QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online 24 September 2003
doi: 10.1242/dev.00759

This Article Summary Full Text Full Text (PDF) An erratum has been published Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Gaengel, K. Articles by Mlodzik, M. Search for Related Content PubMed PubMed Citation Articles by Gaengel, K. Articles by Mlodzik, M.

Egfr signaling regulates ommatidial rotation and cell motility in the Drosophila eye via MAPK/Pnt signaling and the Ras effector Canoe/AF6

Mount Sinai School of Medicine, Brookdale Department of Molecular, Cell and Developmental Biology, 1 Gustave L. Levy Place, New York, NY 10029, USA

View larger version (91K): [in a new window]   Fig. 1. The roulette mutant is an allele of the Egfr-ligand argos. Panels show eye imaginal discs (A-C) or adult eye sections (D-I). Anterior is left and dorsal up. (A) Eye-imaginal disc stained with anti-Elav (red, all photoreceptor precursors) and m0.5-lacZ (blue, R4 precursors) shown as an overlay with a Nomarski optics bright-field view of same disc. The dorsoventral midline, equator (Eq), is marked by white broken line, the position of the morphogenetic furrow (MF) is indicated. (B) Higher magnification of boxed area from A also showing anti-Boss (green, marking the central R8 cell in each cluster). Note regular arrangement and orientation of ommatidial clusters. Overlay of the red and blue channels is for clarity shown in blue. (C) Semi-schematic presentation of ommatidial rotation (generated from real clusters shown in A,B with the `solarize' filter of Adobe Photoshop). Representative clusters for the dorsal and ventral halves are shown. Colors are as in B. R3/R4 photoreceptor precursors are indicated by white numbers. Ommatidial preclusters represent examples from columns 4, 5, 7, 9, 12 and 15, respectively. Yellow arrows indicate rotation of clusters. The rotation angle of individual clusters is indicated above the panel. The `base' of arrows indicates the R3/R4 axis and the arrowheads point towards the middle of cluster. Note successive changes in the rotation angles to the complete 90°. (D) Examples of mature adult ommatidia with numbered photoreceptor rhabdomeres (R1-R7; R8 is below the plane of section) and schematic arrows as shown in E-I. Black arrow: dorsal ommatidium; red arrow: ventral ommatidium. (E-I) Tangential sections of equatorial region of adult eyes with schematic presentations below sections. (E) wild-type (wt), (F) argos-roulette (aosrlt/aosrlt), (G) aosrlt/aos7, (H) aosrlt/Df(3L)st7P, (I) sev-aos/+; aosrlt/aosrlt. Note that aosrlt fails to complement aos alleles and that sev-aos fully rescues the aosrlt phenotype. Ommatidia with a wt photoreceptor number are represented by arrows with flags; clusters with extra photoreceptors are indicated by simple arrows.

View larger version (70K): [in a new window]   Fig. 2. Eye imaginal discs mutant for argos or canoe exhibit defects in ommatidial rotation. Panels show a dorsal field of third instar eye imaginal discs, anterior is left and dorsal up. Discs in A,B are double-stained with anti-Elav (red; all photoreceptors) and svp-lacZ (green; marking R3/R4 and R1/R6). (C-F) Double-labeled with anti-Bar (red; labeling R1/R6) and anti-Boss (green; marking R8). With these markers rotation angles can be unambiguously determined and are schematically shown with arrows below each panel (arrows are drawn according to Fig. 1C). (A,C) wild-type, (B,D) aosrlt/aosrlt, (E) aosw11/aosw11. Note misrotations in both aos alleles. (F) cnomis1/cnomis1. Discs were costained with anti-Elav to ensure that rotation abnormalities are not because of photoreceptor loss (blue channel, not shown).

