Abstract
Histone variants are an important part of the histone contribution to chromatin epigenetics. In this review, we describe how the known structural differences of these variants from their canonical histone counterparts impart a chromatin signature ultimately responsible for their epigenetic contribution. In terms of the core histones, H2A histone variants are major players while H3 variant CenH3, with a controversial role in the nucleosome conformation, remains the genuine epigenetic histone variant. Linker histone variants (histone H1 family) haven’t often been studied for their role in epigenetics. However, the micro-heterogeneity of the somatic canonical forms of linker histones appears to play an important role in maintaining the cell-differentiated states, while the cell cycle independent linker histone variants are involved in development. A picture starts to emerge in which histone H2A variants, in addition to their individual specific contributions to the nucleosome structure and dynamics, globally impair the accessibility of linker histones to defined chromatin locations and may have important consequences for determining different states of chromatin metabolism.
Highlights
Histone variants are an important part of the histone contribution to chromatin epigenetics
Linker histones (H1 family) are 200–400 amino acid long proteins that bind to these regions and play an important role in the modulation of the chromatin fiber folding [7]
Histone H2A family represent the most abundant class [75]. Their structural and functional characteristics are mainly exerted through their N-and C-terminal tails [31], with the length of the C-terminal end playing a critical role in nucleosome stability—as evidenced by the low stability of H2A variants such as H2A.Z.2.2 and H2A.Bbd that are truncated at this region
Summary
Several recent reviews have highlighted the epigenetic role of histone variants [33,34,37,38]. One of the most dramatic compositional and conformational changes of chromatin in metazoan organisms takes place during the late stages of the spermatogenesis, after meiosis (spermiogenesis). During this time, in many invertebrate and vertebrate organisms (but not all), the nucleosomal chromatin organization disappears, and most of the histones are replaced by small arginine-rich chromosomal proteins known as protamines [45]. The centromeric regions are only partly affected by this drastic chromatin remodelling [48], and CenH3 (CID in Drosophila) is retained at these centromeric regions [49,50]. We will be following the recently proposed unified phylogeny-based nomenclature for histone variants [36]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
