Monitoring Smad Activity In Vivo Using the Xenopus Model System

The embryo of the African clawed frog Xenopus laevis plays a central role in the field of cell and developmental biology. One of the strengths of Xenopus as model system lies in the high degree of conservation between amphibians and mammals in the molecular mechanisms controlling tissue patterning and differentiation. As such, many signaling cascades were first investigated in frog embryos and then confirmed in mouse and/or human cells. The TGF-β signaling cascade greatly benefited from this model system. Here we review the overall logic and experimental planning for studying Smad activity in vivo in the context of Xenopus embryonic development, and provide a guide for the interpretation of the results.