A key cellular mechanism that integrates diverse environmental stimuli with changes in gene expression is chromatin remodeling [19, 20]. Signal-dependent enzymes can alter the structure of chromatin at specific gene loci to facilitate the activation or repression of specific transcriptional programs. Chromatin is made up of DNA and the histone proteins around which the DNA is wrapped. Histones are assembled into an octamer composed of two copies each of H2A, H2B, H3, and H4 [21]. Through a complex process not completely understood, chromatin is supercoiled into a highly condense structure that packages and organizes many meters of DNA into the nucleus of each cell. This highly condensed structure provides chromatin unique control over gene expression by gating access of transcriptional activators to DNA [22, 23]. Chromatin structure itself is regulated at specific gene loci by numerous mechanisms that serve to either physically relax (e.g. histone acetylation) or remodel (e.g. SWI-SNF-dependent nucleosome remodeling) chromatin structure, or provide docking sites to recruit additional transcriptional co-activators or repressors [24]. Such modifications include histone acetylation, phosphorylation, and methylation, among several others, which together determine
