SpGataE, a Strongylocentrotus purpuratus ortholog of mammalian Gata4/5/6: protein expression, interaction with putative target gene spec2a, and identification of friend of Gata factor SpFog1

In the sea urchin Strongylocentrotus purpuatus, SpGataE, an ortholog of the vertebrate zinc-finger transcription factors Gata4/5/6, occupies a key position in the gene regulatory network for endomesoderm specification. We have posited that in addition to regulating gene activity required for endomesoderm specification, SpGataE also represses the expression of the aboral ectoderm-specific spec2a gene in endomesoderm territories. Although the expression pattern of spgatae and its role in endomesoderm specification have been described in considerable detail, little is known about SpGataE protein accumulation and its interactions with target genes and coregulatory factors. Our purpose here was to gain further insight into the mechanisms by which SpGataE functions as a transcriptional regulator. To achieve this, we generated an anti-SpGataE antibody to determine the spatiotemporal expression pattern of SpGataE protein and establish whether it plays a role in repressing spec2a by binding to gata cis-regulatory elements within the endogenous spec2a enhancer. Because Gata proteins often associate with friend of Gata (Fog) coregulators, we identified an S. purpuratus fog ortholog, spfog1, and showed that SpGataE and SpFog1 physically interacted. Spfog1 transcripts were maximal by early blastula stage but continued thereafter to be expressed at low levels. Knockdown of spfog1 using antisense morpholino oligonucleotides did not produce notable effects on endomesoderm specification or spec2a enhancer activity, suggesting that SpGataE exerts these functions independently of SpFog1. In addition to providing new information on Gata and Fog proteins in sea urchins, the anti-SpGataE antibody developed here should be a useful reagent for future analysis of SpGataE function.