The light-sensitive outer segment organelle of the vertebrate photoreceptor cell is a modified cilium filled with hundreds of flattened ‘disc’ membranes that provide vast light-absorbing surfaces. The outer segment is constantly renewed with new discs added at its base every day. This continuous process is essential for photoreceptor viability. In this review, we describe recent breakthroughs in the understanding of disc morphogenesis, with a focus on the molecular mechanisms responsible for initiating disc formation from the ciliary membrane. We highlight the discoveries that this mechanism evolved from an innate ciliary process of releasing small extracellular vesicles, or ectosomes, and that both disc formation and ectosome release rely on the actin cytoskeleton.

脊椎动物感光细胞的光敏外段细胞器是一种改良的纤毛，充满了数百个扁平的“圆盘”膜，提供了广阔的吸光表面。外部部分不断更新，每天在其底部添加新的光盘。这种连续的过程对于光感受器的生存能力是必不可少的。在这篇综述中，我们描述了最近在理解椎间盘形态发生方面的突破，重点是负责从睫状膜启动椎间盘形成的分子机制。我们强调了这一机制从释放小细胞外囊泡或胞外体的先天纤毛过程演变而来的发现，并且椎间盘形成和胞外体释放都依赖于肌动蛋白细胞骨架。