Tangential processes on photoreceptor progenitors and differentiating photoreceptors in the 72 hpf retina. (A) Apical view of the peripheral-most crx:EGFP-CAAX (crx:GFP) expression area, showing a few photoreceptor progenitors profusely extending tangential processes (arrowheads). F-actin staining with TRITC–phalloidin highlights the subapical adhesion rings. (A′) Diagram depicting the orientation of acquisition in A; L, lens; NR, neural retina. (B) Time-lapse experiment of crx:GFP-injected embryos, showing a peripheral area of the retina displaying photoreceptor progenitors extending highly dynamic tangential processes on the apical surface (arrowheads). (C) Early differentiating photoreceptor, displaying long tangential processes (arrowheads). (D) Differentiating photoreceptors at the IS-forming stage, showing short processes extending from this expanding apical membrane. Some of the processes are connected at the OLM, indicating they might be tangential processes (yellow arrowheads), whereas others originate at more apical positions and extend in different directions (white arrowheads). Number of embryos analysed: n=8 (A,C,D), n=4 (B). Scale bars: 5 µm.
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