SpRunt-1, a new member of the runt domain family of transcription factors, is a positive regulator of the aboral ectoderm-specific CyIIIA gene in sea urchin embryos

Abstract

In this paper we present a structural and functional characterization of a new sea urchin embryo transcription factor, SpRunt-1. This factor was isolated by means of its specific interaction with a cis-regulatory target site of the CyIIIa gene. Here we show that this target site, the P7I site, is required for normal embryonic activation of CyIIIa CAT reporter gene constructs. An oligonucleotide affinity column bearing the P7I target site purifies a 21-kDa polypeptide from blastula-stage nuclear extracts, and the amino acid sequence obtained from this polypeptide was used to generate a nucleic acid probe with which the corresponding cDNA was cloned. The cDNA encodes an approximately 60-kDa protein, SpRunt-1, which includes a 'runt domain' that is closely homologous to those of Drosophila and mammalian runt domain transcription factors. RNA and genomic blots show that SpRunt-1 is represented by a single embryonic transcript, encoded by one of possibly two runt-domain-containing genes. By RNA probe protection we found that transcripts of SpRunt-1 increase in concentration dramatically after the blastula stage of development, suggesting that the up-regulation of CyIIIa that occurs after blastula stage is a function of zygotically transcribed SpRunt-1. These results are discussed with reference to known features of the runt domain family of transcription factors.