The mesoderm of the amphibian embryo is induced by signals derived from the vegetal hemisphere of the embryo, which act on overlying equatorial cells. This proposal investigates the role and mode olfaction of the mesoderm-inducing factor active; recent experiments using antisepses morpholinooligonucleotides have shown that active is required, in a dose-dependent fashion, for normal mesoderm formation. We shall first use DNA microarray to identify genes that are down regulated in embryos in whichactivin signalling is reduced or abolished. The expression patterns of genes identified in this way will be investigated by in site hybridisation and their responses to different levels of active signalling will be studied. The 5' regulatory regions of active target genes will be analysed to ask if they share common motifs or transcription factor binding sites. The second series of experiments investigates the range of active signalling; experiments in whichactivin is miss-expressed in ectodermic tissue indicate that active can exert its effects over many cell diameters. However, it is important to know the range of endogenous active signalling in the intact embryo and whether this varies in different regions of the embryo. This will be studied by making clones of cells in which active translation is inhibited and asking to what extent neighbouring cells can’ rescue' target gene expression in those cells. The third question concerns post-transcriptional regulation of active; the effects of active are exerted predominantly in the vegetal hemisphere and marginal zone of the embryo, but active B mRNA is expressed in the animal hemisphere as well as in vegetal cells.
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