EXPRESSION OF THE T-BOX FAMILY GENES, TBX1-TBX5, DURING EARLY MOUSE DEVELOPMENT

A novel family of genes, characterized by the presence of a region of homology to the DNA-binding domain of the Brachyury (T) locus product, has recently been identified. The region of homology has been named t he T-box, and the new mouse genes that contain the T-box domain have b een named T-box 1-6 (Tbx1 through Tbx6). As the basis for further stud y of the function and evolution of these genes, we have examined the e xpression of 5 of these genes, Tbx1-Tbx5, across a wide range of embry onic stages from blastocyst through gastrulation and early organogenes is by in situ hybridization of whole-mounts and tissue sections. Tbx3 is expressed earliest, in the inner cell mass of the blastocyst. Four of the genes are expressed in different components of the mesoderm or mesoderm/endoderm during gastrulation (Tbx1 and Tbx3-5). All of these genes have highly specific patterns of expression during later embryog enesis, notably in areas undergoing inductive tissue interactions. In several cases there is complementary expression of different genes in 2 interacting tissues, as in the lung epithelium (Tbx1) and lung mesen chyme (Tbx2-5), and in mammary buds (Tbx3) and mammary stroma (Tbx2). Tbx1 shows very little overlap in the sites of expression with the oth er 4 genes, in contrast to a striking similarity in expression between members of the 2 cognate gene sets, Tbx2/Tbx3 and Tbx4/Tbx5. This is a clear reflection of the evolutionary relationship between the 5 gene s since the divergence of Tbx1 occurred long before the relatively rec ent divergence of Tbx2 and 3 and Tbx4 and 5 from common ancestral gene s. These studies are a good indication that the T-box family of genes has important roles in inductive interactions in many stages of mammal ian embryogenesis. (C) 1996 Wiley-Liss, Inc.