7 - Examining the Role of Mechanical Forces on Heterotaxy Syndrome

Poster Board Number: 7
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Co-authors:

Raj Kumar Manna - Department of Physics - Syracuse University; Paula Sanematsu - Department of Physics - Syracuse University; M.lisa Manning - Department of Physics - Syracuse University; Jeffrey Amack - Cell and Developmental Biology - SUNY Upstate Medical University

Abstract Body : Despite the external symmetry of vertebrates, several internal organs develop asymmetrically along the left-right (LR) body axis. Heterotaxy syndrome occurs 1 in 10,000 live births and is characterized by defects in LR organ asymmetry that result in a broad spectrum of clinical complications including severe congenital heart defects. The underlying causes of heterotaxy syndrome are not fully understood. A transient structure referred to as the ‘left-right organizer’ (LRO) directs LR patterning of vertebrate embryos and is the focus of our investigation. Our research uses a zebrafish model organism as their embryos are abundant, transparent, and fast growing outside of the body allowing us to observe organ morphogenesis and patterning easily and efficiently. During morphogenesis of the zebrafish embryo’s LRO, which is called Kupffer’s vesicle (KV), LRO cells bearing motile cilia undergo regional shape changes along the anterior-posterior (AP) axis. Anterior cells take on columnar shapes that allow tight packing, whereas posterior cells become cuboidal-like and more widely spaced apart. These shape changes create an AP asymmetric concentration of beating cilia that is critical for establishing LR an asymmetric flow of extraembryonic fluid that generates patterning cues leading to downstream organ LR asymmetry. However, the mechanisms that control LRO cell shape changes are not understood. The goal of this project is to investigate the previously under-studied role of biophysical forces on LRO morphogenesis. We are using a combination of quantitative live imaging and 3-dimensional (3D) computational modeling to test the hypothesis that coordinated biophysical forces from external tissues provide a mechanical mechanism that regulates LRO morphogenesis. 3D modeling simulations indicate that drag forces generated as the LRO moves through its surrounding cellular environment can drive LRO cell shape changes. To experimentally test the impact of drag forces in vivo, we use light-activated small molecules to alter mechanical properties in selected cells surrounding the LRO. This optical approach allows spatial and temporal of control of the mechanical properties of tissues that interact with the developing LRO. Using this method, we find that altering the mechanical properties of the tissues surrounding the LRO disrupts tissue flow, decreases LRO velocity through surrounding tissue—which is predicted to decrease drag forces—and leads to a failure of LRO cells to undergo regional shape changes. These results indicate drag forces play a role in LRO morphogenesis, and that altered biophysical forces during embryogenesis could underlie altered LR organ asymmetry in heterotaxy syndrome. This work is supported by NIH grant R01HD099031.