Efficient production of offspring from Japanese wild-derived strains of mice (Mus musculus molossinus) by improved assisted reproductive technologies

Inter-subspecies mouse F1 hybrid embryonic stem cell lines newly established for studies of allelic imbalance in gene expression

Allele-specific monoallelic gene expression is a unique phenomenon and a great resource for analyzing gene regulation. To study this phenomenon, we established new embryonic stem (ES) cell lines derived from F1 hybrid blastocysts from crosses between four mouse subspecies (Mus musculus domesticus, C57BL/6; M. musculus molossinus, MSM/Ms; M. musculus musculus, PWK; M. musculus castaneus, HMI/Ms) and analyzed the expression levels of undifferentiated pluripotent stem cell markers and karyotypes of each line. To demonstrate the utility of our cell lines, we analyzed the allele-specific expression pattern of the Inpp5d gene as an example. The allelic expression depended on the parental alleles; this dependence could be a consequence of differences in compatibility between cis- and trans-elements of the Inpp5d gene from different subspecies. The use of parental mice from four subspecies greatly enhanced genetic polymorphism. The F1 hybrid ES cells retained this polymorphism not only in the Inpp5d gene, but also at a genome-wide level. As we demonstrated for the Inpp5d gene, the established cell lines can contribute to the analysis of allelic expression imbalance based on the incompatibility between cis- and trans-elements and of phenotypes related to this incompatibility.

Superovulation with an anti-inhibin monoclonal antibody improves the reproductive performance of rat strains by increasing the pregnancy rate and the litter size

Rats are multiparous rodents that have been used extensively in research; however, the low reproductive performance of some rat strains hampers the broader use of rats as a biomedical model. In this study, the possibility of increasing the litter size after natural mating in rats through superovulation using an anti-inhibin monoclonal antibody (AIMA) was examined. In outbred Wistar rats, AIMA increased the number of ovulated oocytes by 1.3-fold. AIMA did not affect fertilization and subsequent embryonic development, resulting in a 1.4-fold increase in litter size and a high pregnancy rate (86%). In contrast, conventional superovulation by eCG/hCG administration decreased the pregnancy rate to 6-40% and did not increase the litter size. In inbred Brown Norway rats, AIMA increased the litter size by 1.2-fold, and the pregnancy rate increased more than twice (86% versus 38% in controls). AIMA also increased the litter size by 1.5-fold in inbred Tokai High Avoiders and Fischer 344 rats. AIMA increased the efficiency of offspring production by 1.5-, 2.7-, 1.4-, and 1.4-fold, respectively, in the four rat strains. Thus, AIMA may consistently improve the reproductive performance through natural mating in rats, which could promote the use of AIMA in biomedical research.

A universal method for generating knockout mice in multiple genetic backgrounds using zygote electroporation

Genetically engineered mouse models are essential tools for understanding mammalian gene functions and disease pathogenesis. Genome editing allows the generation of these models in multiple inbred strains of mice without backcrossing. Zygote electroporation dramatically removed the barrier for introducing the CRISPR-Cas9 complex in terms of cost and labour. Here, we demonstrate that the generalised zygote electroporation method is also effective for generating knockout mice in multiple inbred strains. By combining in vitro fertilisation and electroporation, we obtained founders for knockout alleles in eight common inbred strains. Long-read sequencing analysis detected not only intended mutant alleles but also differences in read frequency of intended and unintended alleles among strains. Successful germline transmission of knockout alleles demonstrated that our approach can establish mutant mice targeting the same locus in multiple inbred strains for phenotyping analysis, contributing to reverse genetics and human disease research.

Derivation of embryonic stem cells from wild-derived mouse strains by nuclear transfer using peripheral blood cells

Wild-derived mouse strains have been extensively used in biomedical research because of the high level of inter-strain polymorphisms and phenotypic variations. However, they often show poor reproductive performance and are difficult to maintain by conventional in vitro fertilization and embryo transfer. In this study, we examined the technical feasibility of derivation of nuclear transfer embryonic stem cells (ntESCs) from wild-derived mouse strains for their safe genetic preservation. We used leukocytes collected from peripheral blood as nuclear donors without sacrificing them. We successfully established 24 ntESC lines from two wild-derived strains of CAST/Ei and CASP/1Nga (11 and 13 lines, respectively), both belonging to Mus musculus castaneus, a subspecies of laboratory mouse. Most (23/24) of these lines had normal karyotype, and all lines examined showed teratoma formation ability (4 lines) and pluripotent marker gene expression (8 lines). Two male lines examined (one from each strain) were proven to be competent to produce chimeric mice following injection into host embryos. By natural mating of these chimeric mice, the CAST/Ei male line was confirmed to have germline transmission ability. Our results demonstrate that inter-subspecific ntESCs derived from peripheral leukocytes could provide an alternative strategy for preserving invaluable genetic resources of wild-derived mouse strains.

