Human Testis/Sperm-specific Histone H2B (hTSH2B)

Abstract

Human sperm, unlike the sperm of other mammals, contain replacement histones with unknown biological functions. Here, we report the identification of the novel human gene coding for a testis/sperm-specific histone H2B (hTSH2B). This variant histone is 85% homologous to somatic H2B and has over 93% homology with the testis H2B of rodents. Using genomic PCR, two genetic alleles of hTSH2B were found in the human population. The hTSH2B gene is transcribed exclusively in testis, and the corresponding protein is also present in mature sperm. We expressed recombinant hTSH2B and identified this protein with a particular H2B subtype expressed in vivo. The subnuclear distribution of H2B variants in sperm was determined using biochemical fractionation and immunoblotting. The H2B variant associated with telomere-binding activity (15) was solubilized by Triton X-100 or micrococcal nuclease extraction, whereas hTSH2B was relatively tightly bound in nuclei. Immunofluorescence showed that hTSH2B was concentrated in spots located at the basal nuclear area of a subpopulation (20% of cells) of mature sperm. This fact may be of particular importance, because the hTSH2B "positive" and "negative" sperm cells may undergo significantly different decondensation processes following fertilization.During mammalian spermatogenesis, chromatin undergoes stage-specific structural reorganization. Testis-specific variants of histones, transitional proteins, and finally protamines replace somatic histones as the DNA condenses (1, 2). The complement of spermatogenic histones changes during differentiation, and this process has been described in detail for rodents (1). Whereas some testis histones (TH) 1 appear in the early stages of spermatogenesis for instance in spermatogonia (3) and some appear at late stages (e.g. in spermatids (4, 5)), the majority of TH are synthesized and incorporated into chromatin during meiosis (6). Rodent testis histones are replacement subtypes that differ in primary structure from the major somatic variants (3-5, 7-9). Although it is generally assumed that histone variants of germ line cells contribute to the restructuring of chromatin during spermatogenesis, their specific biological functions remain to be established.In contrast to other mammals, mature human sperm retains a set of core histones representing 10 -15% of basic proteins (10 -12). Of these, histone H2B fraction (hSH2B) is the most abundant (10, 13). A complex composition of the hSH2B has been indicated (12). Although 17 replication-dependent H2B genes have been identified so far in the human genome (14), this complement contains neither testis-nor sperm-specific genes. We were particularly interested in the characterization of sperm H2B because of our recent finding that a H2B-related protein is an essential part of the telomere-binding complex in human sperm (15).In this paper, the hSH2B group has been characterized using a combination of biochemical and immunochemical techniques. Further, a gene for a novel human histone H2B variant belonging to thi...

Histone structure and nucleosome stability

“…The H2B variant documented in sea urchin has an N-terminal tail with a characteristic pentapeptide repeat that is highly charged [48,49]. Additional H2B variants have also been found in male gametic cells from lily [50] and, more recently, in bovine [51] and human spermatozoa [52], however, their specific roles remain to be elucidated.…”

Somatic Histones Are Components of the Perinuclear Theca in Bovine Spermatozoa

“…Failure of H2A and H4 detection by N-terminal sequencing can be attributed to N-terminal acetylation reported in these latter histones (48 -50), which blocks the N-terminal sequencing procedure. PTderived histone sequences do not share any homology to mammalian testis-specific histone variants (51,52), although no bovine testis-specific histone variant has been characterized to date (53). Furthermore, 2D AUT/SDS-PAGE, and subsequent immunoblot analysis confirmed that these PT-derived histones are somatic-type, based on their identical characteristics to calf thymus core somatic histones.…”

Kinetics of human male pronuclear development in a heterologous ICSI model

“…This may reflect the intrinsic heterogeneity in the mature human sperm population. One of the possible reasons for such variation may be due to the sperm-specific histone TSH2B [31,32]. This histone is present in only a 30% subpopulation of sperm cells.…”