Regulatory mechanisms of competence to respond to BMP signaling

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The purpose of this research is to understand the regulatory mechanisms of cellular competence to respond to bone morphogenetic proteins (BMPs) during early vertebrate embryogenesis. We have previously found that Xenopus Oct-25 (XOct-25) plays an important role in the cell fate decision between neural and epidermal cells by inhibiting the competence of ectodermal cells to BMP signaling. In addition, we suggested the possibility that XOct-25 indirectly suppresses BMP signaling by activating downstream target genes. Here, we isolated genes activated by XOct-25 in the ectoderm through a microarray approach and characterized their functions in ectodermal development. Our findings are listed below:(1) We found that one of the XOct-25 down-stream genes (CIB2) was spatiotemporally co-expressed with XOct-25 in the posterior region of the neural plate during early Xenopus embryogenesis. Overexpression of CIB2 in the ectodermal explants suppressed BMP-mediated epidermis formation and weakly neuralized the ectoderm. In addition, CIB2 induced posterior neural tissue when combined with an anterior neural inducer suggesting that CIB2 has a posteriorizing activity in the ectoderm.(2) Loss-of-function analyses of CIB2 in embryos resulted in defects in the formation of trunk and tail regions at tailbud stages. Whole-mount in situ hybridization analyses revealed that CIB2 is required for the specification of posterior neural tissue during early neurula stages.Our results suggest a role of the XOct-25 down stream gene CIB2 in the induction and patterning of Xenopus neural tissues. Mechanisms of suppression of BMP-mediated epidermis formation and patterning of neural tissue along the anterior-posterior axis are currently being investigated.