Id4 expression and its relationship to other Id genes during avian embryonic development.

We present the sequence and expression pattern of chick Id4 and compare its distribution to that of other vertebrate Id genes. At early stages, Id4 expression is discrete, with transcript transiently expressed in subsets of migrating neural crest cells, the dorsal myocardium, the segmental plate mesoderm, and the tail bud. Later, expression is also observed in the telencephalic vesicles and corneal epithelium. Of all the Id genes, Id4 exhibits the most restricted pattern in the developing nervous system, with little expression in the presumptive neural crest or placodes. Id4 appears in the neural tube much later than other Id genes. However, all four Id genes display overlapping patterns in the branchial arches and tail bud.