Xenopus Embryo: Mesoderm Induction

Abstract

Abstract During early embryogenesis, the three germ layers (mesoderm, endoderm and ectoderm) must form in the correct positions for normal development to proceed. In the amphibian embryo, mesoderm is induced at the late blastula stage, in the equatorial marginal zone of the spherical embryo, by signals emanating from the vegetal hemisphere. Later, during gastrulation, mesoderm is further patterned by signals from the dorsal organiser. Vegetal mesoderm inducing signals are members of the transforming growth factor‐beta (TGFβ) family, which are transcribed in response to vegetal localised maternal transcription factors. Limiting mesoderm induction to the marginal zone is controlled by TGFβ inhibitors in the animal hemisphere. Mesoderm is maintained in the marginal zone by FGF signals and patterned, during gastrulation, by BMP signals. Key Concepts Mesoderm is induced the marginal zone of the Xenopus blastula stage embryo in response to signals secreted from the vegetal hemisphere. Mesoderm is induced by members of the Nodal/Activin subfamily of the transforming growth factor‐beta (TGF‐β) family of secreted signalling factors. Fibroblast growth factor (FGF) family members maintain mesoderm. Mesoderm induction is limited to the marginal zone of the embryo by TGF‐β signalling inhibitors expressed in the animal hemisphere . Maternal transcription factors, such as VegT and β‐catenin, activate expression of TGF‐β genes. Mesoderm is further patterned during gastrulation through both activation and inhibition of BMP signalling.