THE ZEBRAFISH EGR1 GENE ENCODES A HIGHLY CONSERVED, ZINC-FINGER TRANSCRIPTIONAL REGULATOR

The Egr family of transcriptional regulators comprises a group of gene s which encode members of the Cys(2)-His(2) class of zinc-finger prote ins. We have isolated a zebrafish egr1 homologue by screening a zebraf ish genomic library with a mouse Egr1 zinc finger probe. Southern blot ting indicated the existence of a single zebrafish egr1 gene and, as i n higher vertebrates, the presence of related members of a larger gene family. Sequence analysis of the zebrafish egr1 coding region reveale d a high level of homology to the mouse, rat, and human Egr1 genes wit h the notable exception of a polymorphic, triplet nucleotide repeat se quence in the region coding for the amino terminus of the Egr1 protein . The predicted DNA-binding, zinc-finger domain protein sequence was s trictly conserved. The 5' region of the zebrafish egr1 gene contained a variety of transcription factor binding sites, also present in the m ouse gene, for serum response factor, CREB and c-Ets. The zebrafish eg r1 transcript was approximately 3.4 kb in size and was expressed in ad ult zebrafish brain and muscle RNA, a pattern of expression similar to that observed in mice. The potential for zebrafish egr1 to function a s a transcriptional regulator was tested by constructing an expression vector containing zebrafish egr1 coding sequences under the control o f a cytomegalovirus promoter. This construct was found to activate tra nscription of a reporter plasmid bearing multiple Egr1 binding sites w hen transiently cotransfected into mouse 3T3 cells. Our results indica te that the structure, regulation, and function of the Egr1 gene have been highly conserved during vertebrate evolution and suggest an impor tant role for this gene in growth and development.