Physical, cellular, and molecular control of tissue fission and fusion

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Project Summary Tissue fission and fusion give forms to functional organs during embryonic development. Abnormalities in these processes can lead to congenital birth defects and syndromes such as cleft palate, Meckel-Gruber syndrome, and persistent truncus arteriosus. During remodeling, cells must generate force, reconfigure cell contacts, and interact with their surroundings. The mechanisms underlying the cellular and molecular regulation mechanisms underlying tissue fission and fusion are poorly understood. The formation of mechano-sensory organs called neuromasts in zebrafish provides an ideal model in which to decipher these processes. During neuromast morphogenesis, the pro-neuromast splits from the migrating posterior lateral line primordium and later fuses with skin to open tricellular junctions in skin cells; hence, I can study both tissue fission and fusion in this morphogenetic event. In this model, my preliminary findings suggest a mechanical ‘tug of war’ between cells and tissues in primordium splitting and neuromast fusion with the skin. In the proposed research, I will apply state- of-the-art in vivo biophysical measurements to determine whether RhoA-mediated actomyosin drives neuromast deposition (Aim 1). I will then use a novel protein depletion approach that offers spatial and temporal control to test whether cell-cell and cell-extracellular matrix (ECM) adhesions mediate neuromast budding (Aim 2) and investigate the mechanism by which neuromasts fuse with skin (Aim 3). The physical, molecular and cellular principles revealed in this study will be widely applicable to morphogenetic events involving tissue fission and fusion while maintaining the integrity of single cells. Moreover, findings from this study will improve our understanding of congenital birth defects due to abnormal tissue fission and fusion and further inform strategies to correct these defects. To accomplish the proposed research, I will combine my skills in cell mechanics analyses developed as a graduate student; new skills acquired in my early postdoctoral training in zebrafish genetics, molecular biology and high-resolution live imaging; and the proposed technical training during the K99 phase to implement in vivo biophysical measurements, including measuring in vivo cell-ECM stress and cell-cell adhesion tension. As I start my own lab, I will be mentored by Drs. Holger Knaut, Daniele Panozzo, Anna- Katerina Hadjantonakis, Jeremy Nance, Carsten Grashoff, and Johannes Stegmaier. They will offer not only their scientific expertise in zebrafish genetics, biophysics, quantitative imaging, and modeling but also with their valuable experience in mentoring students, grantsmanship, publication, establishing scientific collaborations, and lab management. My long-term career goal is to head a research laboratory and uncover the genetic, biophysical, cellular, and molecular regulation of cell and tissue mechanics in embryonic morphogenesis. I have made significant progress toward this goal with research experience, successful collaborations, and publications. However, I firmly believe that the additional technical and career training proposed during the K99 mentored phase is necessary for me to successfully transition to my independence.