Squeezing an egg into a worm: C. elegans embryonic morphogenesis.

We review key morphogenetic events that occur during Caenorhabditis elegans (www.wormbase.org/) embryogenesis. Morphogenesis transforms tissues from one shape into another through cell migrations and shape changes, often utilizing highly conserved actin-based contractile systems. Three major morphogenetic events occur during C. elegans embryogenesis: (1) dorsal intercalation, during which two rows of dorsal epidermal cells intercalate to form a single row; (2) ventral enclosure, where the dorsally located sheet of epidermal cells stretches to the ventral midline, encasing the embryo within a single epithelial sheet; and (3) elongation, during which actin-mediated contractions within the epithelial sheet lengthens the embryo. Here, we describe the known molecular players involved in each of these processes.