  In embryonic development, programmed cell shape changes are essential for
building functional organs, but in many cases the mechanisms that precisely
regulate these changes remain unknown. We propose that fluid-like drag forces
generated by the motion of an organ through surrounding tissue could generate
changes to its structure that are important for its function. To test this
hypothesis, we study the zebrafish left-right organizer, Kupffer's vesicle
(KV), using experiments and mathematical modeling. During development,
monociliated cells that comprise the KV undergo region-specific shape changes
along the anterior-posterior axis that are critical for KV function: anterior
cells become long and thin, while posterior cells become short and squat. Here,
we develop a mathematical vertex-like model for cell shapes, which incorporates
both tissue rheology and cell motility, and constrain the model parameters
using previously published rheological data for the zebrafish tailbud [Serwane
et al.] as well as our own measurements of the KV speed. We find that drag
forces due to dynamics of cells surrounding the KV could be sufficient to drive
KV cell shape changes during KV development. More broadly, these results
suggest that cell shape changes could be driven by dynamic forces not typically
considered in models or experiments.
