Fig. 8.

TBX3 restricts the posterior boundary of anteriorly expressed genes and TBX3 interacts with HAND2 to upregulate posterior gene expression. Scheme summarising the major findings of this study. TBX3 functions in AP boundary formation by restricting anterior genes from being expressed in the posterior limb bud mesenchyme (red lines). The four limb bud enhancers for Gli3 are indicated (mm1179 and mm-hs1586, Fig. 7A; mm682, Fig. S8; RII: Bastida et al., 2020). Two of these are directly repressed by TBX3 (mm1179 and mm-hs1586). In the posterior limb bud mesenchyme, TBX3 interacts with HAND2 to upregulate the expression of key regulatory genes (green arrows). HAND2 is required for posterior Tbx3 expression, and TBX3 in turn reinforces posterior Hand2 expression. The predominant role of HAND2 in positive regulation of posterior genes is indicated by thicker green arrows. All transcription units are shown in grey; CRMs and enhancers are indicated by white boxes.