PMC

Eyelet expressing so-Gal4/UAS-H2B::YFP (Aa–Ac), rh5-Gal4,UAS-H2B::YFP, and UAS-EcR^DN (Ba–Bc), rh5-Gal4,UAS-H2B::YFP,UAS-EcR^RNAi (Ca–Cc), rh6-Gal4,UAS-H2B::YFP,UAS-EcR^DN (Da–Dc) or rh6-Gal4,UAS-H2B::YFP,UAS-EcR^RNAi (Ea–Ec), anti-Rh6 (green), anti-Rh5 (blue) and anti-YFP (red). Interfering with EcR in Rh5 photoreceptors prevents cells from switching to Rh6 (b, c). In Rh6 photoreceptors, it prevents apoptosis (D, E). The eyelet (F) after manipulation of Rh5 (G) or Rh6 photoreceptors (H). I, Transformation of the larval eye into the eyelet. EcR function leads to apoptosis of the Rh6 photoreceptors and the switch to Rh6 of Rh5 photoreceptors.

a, b, d, e, In third-instar larvae, EcR protein (red) is detected in Rh6 photoreceptors (rh6 > H2B::YFP; green) (a) and in Rh5 photoreceptors (rh5 > H2B::YFP; green) (d); anti-Elav (blue). b, e, The same as a, d showing only EcR expression (broken circles highlight Rh6 photoreceptors in a and b, Rh5 photoreceptors in d and e). c, f, EcR activity monitored using 7×EcRE-lacZ (β-Gal, green). Anti-Chp (red) and anti-Elav (blue) marked photoreceptors. No EcR activity is detected during mid-third instar (c) but is present from late third-instar larval (f) to prepupal stages.

a, Inhibition of larval Rh6 photoreceptor development (so > H2B::YFP,EGFR^DN): only the Rh5 subtype is present in larvae (blue), whereas (d) the eyelet remains unaffected (anti-Rh6, green; anti-Rh5, blue; anti-YFP, red). b, In the larva, Svp (svp > H2B::YFP, red) is expressed in Rh6 (green) but not Rh5 photoreceptors (blue), whereas (e) the eyelet does not express Svp (anti-Rh6, green). c, In the larva, Sal (sal > H2B::YFP, red) is expressed in Rh5 photoreceptors (blue) but not in Rh6 photoreceptors (green) (f). Sal (red) is expressed in the eyelet (anti-Rh6, green). g, h, rh5-Gal4,UAS-hid,rpr ablates Rh5 photoreceptors (g, arrow) and eyelet (h, arrow) (anti-Rh5, blue; anti Rh6, green; anti Elav, red). i, rh6-Gal4/UAS-p35 prevents apoptosis of Rh6 photoreceptors (anti-Rh6, green; anti-YFP, red). j, k, Sens (red) is detected in the larval Rh5 subtype (rh5 > H2B::YFP, blue; anti-Chp, green) and the eyelet (rh6 > H2B::YFP; anti-YFP, blue; anti-Rh6, green). l, Misexpression of UAS-sens in Rh6 photoreceptors (rh6 > H2B::YFP > sens) prevents their apoptosis (anti-Rh6, green; anti-YFP, red; anti-Rh5, blue). The same phenotype is obtained with GMR-Gal4;UAS-sens (data not shown).

a, b, The eyelet locates between the optic ganglia (anti-Elav, red; La, lamina; Me, medulla) and retina (anti-Chp, blue; rPR, retinal photoreceptors). b, The eyelet only expresses Rh6 (green). c, Larval photoreceptors express Rh6 (green) or Rh5 (blue), nuclei in red (GMR > H2B::YFP). d, Rh6 photoreceptors (green) degenerate during prepupation (arrow), Rh5 photoreceptors (rh5 > GFP, blue) remain, nuclei in red (anti-Elav). e, High magnification of eyelet photoreceptors expressing Rh6 (green) not Rh5 (blue), nuclei in red (GMR > H2B::YFP). f, Transformation of larval photoreceptors: Rh6 photoreceptors degenerate, Rh5 photoreceptors remain at prepupation stages but express Rh6 in the eyelet. g–i, Rh5 photoreceptors tracked through metamorphosis using rh5 > H2B::YFP (red), anti-Rh6 (green) and anti-Rh5 (blue): g, during third-instar larva; h, mid-pupation (neither Rh5 nor Rh6 detectable); i, eyelet photoreceptors now expressing Rh6. j, By mid-pupation, Rh6 photoreceptors have degenerated whereas Rh5 photoreceptors are now empty, they later switch to express Rh6. k, No rh5 > lacZ expression can be detected in the eyelet. l, Genetic memory experiment (rh5-Gal4/UAS-Flp;Act-FRT > STOP > FRT-nlacZ): lacZ detected in eyelet (anti β-Gal, red; anti-RH6, green). m, n, Projections of Rh6 photoreceptors undergo fragmentation during prepupation (n, arrow, labelled with anti-Rh6), whereas Rh5 photoreceptor projections remain (m, Rh5 photoreceptor projections are shown by rh5-GFP; anti-Elav, red).