ABSTRACT
How a single cell gives rise to progeny with differing fates remains poorly understood. We examined cells lacking methyl CpG binding domain protein-2 (MBD2), a molecule that has been proposed to link DNA methylation to silent chromatin. Helper T cells from Mbd2(-/-) mice exhibit disordered differentiation. IL-4, the signature of a restricted set of progeny, is expressed ectopically in Mbd2(-/-) parent and daughter cells. Loss of MBD2-mediated silencing renders the normally essential activator, Gata-3, dispensable for IL-4 induction. Gata-3 and MBD2 act in competition, wherein each factor independently, and quantitatively, regulates the binary choice of whether heritable IL-4 expression is established. Gata-3 functions, in part, to displace MBD2 from methylated DNA. These results suggest that activating and silencing signals integrate to provide spatially and temporally restricted patterns of gene activity.
Subject(s)
DNA-Binding Proteins/metabolism , Gene Expression Regulation, Developmental , Gene Silencing , Trans-Activators/metabolism , Animals , Binding, Competitive , Cell Differentiation , Cell Line , Cell Lineage , Chromatin/metabolism , CpG Islands/genetics , DNA Methylation , DNA-Binding Proteins/deficiency , DNA-Binding Proteins/genetics , Flow Cytometry , GATA3 Transcription Factor , Gene Deletion , Interleukin-4/genetics , Interleukin-4/metabolism , Mice , Mice, Inbred C57BL , Mice, Knockout , T-Lymphocytes, Helper-Inducer/cytology , T-Lymphocytes, Helper-Inducer/metabolism , Trans-Activators/deficiency , Trans-Activators/geneticsABSTRACT
Type 1 helper T (T(H)1) cells are essential for cellular immunity, but their ontogeny, maturation and durability remain poorly understood. By constructing a dominant-negative form of T-bet, we were able to determine the role played by this lineage-inducing trans-activator in the establishment and maintenance of heritable T(H)1 gene expression. Optimal induction of interferon-gamma (IFN-gamma) expression required genetic interaction between T-bet and its target, the homeoprotein Hlx. In fully mature T(H)1 cells, reiteration of IFN-gamma expression and stable chromatin remodeling became relatively independent of T-bet activity and coincided with demethylation of DNA. In contrast, some lineage attributes, such as expression of IL-12R beta 2 (interleukin 12 receptor beta 2), required ongoing T-bet activity in mature T(H)1 cells and their progeny. These findings suggest that heritable states of gene expression might be maintained by continued expression of the inducing factor or by a mechanism that confers a stable imprint of the induced state.
