Chromatin remodeling by nuclear receptors

The eukaryotic genome is structurally organized into nucleosomes to form chromatin, which regulates gene expression, in part, by controlling the accessibility of regulatory factors. When packaged as chromatin, many promoters are transcriptionally repressed, thus reducing the access of transcription factors to their binding sites. However, nuclear receptors (NRs) are a group of transcription factors that have the ability to access their binding sites in this repressive chromatin structure. Nuclear receptors are able to bind to their sites and recruit chromatin-remodeling proteins such as ATP-dependent chromatin-remodeling complexes and histone-modifying enzymes, resulting in transcriptional activation. In this review, we present the role of NRs in recruiting these chromatin-modifying enzymes by means of an extensively studied model system, the glucocorticoid receptor-mediated transactivation of the mouse mammary tumor virus (MMTV) promoter. We use these findings as a template to begin to understand the effect of chromatin changes on gene expression during spermatogenesis.