Heterozygous loss-of-function DHX9 variants are associated with neurodevelopmental disorders: Human genetic and experimental evidences

DExH-box helicases are involved in unwinding of RNA and DNA. Among the 16 DExH-box genes, monoallelic variants of DHX16, DHX30, DHX34, and DHX37 are known to be associated with neurodevelopmental disorders. In particular, DHX30 is well established as a causative gene for neurodevelopmental disorders. Germline variants of DHX9, the closest homolog of DHX30, have not been reported until now as being associated with congenital disorders in humans, except that one de novo heterozygous variant, p.(Arg1052Gln) of the gene was identified during comprehensive screening in a patient with autism; unfortunately, the phenotypic details of this individual are unknown. Herein, we report a patient with a heterozygous de novo missense variant, p.(Gly414Arg) of DHX9 who presented with a short stature, intellectual disability, and ventricular non-compaction cardiomyopathy. The variant was located in the glycine codon of the ATP-binding site, G-C-G-K-T. To assess the pathogenicity of this variants, we generated transgenic Drosophila lines expressing human wild-type and mutant DHX9 proteins: 1) the mutant proteins showed aberrant localization both in the nucleus and the cytoplasm; 2) ectopic expression of wild-type protein in the visual system led to the rough eye phenotype, whereas expression of the mutant proteins had minimal effect; 3) overexpression of the wild-type protein in the retina led to a reduction in axonal numbers, whereas expression of the mutant proteins had a less pronounced effect. Furthermore, in a gene-editing experiment of Dhx9 G416 to R416, corresponding to p.(Gly414Arg) in humans, heterozygous mice showed a reduced body size, reduced emotionality, and cardiac conduction abnormality. In conclusion, we established that heterozygosity for a loss-of-function variant of DHX9 can lead to a new neurodevelopmental disorder.

Efficient genome editing in wild strains of mice using the i-GONAD method

Wild mouse strains have been used for many research studies, because of the high level of inter-strain genetic and phenotypic variations in them, in addition to the characteristic phenotype maintained from wild mice. However, since application of the current genetic engineering method on wild strains is not easy, there are limited studies that have attempted to apply gene modification techniques in wild strains. Recently, i-GONAD, a new method for genome editing that does not involve any ex vivo manipulation of unfertilized or fertilized eggs has been reported. We applied i-GONAD method for genome editing on a series of wild strains and showed that genome editing is efficiently possible using this method. We successfully made genetically engineered mice in seven out of the nine wild strains. Moreover, we believe that it is still possible to apply milder conditions and improve the efficiencies for the remaining two strains. These results will open avenues for studying the genetic basis of various phenotypes that are characteristic to wild strains. Furthermore, applying i-GONAD will be also useful for other mouse resources in which genetic manipulation is difficult using the method of microinjection into fertilized eggs.

The role of PIP5K1A in cancer development and progression

Malignant tumors are formed via a pathological process of uncontrolled cell division that seriously endangers human physical and mental health. The PI3K/AKT signaling pathway plays an important role in the occurrence and development of various cancers. As a lipid kinase, PIP5K1A acts on the upstream of the PI3K/AKT signaling pathway and has a variety of biological functions, including cell differentiation, cell migration, and sperm development. An increasing number of studies have shown that the overexpression of PIP5K1A promotes the growth, invasion, and migration of cancer cells, and the inhibition of PIP5K1A can effectively hinder tumor progression. These findings imply that PIP5K1A are potential markers and targets for cancers. The aim of this study was to systemically review the structure and function of PIP5K1A, the relationship between PIP5K1A and tumors and the potential therapeutic value of PIP5K1A inhibitors in cancer. PIP5K1A affects the occurrence and progression of many tumors and will provide new strategies for cancer diagnosis and treatment.

Use of anti-inhibin monoclonal antibody for increasing the litter size of mouse strains and its application to i-GONAD

The litter size of mouse strains is determined by the number of oocytes naturally ovulated. Many attempts have been made to increase litter sizes by conventional superovulation regimens (e.g., using equine or human gonadotropins, eCG/hCG but had limited success because of unexpected decreases in the numbers of embryos surviving to term. Here, we examined whether rat-derived anti-inhibin monoclonal antibodies (AIMAs) could be used for this purpose. When C57BL/6 female mice were treated with an AIMA and mated, the number of healthy offspring per mouse increased by 1.4-fold (11.9 vs. 8.6 in controls). By contrast, treatment with eCG/hCG or anti-inhibin serum resulted in fewer offspring than in nontreated controls. The overall efficiency of production based on all females treated (including nonpregnant ones) was improved 2.4 times with AIMA compared with nontreated controls. The AIMA treatment was also effective in ICR mice, increasing the litter size from 15.3 to 21.2 pups. We then applied this technique to an in vivo genome-editing method (improved genome-editing via oviductal nucleic acid delivery, i-GONAD) to produce C57BL/6 mice deficient for tyrosinase. The mean litter size following i-GONAD increased from 4.8 to 7.3 after the AIMA treatment and genetic modifications were confirmed in 80/88 (91%) of the offspring. Thus, AIMA treatment is a promising method for increasing the litter size of mice and may be applied for the easy proliferation of mouse colonies as well as in vivo genetic manipulation, especially when the mouse strains are sensitive to handling.

