Functional analysis of cis-regulatory elements controlling initiation and maintenance of early Cdx1 gene expression in the mouse

Members of the Caudal-related homeobox gene family are implicated in anteroposterior (AP) patterning and posterior axis elongation in mammals. Previously, we found that Caudal-related homeobox gene1 (Cdx1) is directly regulated by the Wnt/beta-catenin signaling pathway, and we identified Wnt/beta-catenin responsive elements in the Cdx1 promoter. Here, we have generated a series of transgenic mouse lines to determine if the Cdx1 promoter region (-3.6 kb to -0.7 kb) sufficient to drive reporter gene expression in the normal Cdx1 expression domains. A 0.7-kb Cdx1 upstream regulatory sequence is sufficient to give the early phase of Cdxl expression in the primitive streak. However, none of the reporter constructs was able to drive expression in the definitive endoderm at later stages of development. More detailed analysis of the cis-regulatory elements of this 0.7-kb Cdx1 promoter region revealed that two Wnt/beta-catenin responsive elements are important for initiation of Cdxl expression in the primitive streak and one retinoic acid response element for maintenance. Our analysis demonstrates that the early Cdxl expression is regulated through the caudalizing Wnt/beta-catenin and RA activities. (C) 2002 Wiley-Liss, Inc.