Human, fly and even worm embryos all start off looking very similar. Early on they exist as a hollow ball of cells. A dip in the ball gives way to something akin to a landslide, during which the cells collapse inwards to form a bowl, which then closes over. Consequently the embryo has three layers of cells, which become the nervous system, gut and internal organs. The worm (Caenorhabditis elegans) embryos pictured are just beginning this process of gastrulation, which has long fascinated scientists. Just how the cells in the dip (here coloured blue, top embryo is five minutes behind bottom embryo) shrink in on themselves is a matter yet to be fully resolved. Cells in the dip have very high tension, mediated by their contractile skeletons and the contacts they make with their neighbours. New research suggests that the process is driven by a molecular clutch.
Written by Brona McVittie
BPoD stands for Biomedical Picture of the Day. Managed by the MRC London Institute of Medical Sciences the website aims to engage everyone, young and old, in the wonders of biomedicine. Images are kindly provided for inclusion on this website through the generosity of scientists across the globe.