View larger version (100K): [in a new window]   Fig. 3. Reduction in Egfr signaling affects ommatidial rotation. Panels show tangential adult eye sections around the equator and corresponding schemes reflecting ommatidial rotation. Orientation and arrows are as in Fig. 1, `circles' represent ommatidia with loss of photoreceptors that cannot be unambiguously scored (`asterisk' indicates the rare event of a symmetrical ommatidium). (A) Egfrtop1/Egfrtop1, (B) Egfrtop1/EgfrtopEC20. The hypomorphic Egfrtop1 allele and Egfrtop1/EgfrEC20 allelic combination show typical rotation defects. Reduction of Egfr activity in Star–/+ causes rotation defects and is dominantly enhanced by components of Egfr signaling. Star is haplo-insufficient for eye development (note rare photoreceptor loss and rotation defects). The rotation defects are dominantly enhanced by removal of components of the Egfr/Ras pathway (compare C with D,E). Note that canoe, flamingo and zipper heterozygosity also enhances the S–/+ phenotype (see Table 1 for other genotypes and quantification). (C) S48-5/+, (D) S48-5/+, Egfrtop1/+, (E) S48-5/+; ras1e2F/+, (F) S48-5/+; cno2/+, (G) S48-5/+; fmiE59/+, (H) S48-5/+; zipper02957/+.

View larger version (67K): [in a new window]   Fig. 4. aosrlt is dominantly suppressed by components of the Egfr pathway and nemo. Panels show tangential adult eye sections through equatorial regions and corresponding schematic drawings indicating ommatidial rotation. Orientation and arrows are as in Fig. 1, `stars' indicate rare event of symmetrical ommatidia. (A) aosrlt/aosrlt. (B) Egfrtop1/+; aosrlt/aosrlt, (C) ras1e2F/+, aosrlt/aosrlt. (D) pnt88/+; aosrlt/aosrlt. (E) nmoP1/+, aosrlt/aosrlt.

View larger version (65K): [in a new window]   Fig. 5. Expression of Ras-effector loop mutations affects ommatidial rotation. (A-F) Tangential sections of adult eyes through equatorial regions and corresponding schematic drawings indicating ommatidial rotation. Orientation, arrows and circles are as in Figs 1, 3. (A) m0.5Gal4>UAS-RasV12 (A similar, but weaker effect was generated by activated Egfr {-top} under m0.5Gal4 control; not shown), (B) m0.5Gal4>UAS-RasV12[S35]. (C) m0.5Gal4>UAS-RasV12[G37], (D) m0.5Gal4>UAS-RasV12[C40], (E) sevGal4>UASRasV12[G37], (F) sevGal4>UAS-RasV12[C40].

View larger version (78K): [in a new window]   Fig. 6. Effects of Ral and Canoe on ommatidial rotation. (A,B) Tangential sections of adult eyes. An equatorial region is shown with the corresponding schematic presentation. Arrows and circles are drawn as in Figs 1, 3. (A) GMR-RalG23V (an activated isoform of Ral); (B) cnomis1/cno2, a subviable hypomorphic allelic combination. Note the severe rotation defects in the cno mutant background.

View larger version (114K): [in a new window]   Fig. 7. Expression of the atypical cadherin Flamingo is altered within the R3/R4 precursor pair in argosrlt discs. Confocal images of third instar eye discs are shown, anterior is left. The morphogenetic furrow is at the left edge of each panel. (A,C,G) wild-type (WT) and (B,D,H) aosrlt discs stained with anti-Fmi (green in A-D, black and white in A' and B'), anti-DE-cadherin (magenta in A,B and b/w in A'' and B'') and F-actin (red, labeled by Phalloidin, in C,D and b/w in C',D'). A higher magnification of the Fmi and DE-cadherin stainings in similar discs is shown in G and H (ommatidial rows 1-11). Note that Fmi, in WT downregulated in the R3 precursor by row 7 and subsequently detected only around R4, is still present in R3 cells in aosrlt until rows 11-12 and beyond. Typical WT and mutant examples are highlighted with yellow arrowheads in A',B',G,H. Abnormal localization of Fmi does not correlate with R3/R4 cell-fate defects, as the R4-specific marker m-lacZ is restricted to R4 in WT (E) and aosrlt mutant (F) preclusters.

View larger version (41K): [in a new window]   Fig. 8. Model for the role of Egfr/Ras signaling in the context of ommatidial rotation. Raf/MAPK nuclear signaling to Pnt upregulates the transcription of activating (spi) and inhibiting (aos) Egfr ligands and might regulate transcription of additional genes important for ommatidial rotation. Egfr/Ras signal via Canoe to affect cytoskeletal and/or cell junctional elements (junctions are schematized as black oval regions on membrane). In addition, Egfr signaling affects Flamingo localization (the effector regulating this aspect is not known).