In Vitro Fertilization in Mice Using the MBCD-GSH Protocol

Influence of the storage conditions of embryo culture media on mouse development

The culture of preimplantation embryos in vitro is an important method for human and mouse reproductive technology. This study aims to investigate the influence of different conditions of culture media on the preimplantation stage of mouse embryos cultured in vitro, and monitor the post-implantation development of new mice after embryo transfer to surrogate females. We demonstrated here that mouse embryos cultured in vitro in fresh M16, KSOM, Global, and HTF embryo culture media from one cell to the blastocyst stage and the subsequent embryo transfer to surrogate females are able to proceed through post-implantation development and, after birth, develop into healthy mice. However, culture of embryos in differently aged media shows various (often unpredictable) results. To find the optimal storage conditions of culture media, we suggest that the freezing and long-term storage of these media at - 80°C will not influence the quality of the media. To test this hypothesis, we grew embryos from one cell to blastocysts in vitro in the selected media after thawing and subsequently transferring them to surrogate females. Embryo culture in these four media after thawing does not affect preimplantation and postnatal mouse development. Thus, we have shown that storage of embryo culture media at low temperature (- 80°C) does not impact the quality of the media, and subsequently, it can be used for the culture of embryos for the full preimplantation period, the same as in fresh media.

Epg5 deficiency leads to primary ovarian insufficiency due to WT1 accumulation in mouse granulosa cells

Primary ovarian insufficiency (POI), also known as premature ovarian failure, is an ovarian defect in humans characterized by the premature depletion of ovarian follicles before the age of 40. However, the mechanisms underlying POI remain largely unknown. Here, we show that knockout of Epg5 (ectopic P-granules autophagy protein 5 homolog (C. elegans)) results in subfertility in female mice, which exhibit a POI-like phenotype. Single-cell RNA sequencing analysis revealed that the knockout of Epg5 affected the differentiation of granulosa cells (GCs). Further investigation demonstrated that knockout of Epg5 blocks macroautophagic/autophagic flux, resulting in the accumulation of WT1 (WT1 transcription factor), an essential transcription factor for GCs, suggesting WT1 needs to be selectively degraded by the autophagy pathway. We found that the insufficient degradation of WT1 in the antral follicular stage contributes to reduced expression of steroidogenesis-related genes, thereby disrupting GC differentiation. Collectively, our studies show that EPG5 promotes WT1 degradation in GCs, indicating that the dysregulation of Epg5 in GCs can trigger POI pathogenesis.Abbreviations: 3-MA, 3-methyladenine; CHX, cycloheximide; CQ, chloroquine; EPG5, ectopic P-granules autophagy protein 5 homolog (C. elegans); GC, granulosa cell; MAP1LC3/LC3, microtubule-associated protein 1 light chain 3; MII, metaphase II; POI, primary ovarian insufficiency; PB1, polar body 1; SQSTM1/p62, sequestosome 1; WT1, WT1 transcription factor.

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.

Archiving genetically altered animals: a review of cryopreservation and recovery methods for genome edited animals

With the ever-expanding numbers of genetically altered (GA) animals created in this new age of CRISPR/Cas, tools for helping the management of this vast and valuable resource are essential. Cryopreservation of embryos and germplasm of GA animals has been a widely used tool for many years now, allowing for the archiving, distribution and colony management of stock. However, each year brings an array of advances, improving survival rates of embryos, success rates of in-vitro fertilisation and the ability to better share lines and refine the methods to preserve them. This article will focus on the mouse field, referencing the latest developments and assessing their efficacy and ease of implementation, with a brief note on other common genetically altered species (rat, zebrafish, Xenopus, avian species and non-human Primates).

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.

Graphene Oxide Improves in vitro Fertilization in Mice With No Impact on Embryo Development and Preserves the Membrane Microdomains Architecture

