Ectoderm specification
In Xenopus laevis, the specification of the three germ layers (endoderm, mesoderm and ectoderm) occurs at the blastula stage. Great efforts have been made to determine the factors that specify the endoderm and mesoderm. On the other hand, only a few examples of genes that are required for ectoderm specification have been described in the last decade. The first molecule identified to be required for the specification of ectoderm was the ubiquitin ligase Ectodermin (Ecto, TIF1-γ, TRIM33); later, it was found that the deubiquitinating enzyme, FAM/USP9x, is able to overcome the effects of ubiquitination made by Ectodermin in Smad4 (Dupont et al., 2009). Two transcription factors have been proposed to control gene expression of ectodermal specific genes: POU91/Oct3/4 and FoxIe1/Xema. A new factor specific for the ectoderm, XFDL156, has shown to be essential for suppression of mesoderm differentiation from pluripotent cells. Ectodermin and FAM Biological role of Ectodermin and FAM The protein Ectodermin, firstly identified in Xenopus embryos, promotes ectodermal fate and suppresses the mesoderm formation mediated by the signaling of Transforming Growth Factor β (TGFβ) and Bone Morphogenic Proteins (BMP), members of the TGFβ-superfamily. When the TGFβ ligands bind to TGFβ receptors, they cause the activation of the signal