Mouse resources at the RIKEN BioResource Research Center and the National BioResource Project core facility in Japan

The RIKEN BioResource Research Center (BRC) was established in 2001 as a comprehensive biological resource center in Japan. The Experimental Animal Division, one of the BRC infrastructure divisions, has been designated as the core facility for mouse resources within the National BioResource Project (NBRP) by the Japanese government since FY2002. Our activities regarding the collection, preservation, quality control, and distribution of mouse resources have been supported by the research community, including evaluations and guidance on advancing social and research needs, as well as the operations and future direction of the BRC. Expenditure for collection, preservation, and quality-control operations of the BRC, as a national core facility, has been funded by the government, while distribution has been separately funded by users' reimbursement fees. We have collected over 9000 strains created mainly by Japanese scientists including Nobel laureates and researchers in cutting-edge fields and distributed mice to 7000 scientists with 1500 organizations in Japan and globally. Our users have published 1000 outstanding papers and a few dozen patents. The collected mouse resources are accessible via the RIKEN BRC website, with a revised version of the searchable online catalog. In addition, to enhance the visibility of useful strains, we have launched web corners designated as the "Mouse of the Month" and "Today's Tool and Model." Only high-demand strains are maintained in live colonies, while other strains are cryopreserved as embryos or sperm to achieve cost-effective management. Since 2007, the RIKEN BRC has built up a back-up facility in the RIKEN Harima branch to protect the deposited strains from disasters. Our mice have been distributed with high quality through the application of strict microbial and genetic quality control programs that cover a globally accepted pathogens list and mutated alleles generated by various methods. Added value features, such as information about users' publications, standardized phenotyping data, and genome sequences of the collected strains, are important to facilitate the use of our resources. We have added and disseminated such information in collaboration with the NBRP Information Center and the NBRP Genome Information Upgrading Program. The RIKEN BRC has participated in international mouse resource networks such as the International Mouse Strain Resource, International Mouse Phenotyping Consortium, and Asian Mouse Mutagenesis and Resource Association to facilitate the worldwide use of high-quality mouse resources, and as a consequence it contributes to reproducible life science studies and innovation around the globe.

Morphometric, subcellular, in vitro fertilisation and embryonic developmental assessment of mouse oocytes produced by anti-inhibin serum or pregnant mare serum gonadotrophin superovulation

This study compared the morphometric, subcellular characteristics, in vitro fertilisation (IVF) and embryonic developmental potential of metaphase II (MII) mouse oocytes obtained from females superovulated with either anti-inhibin serum-human chorionic gonadotrophin (AIS-hCG) or pregnant mare serum gonadotrophin (PMSG)-hCG. The oocyte's quantity, quality, zona pellucida (ZP) thickness, perivitelline space (PVS), diameter, microtubules, F-actin, cortical granules (CGs) and mitochondrial distribution were determined. Superovulation using AIS-hCG resulted in a higher numbers of oocyte/donor compared with PMSG-hCG (P=0.002). There was no difference in morphologically normal and abnormal oocytes between AIS-hCG and PMSG-hCG (P=0.425 and P=0.194, respectively). The morphometric measurements showed no difference in oocyte diameter between AIS-hCG and PMSG-hCG (P=0.289). However, the thickness of the ZP of oocytes from AIS-hCG females was decreased compared with PMSG-hCG (P<0.001). The PVS of oocytes from the AIS-hCG was larger than with PMSG-hCG (P<0.001). The microtubules of oocytes from both AIS-hCG and PMSG-hCG were normal, although there was an increased fluorescence intensity in the AIS-hCG oocytes (P<0.001). The F-actin and CGs distribution in oocytes from both AIS-hCG and PMSG-hCG were similar (P=0.330 and P=0.13, respectively). Although the oocytes from PMSG-hCG females had homogenously distributed mitochondria, AIS-hCG oocytes showed more peripheral distribution with no differences in fluorescence intensity (P=0.137). The blastocyst development rates after IVF with fresh sperm showed no difference between AIS-hCG and PMSG-hCG (P=0.235). These data suggested that AIS-hCG superovulation produces high numbers of morphologically normal oocytes that also possess normal subcellular structures, good morphological characteristics and had high invitro embryonic developmental potential.

