Conservation of Mouse Models Through Embryo Freezing

Oral D-Aspartate Treatment Improves Sperm Fertility in Both Young and Adult B6N Mice

Simple Summary

Investigations concerning the impact of D-Aspartate on fertility suggest that it has a positive influence on the in vitro fertilization rate in young C57BL/6N mice. Here, we demonstrated that adult C57BL/6N mice that received an oral treatment of D-Aspartate also have a higher fertilizing capability and the quality of their spermatozoa increased after only two weeks of treatment. Hence, this study gives us new insights on the role of D-Aspartate in the regulation of the reproductive activity in both young and adult mice.

Abstract

D-Aspartate (D-Asp) treatment improved the fertility of young male C57BL/6N mice in vivo revealing a direct role on capacitation, acrosome reaction, and fertility in vitro in young males only. We investigated whether the positive effect of D-Asp on fertility could be extended to adult males and evaluated the efficacy of a 2- or 4-week-treatment in vivo. Therefore, 20 mM sodium D-Asp was supplied in drinking water to males of different ages so that they were 9 or 16 weeks old at the end of the experiments. After sperm freezing, the in vitro fertilization (IVF) rate, the birth rate, hormone levels (luteinizing hormone (LH), epitestosterone, and testosterone), the sperm quality (morphology, abnormalities, motility, and velocity), the capacitation rate, and the acrosome reaction were investigated. Oral D-Asp treatment improves the fertilizing capability in mice regardless of the age of the animals. Importantly, a short D-Asp treatment of 2 weeks in young males elevates sperm parameters to the levels of untreated adult animals. In vivo, D-Asp treatment highly improves sperm quality but not sperm concentration. Therefore, D-Asp plays a beneficial role in mouse male fertility and may be highly relevant for cryorepositories to improve mouse sperm biobanking.

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 Till date, more than 60,000 strains of genetically engineered mice have been archived in mouse banks worldwide.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.

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.