Newly identified paralogous groups on mouse chromosomes 5 and 11 reveal the age of a T-box cluster duplication.

A novel family of ancient transcription factors, the T-box family, involved in embryonic development in metazoans, was described recently. Four members of this family are grouped in two tightly linked pairs within the mouse genome. This arrangement can be explained by an original cluster formation followed by an en masse duplication. Here we demonstrate that this duplication event also included several closely linked genes. Using data obtained from linked paralogous genes, we show that the T-box cluster duplication occurred prior to the divergence between bony fish and tetrapods around 400 million years ago. This work facilitates our understanding of the status of the T-box gene family in different vertebrate lineages and also defines a novel paralogy group within the mouse genome.