Drosophila gastrulation: from pattern formation to morphogenesis.

The major morphogenetic movements during Drosophila gastrulation--germ band extension and the invagination of the mesoderm and endoderm--are driven by cell intercalation and cell shape changes, respectively. The regions of the early embryo in which these movements occur and which give rise to the germ layers are demarcated by a small number of zygotically expressed genes. These genes code for transcription factors that regulate cell behavior by controlling expression of target genes whose products modulate the cytoskeleton and other subcellular compartments.