Gene expression during early embryogenesis of sea urchin: the histone and homeobox genes

Summary Transcriptional regulators are thought to play a key role in cell fate determination and territorial specification in sea urchin. Our goals are to clone transcription factors for studying embryonic development. One approach has been to use promoter binding and gene transfer technology to investigate the mechanisms of transcriptional activation and repression of the early H2A histone gene. By this analysis we identified a transcriptional activator, the MBF-1, that binds to the modulator element of the H2A gene and enhances the activity of the H2A promoter. However, the enhancer activity of the modulator and its interaction with MBF-1 also occurs at the gastrula stage when the early histone genes are shut off. Therefore, the silencing of the early H2A histone gene at late stages of development requires the inactivation of the modulator function. To search for antimodulator sequence elements, we took advantage of our previous work showing the presence of phased nucleosomes specifically positioned on ...