Fig. 6. rdx regulates ommatidial packing. Eyes comprised of mostly rdx mutant cells were generated by mitotic recombination, where the wild-type daughter cells were eliminated by a cell-lethal mutation (A,B,E). SEM of hypomorphic rdx¹ mutant eyes (A, left and middle panels) showed wild type patterning, including an ordered hexagonal array of ommatidia with bristles at alternate interstices; rdx⁵ loss-of-function eyes had disrupted ommatidial organization and loss of bristles (B, left and middle panels). Cross-sections of rdx¹ mutant eyes (A, right panel) showed normal patterning; the rhabdomeres of seven photoreceptors (dark spots) per ommatidium are arranged in a distinctive trapezoidal pattern. Cross-sections of rdx⁵ eyes had seven rhabdomeres in most ommatidia, but their packing was looser and not so clearly trapezoidal (B, right panel). The cellular architecture of apical surface of pupal eyes 36 hours after puparium formation is visualized with Armadillo (Arm) (C,E) and schematized (D,F). Wild type (C,D) shows the regularly packed hexagonal array with the appropriate arrangement of four cone cells (c), two primary pigment cells (1°) and 12 lattice cells – six secondary pigment cells (2°) along the faces of the hexagon, with bristle (b) or tertiary pigment cells (3°) at alternating vertices. The lattice cells are shared between adjacent ommatidia. The junctions between 1° cells always align perpendicular to the anteroposterior axis and always contact 2° cells. rdx⁵ mutant eyes (E,F) showed misaligned 1° cells (green diamonds), 1° cells failing to wrap around cone cells (yellow stars) and displaced bristles (red triangles).