T-PROMOTER ACTIVITY IN THE ABSENCE OF FUNCTIONAL T-PROTEIN DURING AXIS FORMATION AND ELONGATION IN THE MOUSE

The T (Brachyury) gene, which encodes a transcription factor, is invol ved in the formation of posterior mesoderm. Although studies in Xenopu s have shown that T gene expression is responsive to mesoderm inducing factors and furthermore suggest the existence of an autoregulatory lo op involving T itself, eFGF, and the EGF receptor, little is known abo ut the regulation of T expression in the mouse. We report here that in the mouse the expression of fgf-4, the putative homologue of Xenopus efgf, is not dependent on the presence of T protein during the first 4 8 hr of gastrulation. Furthermore, we address the question of autoregu lation using a chimeric approach. Introduction of a T promoter-lacZ co nstruct into TIT ES cells results in T promoter activity in the primit ive streak and tail bud in the absence of functional T protein. Theref ore, we suggest that a direct FGF and T autoregulatory loop is unlikel y to operate during gastrulation and axis elongation in the mouse. (C) 1997 Academic Press.