Abstract
Yin Yang 1 (YY1) is a multifunctional transcription factor that activates, represses, or initiates transcription of a diverse assortment of genes. Previous studies suggest a role for YY1 in cellular growth and differentiation, but its biological function during development of the vertebrate oocyte or embryo remains to be determined. We recently showed that YY1 is abundantly expressed throughout oogenesis and early embryonic stages of Xenopus, but it is sequestered in the cytoplasm and does not function directly in transcriptional regulation. In the present study we used a series of biochemical analyses to explore the potential function of YY1 in the oocyte cytoplasm. YY1 was isolated from oocyte lysates by oligo(dT)-cellulose chromatography, suggesting that it associates with maternally expressed mRNA in vivo. RNA mobility shift assays demonstrate that endogenous YY1 binds to labeled histone mRNA. Size exclusion chromatography of oocyte lysates revealed that YY1 exists in high molecular mass complexes in the range of 480 kDa. Destruction of endogenous RNA by RNase treatment of lysates, abolished the binding of YY1 to oligo(dT)-cellulose and resulted in redistribution from 480-kDa complexes to the monomeric form. Microinjection of RNase directly into the cytoplasm released YY1 from 480-kDa complexes and unmasked its DNA-binding activity, but did not promote translocation to the nucleus. These results provide evidence that YY1 is a component of ribonucleoprotein (mRNP) complexes in the Xenopus oocyte, indicating a novel function for YY1 in the storage or metabolism of maternal transcripts.
Highlights
Yin Yang 1 (YY1)1 is a highly conserved GLI-Kruppel transcription factor that functions as a repressor, activator, or initiator of transcription of a large number of cellular and viral genes
The cytoplasm is packed with vast amounts of maternal mRNAs, most of which are stored in ribonucleoprotein particles that protect mRNA from degradation and prevent premature translation
The results shown here establish that YY1 associates with maternal mRNA in high molecular weight most of which are stored in ribonucleoprotein (mRNP) complexes
Summary
Yin Yang 1 (YY1)1 is a highly conserved GLI-Kruppel transcription factor that functions as a repressor, activator, or initiator of transcription of a large number of cellular and viral genes (reviewed in Refs. 1 and 2). YY1 was isolated from oocyte lysates by oligo(dT)-cellulose chromatography, suggesting that it associates with maternally expressed mRNA in vivo. This data confirms that native YY1 in oocyte lysates is capable of associating with mRNA, but whether YY1 binds directly or as part of a larger multi-protein complex, or if there is sequence-specificity, remains to be determined.
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