A human-based assisted reproduction protocol for the menstruating spiny mouse, Acomys cahirinus

The Egyptian or Common spiny mouse (A. cahirinus) is the first rodent species to show human-like menstruation and spontaneous decidualisation. We consider from these, and its other, human-like characteristics that this species will be a more useful and appropriate small animal model for human reproductive studies. Based on this, there is a need to develop specific laboratory-based assisted reproduction protocols including superovulation, in-vitro fertilisation, embryo cryopreservation and transfer to expand and make this model more relevant. Because standard rodent superovulation has not been successful in the spiny mouse, we have selected to test a human protocol. Female spiny mice will receive a subcutaneous GnRH agonist implant and be allowed to recover. Menstrual cycle lengths will then be allowed to stabilize prior to ovarian stimulation. After recovery, females will be injected IP once a day for 4 days with a FSH analogue, to induce follicular growth, and on day 5 will be injected IP with a hCG analogue to trigger ovulation. Females will either be culled 36hrs after trigger to collect oocytes or immediately paired with a stud male and two cell embryos collected 48hrs later. Mature oocytes will be inseminated using fresh spiny mouse spermatozoa and all in-vitro grown and in-vivo collected two cell embryos will be cryopreserved using methods developed in a close spiny mouse relative, the Mongolian gerbil. For embryo transfer, vitrified embryos will be rapidly warmed and non-surgically transferred to surrogate mice. Surrogates will be monitored until pregnancy is apparent (roughly 30 days) and then left undisturbed until birth, 38-40 days after transfer. By successfully developing robust assisted reproduction protocols in A. cahirinus we will be able to use this rodent as a more effective model for human reproduction.

Improving ovulation in gilts using anti-inhibin serum treatment combined with fixed-time artificial insemination

For successful batch farrowing, porcine oestrus and ovulation must be synchronized using fixed-time artificial insemination (FTAI). However, exogenous gonadotropins, which are currently used in FTAI, negatively affect gilt ovulation. Here, we aimed to improve sexually mature gilt superovulation efficiency using passive immunization against inhibin during FTAI. Altrenogest-treated gilts were challenged with 10 ml anti-inhibin serum (AIS group, n = 6), 1,000 IU pregnant mare serum gonadotropin (PMSG group, n = 6), or 10 ml goat serum (control group, n = 6). Gilts in the AIS and PMSG groups were inseminated according to the FTAI protocol, and gilts in the control group were inseminated during natural oestrus. When PMSG was replaced by AIS during FTAI of gilts, ovulation rate and embryos recovered were significantly greater in the AIS group as compared to the other two groups (p < .05). Especially the average number of 6-8-cell embryos in the AIS group was significantly higher than that in the PMSG group (p < .01). Moreover, the blastocyst number in the AIS group was significantly higher than that in the PMSG group and the control group (p < .05). But there was no significant difference in the blastocyst number between the PMSG group and the control group (p > .05). Besides, plasma levels of estradiol-β (E2) and progesterone (P4) were significantly greater in the AIS group as compared to the other two groups on Day 23 and D 27, respectively (p < .01). In summary, we devised an improved high-yield FTAI protocol for sexually mature gilts using AIS; this protocol had a greater superovulation efficiency than the FTAI using PMSG.

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.

Early production of offspring by in vitro fertilization using first-wave spermatozoa from prepubertal male mice

Mature male mice (aged 10–12 weeks or older) are conventionally used for in vitro fertilization (IVF) in order to achieve high fertilization rates (e.g., > 70%). Here, we sought to determine the earliest age at which male mice (C57BL/6J strain) can be used efficiently for producing offspring via IVF. Because we noted that the addition of reduced glutathione (GSH) to the IVF medium significantly increased the fertilizing ability of spermatozoa from prepubertal males, we used this IVF protocol for all experiments. Spermatozoa first reached the caudal region of the epididymides at day 35; however, they were unable to fertilize oocytes. Caudal epididymal spermatozoa first became competent for oocyte fertilization at day 37, albeit at a low rate (2.9%). A high fertilization rate (72.0%) was obtained at day 40, and 52.4% of the embryos thus obtained developed into offspring after embryo transfer. Moreover, we found that corpus epididymal spermatozoa in prepubertal mice could fertilize oocytes; however, the fertilization rates were always < 50%, regardless of the age of the males. Caput epididymal spermatozoa failed to fertilize oocytes irrespective of the age of the males. Therefore, we propose that caudal epididymal spermatozoa from male mice aged 40 days can be efficiently used for IVF, to obtain offspring in the shortest attainable time. This protocol will reduce the turnover time required for the generation of mice by ~1 month compared with that of the conventional IVF protocol.

