Epigenetics of Psychiatric Diseases

Epigenetics refers to changes in gene expression that occur without altering the underlying deoxyribonucleic acid (DNA) sequence. Epigenetic changes can be faithfully inherited and replicated through generations of somatic cell division. Furthermore, epigenetic changes result in stable phenotypic alterations for the organism. In recent years, a number of molecular pathways have been identified that mediate the establishment, maintenance, and interpretation of the epigenetic code. In this chapter, we provide a brief primer on the epigenetic mechanisms that are currently known to exist in humans: DNA methylation, covalent histone modification, chromatin remodeling by PolycombGroup (PcG) and trithorax-Group (trxG) proteins, ribonucleic acid (RNA) interference, and imprinting. Following that, we discuss examples whereby errors in these processes contribute to the pathogenesis of psychiatric diseases.

Knockdown of ALR (MLL2) Reveals ALR Target Genes and Leads to Alterations in Cell Adhesion and Growth

ABSTRACT ALR (MLL2) is a member of the human MLL family, which belongs to a larger SET1 family of histone methyltransferases. We found that ALR is present within a stable multiprotein complex containing a cohort of proteins shared with other SET1 family complexes and several unique components, such as PTIP and the jumonji family member UTX. Like other complexes formed by SET1 family members, the ALR complex exhibited strong H3K4 methyltransferase activity, conferred by the ALR SET domain. By generating ALR knockdown cell lines and comparing their expression profiles to that of control cells, we identified a set of genes whose expression is activated by ALR. Some of these genes were identified by chromatin immunoprecipitation as direct ALR targets. The ALR complex was found to associate in an ALR-dependent fashion with promoters and transcription initiation sites of target genes and to induce H3K4 trimethylation. The most characteristic features of the ALR knockdown cells were changes in the dynamics and mode of cell spreading/polarization, reduced migration capacity, impaired anchorage-dependent and -independent growth, and decreased tumorigenicity in mice. Taken together, our results suggest that ALR is a transcriptional activator that induces the transcription of target genes by covalent histone modification. ALR appears to be involved in the regulation of adhesion-related cytoskeletal events, which might affect cell growth and survival.