| Transcription factors of the T-box family are essential for proper development of various tissues and organs. In mice, Tbx4 is required for maintenance of hindlimb bud outgrowth. A closely related family member, Tbx5, is involved in cardiac and forelimb development. To determine the roles that these T-box genes play in specifying limb identity in the mouse, I developed a knock-in strategy to target the Tbx5 locus with Tbx4 sequences in embryonic stem cells.; To further investigate the functional overlap of these paralogous genes, in vitro luciferase reporter assays were conducted. Both Tbx4 and Tbx5 robustly activated Fgf10, ANF and alpha-MyHC enhancer elements to the same degree with a difference existing in the presence of the Cx40 promoter. The activation of Fgf10 was specific to a region that when mutated, abrogated DNA binding. In the presence of additional transcriptional partners like Nkx2.5 and Gata4, differential activation could represent a novel function of Tbx4 not previously described. The biological significance of these results relates to Tbx4 and Tbx5 function in limb and heart development. |
