DNA-Strangbrüche in männlichen Keimzellen der Maus

Abstract

Involuntary childlessness is caused by men in 30% of cases. Infertility is attributable to genetics in 10-15% of infertile couples. Recently DNA-strand breaks in sperm gained importance in diagnosis of infertility as well as in subsequent assisted reproductive technologies. To date, analysis of strand breaks is used as a standard method to determine male infertility. An increasing number of studies reveal a direct link between DNA-strand breaks, male infertility and the outcome of both, in vitro fertilization (IVF) and artificial insemination (AI); however, a link between DNA strand breaks and intracytoplasmic sperm injection (ICSI) is questionable. Compared to humans, mice show significantly less sperm with fragmented DNA. Furthermore, data described in the literature is hard to compare. Examination of DNA strand breaks as a standard method was recommended by the WHO in 2010, but further methods need to be developed. Within this thesis, studies using different knockout mice revealed an increase in incomplete protamination, but (also revealed) only a slight increase in DNA strand breaks in sperm with accumulating amounts of knockout genes. Even though correlation between protamination and DNA strand breaks could be shown, the intensity of increases differed. Furthermore, a steady rise in protamination was revealed although only two of six knockout genes influenced protamination directly. The remainder of knockout genes is presumed being involved in protamination as well. In order to verify this hypothesis, the actual interactions need to be studied further. Comparison of young and aged mice showed a significant higher number of apoptotic gametes in younger male compared to older ones. Regarding the number of sperm with DNA strand breaks, no significant difference could be proven. Studying Pxt1-knockout mice revealed that sperm with fragmented DNA differ between these knockout mice and 129/Sv-wildtype mice. No difference could be determined by induction of DNA strand breaks with DNase I. The Pxt1-gene appears to be involved in physiological elimination of defect sperm and was not influenced by induction of DNA strand breaks by DNase I. Further experiments with other induction methods need to be carried out in order to determine the relevance of Pxt1. Altogether, it could be said that the mouse is not a suitable model organism for studying the impact of DNA strand breaks in terms of fertility. Compared to humans, mice have a lower amount of sperm with DNA strand breaks (8-19% compared to less than 2%) which necessitates the search for a better model organism. These results as well as in other studies differ within examined animal species. The Species examined here did not resulted in a suitable animal model that is applicable to humans.