In toto Image Analysis of Tissue Mechanics during Vertebrate Ear Development

Harvard Medical School, Boston MA

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Abstract

DESCRIPTION (provided by candidate): In toto Image Analysis of Tissue Mechanics during Vertebrate Ear Morphogenesis Understanding ear development is key to developing clinical therapies for early/late-onset deafness, whether of genetic or environmental etiology. The goal of the proposed study is to determine the mechanical contribution of patterning circuits involved in vertebrate ear development. My focus is on the morphogenesis of the otic-vesicle tissue, which plays a fundamental role in the generation of specialized organs responsible for the sense of hearing and balance. The otic vesicle develops from an initially thickened ectodermal placode that is induced to form a subcutaneous, hollow epithelialized shell filled with endolymph. The proposed research uses the zebrafish model system and addresses three fundamental questions: (A) How does the otic tissue transform from a sheet of newly recruited otic placode cells into radially polarized epithelial tissue with a specific tissue/cell morphology (B) What is the role of endolymph pressure in driving the growth of the otic vesicle to the right shape/size? As such, large- scale organizational changes arising from changes in cell number and localized cell shape are observable along the otic-vesicle perimeter. (C) How does endolymph pressure equilibrate with intercellular forces of adhesion and cortical tension that affect cell/tissue shape? To address these questions, the following three aims are proposed: (1) I propose to conduct in toto imaging with fluorescent reporters to generate 4-dimensional cellular descriptions of the morphogenesis process. By using image analysis, I will comprehensively reconstruct the locations, tracks, and cell divisions of placode cells involved in otic-vesicle formation and learn how otic placode cells delaminate from ectoderm tissue and rearrange into radially polarized hollow tissue. (2) I will model the otic vesicle as a pressurize shell using a finite-element representation to understand tissue mechanics of otic-vesicle growth. A finite-element cell model will reveal how rearrangement forces from endolymph secretion drive tissue shape change. (3) I will integrate the model with the function of patterning genes for transepithelial transport and inter- cellular adhesion. By using the biophysical model, I will test model outcomes with pharmacological and genetic perturbations (mutants+morphants) by altering cell-cell adhesion protein expression and endolymph pressure. These perturbations will demonstrate how patterning circuits at a cellular level control specific aspects of the morphogenesis process. Together, these aims will elucidate how patterning inputs coordinate cell mechanics for ear morphogenesis by controlling endolymph secretion and spatiotemporal adhesion protein expression.