Developmental Remodeling of the Auditory Hair Cell Cuticular Plate Defines Transient and Mature Structural Domains

The cuticular plate, a dense F-actin meshwork anchoring stereocilia in auditory hair cells (HCs), undergoes dynamic remodeling during development, but its structural transitions remain poorly understood. Here, we identified two distinct structural domains associated with this maturation. First, a transient F-actin-free area emerges within the lateral periphery of the developing cuticular plate, presenting as a crescent-shaped region that disappears upon HC maturation. Second, the lateral margin of the mature cuticular plate itself remodels into a persistent step-like structure, exhibiting cell-type-specific geometries in inner versus outer HCs. The consistent coincidence between Gαi-GPSM2 complex disruption and aberrant development of both structures in mutant mice implies a role for this complex in their formation. Additionally, microtubules spatially complemented F-actin distribution, suggesting coordinated cytoskeletal regulation. These findings revealed a sophisticated developmental program for cuticular plate maturation.