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First published online 3 August 2006
doi: 10.1242/dev.02511
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maintains vestigial-expressing cells within the Drosophila wing disc epithelium
1 Developmental Biology Institute of Marseille Luminy, UMR6216 - Case 907, Parc
Scientific de Luminy, 13288 Marseille Cedex 09, France.
2 Skirball Institute of Biomolecular Medicine and Department of Cell Biology,
NYU School of Medicine, New York, NY 10016, USA.
Author for correspondence (e-mail:
fjanody{at}igc.gulbenkian.pt)
Accepted 26 June 2006
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SUMMARY |
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 TOP SUMMARY INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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(Cpa) and Capping protein ß (Cpb), which prevent
extension of the barbed ends of actin filaments, are specifically required in
the wing blade primordium of the Drosophila wing disc. cpa
or cpb mutant cells in this region, but not in the remainder of the
wing disc, are extruded from the epithelium and undergo apoptosis. Excessive
actin filament polymerization is not sufficient to explain this phenotype, as
loss of Cofilin or Cyclase-associated protein does not cause cell extrusion or
death. Misexpression of Vestigial, the transcription factor that specifies the
wing blade, both increases cpa transcription and makes cells
dependent on cpa for their maintenance in the epithelium. Our results
suggest that Vestigial specifies the cytoskeletal changes that lead to
morphogenesis of the adult wing.
Key words: Actin, Cytoskeleton, Capping protein, Wing disc, Vestigial, Epithelium, Drosophila
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INTRODUCTION |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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;
Jamora and Fuchs, 2002). The
actin cytoskeleton controls cell morphology and polarity, endocytosis,
intracellular trafficking, contractility and cell division. Filamentous (F)
actin is assembled from monomeric (G) actin subunits. Polymerization occurs
predominantly by extension of the fast-growing barbed ends of the filaments,
while filaments are disassembled by loss of monomers from the slow-growing
pointed ends. Actin filament growth, stability and disassembly are controlled
by a plethora of actin-binding proteins. Profilin, formins and Enabled/VASP
(Ena/VASP) family proteins promote actin polymerization, while Cofilin,
Cyclase-associated protein (CAP) and capping proteins (CPs) restrict actin
polymerization by different mechanisms
(dos Remedios et al., 2003;
Wear and Cooper, 2004;
Winder and Ayscough, 2005).
Cofilin severs filaments and enhances dissociation of actin monomers from the
pointed end (Bamburg, 1999);
CAP sequesters actin monomers, preventing their incorporation into filaments
(Amberg et al., 1995;
Gottwald et al., 1996); and
CPs restrict accessibility of the barbed end, inhibiting addition or loss of
actin monomers (Schafer et al.,
1995).
Functional CPs are a highly conserved ß heterodimer that bind
the barbed ends of actin filaments through the C-terminal regions of both
subunits (Amatruda et al.,
1992; Schafer et al.,
1992; Wear and Cooper,
2004). CPs and the Arp2/3 complex, which promotes filament
branching, favor formation of the short highly branched actin filaments
required to generate protrusive force at the leading edge of migrating cells.
Ena/VASP proteins have the opposite activity, promoting formation of long
unbranched parallel bundles of actin filaments
(Bear et al., 2002;
Pantaloni et al., 2000;
Pollard and Borisy, 2003). In
mouse or Dictyostelium cells, depletion of CPs can cause extensive
formation of filopodia and increase the length and bundling of actin
filaments, reducing cell motility (Hug et
al., 1995; Mejillano et al.,
2004). Another function of CPs is to cap a short filament of the
actin-related protein Arp1 in the Dynactin complex, which is required for
Dynein-mediated transport along microtubules
(Schafer et al., 1994).
Drosophila imaginal discs are bilayered epithelial tissues
consisting of a columnar monolayer epithelium covered by a squamous peripodial
epithelium. The columnar epithelial cells are polarized along the apicobasal
axis. Adherens junctions (AJ) composed of E-cadherin and - and
ß-catenin link the actin cytoskeleton of neighboring cells, forming an
adhesive belt. In Drosophila, two complexes important for polarity
are present in the subapical region just apical to the AJ: the
Bazooka/Par-6/aPKC complex and the Crumbs/Stardust/Pals-associated tight
junction (Patj) complex. Finally, the septate junction, basal to the AJ and
formed by the Discs-large (Dlg)/Scribble/Lethal giant larvae complex,
establishes a barrier preventing the diffusion of solutes across the
epithelium (Gibson and Perrimon,
2003). Cells that lack these apical complexes are defined as
mesenchymal (Fristrom,
1988).
