Abstract
Yin-Yang 1 (YY1) is a highly conserved transcription factor possessing RNA-binding activity. A putative YY1 homologue was previously identified in the developmental model organism Strongylocentrotus purpuratus (the purple sea urchin) by genomic sequencing. We identified a high degree of sequence similarity with YY1 homologues of vertebrate origin which shared 100% protein sequence identity over the DNA- and RNA-binding zinc-finger region with high similarity in the N-terminal transcriptional activation domain. SpYY1 demonstrated identical DNA- and RNA-binding characteristics between Xenopus laevis and S. purpuratus indicating that it maintains similar functional and biochemical properties across widely divergent deuterostome species. SpYY1 binds to the consensus YY1 DNA element, and also to U-rich RNA sequences. Although we detected SpYY1 RNA-binding activity in ova lysates and observed cytoplasmic localization, SpYY1 was not associated with maternal mRNA in ova. SpYY1 expressed in Xenopus oocytes was excluded from the nucleus and associated with maternally expressed cytoplasmic mRNA molecules. These data demonstrate the existence of an YY1 homologue in S. purpuratus with similar structural and biochemical features to those of the well-studied vertebrate YY1; however, the data reveal major differences in the biological role of YY1 in the regulation of maternally expressed mRNA in the two species.
Highlights
Yin-Yang 1 (YY1) is a member of the GLI-Kruppel family of transcription factors with activity in activation, repression, or initiation of transcription at numerous cellular and viral promoters depending on the cellular context[1,2,3,4,5,6]
Previous observations of an unidentified nucleic acid-binding activity with affinity for the consensus YY1 DNA-binding element suggested that S. purpuratus YY1 (SpYY1) is expressed in embryos of S. purpuratus[48]
Initial Western blots of S. purpuratus ova lysate probed with anti-Xenopus YY1 antibodies revealed a single ~47 kDa band consistent with the predicted size of SpYY1 based on genomic sequencing
Summary
Yin-Yang 1 (YY1) is a member of the GLI-Kruppel family of transcription factors with activity in activation, repression, or initiation of transcription at numerous cellular and viral promoters depending on the cellular context[1,2,3,4,5,6]. A putative YY1 consensus binding site has been identified in the promotor of the Hbox[12] gene of the sea urchin Paracentrotus lividus and its deletion affects the spatial, temporal, and magnitude of expression of Hbox12-promoter driven GFP fusion reporter constructs[49] These analysis demonstrated transcriptional activity from the YY1 consensus binding site in fertilized eggs and early morula-stage embryos, implying that YY1 functions as a nuclear transcription factor early in development, though the specific stage at which YY1-modulated transcription begins in the ovum or embryo is unknown[48,49,50]. NW_011983912.1) predicts a 1,203 bp open reading frame (XM_785095.4) encoding a 400 amino acid polypeptide (XP_790188) with Mr = 44.6 kDa and high sequence similarity to the vertebrate nucleic acid binding protein YY1 These data strongly indicates the presence of a functional YY1 homologue in S. purpuratus, to date no such protein has been cloned or characterized. We suggest the use of the name SpYY1 for this gene and its protein product since our analysis described below shows far closer sequence homology of the sea urchin protein to mammalian YY1 than to the Drosophila melanogaster YY1 homologue PHO
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