Prior to gastrulation, the chick embryo consists primarily of a
quasi-two-dimensional disc of about 50,000 cells. The first visible
morphogenetic process of gastrulation is extension of the primitive
streak. The streak, which is formed from a narrow multilayer cohort of
cells originating from the posterior marginal zone, establishes the
future vertebrate axis of the organism. Early gastrulation in humans is
based on the same fundamental process of primitive streak extension.
Recent live-cell imaging studies of chick gastrulation in the Weijer lab
have shown that just prior to (and during) streak extension, cells in
the disc undergo collective movement, tracing out two large
counter-rotating vortices. The mechanisms underlying extension of the
streak and the vortex motion are presently unknown, although
experimental evidence points to either cell intercalation or chemotaxis
as plausible candidates. In this talk I will present three disparate
theoretical ideas, originating from physical analogs of vortex
formation, concerning these mechanisms, along with instantiations of
these ideas using grid-free computer simulations of streak formation.