The wing disc has a concentrically organized proximodistal (PD) axis; the
primordium of the wing blade is in the center, surrounded by the wing hinge
primordium, with the notum and pleura at the periphery. During the second
larval instar, an antagonistic relationship between epidermal growth factor
(EGF) and Wingless (Wg) signaling divides the disc into a dorsal region that
gives rise to the notum, and a ventral region that forms the wing. The wing is
further subdivided by expression of the selector genes vestigial
(vg) and scalloped (sd) in the wing blade and
homothorax (hth) in the wing hinge
(Klein, 2001). Vg and Sd
encode subunits of a heterodimeric transcription factor that controls wing
identity (de Celis, 1999);
vg is required for wing formation
(Williams et al., 1991) and
its misexpression can induce ectopic wing tissue
(Kim et al., 1996).
In a mosaic genetic screen for genes required during early eye
differentiation (Janody et al.,
2004), we identified loss-of-function mutations in the genes
encoding Capping protein (Cpa), the CAP homolog Capulet (Capt) and the
Cofilin homolog Twinstar (Tsr). Here, we show that Cpa, as well as the
previously identified Capping protein ß (Cpb), prevent extrusion and
death of cells in the wing blade epithelium, but are not required for this
function in other regions of the wing disc. Although cpa, capt and
tsr mutations all increase actin filament polymerization, only
cpa is required to maintain vg-expressing cells within the
epithelium. Furthermore, Vg enhances transcription of cpa in the wing
blade region. These results provide a link between pattern formation
controlled by Vg and morphogenesis of the wing blade through cytoskeletal
regulation mediated by actin capping proteins.
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MATERIALS AND METHODS |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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). Five lethal alleles of cpa
(cpa36P, cpa43D, cpa66A,
cpa69E and cpa107E) and four lethal
alleles of tsr (tsr76E, tsr99E,
tsr100A and tsr110M) were recovered from a
screen of 45,000 flies on the right arm of the second chromosome.
Recombination mapping relative to P(w+) elements localized
the cpa gene between 57A8-9 and 57D11-12, 1.5 cM proximal to P
element l(2)K02206 and 0.9 cM distal to P element domK08108 (FlyBase). Our
alleles failed to complement the lethal P element CG10540KG02261
(FlyBase), which is inserted in the cpa gene. Recombination mapping
relative to P(w+) elements localized the tsr
alleles to 0.42 cM distal to P element elF6(K13214) (FlyBase) and identified a
lethal P element in the tsr gene, l(2)k05633k05633
(FlyBase), which failed to complement our tsr alleles. Other fly
stocks used were cpbM143, khck13314,
bs2 (FlyBase), captE636,
captE593 (Benlali et al.,
2000), da-Gal4
(Wodarz et al., 1995),
tub-Gal4 (Lee and Luo,
1999), puc-lacZ
(Martin-Blanco et al., 1998),
UAS-th (Ryoo et al.,
2002), UAS-vg23 (Kim
et al., 1996), UAS-Nintra
(Doherty et al., 1996),
UAS-bskDN
(Adachi-Yamada et al., 1999b),
UAS-Mal-D-
N and UAS-diaCA
(Somogyi and Rorth, 2004). To
generate clones marked by the absence of GFP in the wing disc, y, w;
FRT42D, cpa or tsr/CyO P(y+) or y, w;
FRT40, capt/SM6-TM6B males were crossed to y, w, hsFLP122;
FRT42D or 40, ubi-GFP females. To generate clones positively labeled
by GFP, y, w; FRT42D, cpa or tsr/CyO
P(y+) or y, w; FRT40, capt or
cpb/CyO P(y+) males were crossed to y, w,
hsFLP122, UAS-GFP; FRT42D or FRT40, tub-GAL80;
tub-GAL4/TM6B. puc-LacZ, UAS-th, UAS-vg or
UAS-Nintra transgenes were combined with the FRT42D or
FRT42D, cpa chromosomes. The offspring were heat-shocked for 1 hour
at 37°C at both 24 and 48 hours after a 24 hour egg collection,
corresponding to the first and second larval instar. To visualize cpa
or tsr mutant clones at different times after induction, larvae were
heat-shocked for 1 hour at 37°C at 60 hours after a 24 hour egg
collection. Wing discs were dissected from crawling late third instar larvae
either 36 or 60 hours after the heat shock; these had clones induced at early
third instar or at second instar, respectively. All experiments were performed
at 25°C. To rescue survival of cpa mutants, da-GAL4 or
tub-GAL4; cpa/SM6-TM6B flies were crossed to UAS-HA-cpa,
cpa/SM6-TM6B. To rescue cpa mutant clones in the wing imaginal
disc, y, w, hsFLP122, UAS-GFP; FRT42D, tub-GAL80;
tub-GAL4/TM6B flies were crossed to FRT42D, cpa;
UAS-HA-cpa/SM6-TM6B.
