Maternal and embryonic provenance of a sea urchin embryo transcription factor, SpZ12-1.

SpZ12-1 is a zinc-finger transcription factor. Previous work has indicated that this factor functions late in embryogenesis as a spatial transcriptional repressor. We show here that this factor is present in significant quantities even in unfertilized egg cytoplasm, and in similar quantities in mesenchyme blastula-stage embryo cytoplasm. Taken together with earlier measurements of Calzone and associates, our observations indicate that SpZ12-1 enters the embryonic nuclei between late cleavage and mesenchyme blastula stages. A low-prevalence mRNA encoding SpZ12-1 is also present throughout development. Translation of this mRNA could, however, easily account for the complete complement of SpZ12-1 protein in the embryo, as estimated from its DNA binding activity. SpZ12-1 probably functions at several developmental stages and is evidently of both maternal and embryonic provenance.