Differential regulation of hair cell actin cytoskeleton mediated by SRF and MRTFB.

Abstract

The MRTF-SRF pathway has been extensively studied for its crucial role in driving the expression of a large number of genes involved in actin cytoskeleton of various cell types. However, the specific contribution of MRTF-SRF in hair cells remains unknown. In this study, we showed that hair cell-specific deletion of <i>Srf</i> or <i>Mrtfb</i>, but not <i>Mrtf</i>a, leads to similar defects in the development of stereocilia dimensions and the maintenance of cuticular plate integrity. We used fluorescence-activated cell sorting-based hair cell RNA-Seq analysis to investigate the mechanistic underpinnings of the changes observed in <i>Srf</i> and <i>Mrtfb</i> mutants, respectively. Interestingly, the transcriptome analysis revealed distinct profiles of genes regulated by <i>Srf</i> and <i>Mrtfb</i>, suggesting different transcriptional regulation mechanisms of actin cytoskeleton activities mediated by <i>Srf</i> and <i>Mrtfb</i>. Exogenous delivery of calponin 2 using Adeno-associated virus transduction in <i>Srf</i> mutants partially rescued the impairments of stereocilia dimensions and the F-actin intensity of cuticular plate, suggesting the involvement of <i>Cnn2</i>, as an <i>Srf</i> downstream target, in regulating the hair bundle morphology and cuticular plate actin cytoskeleton organization. Our study uncovers, for the first time, the unexpected differential transcriptional regulation of actin cytoskeleton mediated by <i>Srf</i> and <i>Mrtfb</i> in hair cells, and also demonstrates the critical role of SRF-CNN2 in modulating actin dynamics of the stereocilia and cuticular plate, providing new insights into the molecular mechanism underlying hair cell development and maintenance.