Deletion of the Transmembrane Protein Prom1b in Zebrafish Disrupts Outer-segment Morphogenesis and Causes Photoreceptor Degeneration

Mutations in human prominin 1 (), encoding a transmembrane glycoprotein localized mainly to plasma membrane protrusions, have been reported to cause retinitis pigmentosa, macular degeneration, and cone-rod dystrophy. Although the structural role of PROM1 in outer-segment (OS) morphogenesis has been demonstrated in -knockout mouse, the mechanisms underlying these complex disease phenotypes remain unclear. Here, we utilized a zebrafish model to further investigate PROM1's role in the retina. The orthologs in zebrafish include and , and our results showed that , rather than , plays an important role in zebrafish photoreceptors. Loss of disrupted OS morphogenesis, with rods and cones exhibiting differences in impairment: cones degenerated at an early age, whereas rods remained viable but with an abnormal OS, even at 9 months postfertilization. Immunofluorescence experiments with WT zebrafish revealed that Prph2, an ortholog of the human transmembrane protein peripherin 2 and also associated with OS formation, is localized to the edge of OS and is more highly expressed in the cone OS than in the rod OS. Moreover, we found that Prom1b deletion causes mislocalization of Prph2 and disrupts its oligomerization. We conclude that the variation in Prph2 levels between cones and rods was one of the reasons for the different mutation-induced phenotypes of these retinal structures. These findings expand our understanding of the phenotypes caused by mutations and provide critical insights into its function.