Examining the Role of Mechanical Forces in Heterotaxy Syndrome

Abstract Body : Despite the external symmetrical external appearance of vertebrates, several internal organs develop asymmetrically along the left-right (LR) body axis. Defects in LR asymmetry can cause heterotaxy syndrome, which is characterized by a broad spectrum of clinical complications that typically include a congenital heart defect. The underlying causes of LR asymmetry defects are not fully understood. To identify mechanisms that control LR asymmetry, we are focused on understanding the form and function of a transient structure referred to as the ‘left-right organizer’ (LRO) that directs LR patterning of vertebrate embryos. During morphogenesis of the zebrafish embryo’s LRO, which is called Kupffer’s vesicle (KV), KV cells bearing motile cilia undergo regional shape changes along the anterior-posterior (AP) axis, which creates an AP asymmetric distribution of beating cilia that is critical for establishing asymmetric fluid flows and LR patterning cues. Using a combination of quantitative live imaging, 3-dimensional (3D) computational modeling, and in vivo manipulations, we are testing the hypothesis that coordinated biophysical forces regulate KV morphogenesis. During early somite stages when the embryonic AP axis extends, we find that KV moves faster towards the posterior of the embryo than surrounding cells. Live imaging of KV interacting with neighboring tissues suggests KV is ‘pushed’ by convergence and extension of cells in the adjacent rod-like notochord. 3D computational modeling predicts that KV movement through the surrounding tissue creates drag forces that can drive regional cell shape changes. To experimentally test the impact of these forces on KV in vivo, we use light-activated small molecules to alter actomyosin contractility in selected cells surrounding KV. This optical approach allows spatial and temporal control of mechanical properties of tissues involved in generating forces on KV, and can be used to systematically define the role of extrinsic mechanical forces on KV morphogenesis and function. This work is supported by NIH grant R01HD099031.