The Role of Methyl CpG Binding Domain Protein 2 (MBD2) in the Regulation of Embryonic and Fetal β-type Globin Genes

The reexpression of the fetal γ-globin gene in adult erythrocytes is of therapeutic interest due to its ameliorating effects in β-hemoglobinopathies. We recently showed that Methyl CpG Binding Domain Protein2 (MBD2) contributes to the silencing of the chicken embryonic ρ-globin and human fetal γ-globin genes. We further biochemically characterized an erythroid MeCP1 complex that is recruited by MBD2 to mediate the silencing of these genes. These observations suggest that the disruption of the MeCP1 complex could augment the expression of the fetal/embryonic globin genes. In the studies presented in chapter 2, we have pursued a structural and biophysical analysis of the interaction between two of the six components of the MeCP1 complex: MBD2 and p66α. These studies show that the coiled coil regions from MBD2 and p66α form a highly stable heterodimeric complex. Further, overexpressing the p66α coiled coil domain in adult erythroid cells can augment the expression of the chicken ρ-globin and human γ-globin genes, by disrupting the assembly of a functional MeCP1 complex. This indicates that the exogenously expressed p66α coiled coil peptide competes with the endogenous p66α for the interaction with the coiled coil domain of MBD2. These studies show that the coiled coil interaction between MBD2 and p66α could serve as a potential targets for the therapeutic induction of fetal hemoglobin. The laboratory showed that knockout of MBD2 in transgenic mice carrying the human β-globin gene cluster, results in an elevated expression of γ-globin in adult erythrocytes. However, MBD2 does not directly bind to the γ-globin gene to mediate its silencing. In the work presented in chapter 3, we have tested the hypothesis that MBD2 may suppress γ-globin gene transcription in adult erythrocytes indirectly, by binding to and repressing transcription of intermediary gene/s which may be involved in γ-globin gene regulation. Employing microarray technology, we have identified Gab1 and ZBTB32 as candidate genes that may be involved in the MBD2 mediated silencing of γ-globin