T-box3 is a ciliary protein and regulates stability of the Gli3 transcription factor to control digit number

Abstract

Crucial roles for T-box3 in development are evident by severe limb malformations and other birth defects caused by T-box3 mutations in humans. Mechanisms whereby T-box3 regulates limb development are poorly understood. We discovered requirements for T-box at multiple stages of mouse limb development and distinct molecular functions in different tissue compartments. Early loss of T-box3 disrupts limb initiation, causing limb defects that phenocopy Sonic Hedgehog (Shh) mutants. Later ablation of T-box3 in posterior limb mesenchyme causes digit loss. In contrast, loss of anterior T-box3 results in preaxial polydactyly, as seen with dysfunction of primary cilia or Gli3-repressor. Remarkably, T-box3 is present in primary cilia where it colocalizes with Gli3. T-box3 interacts with Kif7 and is required for normal stoichiometry and function of a Kif7/Sufu complex that regulates Gli3 stability and processing. Thus, T-box3 controls digit number upstream of Shh-dependent (posterior mesenchyme) and Shh-independent, cilium-based (anterior mesenchyme) Hedgehog pathway function.DOI: http://dx.doi.org/10.7554/eLife.07897.001

Development of a subset of forelimb muscles and their attachment sites requires the ulnar-mammary syndrome gene Tbx3

“…We find that Tbx3 is specifically expressed in the precursors of posterior forelimb bones (ulna and digits 4 and 5) and, as shown previously (Emechebe et al, 2016; Frank et al, 2013), is required for their development. In addition, TBX3 cell-autonomously regulates the development of a subset of bone eminences (greater tubercle of the humerus, deltoid tuberosity and olecranon).…”

“…To determine more definitively which cell types derive from Tbx3 + cells, we utilized Tbx3 merCremer/+ ; Rosa tdTomato/+ embryos (Emechebe et al, 2016) in which Tbx3 + cells were genetically labeled at E9.5 (by means of tamoxifen delivered to pregnant dams) as Tomato+ and then analyzed at E13.5 (Fig. 2).…”

“…In some mutants ( n =3/27) the ulna is absent (Fig. 3I,J) (Emechebe et al, 2016). There is some variability in the earliest time of Cre-mediated deletion by the Prx1Cre transgene, and it is presumably in mice with the earliest Cre-mediated deletion of Tbx3 (at E9.0 in embryos with 14 somites, data not shown) that the ulna is absent.…”

“…8I) (Davenport et al, 2003; Emechebe et al, 2016; Frank et al, 2013). Because Tbx3 is expressed in the ulna and digits 4 and 5 (as revealed by lineage analysis of Tbx3+ cells) and Prx1Cre recombines in all limb bones, this suggests that TBX3 cell-autonomously regulates posterior bone development in the forelimb and explains why only these bones are affected by Tbx3 loss-of-function.…”

“…However, homozygous deletion of Tbx3 in mice leads to limb bone defects that largely phenocopy individuals with UMS, although the resulting embryonic lethality limited analysis of the limb phenotype (Davenport et al, 2003; Frank et al, 2013). Recent conditional deletion of Tbx3 in the lateral plate-derived limb bud has revealed that TBX3 is required for normal levels of SHH signaling, cell proliferation and development of posterior bones (Emechebe et al, 2016). Although descriptions of UMS limb phenotypes have entirely focused on bone phenotypes, the abnormal surface anatomy of UMS individuals (indicative of underlying soft tissue defects; Bamshad et al, 1999) and aberrant locomotion of Tbx3 mutant mice (Emechebe et al, 2016) suggests that TBX3 may play a broader role in musculoskeletal development than previously thought.…”