Individual Somatic H1 Subtypes Are Dispensable for Mouse Development Even in Mice Lacking the H1⁰Replacement Subtype

Abstract

Each of these doubly H1-deficient mice also was fertile and exhibited no anatomic or histological abnormalities. Chromatin from the three double-knockout strains showed no significant change in the ratio of total H1 to nucleosomes. These results suggest that any individual H1 subtype is dispensable for mouse development and that loss of even two subtypes is tolerated if a normal H1-to-nucleosome stoichiometry is maintained. Multiple compound H1 knockouts will probably be needed to disrupt the compensation within this multigene family.DNA in the nuclei of all eukaryotic cells is packaged into repeating units of nucleosomes that form the basic unit of chromatin. Each nucleosome consists of an octamer core containing two molecules of each of the core histones, H2a, H2b, H3, and H4. H1 linker histones bind to the nucleosome core particle and the linker DNA between nucleosomes to facilitate further compaction of chromatin into a 30-nm fiber. Recent studies have shown that the chromatin complex, especially the nucleosome and its modifications, can have a profound influence on transcription (reviewed in references 9 and 26).Although histones are highly conserved proteins, multicellular organisms contain a variety of subtypes exhibiting significant sequence divergence. Among the histone classes, the H1 linker histones are the most divergent group. In mammals, there are at least eight H1 subtypes, including the somatic H1s, H1a to H1e, germ cell-specific H1t and H1oo, and replacement linker histone H1 0 (11, 24). These subtypes exhibit distinct patterns of expression during differentiation and development (12,24). The significance of the diversity present within the H1 family is not understood. The genes for H1a through H1e and H1t are tightly linked on mouse chromosome 13 (25). The H1 0 gene is located on mouse chromosome 15 (2). H1 0 is the smallest and most divergent member of the H1 family (27). H1 0 accumulates in quiescent cells and during terminal differentiation and terminal cell division, reaching levels as high as 30% of the total H1 in certain tissues, such as adult liver. Despite the unique properties and developmental regulation of H1 0 , previous studies in our laboratory showed that mice develop normally without H1 0 (23). Analysis of chromatin from H1 0 -null mice indicated that the level of the somatic H1s, especially H1c, H1d, and H1e, was increased so as to maintain a normal ratio of H1 to nucleosomes in H1 0 -deficient chromatin. In certain tissues, such as adult liver, H1c, H1d, and H1e accounted for 95% of the remaining H1, suggesting that these subtypes are responsible for compensating for loss of H1 0 . The present study was undertaken with the following two experimental objectives: first, to determine whether or not any one of several H1 subtypes is essential for mouse development; second, to determine whether H1c, H1d, or H1e is responsible for compensating for the loss of H1 0 in H1 0Ϫ/Ϫ mice. To achieve the first goal, we generated null mutations in each of the three somatic H1 genes by homolo...

H1 linker histone promotes epigenetic silencing by regulating both DNA methylation and histone H3 methylation

“…Expression of the chimeric H1 also led to recruitment of DNMT1 and DNMT3B to the H19 and Gtl2 ICRs, whereas expression of H1c and a truncated H1d lacking this region of the CTD did not lead to recruitment of the two DNMTs. Gene inactivation studies in mice have not revealed essential functions for any of these histone H1 subtypes, including H1c and H1(0) (15)(16)(17). Interestingly however, we reported previously that the genes encoding H1(0) and H1c exhibit differences in their regulation compared with the genes encoding the four other subtypes (40)(41)(42).…”

“…Mammals contain at least eight histone H1 subtypes or variants that differ in amino acid sequences and expression during development (12)(13)(14). Functional differences among these subtypes have been difficult to identify because they appear to act redundantly in development (14)(15)(16)(17). Although the precise location of histone H1 within the chromatin fiber is uncertain, it is known that histone H1 resides outside the nucleosome core particle, where it associates with the DNA as it enters and exits the core particle and protects an additional ∼20 bp of DNA (linker DNA).…”

Translocation of histone H1 subtypes between chromatin and cytoplasm during mitosis in normal human fibroblasts

“…Furthermore, H1.2 expression is not restricted to Sphase, like the other somatic subtypes (33). Clear is, however, that relocation of H1.2 cannot be essential for mitotic compaction as H1.2 knockout mice develop normally (10). In case there is such a role, other H1 subtypes may have overlapping functions.…”

“…The function of having multiple subtypes has not yet been clarified, [for review see (9)]. Although there seems to be a noteworthy redundancy among the histone H1 subtypes (10), evolutionary data indicate that they posses different functional roles (11). They differ in affinity for chromatin (12,13), ability to affect gene regulation (14), and are found to localize to different parts of the nuclei (12).…”

The ISWI ATPase Snf2h is required for early mouse development

“…NT 039467) containing exons 9b and 10 was cloned into pBlueScript SK(ϩ). A 2-kb HindIII-HpaI fragment from the plNTK plasmid containing the PGK-Neo cassette surrounded by LoxP1 sites (27) (28). Electroporated cells (10 8 ) were transferred to eight gelatinized plates containing irradiated 40% confluent, G418-resistant feeder cells (leukemia inhibitory factor-expressing STO fibroblasts, American Type Culture Collection).…”