The Roles of T-Box Genes in Vertebrate Limb Development

Members of the T-box gene family have diverse roles during embryogenesis and many play critical roles in the developing limb. This is exemplified by the fact that, in humans, mutations in T-box genes are associated with several congenital syndromes that include limb defects as part of their characteristic spectrum of abnormalities. T-box genes encode for evolutionary conserved transcription factors that include both transcriptional activators and repressors. The hallmark of T-box gene members is the presence of the eponymous DNA-binding T-box domain. There are 17 mammalian T-box genes, which based on the sequence homology of the T-box domain, are grouped into five subfamilies, namely, T, Tbx1, Tbx2, Tbx6, and Tbr1. At least nine T-box genes are expressed during limb development with distinct and dynamic expression patterns. All four members of Tbx2 subfamily (Tbx2, Tbx3, Tbx4, Tbx5) and three members of Tbx1 (Tbx1, Tbx15, Tbx18), Brachyury (T) and Eomes (Tbr2) are expressed in the developing limb.