Four-dimensional prediction and quantification of how physical forces impact organogenesis in zebrafish - PROJECT SUMMARY/ABSTRACT
Defects in programmed cell shape changes during embryonic development can disrupt organ morphogenesis
and cause structural birth defects. There are fundamental gaps in our understanding of how cells change their
shape during organ formation. While the biochemical signals and morphogen gradients that help govern
organogenesis are well-studied, evidence is growing that robust control of organ form and function often also
depends on multiple mechanical mechanisms that remain poorly understood. Thus, there is a critical need to
tease apart how multiple mechanisms – including tissue-scale dynamic forces and cell-autonomous
contractile forces – work together to generate “mechanical gradients” that program cell and organ
shape during organ formation. A challenge is that mechanical perturbations that affect the entire embryo
often result in the same global phenotype, making it difficult to pinpoint the role of each mechanism. Our long-
term goal is to develop a combined cell biology and modeling toolkit that allows us to predict cell-scale
phenotypes and appropriate perturbations that can be used to distinguish between multiple mechanical
mechanisms. This project uses Kupffer’s vesicle (KV), a transient epithelial organ that establishes left-right
asymmetry in the zebrafish embryo, as a model system. No upstream biochemical signaling gradients have
been identified that regulate KV cell shapes as required for left-right patterning, but multiple mechanical
mechanisms have been implicated. Preliminary results – from (4D = 3D + time) experimental perturbations and
measurements of single KV cell shapes, and novel mathematical models that simulate interacting 3D tissue
structures while retaining cell-scale resolution – lead us to formulate our central hypothesis that cell shape
changes critical for KV organogenesis result from mechanical gradients generated by interactions between the
KV and surrounding tissue structures as well as cell-autonomous contractile forces from inside KV. The goal of
Aim 1 is to determine how interactions between KV and notochord impact cell shape changes. 4D modeling
predictions for cell shapes and cell movement combined with live in vivo imaging and localized laser ablations
will determine how asymmetric forces generated by the rod-like notochord impact KV cell shape changes
during organogenesis. The goal of Aim 2 is to understand mechanisms by which actomyosin contractility in
surrounding tailbud cells and inside KV generate KV cell shape changes. Novel mathematical models will
predict how localized optical perturbations to tailbud mechanics, as well as perturbations to volume and cell-
autonomous contractility in cells inside the KV, affect KV organ shape. Key outputs include a modeling toolkit
for high-throughput simulations of dynamic interactions between complex 3D tissue structures complemented
by a cell biology toolkit that tests model predictions with spatially and temporally modulated activation of
biomechanical and biochemical signaling molecules. These results will pinpoint mechanical mechanisms that
regulate organogenesis, and may ultimately aid in the prediction or prevention of birth defects.
