The Role of GLP Domains in Spreading of the G9a/GLP Complex and Regulation of the β-globin Gene Expression

Abstract

Marked by a defect in the production of the Beta (β)-globin chain that make-up hemoglobin, Beta (β)-thalassemia is the most prevalent form of inherited single-gene disorders in the world. To understand the molecular mechanisms that govern the expression of the β-globin polypeptide encoded by the β-globin locus, we examined closely the enzymes involved in the epigenetic regulation of gene expression through histone 3 lysine 9 mono and di-methylation (H3K9 me1/2). G9a-like protein (GLP), a mammalian methyltransferase involved in the establishment and maintenance of H3K9 me1/2 mark at euchromatin, regions was found to be critical for the full activation of the adult β-globin genes in vivo during Murine erythroleukemia cell line (MEL) differentiation. Though it was initially hypothesized that GLP binding to H3K9 me1/2 mark through its Ankyrin domain was key to its activating function, we found that Flag- GLP ankyrin mutants E817R and W791A unable to bind to the methyl mark, are able to activate β-globin genes as well as their wild-type counterpart. Additionally, this study found that the embryonic gene εγ, known to be re-activated after G9a KD at the mRNA level, was effectively transcribed at the protein level using Triton Urea Acetic acid (TAU) western blots, thereby identifying potential therapeutic applications for treatment for β-thalassemia patients.