In vertebrates, the patterning of anterior-posterior (AP) axis is a fundamental process during embryogenesis. Wnt and FGF signalling pathways play important roles in regulating the patterning of embryo AP axis. Mouse Tbx6 encodes a transcription factor that has been demonstrated to be involved in the specification of the posterior tissue in mouse embryonic body. Here, we prove that morpholino-induced knockdown of XTbx6 impairs posterior development, indicating the requirement of XTbx6 in this process. Meanwhile, gain of XTbx6 function is sufficient to induce ectopic posterior structures in Xenopus embryos. Furthermore, XTbx6 activates the expression of Xwnt8 and FGF8, which are two mediators of posterior development, suggesting a mechanism by which XTbx6 modulates posterior patterning via Wnt and FGF signalling pathway activation.

Tbx6 is critical for somite specification and myogenesis initiation. It has been shown that Activin/Nodal, VegT/Nodal, FGF, and BMP signaling pathways are involved early in specifying mesoderm or later in patterning mesoderm, and Xnot plays roles in setting up the boundary between notochord and paraxial mesoderm. In this study, we introduce the dominant negative form of above genes into embryos to evaluate if they are responsible for regulating Tbx6 expression. The results show that: (1) Activin/Nodal and VegT/Nodal signals are necessary for both initiation and maintenance of Tbx6 expression, and Nodal is sufficient to induce ectopic Tbx6 expression; (2) FGF signal is necessary for the initiation and maintenance of Tbx6, but it is not sufficient to induce Tbx6 expression; (3) BMP is also necessary for the expression of Tbx6, and the induction of Tbx6 expression by BMP is dose dependent; (4) Xnot has no effect on the expression of Tbx6. Our results suggest that several signaling pathways are involved in regulating Tbx6 expression, and pave the route to reveal the molecular mechanism of initiating myogenesis.