Developmentally regulated expression of linker‐histone variants in vertebrates

Abstract

The identification of histone H1 variants in vertebrates suggests that these proteins may have specialized functions. During embryonic development, a correspondence between the expression of each of the linker-histone variants and the proliferative and transcriptional activity of embryonic cells can be observed. Analysis of the developmentally regulated expression of these variants leads to the subdivision of these variants into distinct classes. This subdivision may also provide insight into the significance of the differential expression of variants and the roles individual linker histones have in chromatin structure and function.Linker histones have long been known to interact with the variable length of linker DNA that lies between nucleosome cores within chromatin (van Holde, 1989). This interaction is believed to facilitate the folding of nucleosomal arrays into higher-order structures. This mundane packaging role is, not, however, the only role linker histones have to play. Studies on the structure of linker histones, their interaction with the nucleosome and their roles in controlling gene activity indicate that this family of proteins has not only an important architectural role, but also an essential regulatory role in transcription. In vertebrates, several different variants of linker histones have been described and the expression of their genes studied. It is useful to examine the properties and expression of these variants, since this analysis leads to a better understanding of the relevance of this diversity for particular cellular activities during development.Linker histones may be subdivided into four major classes according to both the timing of their expression and their cell-type specificity during development. This division, based on the pattern of expression, corresponds also to distinct properties of proteins in each class. In general, a linker histone presents a tripartite structure; an N-terminal tail, a globular domain and a relatively long C-terminal tail. Members of each class have conserved this structural feature but can ble distinguished mainly by the length of the N-terminal and C-terminal tails and the nature of the peptide sequence, i.e. the number of acidic and basic amino acids as well as the nature of the basic residues.Cleavage linker histones are expressed during oogenesis and during early embryogenesis. The normal somatic form of linker histone (Hl) progressively accumulates in nuclei after the initiation of zygotic expression and, thereafter, is Correspondence to S. Khochbin,

The Centromeric/Nucleolar Chromatin Protein ZFP-37 May Function to Specify Neuronal Nuclear Domains

“…Interestingly, the histone H1-like domain of ZFP-37 resembles more the COOH termini of the replacement type histones H1 0 and H5 than those of the cell cycle-dependent histones. Like ZFP-37, histone H1 0 and H5 are present in terminally differentiated cell types (58), and it is thought that the higher content of basic amino acid residues in their tails reflects their capacity to condense DNA to a higher extent (59). Further research will have to determine how the linker region of ZFP-37 binds to DNA and to what extent this domain cooperates with the KRAB and zinc finger regions to yield a functional protein.…”

Induction of Secondary Structure in a COOH-terminal Peptide of Histone H1 by Interaction with the DNA

“…Participation in nucleosome positioning has been proposed as a possible mechanism by which H1 could contribute to transcriptional regulation (5,6). Experiments in vivo indicate that H1 does not function as a global transcriptional repressor, but instead participates in complexes that either activate or repress specific genes (7)(8)(9)(10)(11). Previous work has established that the globular domain of H1 is sufficient to direct specific gene repression in early Xenopus embryos (12).…”

H10 RNA-binding Proteins Specifically Expressed in the Rat Brain

“…On the basis of several studies, it appears that the fine control of these aspects of protein metabolism depends largely on post-transcriptional regulation of the metabolism of the corresponding mRNAs (29, 46 -53). Among the gene products whose concentration changes during neural cell maturation, differentiation-associated variants of both linker (such as H1 0 ) and core histones (such as H3.3) are of great interest, as their entering chromatin may further affect the transcriptional potential of the genome (54,55).…”