Immunohistochemistry and in situ hybridization
Third instar larval imaginal discs were stained with antibodies as
described (Lee and Treisman,
2001). Antibodies used were guinea pig anti-Dlg (1:300; gift from
P. J. Bryant), mouse anti-Arm [N2 7A1, 1:10; Developmental Studies Hybridoma
Bank (DSHB)], rabbit anti-Caspase 3 (1:500; BD Bioscience), mouse
anti-ß-galactosidase (1:200; Promega), rabbit anti-Vg (1:20);
(Williams et al., 1993), mouse
anti-HA (1/5000; Covance). Secondary antibodies were from Jackson
Immunoresearch, used at 1:200 or Molecular Probes, used at 1:500, conjugated
to FITC, Texas Red or Cy5. Rhodamine-conjugated phalloidin (Sigma) was used at
a concentration of 0.3 µM. Fluorescence images were obtained on a Leica TCS
NT confocal microscope or on a LSM 510 Zeiss confocal microscope. For in situ
hybridization, antisense or sense RNA probes, labeled with digoxigenin-UTP
(Roche), and encompassing the entire cpa cDNA were used. In situ
hybridization was performed as described
(Maurel-Zaffran and Treisman,
2000), except that a biotinylated anti-digoxigenin antibody (1:500
Jackson Immunoresearch) was followed by TSA enhancement (TSA-indirect Perkin
Elmer Life Science) coupled to Streptavidin Texas Red or Fluorescein (1:100,
Perkin Elmer Life Science). Imaginal discs were mounted in Vectashield medium
(Vector Laboratories).
Molecular biology
The cpa cDNA clone (GH10050) was obtained from the Berkeley
Drosophila genome project, and was amplified by PCR and cloned into
HA-pUAST as an EcoRI fragment to generate UAS-HA-cpa.
Transgenic flies were generated by standard methods. For each of the five
cpa or four tsr alleles recovered in our screen, the coding
region was amplified by PCR from DNA obtained from homozygous mutant first
instar larvae and from the isogenic FRT42D line. cpa107E,
cpa36P and cpa69E contain nonsense
mutations at amino acids 162, 174 and 180, respectively, that would truncate
the Cpa protein before the actin-binding domain. cpa43D
contains a nucleotide substitution that changes Asn190 to Gly. The four tsr
alleles contain missense mutations: tsr76E changes Gly79
to Asp, tsr99E changes Asp146 to Asn,
tsr100A changes Leu89 to Gln, and
tsr110M changes Gly67 to Glu.
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RESULTS |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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), we identified lethal alleles of cpa, tsr and
capt. Capping protein, Cofilin and CAP all restrict actin filament
polymerization (Bamburg, 1999;
Gottwald et al., 1996;
Schafer et al., 1995), and
loss of any of these genes results in a severe degenerative phenotype in the
adult eye (Delalle et al.,
2005) (and data not shown).
Surprisingly, we found a region-specific requirement for cpa in
the wing disc: cpa mutant clones induced at the first or second
larval instar could not be recovered in the wing blade epithelium, although
mutant clones could develop in the remainder of the wing disc
(Fig. 1A). By contrast, clones
mutant for tsr or capt survived equally well in all regions
of the disc (Fig. 1B,C).
Optical cross-sections through the wing disc showed that in the wing blade
region, positively labeled cpa mutant cells were found on the basal
surface of the disc rather than within the epithelium
(Fig. 1D). However,
tsr and capt mutant clones were maintained within the
epithelium in all regions of the wing disc
(Fig. 1F,G). Cpa functions as a
heterodimer with its partner Capping protein ß (Cpb)
(Amatruda et al., 1992;
Schafer et al., 1992), and the
stability of each subunit depends on its association with the other
(Casella and Torres, 1994;
Mejillano et al., 2004). As
expected, we found that cpb mutant cells were also extruded on the
basal surface in the wing blade region, but not in the remainder of the wing
disc (Fig. 1E). Thus,
cpa and cpb are both required to maintain epithelial
integrity specifically in the wing blade primordium, suggesting that this
subregion of the epithelium has a distinct cellular organization.
