Abnormal Spermatogenesis and Reduced Fertility in Transition Nuclear Protein 1-Deficient Mice

• Published in: Proceedings of the National Academy of Sciences - PNAS 2000-04, Vol.97 (9), p.4683-4688
• Main Authors: Yu, Y. Eugene, Zhang, Yun, Unni, Emmanual, Shirley, Cynthia R., Deng, Jian M., Russell, Lonnie D., Weil, Michael M., Behringer, Richard R., Meistrich, Marvin L.
• Format: Article
• Language: English
• Subjects: Animals; Biological Sciences; Cellular biology; Chromatin; Chromatin - ultrastructure; Chromosomal Proteins, Non-Histone - deficiency; Chromosomal Proteins, Non-Histone - genetics; Chromosomal Proteins, Non-Histone - physiology; Condensation; Epididymis; Fertility; Fertility - genetics; Gene Deletion; Heterozygotes; Histones; Male; Mice; Mice, Knockout; Mutation; nuclear protein 1; nuclear protein 2; Nuclear proteins; Nuclear Proteins - metabolism; Organ Size; protamine 2; Protamines; Proteins; Seminal Vesicles - anatomy & histology; Sperm Count; Sperm Head - ultrastructure; Spermatids; Spermatogenesis - genetics; Spermatozoa; Testes; Testis - anatomy & histology; Tnp1 gene; Transition nuclear proteins
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.97.9.4683

Transition nuclear proteins (TPs), the major proteins found in chromatin of condensing spermatids, are believed to be important for histone displacement and chromatin condensation during mammalian spermatogenesis. We generated mice lacking the major TP, TP1, by targeted deletion of the Tnp1 gene in mouse embryonic stem cells. Surprisingly, testis weights and sperm production were normal in the mutant mice, and only subtle abnormalities were observed in sperm morphology. Electron microscopy revealed large rod-like structures in the chromatin of mutant step 13 spermatids, in contrast to the fine chromatin fibrils observed in wild type. Steps 12-13 spermatid nuclei from the testis of Tnp1-null mice contained, in place of TP1, elevated levels of TP2 and some protamine 2 (P2) precursor. Most of the precursor was processed to mature P2, but high levels of incompletely processed forms remained in epididymal spermatozoa. Sperm motility was reduced severely, and ≈ 60% of Tnp1-null males were infertile. We concluded that TP1 is not essential for histone displacement or chromatin condensation. The absence of TP1 may partially be compensated for by TP2 and P2 precursor, but this dysregulation of nucleoprotein replacement results in an abnormal pattern of chromatin condensation and in reduced fertility.