A novel role for Tbx3 in regulating digit number in the developing limb by Shh dependent and independent mechanisms

Abstract

The crucial roles of TBX3 in development are evident in the fact that heterozygous mutations of TBX3 cause human Ulnar–mammary syndrome (UMS) including limb malformations, apocrine and mammary gland hypoplasia, dental and genital defects. Although germline deletion of Tbx3 in mice generates UMS‐like phenotypes, embryonic lethality has previously prevented investigating its precise role during limb development. To overcome this, we conditionally ablated Tbx3 in critical signaling compartments in the developing forelimb and discovered distinct functions in anterior and posterior mesenchyme. We found that Tbx3 promotes posterior digit development by positively regulating the Hand2/Shh signaling pathway. In anterior mesenchyme, Tbx3 constrains digit number by increasing the level of Gli3R and preventing expression of Hand1. The molecular basis for the effect of Tbx3 on Gli3R is at least in part via post‐transcriptional regulation of Suppressor of fused (Sufu). Loss of Tbx3 results in increased Sufu protein and altered Gli3R processing in primary cilia. Furthermore, mutants with complete loss of Tbx3 phenocopy the severe limb defects of Shh and Hand2 null mutants. In total, Tbx3 controls digit number by regulating Shh signaling in both ligand dependent (posterior mesenchyme) and ligand independent (anterior mesenchyme) mechanisms.This work was supported by a March of Dimes Basil O'Connor Award (AMM), and NIH R01HD046767 (AMM).Grant Funding Source: N/A