Super-resolution mapping of the ankle link proteins ADGRV1 and PDZD7 in developing auditory hair cells

Auditory hair cells convert mechanical stimuli into electrical signals. Inner hair cells (IHCs) serve as primary sensory receptors, while outer hair cells (OHCs) function as cochlear amplifiers. During development, the G-protein-coupled receptor ADGRV1, along with usherin, whirlin, and PDZD7, interacts at the base of stereocilia to form the transient ankle-link complex. The long extracellular domain of ADGRV1 bridges adjacent stereocilia, while its intracellular domain binds to whirlin and PDZD7. Using STED nanoscopy on juvenile mouse hair cells, we mapped the spatial distribution of ADGRV1 regions and PDZD7, revealing highly asymmetric localization patterns within stereocilia rows and between IHCs and OHCs. These distinct distributions reflect tightly regulated subcellular targeting of the proteins, which show strong colocalization. Interestingly, while the extracellular portion of ADGRV1 is no longer detectable after postnatal day 12, the GPCR domain persists until P21, suggesting that ADGRV1 may also play a signaling role beyond its scaffolding function.