Efficient derivation of knock-out and knock-in rats using embryos obtained by in vitro fertilization

Rats are effective model animals and have contributed to the development of human medicine and basic research. However, the application of reproductive engineering techniques to rats is not as advanced compared with mice, and genome editing in rats has not been achieved using embryos obtained by in vitro fertilization (IVF). In this study, we conducted superovulation, IVF, and knock out and knock in using IVF rat embryos. We found that superovulation effectively occurred in the synchronized oestrus cycle and with anti-inhibin antiserum treatment in immature rats, including the Brown Norway rat, which is a very difficult rat strain to superovulate. Next, we collected superovulated oocytes under anaesthesia, and offspring derived from IVF embryos were obtained from all of the rat strains that we examined. When the tyrosinase gene was targeted by electroporation in these embryos, both alleles were disrupted with 100% efficiency. Furthermore, we conducted long DNA fragment knock in using adeno-associated virus and found that the knock-in litter was obtained with high efficiency (33.3–47.4%). Thus, in this study, we developed methods to allow the simple and efficient production of model rats.

Off- and on-target effects of genome editing in mouse embryos

Clustered regularly interspaced short palindromic repeats (CRISPR)-Cas-based genome editing technology has enabled manipulation of the embryonic genome. Unbiased whole genome sequencing comparing parents to progeny has revealed that the rate of Cas9-induced mutagenesis in mouse embryos is indistinguishable from the background rate of de novo mutation. However, establishing the best practice to confirm on-target alleles of interest remains a challenge. We believe that improvement in editing strategies and screening methods for founder mice will contribute to the generation of quality-controlled animals, thereby ensuring reproducibility of results in animal studies and advancing the 3Rs (replacement, reduction, and refinement).

Efficient and scheduled production of pseudopregnant female mice for embryo transfer by estrous cycle synchronization

In embryo transfer experiments in mice, pseudopregnant females as recipients are prepared by sterile mating with vasectomized males. Because only females at the proestrus stage accept males, such females are selected from a stock of animals based on the appearance of their external genital tract. Therefore, the efficiency of preparing pseudopregnant females largely depends on the size of female colonies and the skill of the operators who select females for sterile mating. In this study, we examined whether the efficiency of preparing pseudopregnant females could be improved by applying an estrous cycle synchronization method by progesterone (P4) pretreatment, which significantly enhances the superovulation outcome in mice. We confirmed that after two daily injections of P4 (designated Days 1 and 2) in randomly selected females, the estrous cycles of most females (about 85%) were synchronized at metestrus on Day 3. When P4-treated females were paired with vasectomized males for 4 days (Days 4–8), a vaginal plug was found in 63% (20/32) of the females on Day 7. After the transfer of vitrified-warmed embryos into their oviducts, 52% (73/140) of the embryos successfully developed into offspring, the rate being comparable to that of the conventional embryo transfer procedure. Similarly, 77% (24/31) of females became pregnant by fertile mating with intact males for 3 days, which allowed the scheduled preparation of foster mothers. Thus, our estrous cycle synchronization method may omit the conventional experience-based process of visually observing the vagina to choose females for embryo transfer. Furthermore, it is expected that the size of female stocks for recipients can be reduced to less than 20%, which could be a great advantage for facilities/laboratories undertaking mouse-assisted reproductive technology.

Morphofunctional evaluation of the testis, duration of spermatogenesis and spermatogenic efficiency in the Japanese fancy mouse (Mus musculus molossinus)

Japanese fancy mouse, mini mouse or pet mouse are common names used to refer to strains of mice that present with different colour varieties and coat types. Although many genetic studies that involve spotting phenotype based on the coat have been performed in these mice, there are no reports of quantitative data in the literature regarding testis structure and spermatogenic efficiency. Hence, in this study we researched testis function and spermatogenesis in the adult Japanese fancy mouse. The following values of 68 ± 6 mg and 0.94 ± 0.1% were obtained as mean testis weight and gonadosomatic index, respectively. In comparison with other investigated mice strains, the fancy mouse Leydig cell individual size was much smaller, resulting in higher numbers of these cells per gram of testis. As found for laboratory mice strains, as a result of the development of the acrosomic system, 12 stages of the seminiferous epithelium cycle have been described in this study. The combined frequencies of pre-meiotic and post-meiotic stages were respectively 24% and 64% and very similar to the laboratory mice. The more differentiated germ cell types marked at 1 h or 9 days after tritiated thymidine administration were preleptotene/leptotene and pachytene spermatocytes at the same stage (VIII). The mean duration of one spermatogenic cycle was 8.8 ± 0.01 days and the total length of spermatogenesis lasted 37.8 ± 0.01 days (4.5 cycles). A high number of germ cell apoptosis was evident during meiosis, resulting in lower Sertoli cell and spermatogenic efficiencies, when compared with laboratory mice strains.

