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

doi: 10.1242/10.1242/dev.00602

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Related articles in Development 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 Google Scholar Google Scholar Articles by Rawlins, E. L. Articles by Jarman, A. P. Search for Related Content PubMed PubMed Citation Articles by Rawlins, E. L. Articles by Jarman, A. P.

Echinoid limits R8 photoreceptor specification by inhibiting inappropriate EGF receptor signalling within R8 equivalence groups

Wellcome Trust Centre for Cell Biology, Institute of Cell and Molecular Biology, University of Edinburgh, King's Buildings, Edinburgh EH9 3JR, UK

View larger version (153K): [in a new window]   Fig. 1. E(ato109-68)4.12 enhances the rough eye phenotype of ato109-68 and also displays a rough eye as a homozygote. (A-D) Scanning electron microscopy of the adult compound eye. (A) Wild type. (B) ato109-68. (C) ato109-68/E(ato109-68)4.12. (D) E(ato109-68)4.12/E(ato109-68)4.12.

View larger version (113K): [in a new window]   Fig. 2. R8 photoreceptors are frequently twinned in ed mutants. (A-E) Confocal microscopy for immunohistochemical detection of Ato (green) and Sens (red) (A,C,E), and Ato (green) and Boss (red) (B,D) in third larval instar eye discs. (A,B) Wild type. (C,D) ed4.12/ed4.12. (E) edlH23/Df(2L)ed-dp. A twinned R8 precursor pair is indicated by the arrow. (F) Expression of an R7 enhancer trap (R70-9) in an ed4.12 mutant background. Immunohistochemical detection of Sens (red) and ß-galactosidase (green). The open arrow indicates a wild-type R8/7 pair. The closed arrow indicates twinned R8s with associated twinned R7s. The arrowhead indicates a twinned R8 with a single R7. Anterior is towards the left in all figures.

View larger version (148K): [in a new window]   Fig. 3. ed is independent of the R8 twinning mutants ro and sca. (A-I) Confocal microscopy of third larval instar eye imaginal discs. (A-E) Immunohistochemical detection of Ato (green) and Sens (red). (A) ed4.12/ed4.12. (B) roX63/roX63. (C) scaBP2/scaBP2. The phenotypes of the three mutants are distinct. (D) ed4.12/ed4.12;roX63/roX63. (E) ed4.12,scaBP2/ed4.12,scaBP2, twinning is not completely penetrant in D or E and arrows indicate single R8 cells. (F,G) Immunohistochemical detection of Ato (green) and Ro (red). (F) Wild type. (G) ed4.12/ed4.12, expression of Ato and Ro remains mutually exclusive in the ed mutant. (H,I) Immunohistochemical detection of Ato (green) and Sca (red). (H) Wild type. (I) ed4.12/ed4.12, the additional R8 precursors express Sca.

View larger version (95K): [in a new window]   Fig. 4. Egfr signalling is responsible for R8 twinning in ed4.12. (A) Graph to show the interactions between ed4.12 and the Egfr pathway. Genotype is plotted against the proportion of equivalence groups not resolving to single R8 cells. The line above each bar represents the standard error of the mean. Six to nine eye discs were counted of each genotype. (B-H) Confocal microscopy of third larval instar eye imaginal discs. (B,C) Suppression of R8 twinning (Sens expression) by EgfrIK35. (B) Homozygous ed (ed4.12/ed4.12). (C) Homozygous ed with loss of one copy of Egfr (ed4.12 EgfrIK35/ed4.12 +). (D-E'') Loss of R8 twinning in Egfr clones. (D,E) EgfrIK35 homozygous clones in an ed4.12/ed4.12 background. Immunohistochemical detection of Sens (red, D,D',E,E''), ß-galactosidase (green, D,D'',E,E'') and DAPI (blue). The absence of the green ß-galactosidase staining marks the Egfr homozygous clone. Arrows indicate single R8 cells within the clone. (F,F') spiSC2 clone in an ed4.12/ed4.12 background. Immunohistochemical detection of Sens (red) and nlsGFP (green). The absence of the nlsGFP marks the spi-null region, twinned R8 precursors can be seen in both the presence and absence of spi. (G,G') EgfrIK35 clone in an scaBP2/scaBP2 background. Immunohistochemical detection of Sens (red) and ß-galactosidase (green). The absence of the green ß-galactosidase staining indicates the sca Egfr double homozygous clone (the rest of the disc is heterozygous for sca and Egfr and so displays no R8 phenotype). G is a more basal section than G', twins and triplets of R8s can readily be seen in the more apical sections of the clone (arrow). (H) Overexpression of pnt-P1 posterior to the morphogenetic furrow (genotype GMR-Gal4/UAS-pntP1). Immunohistochemical detection of Sens (red) and Ato (green) reveals twinned cells with R8 characteristics (arrows).

View larger version (102K): [in a new window]   Fig. 5. Levels of Egfr signalling are increased in ed mutants. (A-B') Confocal microscopy for immunohistochemical detection of Ato (green) and mAb323, which detects multiple E(spl) proteins (red), in third larval instar eye discs. (A,A') Wild type. (B,B') ed4.12/ed4.12. Levels of E(spl) are not altered in the mutant morphogenetic furrow (arrowhead). (C,D) Light microscope images of pnt-P1 mRNA in third larval instar eye discs. (C) Wild type, showing expression in the IGs. (D) ed4.12/ed4.12. pnt-P1 expression is greater in D. (E,F) Confocal microscopy for immunohistochemical detection of dp-Erk (green) and Ato (red) in third larval instar eye imaginal discs. (E) Wild type, showing expression in the IGs. (F) ed4.12/ed4.12. Levels of dpErk are higher in F.

View larger version (123K): [in a new window]   Fig. 6. ed is required in the R8 equivalence group to prevent R8 twinning. Mosaic analysis of ed alleles examined by confocal microscopy for immunohistochemical detection of Sens (red), Boss (blue) and nlsGFP (green) in third larval instar eye imaginal discs. The mosaic clone is distinguished by the absence of nlsGFP and the border has been marked with a white line. (A) ed6.1 homozygous clone. (A) Overlay. (A') Red channel. (A'') Blue channel. A mixed twin of a mutant and a wild-type R8 at the clone border has been marked by an arrow. (B) ed4.4 homozygous clone. (B) Overlay. (B') Red channel. (B'') Green channel. An R8 twin consisting of two wild-type cells at the clone border is marked with an arrowhead.

View larger version (22K): [in a new window]   Fig. 7. Schematic representing the Egfr-mediated signalling events during Ato expression (green). In wild type, Egfr signalling is occurring in the IGs. This signalling occurs at the same time as R8 precursor selection within the equivalence group, and the role of Ed is to prevent the Egfr signalling from interfering with this process. In ed mutants, there is no Ed protein and Egfr signalling has a local inductive effect on the cells of the equivalence group resulting in the selection of more than one R8 precursor.