Fig. 1. TRP and Rh1 accumulate in large cytoplasmic vesicles during photoreceptor maturation. Confocal cross-sections of staged pupal eyes (% pd=% pupal development) stained for F-actin using rhodamine-phalloidin (red) and either (A) anti-TRP or (B) anti-Rh1 (green). Actin-rich rhabdomeres stain red at all stages; overlapping green immunostain (Rh1 or TRP) renders rhabdomeres yellow. The yellow-red boundary marks the rhabdomere base, the cytoplasmic ends of microvilli and the origin of the actin-rich rhabdomere terminal web (RTW). (A) TRP concentrates in large cytoplasmic vesicles during its synthetic peak, between 50 and 80% pd. (B) Following the onset of Rh1 expression at about 70% pd, the protein concentrates in large cytoplasmic (Rh1-containing large) vesicles (RLVs), before it is detected in rhabdomeres at 70% pd. (C) TRP and Rh1 colocalize in RLVs of 74% pd photoreceptors. (D) A side view of an ommatidium isolated from a newly eclosed wild-type fly shows RLVs associate with one or more small dots of F-actin. (E) Most RLVs appear tethered to the RTW via actin patches. (F) A side view of a live ommatidium isolated from a 6-day-old fly expressing GFP-actin driven by Rh1Gal4. Actin patches decorate the RTW of living cells. Scale bar: 2 µm in A-D; 1 µm in E; 5 µm in F.