The homologous membrane proteins Rom-1 and peripherin-2 are localized to th
e disk rims of photoreceptor outer segments (OSs), where they associate as
tetramers and larger oligomers(1-3). Disk rims are thought to be critical f
or disk morphogenesis, OS renewal(4) and the maintenance of OS structure(5)
, but the molecules which regulate these processes are unknown. Although pe
ripherin-2 is known to be required for OS formation (because Prph2(-/-) mic
e do not form OSs; ref. 6), and mutations in RDS (the human homologue of Pr
ph2) cause retinal degeneration(7), the relationship of Rom-1 to these proc
esses is uncertain. Here we show that Rom1(-/-) mice form OSs in which peri
pherin-2 homotetramers are localized to the disk rims, indicating that peri
pherin-2 alone is sufficient for both disk and OS morphogenesis, The disks
produced in Rom1(-/-) mice were large, rod OSs were highly disorganized (a
phenotype which largely normalized with age) and rod photoreceptors died sl
owly by apoptosis. Furthermore, the maximal photoresponse of Rom1(-/-) rod
photoreceptors was lower than that of controls. We conclude that Rom-1 is r
equired for the regulation of disk morphogenesis and the viability of mamma
lian rod photoreceptors, and that mutations in human ROM1 may cause recessi
ve photoreceptor degeneration.