Abstract
Although thousands of genetically modified mouse strains have been cryopreserved by sperm freezing, the likelihood of cryorecovery success cannot be accurately predicted using conventional sperm parameters. The objective of the present study was to assess the extent to which measurement of a sperm DNA fragmentation index (DFI) can predict sperm quality and fertility after cryopreservation. Using a modified TUNEL assay, we measured and correlated the DFI of frozen-thawed sperm from 83 unique mutant mouse strains with sperm count, motility and morphology. We observed a linear inverse correlation between sperm DFI and sperm morphology and motility. Further, sperm DFI was significantly higher from males with low sperm counts compared to males with normal sperm counts (P < 0.0001). Additionally, we found that viable embryos derived using sperm from males with high DFI (62.7 ± 7.2% for IVF and 73.3 ± 8.1% for ICSI) failed to litter after embryo transfer compared to embryos from males with low DFI (20.4 ± 7.9% for IVF and 28.1 ± 10.7 for ICSI). This study reveals that measurement of DFI provides a simple, informative and reliable measure of sperm quality and can accurately predict male mouse fertility.
Highlights
It is well known that normal embryonic development is dependent on the delivery of intact and complete genetic material from sperm to oocyte[1,2]
To determine the extent to which sperm motility and DNA integrity are affected by cryopreservation, total motility, progressive motility and DNA fragmentation index (DFI) of sperm from 24 wildtype C57BL/6N males and 24 mutant males proven fertile by natural mating (1 male per mutant mouse strain) were assessed before and after cryopreservation
We found that sperm DFI was inversely correlated with both total motility (r = −0.90, Fig. 2) and progressive motility (r = −0.96, Fig. 3)
Summary
It is well known that normal embryonic development is dependent on the delivery of intact and complete genetic material from sperm to oocyte[1,2]. Further studies are needed to clarify the exact role of sperm DNA damage within the myriad of other male and female factors contributing to reproductive outcomes after IVF (in vitro fertilization) and ICSI (intracytoplasmic sperm injection)[18,19]. Because of their similarities with human anatomy, physiology and genetics, thousands of genetically modified mice have been used to study human physiology and diseases[22]. To avoid female factor infertility, wildtype oocytes from the same wildtype mouse strain and vendor were used for all IVF and ICSI procedures
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