During the latest years, human infertility worsened all over the world and is nowadays reputed as a global public health issue. As a consequence, the adoption of Assisted Reproductive Technologies (ARTs) such as In Vitro Fertilization (IVF) is undergoing an impressive increase. In this context, one of the most promising strategies is the innovative adoption of extra-physiological materials for advanced sperm preparation methods. Here, by using a murine model, the addition of Graphene Oxide (GO) at a specific concentration has demonstrated to increase the spermatozoa fertilizing ability in an IVF assay, finding that 0.5 μg/ml GO addition to sperm suspensions before IVF is able to increase both the number of fertilized oocytes and embryos created with a healthy offspring given by Embryo Transplantation (ET). In addition, GO treatment has been found more effective than that carried out with methyl-β-cyclodextrin, which represents the gold standard in promoting in vitro fertility of mice spermatozoa. Subsequent biochemical characterization of its interaction with male gametes has been additionally performed. As a result, it was found that GO exerts its positive effect by extracting cholesterol from membranes, without affecting the integrity of microdomains and thus preserving the sperm functions. In conclusion, GO improves IVF outcomes in vitro and in vivo, defining new perspectives for innovative strategies in the treatment of human infertility.

Development of assisted reproductive technologies in small animal species for their efficient preservation and production

Assisted reproductive technologies (ARTs) are widely used in the animal industry, human clinics, and for basic research. In small laboratory animal species such as mice, ARTs are essential for the production of animals for experiments, the preservation of genetic resources, and for the generation of new strains of genetically modified animals. The RIKEN BioResource Research Center (BRC) is one of the largest repositories of such animal bioresources, and maintains approximately 9,500 strains of mice with a variety of genetic backgrounds. We have sought to devise ARTs specific to the reproductive and physiological characteristics of each strain. Such ARTs include superovulation, in vitro fertilization (IVF), the cryopreservation of embryos and spermatozoa, transportation of cryopreserved materials and embryo transfer (ET). Of these, superovulation likely has the most influence on animal production because it determines the quantity of starting material for other ARTs. Superovulation using anti-inhibin serum combined with estrous synchronization has resulted in approximately a three-fold increase in production efficiency with IVF-ET in the C57BL/6J strain. Wild-derived strains are important as genetically diverse resources for murine rodents (Genus Mus), and many are unique to the BRC. We have also successfully developed ARTs for more than 50 wild-derived strains, which have been cryopreserved for future use. Our work to improve and develop ARTs for mice and other small laboratory species will contribute to the cost-effectiveness of routine operations at repository centers, and to the provision of high quality animals for research use.

Bi-allelic Mutations in TTC29 Cause Male Subfertility with Asthenoteratospermia in Humans and Mice

As a type of severe asthenoteratospermia, multiple morphological abnormalities of the flagella (MMAF) are characterized by the presence of immotile spermatozoa with severe flagellar malformations. MMAF is a genetically heterogeneous disorder, and the known MMAF-associated genes can only account for approximately 60% of human MMAF cases. Here we conducted whole-exome sequencing and identified bi-allelic truncating mutations of the TTC29 (tetratricopeptide repeat domain 29) gene in three (3.8%) unrelated cases from a cohort of 80 MMAF-affected Han Chinese men. TTC29 is preferentially expressed in the testis, and TTC29 protein contains the tetratricopeptide repeat domains that play an important role in cilia- and flagella-associated functions. All of the men harboring TTC29 mutations presented a typical MMAF phenotype and dramatic disorganization in axonemal and/or other peri-axonemal structures. Immunofluorescence assays of spermatozoa from men harboring TTC29 mutations showed deficiency of TTC29 and remarkably reduced staining of intraflagellar-transport-complex-B-associated proteins (TTC30A and IFT52). We also generated a Ttc29-mutated mouse model through the use of CRISPR-Cas9 technology. Remarkably, Ttc29-mutated male mice also presented reduced sperm motility, abnormal flagellar ultrastructure, and male subfertility. Furthermore, intracytoplasmic sperm injections performed for Ttc29-mutated mice and men harboring TTC29 mutations consistently acquired satisfactory outcomes. Collectively, our experimental observations in humans and mice suggest that bi-allelic mutations in TTC29, as an important genetic pathogeny, can induce MMAF-related asthenoteratospermia. Our study also provided effective guidance for clinical diagnosis and assisted reproduction treatments.