CRISPR/Cas9-mediated genome editing in wild-derived mice: generation of tamed wild-derived strains by mutation of the a (nonagouti) gene

Wild-derived mice have contributed to experimental mouse genetics by virtue of their genetic diversity, which may help increase the chance of identifying novel modifier genes responsible for specific phenotypes and diseases. However, gene targeting using wild-derived mice has been unsuccessful because of the unavailability of stable embryonic stem cells. Here, we report that CRISPR/Cas9-mediated gene targeting can be applied to the Japanese wild-derived MSM/Ms strain (Mus musculus molossinus). We targeted the nonagouti (a) gene encoding the agouti protein that is localized in hair and the brain. We obtained three homozygous knockout mice as founders, all showing black coat colour. While homozygous knockout offspring were physiologically indistinguishable from wild-type litter-mates, they showed specific domesticated behaviours: hypoactivity in the dark phase and a decline in the avoidance of a human hand. These phenotypes were consistent over subsequent generations. Our findings support the empirical hypothesis that nonagouti is a domestication-linked gene, the loss of which might repress aggressive behaviour.

Development of reproductive engineering techniques at the RIKEN BioResource Center

Reproductive engineering techniques are essential for assisted reproduction of animals and generation of genetically modified animals. They may also provide invaluable research models for understanding the mechanisms involved in the developmental and reproductive processes. At the RIKEN BioResource Center (BRC), I have sought to develop new reproductive engineering techniques, especially those related to cryopreservation, microinsemination (sperm injection), nuclear transfer, and generation of new stem cell lines and animals, hoping that they will support the present and future projects at BRC. I also want to combine our techniques with genetic and biochemical analyses to solve important biological questions. We expect that this strategy makes our research more unique and refined by providing deeper insights into the mechanisms that govern the reproductive and developmental systems in mammals. To make this strategy more effective, it is critical to work with experts in different scientific fields. I have enjoyed collaborations with about 100 world-recognized laboratories, and all our collaborations have been successful and fruitful. This review summarizes development of reproductive engineering techniques at BRC during these 15 years.

Structural analyses to identify selective inhibitors of glyceraldehyde 3-phosphate dehydrogenase-S, a sperm-specific glycolytic enzyme

STUDY HYPOTHESIS

Detailed structural comparisons of sperm-specific glyceraldehyde 3-phosphate dehydrogenase, spermatogenic (GAPDHS) and the somatic glyceraldehyde 3-phosphate dehydrogenase (GAPDH) isozyme should facilitate the identification of selective GAPDHS inhibitors for contraceptive development.

STUDY FINDING

This study identified a small-molecule GAPDHS inhibitor with micromolar potency and >10-fold selectivity that exerts the expected inhibitory effects on sperm glycolysis and motility.

WHAT IS KNOWN ALREADY

Glycolytic ATP production is required for sperm motility and male fertility in many mammalian species. Selective inhibition of GAPDHS, one of the glycolytic isozymes with restricted expression during spermatogenesis, is a potential strategy for the development of a non-hormonal contraceptive that directly blocks sperm function.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

Homology modeling and x-ray crystallography were used to identify structural features that are conserved in GAPDHS orthologs in mouse and human sperm, but distinct from the GAPDH orthologs present in somatic tissues. We identified three binding pockets surrounding the substrate and cofactor in these isozymes and conducted a virtual screen to identify small-molecule compounds predicted to bind more tightly to GAPDHS than to GAPDH. Following the production of recombinant human and mouse GAPDHS, candidate compounds were tested in dose-response enzyme assays to identify inhibitors that blocked the activity of GAPDHS more effectively than GAPDH. The effects of a selective inhibitor on the motility of mouse and human sperm were monitored by computer-assisted sperm analysis, and sperm lactate production was measured to assess inhibition of glycolysis in the target cell.

MAIN RESULTS AND THE ROLE OF CHANCE

Our studies produced the first apoenzyme crystal structures for human and mouse GAPDHS and a 1.73 Å crystal structure for NAD(+)-bound human GAPDHS, facilitating the identification of unique structural features of this sperm isozyme. In dose-response assays T0501_7749 inhibited human GAPDHS with an IC50 of 1.2 μM compared with an IC50 of 38.5 μM for the somatic isozyme. This compound caused significant reductions in mouse sperm lactate production (P= 0.017 for 100 μM T0501_7749 versus control) and in the percentage of motile mouse and human sperm (P values from <0.05 to <0.0001, depending on incubation conditions).

LIMITATIONS, REASONS FOR CAUTION

The chemical properties of T0501_7749, including limited solubility and nonspecific protein binding, are not optimal for drug development.

WIDER IMPLICATIONS OF THE FINDINGS

This study provides proof-of-principle evidence that GAPDHS can be selectively inhibited, causing significant reductions in sperm glycolysis and motility. These results highlight the utility of structure-based drug design and support further exploration of GAPDHS, and perhaps other sperm-specific isozymes in the glycolytic pathway, as contraceptive targets.

