Mechanistic Insights into MYO1C-Mediated Rhodopsin Trafficking and Rod Photoreceptor Homeostasis.

Rhodopsin trafficking from the photoreceptor inner segment to the outer segment is essential for photoreceptor function, yet the molecular mechanism(s) regulating this process remain incompletely understood. MYO1C is an actin-based motor protein implicated in intracellular cargo trafficking. Here, we investigated its role in rhodopsin trafficking and photoreceptor cell homeostasis. In-silico docking identified a putative interaction between the MYO1C C-terminal region and the C-terminal region of rhodopsin containing the conserved VxPx ciliary trafficking motif. Biochemical studies confirmed that full-length MYO1C interacts with rhodopsin, whereas deletion of the MYO1C C-terminal domain abolished this interaction. Live-cell imaging, ciliary localization, and fluorescence recovery after photobleaching in hTERT-RPE1 cells demonstrated that the MYO1C C-terminal region is required for efficient rhodopsin trafficking, membrane localization, and ciliary targeting. In native murine rod photoreceptors MYO1C localized to both inner and outer segments. Global Myo1c deficiency in mice caused age-dependent rhodopsin mislocalization, apo-opsin accumulation and progressive retinal dysfunction, characterized primarily by reduced scotopic ERG responses and delayed a-wave recovery, beginning at 6-months, while photopic responses were relatively preserved. Rod-specific Myo1c deletion similarly caused progressive scotopic dysfunction and reduced a-wave recovery following light stimulation. In contrast, cone-specific Myo1c deletion preserved photopic function and a-wave recovery. Together, these findings identify MYO1C as an important regulator of rhodopsin trafficking and demonstrate a preferential, cell-autonomous requirement for MYO1C in maintaining rod photoreceptor homeostasis and phototransduction recovery. These findings establish a mechanistic link between MYO1C-dependent rhodopsin trafficking and age-dependent rod photoreceptor cell dysfunction.