Involvement of Nuclear Architecture in Regulating Gene Expression in Bone Cells

Abstract

This chapter discusses the role played by several indices of nuclear architecture to the control of gene expression in bone cells. It presents cellular, biochemical, molecular, and genetic evidence for linkages of developmental and tissue-specific gene expression with the organization of transcriptional regulatory machinery in subnuclear compartments. While the mechanisms that control gene expression remain to be formally defined, there is growing awareness that the fidelity of gene regulation necessitates the coordination of transcription factor metabolism and the spatial organization of genes and regulatory proteins within the three-dimensional context of nuclear architecture. The parameters of nuclear architecture include the sequence of gene regulatory elements, chromatin structure, and higher order organization of the transcriptional regulatory machinery into subnuclear domains. All of these parameters involve mechanisms that include transcription factor synthesis, nuclear import and retention, posttranslational modifications of factors, and directing factors to subnuclear sites that support gene expression. Hyperacetylation of nuclear proteins alters the chromatin organization of the bone tissue specific osteocalcin gene promoter in a manner that prevents vitamin D-mediated transcriptional upregulation. By combining nuclease accessibility, indirect end labeling, and ligation-mediated polymerase chain reaction (PCR) analysis, it is demonstrated that protein-DNA interactions that promote formation of a distal DNase I hypersensitive site do not occur under conditions of hyperacetylation.