Role of YY1 in regulating human epsilon and gamma-globin gene expression.

Abstract

Transcription factor YY1 is a ubiquitous protein that has many functions. It has been shown to be an activator or a repressor of gene expression and can participate in developmental regulation of gene expression. Early studies in our laboratory identified several conserved YY1 binding sites near the $\varepsilon$ and $\gamma$ globin genes. In transient transfection assays, one of these conserved YY1 binding sites repressed gene expression from a $\gamma$ promoter. This implied that YY1 might play a role in regulating $\varepsilon$ and $\gamma$ gene expression. This study began with the mapping of YY1 genes in the mouse and human. The mouse YY1 gene was found to be a single-copy gene, mapping to mouse Chromosome 12. No known mouse mutations were found to co-localize with YY1. In the human, there is apparently more than one YY1 gene or YY1 gene-like sequence. To study the function of specific YY1 binding sites near the $\varepsilon$ and $\gamma$ genes, two novel constructs were developed and tested in transgenic mice. The constructs contain a region of the $\beta$-globin locus control region (LCR) and the $\varepsilon$ and $\gamma$ globin genes. These constructs displayed stage specific silencing of the $\varepsilon$ and A$\gamma$ genes in transgenic mice. These constructs will be valuable tools for further analysis of the cis elements that control $\varepsilon$ and $\gamma$ gene regulation. The mutation of several YY1 sites upstream from the $\varepsilon$ gene did not produce a detectable phenotype in transgenic mice. In contrast, mutation of an evolutionarily conserved YY1 binding site in the distal A$\gamma$ promoter resulted in reduced A$\gamma$ expression level and altered expression pattern, suggesting that this site is important for proper developmental stage expression of the A$\gamma$ gene in transgenic mice.