Fig. 7. Rhabdomere structure and integrity in hnt mutants. (A) Schematic of a longitudinal section through an adult ommatidium, showing the rhabdomeres (black) extending along the apicobasal axis of the eye epithelium. Gray arrows indicate the level of transverse cross-sections through two distinct mosaic ommatidia, shown in the blue panels either side of the schematic. The mosaic ommatidium on the left has an R5 cell that is mutant for hnt. The R5 rhabdomere is seen in an apical plane of section (yellow asterisk), but does not extend all the way basally, unlike the rhabdomeres belonging to the other, hnt⁺, outer R cells in this ommatidium. The mosaic ommatidium on the right has an R3 cell that is mutant for hnt (yellow asterisk). At an apical plane of section the rhabdomeres have a wild-type appearance, whereas, at more basal levels, the R3 and R4 rhabdomeres have failed to separate. (B) Third instar larval eye disc stained with an -HNT antibody (red), which is absent from the hnt^XO01 patch, and phalloidin-FITC (green), which stains the F-actin concentrated at the apical tips of the developing photoreceptor cell clusters. The F-actin is depleted in the more posterior area of the hnt patch compared with its levels in the adjacent wild-type tissue. (C) Apical section of a late pupal disc stained with -HNT antibody (red) and phalloidin-FITC (green), and containing a clone of hnt^XE81 tissue. In the area where the R cells are all mutant, there is no F-actin accumulation. HNT-positive R cells within two mosaic ommatidia along the clone border (arrows) have less F-actin apically than their genetically wild-type neighbors within the cluster. (D) More basal view of the same clone as in C, showing that there are low levels of F-actin in the more basal regions of these cells (arrows).

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