Analyses of the consequences of a protamine-2-deficiency in mouse and man: molecular mechanisms, reactive oxygen species and an approach to therapy.
Final Report Abstract
During spermatogenesis, most histones are replaced by protamines (Prm1 and Prm2) resulting in sperm chromatin condensation and transcriptional arrest. In the first funding period, Prm2-deficient mice were generated, which were infertile. In the second funding period, we proposed to analyze the molecular mechanism and compare the results to the human situation. Interestingly, in Prm2-deficient mice, the histologically observed morphogenetic processes during the intensive morphological restructuring from round spermatids to elongated spermatozoa are not affected. However, we demonstrated that in Prm2-deficient animals, sperm transit from the testis to the epididymis triggers a response cascade that causes Reactive Oxygen Species (ROS) levels to increase via a reduction in SOD1 and PRDX1. This increased ROS level causes numerous damages to membranes, to proteins and also to DNA, which appears highly fragmented and degraded. Remarkably, using sperm from the testes of Prm2-deficient animals, we were able to successfully fertilize oocytes using intracytoplasmic sperm injection (ICSI), and we were able to observe their further development until the blastocyst stage. This indicates that sperm DNA is intact as far as it goes and also that the postulated epigenetic markers were not necessarily affected by the absence of protamine-2, as early embryogenesis after ICSI appears normal. Prm2 controls the dynamics of DNA-hyperdondensation. Here, the processing of the pre-PRM2 to the mature PRM2 seems relevant. Futher, we find evidence, that Prm is required for the eviction of DNA-associated Histones. Since Prm2-deficient spermatozoa are not available in man, only a comparison with aberrant protamine-ratio can be made. The situation seems comparable with the difference that stress markers are already detectable in the testis. However, since biopsy material is only available from males of subfertile couples, individual germ cells might already show defects despite normal appearing histology. In cases of massive disruption of spermatogenesis (e.g. spermatid arrest), a shift of signals from spermatids to spermatocytes could be observed.
Publications
- (2016). Re-visiting the Protamine-2 locus: deletion, but not haploinsufficiency, renders male mice infertile. Scientific Reports 6, 1–13
Schneider, S., Balbach, M., Jikeli, J.F., Fietz, D., Nettersheim, D., Jostes, S., Schmidt, R., Kressin, M., Bergmann, M., Wachten, D., Steger K and Schorle H.
(See online at https://doi.org/10.1038/srep36764) - (2020) Protamine-2 deficiency initiates a reactive oxygen species (ROS)-mediated destruction cascade during epididymal sperm maturation in mice. Cells 9(8):1789
Schneider S, Shakeri F, Trötschel C, Arévalo L, Kruse A, Buness A, Poetsch A, Steger K, Schorle H
(See online at https://doi.org/10.3390/cells9081789) - (2021). Loss of the cleaved-protamine 2 domain leads to incomplete histone-to-protamine exchange and infertility in mice
Arévalo, L., Merges, G.E., Schneider, S., Oben, F.E., Neumann, I., and Schorle, H.
(See online at https://dx.doi.org/10.1371/journal.pgen.1010272) - (2022) Loss of Prm1 leads to defective chromatin protamination, impaired PRM2 processing, reduced sperm motility and subfertility in male mice. Development 2022
Merges G E, Meier J, Schneider S, Kruse A, Fröbius A C, Kirfel K, Steger K, Arévalo L, Schorle H
(See online at https://doi.org/10.1242/dev.200330)
