Histone variants in development and diseases.

Eukaryotic genomic DNA is highly packaged into chromatin by histones to fit inside the nucleus. Other than the bulk packaging role of canonical histones with an expression peak at S phase and replication-coupled deposition, different histone variants have evolved distinct regulatory mechanisms for their expression, deposition and functional implications. The diversity of histone variants results in structural plasticity of chromatin and highlights functionally distinct chromosomal domain, which plays critical roles in development from a fertilized egg into a complex organism, as well as in aging and diseases. However, the mechanisms of this fundamental process are poorly understood so far. It is of particular interest to investigate how the variants are incorporated into chromatin and mark specific chromatin states to regulate gene expression, and how they are involved in development and diseases. In this review, we focus on recent progress in studies of epigenetic regulation of three extensively investigated variants including H2A.Z, macroH2A and H3.3, and their functional implications in development and diseases.