Network map for specification of endomesodermal lineages. (A) Diagram of the vegetal hemisphere of a Ciona gastrula. Each cell is color coded according to its lineage as indicated by the color labels in the center. (B) Confocal image of an early tailbud embryo stained with phalloidin. Embryonic tissues have been artificially colored in accordance with the color scheme in A to display the fate of each of the lineages. Domains of some tissues are approximate and may not be wholly accurate. (C) Summary of data on interactions between genes involved in specification of endomesodermal lineages. Boxes for each lineage are colored according to the scheme in A and B. Bold lines indicate that this interaction has been verified through the manipulation of binding sites within an enhancer. Asterisks indicate evidence for appropriate binding sites in the noncoding DNA upstream of the target genes. Dotted lines indicate tangential interaction indicated by embryological manipulations. The notochord determinant Brachyury encodes a T-box homeodomain protein. The genes required for specifying different mesodermal lineages (NoTric [previously known as Handlike], Twist-like1, Mesp, MyoD) all encode bHLH transcriptional factors. Further details regarding endomesodermal differentiation can be found in Supplement 1.
