdivision of the wing imaginal disc into DP and PE is critical for wing growth
Previous studies that relied on surgical and genetic ablations of the PE,
and on inhibition of certain signaling pathways within the PE, suggested
important roles for the PE in disc growth and patterning
(Baena-Lopez et al., 2003;
Cho et al., 2000;
Gibson and Schubiger, 2000;
McClure and Schubiger, 2005;
Pallavi and Shashidhara,
2003). We were now able to examine wing development in discs
lacking PE. These discs were significantly smaller than wild type
(Fig. 3B,E;
Fig. 4B-D,F-L), and the notum
was dramatically reduced in size relative to the pouch and hinge
(Fig. 4F). Progenitor cells
that originate in the PE may stream laterally to populate the growing notum
(McClure and Schubiger, 2005;
Pallavi and Shashidhara,
2003), and the loss of this progenitor cell population may account
for the severe reduction in notal growth. The reduction in wing growth could
have resulted from the disruption of Wg or Dpp signaling activities, as these
morphogens control cell survival and cell proliferation in the wing
(Burke and Basler, 1996;
Gibson and Perrimon, 2005;
Giraldez and Cohen, 2003;
Johnston and Sanders, 2003;
Martin-Castellanos and Edgar,
2002; Moreno et al.,
2002; Neumann and Cohen,
1996; Shen and Dahmann,
2005). Indeed, a block to Dpp or Wg signaling results in formation
of tiny wing rudiments (Adachi-Yamada et
al., 1999; Bryant,
1978; Couso et al.,
1993; Morata and Lawrence,
1977; Sharma and Chopra,
1976). However, the expression of Wg and Dpp and their target
genes was normal in these discs, indicating that the reduction in wing growth
was not a consequence of the loss of wg or dpp expression,
or of signaling activities (Fig.
4J,L). Our findings instead suggest that the PE acts in parallel
to the AP, DV and PD patterning systems, in part, by promoting cell survival
in the DP, and in part by promoting the growth of the notum.
|
). lines and bowl act cell autonomously to
control the fate, affinity and the interaction between the PE and the DP. As a
putative transcription factor, Bowl may regulate a developmental program to
control the identity and the behavior of the PE. By inhibiting Bowl
accumulation, lines may allow the execution of an alternative
developmental program in the DP. Our studies define a new system to identify,
in a systematic way, these developmental programs.
Supplementary material
Supplementary material for this article is available at
http://dev.biologists.org/cgi/content/full/135/18/3031/DC1
|
ACKNOWLEDGMENTS |
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|
REFERENCES |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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