The cpa alleles exhibiting this phenotype included likely null
alleles that would truncate the protein before the actin-binding domain. To
confirm that the loss of cells from the wing pouch epithelium was due to
mutations in the cpa gene, we generated transgenic fly lines
expressing the full-length cpa transcript under the control of UAS
sequences (Brand and Perrimon,
1993). Expression of this transcript rescued the cell extrusion
phenotype of cpa mutant clones in the wing blade epithelium
(Fig. 1H). Driving expression
of this transcript ubiquitously throughout development using
daughterless (da)-GAL4 or tubulin
(tub)-GAL4 was also sufficient to rescue the lethality of
cpa mutants, although some of the rescued adults exhibited wing, eye
or bristle defects (Table 1;
data not shown).
|
),
indicating that JNK signaling is activated.
|
). To
determine whether extrusion of cpa mutant cells from the wing blade
epithelium reflects a preliminary stage of apoptosis, we used the MARCM system
to express the Drosophila Inhibitor of Apoptosis Protein
(DIAP1; th - FlyBase) to prevent apoptosis of cpa
mutant cells. Expression of th in wild-type clones had no visible
effect (Fig. 2E,H). Survival of
cpa mutant cells was greatly enhanced when th was
overexpressed (compare Fig. 2D
with 2F); however, mutant cells
still lost contact with the apical epithelial surface and were extruded
basally (Fig. 2I). The same
result was obtained using the caspase inhibitor P35 to block cell death (data
not shown). This suggests that extrusion of cpa mutant cells is
independent of programmed cell death.
|
). Disruption of cortical actin assembly and apicobasal
polarity can induce cell extrusion in the wing disc, as in moesin
mutants (Speck et al., 2003).
By contrast, tkv mutant cells are extruded as cysts that maintain
apical junctions with one another (Gibson
and Perrimon, 2005; Shen and
Dahmann, 2005). Interestingly, we found that an HA-tagged form of
Cpa, which could rescue extrusion of cpa mutant cells, accumulated at
the apical cell membrane in all regions of the wing disc
(Fig. 3A). In the wing blade
primordium, HA-Cpa partly colocalized with components of epithelial junctions,
including Armadillo (Arm) (Fig.
3B-B'''), Discs large (Dlg) and Crumbs (data not shown). We
therefore examined the apicobasal polarity of cpa mutant cells. Cells
that had extruded from the epithelium no longer expressed the AJ components
Arm (Drosophila ß-catenin) or DE-cadherin (DE-Cad), the SJ
component Dlg, or the Crumbs complex component Pals-associated tight junction
protein (Patj) (Fig.
3C-C'' and data not shown). When we examined discs 36 hours
after clone induction, cpa mutant cells in the wing pouch were still
present within the epithelium. In these cells, Arm
(Fig. 3D-D'') and DE-Cad
(data not shown) were mislocalized at basolateral positions, while Dlg
localization was unaffected. However, Arm localization was normal in clones
induced in the notum region (Fig.
3F-F''). This suggests that, in the wing blade epithelium,
Cpa localized at cellular junctions maintains the localization of AJ
components. However, Arm was also mislocalized at basolateral positions in
tsr mutant clones (Fig.
3E-E''), indicating that mislocalization of AJ components is
not sufficient to cause cell extrusion.
|
).
Decreased expression of cpa or cpb in the
Drosophila eye imaginal disc causes actin filament accumulation
(Delalle et al., 2005). To confirm that cpa also restricts growth of
actin filaments in the wing disc epithelium, we stained wing imaginal discs
with phalloidin 36 hours after clone induction, allowing visualization of
mutant clones before cell extrusion. As expected, cpa mutant clones
accumulated actin filaments in all regions of the wing disc
(Fig. 4A-A'). Optical
cross-sections through the notum showed that, like capt mutant cells
(Fig. 4E-E')
(Baum and Perrimon, 2001),
cpa mutant cells accumulated actin filaments near the apical cell
membrane (Fig. 4C-C'').
