Gastrulation: PARtaking of the bottle
Gastrulation in C. elegans embryos involves ingression of individual cells, but is driven by apical constriction of the kind that promotes migration of epithelial cell sheets. Recent work shows that PAR proteins, known for their role in polarization and unequal cell division, are also associated with the polarization that establishes this apical constriction.
Putzke, A.P., and Rothman, J.H. Gastrulation: PARtaking of the Bottle. Curr Biol 13, R223-225. (2003)