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1. Role of the RNA-binding protein XSeb4R in ectoderm formation

We recently provided evidence that the RRM-type RNA binding protein XSeb4R, originaly identified as a proneural factor in retinogenesis, acts at the vegetal pole of the blastula embryo as a post-transcriptional regulator of VegT and as such is required for endoderm specification and mesoderm induction. Maternal XSeb4R transcripts are found uniformely distributed at blastula stage throughout the embryo, suggesting that it might also play a role in ectodermal progenitor specification. To investigate this possibility, we have overexpressed XSeb4R in whole embryos and, interestingly, found that it leads to ectopic expression of a key ectodermal determinant, Sox3. Additionally, XSeb4R was found to interact directly with Sox3 mRNA. Based on those preliminary results, we are pursuing the study of its function in ectoderm formation by performing further overexpression and MO depletion experiments in the frog embryo and by the identification of additional targets. A TAP-tag approach will be also used to identify partners and determine how this single RRM-type RNA binding post-transcriptional regulator specifies its target transcripts. The biological relevance of the identified partnership will be analysed by gain- and loss-of-function investigations in the frog embryo.