Roles of transition nuclear proteins in spermiogenesis

Abstract

The transition nuclear proteins (TPs) constitute 90% of the chromatin basic proteins during the steps of spermiogenesis between histone removal and the deposition of the protamines. We first summarize the properties of the two major transition nuclear proteins, TP1 and TP2, and present concepts, based on their time of appearance in vivo and in vitro properties, regarding their roles. Distinct roles for the two TPs in histone displacement, sperm nuclear shaping, chromatin condensation, and maintenance of DNA integrity have been proposed. More definitive information on their roles in spermiogenesis has recently been obtained using mice with null mutations in the Tnp1 or Tnp2 genes for TP1 and TP2, respectively. In these mice, histone displacement and sperm nuclear shaping appear to progress quite normally. Spermatid nuclear condensation occurs, albeit in an abnormal fashion, and the mature sperm of the Tnp -null mutants are not as condensed as wild-type sperm. There is also evidence that sperm from these mutant mice contain an elevated level of DNA strand breaks. The mutant sperm showed several unexpected phenotypes, including a high incidence of configurational defects, such as heads bent back on midpieces, midpieces in hairpin configurations, coils, and clumps, other midpiece defects, reduced levels of proteolytic processing of protamine 2 during maturation, and reduced motility. The two TPs appear partly to compensate for each other as both Tnp1 - and Tnp2 -null mice were able to produce offspring, and appear to have largely overlapping functions as the two mutants had similar phenotypes.

Poly(ADP-ribose) polymerase-2 contributes to the fidelity of male meiosis I and spermiogenesis

“…These data suggest that Parp-2, in addition to the transition proteins, protamines, and histone variants, is required for normal spermatid differentiation (41,42). It remains to be determined whether Parp-2-dependent poly(ADP-ribosyl)ation of the testis-specific histone variants and͞or basic proteins contributes to their sequential and highly regulated replacement necessary for proper chromatin condensation.…”

The E2 Ubiquitin-conjugating Enzyme UBE2J1 Is Required for Spermiogenesis in Mice

“…In fact, most genes so far associated with defective cytoplasmic removal encode nuclear proteins, such as transition nuclear proteins (Tnp1, Tnp2, Ref. 36) and the protamines (Prm1, Prm2, Ref. 37), none of which are likely to directly participate in cytoplasm removal.…”

Transcriptome profiling of the developing postnatal mouse testis using next-generation sequencing

“…The transition nuclear proteins (TNP) constitute 90% of the chromatin basic proteins, replacing the histones temporarily, and are then switched by protamines (PRM) during spermiogenesis [52]. Smcp and Ropn1l affect sperm motility [53,54], while genes such as Tnp1, Tnp2, Prm1, Prm2, and Smcp are transcribed in round spermatids, but when spermatids undergo nuclear condensation and elongation, their mRNAs are stored in a translationally repressed state in early elongating spermatids [55][56][57][58].…”