Fig. 8.

Cartoon illustrating the role of the WAVE complex in initiating photoreceptor disc formation and functions of proteins implicated in membrane bending and trans-membrane adhesion. The WAVE complex cooperates with Arp2/3 to drive actin polymerization evaginating each nascent disc. A more detailed illustration of WAVE-Arp2/3-driven actin polymerization is presented in SI Appendix, Fig. S1. Extended oligomeric complexes of peripherin-2/ROM1 support the highly curved edges along the entire circumference of mature discs. The leading edges of expanding nascent discs are enriched with prominin-1, which is thought to promote membrane bending at this location. Homotypic rhodopsin interactions have been hypothesized to provide membrane-to-membrane adhesion across the extracellular space between nascent discs and the intradiscal space of mature discs. PDE6 and GARP2 have been hypothesized to connect discs across the cytoplasm throughout the disc surface and near the disc rim, respectively. Proteins whose role in membrane bending or adhesion remains hypothetical are denoted with a question mark. See Discussion for details.