Photoreceptor Disc Morphogenesis: Who Are the Conductors of This Highly Metronomic Process?

To ensure that normal vision is maintained, the photoreceptor must continually renew its outer segment, a massive expanse of ciliary membrane extending from the tip of its connecting cilium. The outer segment is organised into hundreds of flattened discs, the formation of which is highly regulated. Disc morphogenesis requires the metronomic assembly of an actin cytoskeletal network to initiate the necessary membrane deformation and subsequent network disassembly to allow disc completion. Disruption of disc turnover, due to human mutations, results in an inherited retinal dystrophy (IRD), a leading cause of visual loss in children and working adults. This chapter will describe the structural evidence that disc formation is actin-driven and discuss what is known of the molecular mechanisms that govern the process.