Point mutations in an epigenetic factor lead to multiple types of bone tumors: role of H3.3 histone variant in bone development and disease.

Coordinated post-translational modifications (PTMs) of nucleosomal histones emerge as a key mechanism of gene regulation by defining chromatin configuration. Patterns of histone modifications vary in different cells and constitute core elements of cell-specific epigenomes. Recently, in addition to canonical histone proteins produced during the S phase of cell cycle, several non-canonical histone variants have been identified and shown to express in a DNA replication-independent manner. These histone variants generate diversity in nucleosomal structures and add further complexity to mechanisms of epigenetic regulation. Cell-specific functions of histone variants remain to be determined. Several recent studies reported an association between some point mutations in the non-canonical histone H3.3 and particular types of brain and bone tumors. This suggests a possibility of differential physiological effects of histone variants in different cells and tissues, including bone. In this review, we outline the roles of histone variants and their PTMs in the epigenetic regulation of chromatin structure and discuss possible mechanisms of biological effects of the non-canonical histone mutations found in bone tumors on tumorigenesis in differentiating bone stem cells.