Phosphatidylserine on viable sperm and phagocytic machinery in oocytes regulate mammalian fertilization

Fertilization is essential for species survival. Although Izumo1 and Juno are critical for initial interaction between gametes, additional molecules necessary for sperm:egg fusion on both the sperm and the oocyte remain to be defined. Here, we show that phosphatidylserine (PtdSer) is exposed on the head region of viable and motile sperm, with PtdSer exposure progressively increasing during sperm transit through the epididymis. Functionally, masking phosphatidylserine on sperm via three different approaches inhibits fertilization. On the oocyte, phosphatidylserine recognition receptors BAI1, CD36, Tim-4, and Mer-TK contribute to fertilization. Further, oocytes lacking the cytoplasmic ELMO1, or functional disruption of RAC1 (both of which signal downstream of BAI1/BAI3), also affect sperm entry into oocytes. Intriguingly, mammalian sperm could fuse with skeletal myoblasts, requiring PtdSer on sperm and BAI1/3, ELMO2, RAC1 in myoblasts. Collectively, these data identify phosphatidylserine on viable sperm and PtdSer recognition receptors on oocytes as key players in sperm:egg fusion.

The Y227N mutation affects bestrophin-1 protein stability and impairs sperm function in a mouse model of Best vitelliform macular dystrophy

Human bestrophin-1 (BEST1) is an integral membrane protein known to function as a Ca²⁺-activated and volume-regulated chloride channel. The majority of disease-associated mutations in BEST1 constitute missense mutations and were shown in vitro to lead to a reduction in mutant protein half-life causing Best disease (BD), a rare autosomal dominant macular dystrophy. To further delineate BEST1-associated pathology in vivo and to provide an animal model useful to explore experimental treatment efficacies, we have generated a knock-in mouse line (Best1^Y227N). Heterozygous and homozygous mutants revealed no significant ocular abnormalities up to 2 years of age. In contrast, knock-in animals demonstrated a severe phenotype in the male reproductive tract. In heterozygous Best1^Y227N males, Best1 protein was significantly reduced in testis and almost absent in homozygous mutant mice, although mRNA transcription of wild-type and knock-in allele is present and similar in quantity. Degradation of mutant Best1 protein in testis was associated with adverse effects on sperm motility and the capability to fertilize eggs. Based on these results, we conclude that mice carrying the Best1 Y227N mutation reveal a reproducible pathologic phenotype and thus provide a valuable in vivo tool to evaluate efficacy of drug therapies aimed at restoring Best1 protein stability and function.

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.

Cryorecovery of Mouse Sperm by Different IVF Methods Using MBCD and GSH

Different protocols incorporating methyl-β-cyclodextrin (MBCD) and reduced glutathione (GSH) have been reported to improve IVF recovery of cryopreserved mouse sperm on a C57BL/6 (J and N) genetic background. However, it is not clear which IVF protocol is most appropriate when using the various methods to cryorecover sperm with different sperm quality and sample volumes. Therefore, in the present study we correlated sperm motility with fertilization rate and compared the efficiency of different IVF methods using various sperm samples so as to establish general guidelines for mouse sperm cryorecovery by IVF. High linear correlation between sperm fertilization rate and progressive motility was found, R² was 0.9623 and 0.9993 for pre-freezing and post-thaw progressive motility, respectively. High amounts of cryoprotective agent (CPA) were observed to impair both sperm capacitation and fertilization. Moreover, the presence of a large number of immotile sperm in the sperm-oocyte co-incubation drop was found to reduce IVF success which could be partially reversed by supplementation using monothioglycerol (MTG) during centrifugation. It was concluded that the efficiency of IVF using cryorecovered mouse sperm in media containing MBCD and GSH can be predicted from sperm progressive motility. High concentrations of CPA and immotile sperm should be mitigated prior to IVF. The optimum IVF method should be selected based on sperm sample volume and sperm parameters.

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.

Contemporary techniques for freezing mouse spermatozoa

Each year, thousands of new mouse models are generated around the world to further biomedical research. Unfortunately, the cost of maintaining mouse colonies makes it uneconomical to keep strains on the shelf that are not part of active research programs. Ideally, these retired strains should be archived. If this is not done and the line is simply killed off, the genetics are lost to future generations of scientists. Traditionally, embryo freezing has been used to cryopreserve mice, but this is expensive, time consuming, requires large numbers of donor females, and usually involves invasive superovulation procedures. Sperm freezing circumvents all of these disadvantages and is rapidly becoming the technique of choice for many repositories. This has been made possible through the use of refined cryoprotective agents and the development of improved in vitro fertilization techniques. This article describes two popular sperm freezing techniques employed by mouse repositories to archive spermatozoa using cryoprotective agents supplemented with either L-glutamine or monothioglycerol.