However, cpa mutant cells in the wing blade accumulated actin
filaments around the entire cell cortex
(Fig. 4B-B''), resembling
tsr mutant cells (Fig.
4D-D'). As Cpa is concentrated at the apical cell membrane
(Fig. 3A-B'''), the
presence of excess actin filaments in basolateral regions may be due to the
effect of cpa on apicobasal polarity. Indeed, some of these actin
filaments colocalized with Arm displaced from apical adherens junctions
(Fig. 4B-B'').
Vestigial controls the requirement for cpa in the wing blade epithelium
We observed extrusion of cpa mutant clones only in the wing pouch,
indicating that either the position or identity of these cells makes them
dependent on cpa. Signaling pathways activated by Wg, Decapentaplegic
(Dpp) and Notch (N) can influence growth and/or survival in the wing blade
primordium (Klein, 2001).
Target genes of these pathways, including Vg
(Klein and Arias, 1999), were
still expressed in cpa mutant clones
(Fig. 5A-A'' and data not
shown), indicating that cpa is not required for the reception of
these signals. Vg is a nuclear protein that confers a wing blade fate on cells
in which it is expressed (Williams et al.,
1991). We wondered whether transforming hinge or notum cells to
wing blade identity by misexpressing Vg would induce extrusion of cpa
mutant cells. When we misexpressed vg in cpa mutant clones,
we found that clones in all regions of the wing disc were extruded from the
epithelium and contained activated Caspase 3 (compare
Fig. 5B,D with
Fig. 5E,G). Misexpressing
vg in clones that were not mutant for cpa had neither of
these effects (Fig. 5C,F).
Thus, cpa is autonomously required for the survival and maintenance
of vg-expressing cells in the wing disc epithelium, independently of
the identity of the surrounding cells.
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DISCUSSION |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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).
The function of CPs in organelle or vesicle transport is unlikely to
explain the extrusion phenotype. CPs are thought to stabilize the barbed end
of the Arp1 microfilament in the Dynactin complex, which is required for
transport along microtubules (Schafer et
al., 1994). cpa and cpb, like other Dynactin
complex subunits, are required to maintain the position of nuclei in
Drosophila photoreceptor neurons
(Whited et al., 2004) (and
data not shown). However, removal of kinesin heavy chain
(khc), which counteracts Dynein/Dynactin-based transport, failed to
rescue extrusion of cpa mutant cells in the wing disc (see Fig. S1C
in the supplementary material).
We considered the possibility that the cpa phenotype was due to
its effect on monomeric G-actin levels rather than on the filamentous actin
cytoskeleton. G-actin has been shown to negatively regulate the nuclear
localization and activity of Mal, a transcriptional cofactor for SRF
(Miralles et al., 2003), and
overexpression of Mal or of its activator diaphanous
(Somogyi and Rorth, 2004) can
cause extrusion and death of wing epithelial cells (see Fig. S1F,G in the
supplementary material). However, overactivity of the MAL/dSRF pathway is
unlikely to be responsible for extrusion of cpa mutant cells in the
wing blade, as clones mutant for both cpa and blistered
(bs), which encodes Drosophila SRF, were still extruded from
the wing epithelium (see Fig. S1H in the supplementary material).
Extrusion of cpa or cpb mutant cells might be a direct
result of defects in the actin cytoskeleton. Consistent with the requirement
for CPs to inhibit addition of actin monomers to the fast-growing end of actin
filaments (Schafer et al.,
1995), we observed a strong accumulation of actin filaments in
cpa mutant clones. However, tsr and capt mutations
also induce excessive actin filament polymerization
(Fig. 4)
(Baum and Perrimon, 2001) but
do not cause cell extrusion. The major function of Tsr (Cofilin) is to promote
dissociation of ADP-actin from the pointed end of the filament, while Cpa
prevents elongation of the barbed end of each branch and Capt sequesters actin
monomers. The phenotypic differences between cpa, tsr and
capt might therefore be due to different degrees of branching of the
actin network formed in mutant cells (Fig.
7A). Possibly long unbranched filaments do not provide a framework
of sufficient strength to withstand forces that place tension on the cell
within the epithelium.
