MYO3B is an actin-based motor protein with serine/threonine kinase activity that plays critical roles in sensory cell development and function. In the auditory system, MYO3B redundantly regulates stereocilia architecture during cochlear hair bundle morphogenesis 1. It transports the actin regulatory protein espin-1 to stereocilia tips, where espin-1's actin-binding domain enables myosin IIIB to reach and elongate these mechanosensitive protrusions 2. Class III myosins, including MYO3B, unexpectedly limit stereocilia and microvilli elongation, contributing to proper hair bundle shaping and staircase organization 1. MYO3B is also expressed in retinal photoreceptor inner segments across all photoreceptor types and in cone outer segments of S opsin-positive cones, where it may compensate for MYO3A defects and prevent photoreceptor dysfunction 3. MYO3B maps to chromosome 2.1-q31.2, overlapping Bardet-Biedl syndrome locus BBS5, suggesting potential involvement in ciliary diseases 4. Beyond sensory cell function, MYO3B promotes endometrial cancer progression via calcium ion-mediated RhoA/ROCK1 signaling, with elevated expression associated with metastasis 5. Mutations in MYO3B are associated with delayed-onset hearing loss 6. These findings underscore MYO3B's multifaceted roles in cellular motility and disease pathogenesis.