LARGE SCALE DATA

None. Coordinates and data files for three GAPDHS crystal structures were deposited in the RCSB Protein Data Bank (http://www.rcsb.org).

STUDY FUNDING AND COMPETING INTERESTS

This work was supported by grants from the National Institutes of Health (NIH), USA, including U01 HD060481 and cooperative agreement U54 HD35041 as part of the Specialized Cooperative Centers Program in Reproduction and Infertility Research from the Eunice Kennedy Shriver National Institute of Child Health and Human Development, and TW/HD00627 from the NIH Fogarty International Center. Additional support was provided by subproject CIG-05-109 from CICCR, a program of CONRAD, Eastern Virginia Medical School, USA. There are no conflicts of interest.

Immunotherapy using inhibin antiserum enhanced the efficacy of equine chorionic gonadotropin on superovulation in major inbred and outbred mice strains

Improvement of the superovulation technique will help to enhance the efficiency of embryo and animal production. Blocking inhibin using inhibin antiserum (IAS) is known to promote follicular development by increasing the level of FSH. Previously, we reported that coadministration of IAS and eCG produced more than 100 oocytes from a single female C57BL/6 mouse at 4 weeks old. The oocytes derived from the IAS + eCG (IASe) treatment were able to fertilize and develop normally into offspring. In this study, we examined the effect of IASe treatment on the numbers of ovulated oocytes in major inbred (A/J, BALB/cByJ, C3HeJ, DBA/2J, and FVB/NJ) and outbred (CD1) mice strains at 4 weeks old. We confirmed the fertilization and developmental ability of the IASe-derived oocytes. IASe treatment ovulated 1.5 to 3.2 times higher numbers of oocytes than eCG treatment alone. The fertilization rate of IASe-derived oocytes was similar to that of eCG-derived oocytes. In vitro and in vivo developmental rates of the embryos derived from IASe were similar to the rates of embryos derived from eCG. We have shown that superovulation by IASe is very effective in obtaining high numbers of ovulated oocytes from small numbers of oocyte donor in a number of mice strains. The superovulation technique will contribute to the archiving of cryopreserved embryos of genetically engineered mice using small numbers of donors and has the potential to produce more live animals for rederivation of the archived mouse lines in mouse repositories.

High-Yield Superovulation in Adult Mice by Anti-Inhibin Serum Treatment Combined with Estrous Cycle Synchronization

Producing many mature oocytes is of great importance for assisted reproductive technologies. In mice, superovulation by consecutive injections of equine chorionic gonadotropin (eCG) and human chorionic gonadotropin (hCG) has been the gold standard for oocyte collection. However, the yield of mature oocytes by this regimen can fluctuate according to the stage of the estrous cycle, strain, and age. Therefore, our objective was to develop a high-yield superovulation protocol to collect higher numbers of oocytes from adult female mice of different strains and ages. First, we aimed to synchronize the estrous cycle using C57BL/6 (B6) female mice. Most (93%) were synchronized to metestrus after two daily injections of progesterone. Second, we found that with the injection of anti-inhibin serum (AIS) instead of eCG, the mean number of ovulated oocytes almost doubled (21 vs. 41 per mouse). Third, by combining estrous cycle synchronization with two AIS injections, we obtained 62 oocytes per mouse, about three times that with the eCG-hCG protocol. Importantly, this approach increased the proportion of mice that ovulated >25 oocytes from about 40% (eCG-hCG) to 90%. The same protocol was also effective in other inbred (BALB/cA), outbred (ICR), and hybrid (B6D2F1) strains. In addition, B6 female mice aged over 1 yr ovulated 1.8-fold more oocytes by this protocol. Thus, estrous cycle synchronization followed by AIS-hCG yielded a broadly applicable, highly efficient superovulation. This protocol should promote the effective use of invaluable female mouse strains and decrease the numbers of animals euthanized.

Superovulation using the combined administration of inhibin antiserum and equine chorionic gonadotropin increases the number of ovulated oocytes in C57BL/6 female mice

Superovulation is a reproductive technique generally used to produce genetically engineered mice. Superovulation in mice involves the administration of equine chorionic gonadotropin (eCG) to promote follicle growth and then that of human chorionic gonadotropin (hCG) to induce ovulation. Previously, some published studies reported that inhibin antiserum (IAS) increased the number of ovulated oocytes in ddY and wild-derived strains of mice. However, the effect of IAS on the C57BL/6 strain, which is the most widely used inbred strain for the production of genetically engineered mice, has not been investigated. In addition, the combined effect of IAS and eCG (IASe) on the number of ovulated oocytes in superovulation treatment has not been examined. In this study, we examined the effect of IAS and eCG on the number of ovulated oocytes in immature female mice of the C57BL/6 strain in superovulation treatment. Furthermore, we evaluated the quality of obtained oocytes produced by superovulation using IASe by in vitro fertilization (IVF) with sperm from C57BL/6 or genetically engineered mice. The developmental ability of fresh or cryopreserved embryos was examined by embryo transfer. The administration of IAS or eCG had a similar effect on the number of ovulated oocytes in C57BL/6 female mice. The number of ovulated oocytes increased to about 3-fold by the administration of IASe than by the administration of IAS or eCG alone. Oocytes derived from superovulation using IASe normally developed into 2-cell embryos by IVF using sperm from C57BL/6 mice. Fresh or cryopreserved 2-cell embryos produced by IVF between oocytes of C57BL/6 mice and sperm from genetically engineered mice normally developed into live pups following embryo transfer. In summary, a novel technique of superovulation using IASe is extremely useful for producing a great number of oocytes and offspring from genetically engineered mice.

