MURINE CDX-4 BEARS STRIKING SIMILARITIES TO THE DROSOPHILA-CAUDAL GENE IN ITS HOMEODOMAIN SEQUENCE AND EARLY EXPRESSION PATTERN

A third member of the murine caudal-like gene family, Cdx-4, has been isolated. In situ hybridization and immunohistochemistry have been use d to study the localization of mRNA and protein during murine embryoge nesis. Cdx-4 is expressed transiently from 7.0 d.p.c. (days post coitu m) until 10 d.p.c., starting at the beginning of gastrulation (7.0-7.5 d.p.c.) in the allantois and posterior tip of the primitive streak. A t the mid-streak stage, Cdx-4 expression moves rostrally, and protein and mRNA are detected in all cells over the posterior half of the prim itive streak. As development proceeds, Cdx-4 gene products continue to be restricted to the posterior of the embryo, including the remnants of the primitive streak. Cdx-4 is expressed in neurectoderm, presomiti c and lateral plate mesoderm, and hindgut endoderm, but the anterior b oundary in the paraxial mesoderm is staggered with respect to the othe r germ layers. At all stages analyzed, Cdx-4 exhibits a graded express ion pattern with a posterior maximum, a distribution highly reminiscen t of the Drosophila caudal gene. These data add to the recently descri bed distributions of other vertebrate caudal-like genes, and further s upport the idea that members of this homeobox gene subfamily have regu latory roles in the specification of anteroposterior axial polarity in early embryos.