Extrusion is associated with dispersion of the adherens junction components
Arm and DE-Cad along the lateral membranes. However, this defect is also
observed in tsr mutant clones, and mislocalization of adherens
junction components caused by overexpression of a dominant form of the
polarity gene crumbs (Fan et al.,
2003; Grzeschik and Knust,
2005; Izaddoost et al.,
2002) or a dominant-negative form of Dcdc42
(Eaton et al., 1995) does not
lead to cell extrusion. Therefore, mislocalization of AJ components is
unlikely to be sufficient to cause extrusion of cpa mutant cells. By
contrast, expression of dominant-negative Rac1, which prevents actin
localization to adherens junctions, induces cell extrusion and death
(Eaton et al., 1995). Thus,
another possibility is that CPs may be crucial for linking actin filaments to
the membrane, as has been previously proposed in other systems
(Hutchings et al., 2003;
Schafer et al., 1992;
Schafer et al., 1998). Loss of
cpb displaces actin bundles from the cell membrane in
Drosophila bristles by increasing the concentration of non-bundle
actin snarls (Hopmann et al.,
1996; Frank et al.,
2006) and CPs may specify actin filament position in the sarcomere
(Schafer et al., 1995). In the
Drosophila wing blade epithelium, loss of CPs might disrupt
attachment of the actin cytoskeleton to the adherens junctions, breaking the
connection between cells and inducing cell extrusion
(Fig. 7C). The localization of
HA-Cpa to apical junctions and the mislocalization of actin filaments
throughout cpa mutant cells in the wing blade are consistent with
this possibility. Such a role would be restricted to the wing blade, as
cpa mutant cells within the notum epithelium accumulate actin
filaments only at the apical cell membrane.
|
) (and data not shown). The requirement for cpa
depends on the wing blade selector gene Vg, as expression of Vg in notum cells
is sufficient to induce their extrusion in the absence of cpa. Vg
also enhances the transcription of cpa in the wing blade primordium.
Taken together, these results imply that patterning genes regulate
cytoskeletal properties in order to achieve distinct morphological outcomes
(Fig. 7B,C).
The molecular mechanism that makes Vg-expressing cells dependent on CPs for
their maintenance in the epithelium is unknown, although our data support a
cell-autonomous target of Vg. One possibility is that Vg promotes the
expression or recruitment of an actin filament polymerizing factor. The role
of CPs might be to restrict its activity at barbed ends, preventing the
formation of a specific actin-based structure that induces loss of cell-cell
contacts and extrusion. For example, Vg activates the expression of the type
II transmembrane protein Four jointed (Fj), which regulates the activity of
the cadherin Fat (Cho and Irvine,
2004). Mammalian Fat1 can recruit Ena/VASP proteins, which promote
actin polymerization at cell-cell contacts by antagonizing CPs
(Moeller et al., 2004;
Tanoue and Takeichi, 2004).
However, misexpression of fj does not induce extrusion of either
wild-type or cpa mutant cells in the notum
(Cho and Irvine, 2004) (and
data not shown). DE-cadherin levels are also higher in the wing pouch
(Jaiswal et al., 2006), but
increasing them in the hinge or notum by activating Wg signaling does not
cause extrusion of cpa mutant cells (data not shown). Alternatively,
Vg might control the expression of factors that promote the remodeling of cell
junctions required for morphogenesis of the wing. Cpa could be required to
maintain the connection between cells in the epithelium during these
morphogenetic movements.
The non-uniform distribution of and requirement for cpa suggests
that cytoskeletal organization varies in different regions of the wing disc.
Gibson and Perrimon (Gibson and Perrimon,
2005) observed that lateral wing disc cells had moderately reduced
levels of basolateral cortical F-actin. In addition, filopodial extensions
called cytonemes are oriented towards the AP and/or DV boundary within the
wing pouch, while hinge cells do not extend cytonemes and notum cells radiate
short cytonemes in all directions (Hsiung
et al., 2005). Changes in cytoskeletal organization have been
shown to establish cell affinity boundaries
(Major and Irvine, 2005), to
control the subcellular localization of transcription factors
(Miralles et al., 2003) and to
modulate the transport of signaling molecules
(Benlali et al., 2000;
Hsiung et al., 2005).
Investigating the control of cpa by Vg may help us to understand how
and why patterning genes regulate cell architecture. In addition, identifying
additional target genes of Vg may illuminate how actin dynamics and changes in
intercellular adhesion control the formation of the wing blade.
Supplementary material
Supplementary material for this article is available at
http://dev.biologists.org/cgi/content/full/133/17/3349/DC1
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ACKNOWLEDGMENTS |
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Footnotes |
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TOPSUMMARYINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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