Cascade of transcription factors in sea urchin early embryos

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To elucidate a mechanism underlying gene expression during early development, we started a series of research to find a cascade for transcription factors regulating expression of the Ars gene of sea urchin embryos. Results obtained in the present project is as follows.We previously reported that the region around transcription start site of the Ars gene intensely stimulates the promoter activity of this gene. This year we determined cis-active elements present in this region by reporter assays. We found two cis-active elements, one between -72bp and -56bp is homologous to SpZI2/OctI -binding site and the other between +l38bp and +142bp homologous to the binding site for Rel family protein. Both cis-elements not only stimulate the promoter activity but mediate the stimulatory activity of the first intron enhancer. In addition to these elements, the region between -194bp and -144bp stimulate temporally regulated expression of the Ars gene. The AACAAAG strech in this region is a binding site for Sox (SRY-type HMG box) protein, a known positive transcription factor, and we detected by gel shift assay a nuclear protein from sea urchin gastrula that binds to this motif sequence-specifically. This protein is a maternal one that exists until mesenchyme blastulae but declines after gastrula stage. Sea urchin Sox protein synthesized in vitro by using SpSox mRNA bound sequence-specifically to this motif. We also detected in the near upstream of the Sox motif the existence of a cis-element that regulates binding of Sox protein to the Sox motif.