Contemporary techniques for freezing mouse spermatozoa

Influence of sperm cryopreservation on sperm motility and proAKAP4 concentration in mice

Background

The protein proAKAP4 is crucial for sperm motility and has been suggested as an indicator of male fertility. We determined the relationship between proAKAP4 concentration and sperm motility parameters in mice, and investigated the effects of cryopreservation on these variables.

Methods

Computer-assisted sperm analysis and ELISA were applied to determine sperm motility and proAKAP4 concentration in fresh and frozen-thawed epididymal sperm of SWISS, B6D2F1, C57BL/6N, and BALB/c mice.

Results

ProAKAP4 levels ranged between 12 and 89 ng/ml and did not differ between fresh and frozen-thawed samples, or between strains. We found a negative relationship between proAKAP4 levels and some sperm motility parameters. Sperm traits differed between strains, and cryopreservation negatively affected sperm velocity but not sperm direction parameters.

Conclusion

ProAKAP4 levels in epididymal mouse spermatozoa were unaffected by cryopreservation, highlighting the robustness of this parameter as a potentially time-independent marker for sperm motility and fertility. The high individual variation in proAKAP4 levels supports the potential role of proAKAP4 as a marker for sperm quality, though we found no positive, and even negative relationships between proAKAP4 levels and some sperm motility parameters. Future studies have to investigate the significance of proAKAP4 as an indicator for fertility in mice.

Cryopreservation of mouse resources

The cryopreservation of sperm and embryos is useful to efficiently archive valuable resources of genetically engineered mice. Till date, more than 60,000 strains of genetically engineered mice have been archived in mouse banks worldwide. Researchers can request for the archived mouse strains for their research projects. The research infrastructure of mouse banks improves the availability of mouse resources, the productivity of research projects, and the reproducibility of animal experiments. Our research team manages the mouse bank at the Center for Animal Resources and Development in Kumamoto University and continuously develops new techniques in mouse reproductive technology to efficiently improve the system of mouse banking. In this review, we introduce the activities of mouse banks and the latest techniques used in mouse reproductive technology.

DNA fragmentation index (DFI) as a measure of sperm quality and fertility in mice

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.

A new, simple and efficient liquid nitrogen free method to cryopreserve mouse spermatozoa at -80 °C

The mouse is widely used for biomedical research and an increasing number of genetically altered models are currently generated, therefore centralized repositories are essentials to secure the important mouse strains that have been developed. We have previously reported that spermatozoa of wild type and mutant strains frozen using standard laboratory protocols can be transported in dry ice (-79 °C) for 7 days and safely stored in a -80 °C freezer for up to two years. The objective of this new study was to compare the effects of the freezing techniques using LN₂ or -80 °C freezer on fertility of frozen-thawed mouse spermatozoa. After thawing, sperm fertility was comparable (P > 0,05) between the LN₂ and the -80 °C samples for at least 1 year. Furthermore, we showed that it is possible to freeze and store mouse semen directly at -80 °C and eventually transfer it to LN₂ irrespective of storage time. This study is relevant because it shows for the first time that mouse spermatozoa can be efficiently frozen and stored at -80 °C with no use of liquid nitrogen for a long period of time. A new, simple, efficient and flexible, liquid nitrogen free, method was developed for freezing and maintaining spermatozoa of wild type and mutant C57BL/6N lines. Lines on this genetic background are used in collaborative research infrastructures for systematic phenotyping, e.g. the International Mouse Phenotyping Consortium (IMPC) and therefore largely cryopreserved in repositories like EMMA/Infrafrontier. The importance of this finding will be especially useful for small laboratories with no or limited access to liquid nitrogen and for laboratories generating many mouse mutant lines by CRISPR/Cas9 who do not want to saturate the limited space of a LN₂ tank, using a more accessible -80 °C freezer. This study underlines, once more, that mouse spermatozoa are very resistant and can be frozen, transported, shared and stored at -80 °C for a long time without a significant loss of viability. This new approach simplifies the freezing process and facilitates the long term storage of mouse spermatozoa at -80 °C, always allowing the transfer to LN₂ for indefinite storage without noticeable detrimental effects.