Devising assisted reproductive technologies for wild-derived strains of mice: 37 strains from five subspecies of Mus musculus

Wild-derived mice have long offered invaluable experimental models for mouse genetics because of their high evolutionary divergence from laboratory mice. A number of wild-derived strains are available from the RIKEN BioResource Center (BRC), but they have been maintained as living stocks because of the unavailability of assisted reproductive technology (ART). In this study, we sought to devise ART for 37 wild-derived strains from five subspecies of Mus musculus maintained at the BRC. Superovulation of females was effective (more than 15 oocytes per female) for 34 out of 37 strains by treatment with either equine chorionic gonadotropin or anti-inhibin serum, depending on their genetic background (subspecies). The collected oocytes could be fertilized in vitro at mean rates of 79.0% and 54.6% by the optimized protocol using fresh or frozen-thawed spermatozoa, respectively. They were cryopreserved at the 2-cell stage by vitrification with an ethylene glycol-based solution. In total, 94.6% of cryopreserved embryos survived the vitrification procedure and restored their normal morphology after warming. A conventional embryo transfer protocol could be applied to 25 out of the 35 strains tested. In the remaining 10 strains, live offspring could be obtained by a modified embryo transfer protocol using cyclosporin A treatment and co-transfer of ICR (laboratory mouse strain) embryos. Thus, ART for 37 wild-derived strains was devised successfully and is now routinely used for their preservation and transportation. The information provided here might facilitate broader use and wider distribution of wild-derived mice for biomedical research.

Littermate influence on infant growth in mice: comparison of SJL/J and ICR as cotransferred carrier embryos

In mice, a minimum number of healthy embryos is required to trigger and maintain pregnancy. Therefore, when recovering mouse embryos from a limited litter, one useful technique is to transfer carrier ICR embryos along with the embryos of interest, a technique referred to as cotransfer. In this study, we examined suitable mouse strains for cotransfer with C57BL/6J (B6) embryos in regards to the maintenance of pregnancy, number of pups born, intrauterine growth, and postnatal growth. Because the coat color of B6 is black, we compared two white coat-colored strains, SJL/J and ICR. Cotransfer of SJL/J and ICR embryos had similar effects on maintenance of pregnancy, number of pups born, and intrauterine growth. However, the postnatal growth of B6 mouse pups cotransferred and grown with SJL/J pups was better than for B6 mouse pups cotransferred and grown with ICR pups, suggesting competition among littermates. These results demonstrate that cotransfer of SJL/J embryos will be useful not only as carrier embryos with B6-background embryos but also as a model system to examine littermate competition.

Microdroplet in vitro fertilization can reduce the number of spermatozoa necessary for fertilizing oocytes

Successful in vitro fertilization (IVF) in mice has been achieved using spermatozoa at concentrations specifically optimized for the experimental conditions, such as species and source of spermatozoa. Although IVF in mice is mostly performed using about 80–500 µl drops, it is expected that the number of spermatozoa used for insemination can be reduced by decreasing the size of the IVF drops. The present study was undertaken to examine the extent to which the number of spermatozoa used for IVF could be reduced by using small droplets (1 µl). We devised the experimental parameters using frozen–thawed spermatozoa from C57BL/6 mice in anticipation of broader applications to other mouse facilities. We found that as few as 5 spermatozoa per droplet could fertilize oocytes (1 or 3 oocytes per droplet), although the fertilization rates were low (13–15%). Practical fertilization rates (> 40%) could be achieved with frozen-thawed C57BL/6J spermatozoa, which are sensitive to cryopreservation, when 20 sperm per droplet were used to inseminate 3 oocytes. Even with spermatozoa from a very poor quality suspension (10% motility), about 25% of oocytes were fertilized. Our calculations indicate that the number of inseminated spermatozoa per oocyte can be reduced to 1/96–1/240 by this method. In two separate embryo transfer experiments, 60% and 47%, respectively, of embryos developed to term. Our microdroplet IVF method may be particularly advantageous when only a limited number of motile spermatozoa are available because of inadequate freezing-thawing or genetic reasons.