Project 3: Mechanism of Cochlear Radial Patterning

Project Summary/abstract Hearing loss is the most frequent sensory disease affecting more than 38 million people in the United States. The mammalian cochlea contains a highly organized structure called the organ of Corti that is responsible for sound detection. The organ of Corti is comprised of hair cells and supporting cells. Hair cells detect sound and relay it to the brain, and supporting cells maintain structural integrity and an environment for the organ of Corti. Understanding cellular and molecular mechanisms of cochlear development is required to enhance diagnosis and therapy for hearing loss. During development, the organ of Corti differentiates along the cochlea (longitudinally) and across the organ of Corti (radially). Using mouse models, we have identified that beta-catenin is required for hair cell and supporting cell specification during radial patterning of the organ of Corti. Deleting beta-catenin causes infiltration of inner hair cells in the outer hair cell area along the cochlea. In the supporting cell region, beta-catenin mutant mice contain ectopic outer pillar cells with loss of inner pillar cells. In addition, the mice retaining cell-to-cell adhesion function but lacking transcriptional activity of beta-Catenin maintain defects in supporting cells but do not present hair cell phenotypes. We further identified that deletion of ETV transcription factors, ETV1, ETV4, and ETV5 showed similar supporting cell defects. Therefore, we hypothesize that cell-to-cell adhesion is required for hair cell specification and canonical Wnt/beta-Catenin signaling is required for supporting cell specification during radial patterning of the organ of Corti. To test the hypothesis, we propose three specific aims. Aim 1 is to determine the role of cell adhesion to the hair cell specification during radial patterning of the organ of Corti. Understanding the role of cell adhesion using beta-catenin null mutants is limited because both cell adhesion and transcriptional function are disrupted. beta-Catenin-dependent cell adhesion is fulfilled by alpha-Catenin and Actomyosin complexes. We will determine whether cell adhesion is required for hair cell patterning by deleting alpha-Catenin during cochlear development. We will also test the function of actomyosin using chemical inhibitors in cochlear explants. In aim 2, we will determine whether ETV transcription factors function together with canonical Wnt/beta-Catenin during supporting cell development. We will comprehensively analyze the phenotypes of ETV mutant cochlear and compare it with beta-catenin mutants. We will also investigate interaction between canonical Wnt/beta-Catenin and FGF/ETV during supporting cell development. In aim 3, using single cell RNA sequencing, we will elucidate signaling network during radial patterning of organ of Corti. The proposed research will identify the mechanism of hair cell and supporting cell specification during radial patterning of the organ of Corti and will help to understand hearing loss caused by a radial patterning defect.