Generation and Identification of Mutations Resulting in Chronic and Age-Related Phenotypes in Mice

Aging is inevitable, and our society must deal with the consequences: namely, an increased incidence of disease and ill health. Many mouse models of disease are acute or early onset or are induced in young mice, despite the fact that aging is a significant risk factor for a range of significant diseases. To improve modeling of such diseases, we should incorporate aging into our models. Many systems are affected by aging, with a decline in mitochondrial function, an increase in senescence, a loss of resilience, telomere shortening, and a decline in immune function being key factors in the increased susceptibility to disease that is associated with aging. To develop novel models of age-related disease, we undertook a phenotype-driven screen of a pipeline of mutagenized mice. Here, we describe some of the underlying protocols and outline important aspects to consider when studying aged mice. © 2018 by John Wiley & Sons, Inc.

Successful in vitro fertilization and generation of transgenics in Black and Tan Brachyury (BTBR) mice

The Black and Tan Brachyury (BTBR) mouse strain is a valuable model for the study of long-term complications from obesity-induced type 2 diabetes mellitus and autism spectrum disorder. Due to technical difficulties with assisted reproduction, genetically modified animals on this background have previously been generated through extensive backcrossing, which is expensive and time-consuming. We successfully generated two separate transgenic mouse lines after direct zygote microinjection into this background strain. Additionally, we developed in vitro fertilization (IVF) methods for the BTBR mouse. We found low rates of fertilization and implantation in this strain, and identified the BTBR oocyte as the primary culprit of low success with BTBR IVF. We achieved an increase in live born pups from 5.9 to 35.6 % with IVF in the BTBR strain by use of BTBR females at a younger age (18-25 days), collection of oocytes 15-17 h after superovulation, and the use of supplemented fertilization media. This method eliminates the need for time consuming assisted embryo manipulations that are otherwise required for success with BTBR oocytes. This advancement provides an exciting opportunity to directly generate BTBR transgenics and gene-edited mice using both traditional and emerging genomic editing techniques, such as CRISPR/Cas9. These methods also allow effective colony preservation and rederivation with these strains. To our knowledge, this is the first report describing embryo manipulations in BTBR mice.

INFRAFRONTIER: a European resource for studying the functional basis of human disease

Ageing research and more generally the study of the functional basis of human diseases profit enormously from the large-scale approaches and resources in mouse functional genomics: systematic targeted mutation of the mouse genome, systemic phenotyping in mouse clinics, and the archiving and distribution of the mouse resources in public repositories. INFRAFRONTIER, the European research infrastructure for the development, systemic phenotyping, archiving and distribution of mammalian models, offers access to sustainable mouse resources for biomedical research. INFRAFRONTIER promotes the global sharing of high-quality resources and data and thus contributes to data reproducibility and animal welfare. INFRAFRONTIER puts great effort into international standardisation and quality control and into technology development to improve and expand experimental protocols, reduce the use of animals in research and increase the reproducibility of results. In concert with the research community and the International Mouse Phenotyping Consortium (IMPC), INFRAFRONTIER is currently developing new pilot platforms and services for the research on ageing and age-related diseases.

Lack of transmission of murine norovirus to mice via in vitro fertilization, intracytoplasmic sperm injection, and ovary transplantation

Since its discovery in 2003, murine norovirus (MNV) is still endemic in many rodent animal facilities. Our aim was to determine the risk of transmission of MNV (91% homology to MNV3) to embryo recipients and pups via assisted reproductive technologies, especially those which compromise the integrity of the zona pellucida. In vitro fertilization (IVF), assisted in vitro fertilization (AIVF) with reduced glutathione, intracytoplasmic sperm injection, and ovary transplantation were performed. Murine norovirus was detected by qualitative and quantitative reverse transcription polymerase chain reaction. After natural infection of immunocompetent C57BL/6NTacCnrm and immunodeficient athymic nude mice with MNV, the mesenteric lymph nodes, small intestine, spleen, liver, lung, brain, ovary, and testis were infected at specific intervals for more than a 1-year period. At Week 12, the number of viral genomes per milligram of gonad from both strains was 20 to 50. Murine norovirus strictly adhered to spermatozoa collected from infected mice because three washes did not remove MNV from the sperm. After using MNV-positive sperm for IVF, AIVF, and intracytoplasmic sperm injection, 27 to 30 genomes were detected in IVF (n = 100) and AIVF (n = 100) embryos from both mouse strains. Approximately 87% of MNV detected in these embryos was found in the zona pellucida. However, all embryo transfer recipients, pups, and ovary recipients were MNV-negative. The results indicate that manipulation of the germplasm through assisted reproductive technologies did not lead to transmission of MNV to mice. This may be because of the absence of an infectious dose or failure of the MNV strain to replicate effectively in developing embryos and the reproductive tract.