Microinsemination and Nuclear Transfer Using Male Germ Cells

Restoration of fertility in nonablated recipient mice after spermatogonial stem cell transplantation

Spermatogonial stem cell (SSC) transplantation is a valuable tool for studying stem cell-niche interaction. However, the conventional approach requires the removal of endogenous SSCs, causing damage to the niche. Here we introduce WIN18,446, an ALDH1A2 inhibitor, to enhance SSC colonization in nonablated recipients. Pre-transplantation treatment with WIN18,446 induced abnormal claudin protein expression, which comprises the blood-testis barrier and impedes SSC colonization. Consequently, WIN18,446 increased colonization efficiency by 4.6-fold compared with untreated host. WIN18,446-treated testes remained small despite the cessation of WIN18,446, suggesting its irreversible effect. Offspring were born by microinsemination using donor-derived sperm. While WIN18,446 was lethal to busulfan-treated mice, cyclophosphamide- or radiation-treated animals survived after WIN18,446 treatment. Although WIN18,446 is not applicable to humans due to toxicity, similar ALDH1A2 inhibitors may be useful for SSC transplantation into nonablated testes, shedding light on the role of retinoid metabolism on SSC-niche interactions and advancing SSC research in animal models and humans.

Regeneration of spermatogenesis by mouse germ cell transplantation into allogeneic and xenogeneic testis primordia or organoids

Gametogenesis requires close interactions between germ cells and somatic cells. Derivation of sperm from spermatogonial stem cells (SSCs) is hampered by the inefficiency of spermatogonial transplantation technique in many animal species because it requires a large number of SSCs and depletion of endogenous spermatogenesis. Here we used mouse testis primordia and organoids to induce spermatogenesis from SSCs. We microinjected mouse SSCs into embryonic gonads or reaggregated neonatal testis organoids, which were transplanted under the tunica albuginea of mature testes. As few as 1 × 10⁴ donor cells colonized both types of transplants and produced sperm. Moreover, rat embryonic gonads supported xenogeneic spermatogenesis from mouse SSCs when transplanted in testes of immunodeficient mice. Offspring with normal genomic imprinting patterns were born after microinsemination. These results demonstrate remarkable flexibility of the germ cell-somatic cell interaction and raise new strategies of SSC manipulation for animal transgenesis and analysis of male infertility.

•

SSCs can be injected into embryonic gonads or reaggregated neonatal testes

•

Spermatogenesis occurs in the gonads or reaggregated testes after transplantation

•

Offspring are born from SSC-derived sperm using microinsemination

•

Offspring show normal DNA methylation in imprinted genes

Tricostatin A-treated round spermatid enhances preimplantation embryo developmental competency following round spermatid injection in mice

It has been documented that the inefficacy of round spermatid injection (ROSI) might be caused by abnormal epigenetic modifications. Therefore, this study aimed to evaluate the effect of trichostatin A (TSA) as an epigenetic modifier of preimplantation embryo development in activated ROSI oocytes. Matured oocytes were collected from superovulated female mice. Testes were placed in human tubal fluid medium and masses were then cut into small pieces to disperse spermatogenic cells. Round spermatids were treated with TSA and subsequently injected into oocytes. The expression level of the development-related genes including Oct4, Sox2, Nanog, Dnmt and Hdac transcripts were evaluated using qRT-PCR. Immunohistochemistry was performed to confirm the presence of Oct-4 protein at the blastocyst stage. There was no statistically significant difference in fertilization rate following ROSI/+TSA compared with the non-treated ROSI and intracytoplasmic sperm injection (ICSI) groups. Importantly, TSA treatment increased blastocyst formation from 38% in non-treated ROSI to 68%. The relative expression level of developmentally related genes increased and Dnmt transcripts decreased in ROSI/+TSA-derived embryos, similar to the expression levels observed in the ICSI-derived embryos. In conclusion, our results indicate that spermatid treatment with TSA prior to ROSI would increase the success rate of development to the blastocyst stage and proportion of pluripotent cells.

Transcriptome and DNA Methylation Profiles of Mouse Fetus and Placenta Generated by Round Spermatid Injection

Low birth efficiency and developmental abnormalities in embryos derived using round spermatid injection (ROSI) limit the clinical application of this method. Further, the underlying molecular mechanisms remain elusive and warrant further in-depth study. In this study, the embryonic day (E) 11.5 mouse fetuses and corresponding placentas derived upon using ROSI, intracytoplasmic sperm injection (ICSI), and natural in vivo fertilized (control) embryos were collected. Transcriptome and DNA methylation profiles were analyzed and compared using RNA-sequencing (RNA-seq) and whole-genome bisulfite sequencing, respectively. RNA-seq results revealed similar gene expression profiles in the ROSI, ICSI, and control fetuses and placentas. Compared with the other two groups, seven differentially expressed genes (DEGs) were identified in ROSI fetuses, and ten DEGs were identified in the corresponding placentas. However, no differences in CpG methylation were observed in fetuses and placentas from the three groups. Imprinting control region methylation and imprinted gene expression were the same between the three fetus and placenta groups. Although 49 repetitive DNA sequences (RS) were abnormally activated in ROSI fetuses, RS DNA methylation did not differ between the three groups. Interestingly, abnormal hypermethylation in promoter regions and low expression of Fggy and Rec8 were correlated with a crown-rump length less than 6 mm in one ROSI fetus. Our study demonstrates that the transcriptome and DNA methylation in ROSI-derived E11.5 mouse fetuses and placentas were comparable with those in the other two groups. However, some abnormally expressed genes in the ROSI fetus and placenta warrant further investigation to elucidate their effect on the development of ROSI-derived embryos.

Loss of H3K27me3 Imprinting in Somatic Cell Nuclear Transfer Embryos Disrupts Post-Implantation Development

Animal cloning can be achieved through somatic cell nuclear transfer (SCNT), although the live birth rate is relatively low. Recent studies have identified H3K9me3 in donor cells and abnormal Xist activation as epigenetic barriers that impede SCNT. Here we overcome these barriers using a combination of Xist knockout donor cells and overexpression of Kdm4 to achieve more than 20% efficiency of mouse SCNT. However, post-implantation defects and abnormal placentas were still observed, indicating that additional epigenetic barriers impede SCNT cloning. Comparative DNA methylome analysis of IVF and SCNT blastocysts identified abnormally methylated regions in SCNT embryos despite successful global reprogramming of the methylome. Strikingly, allelic transcriptomic and ChIP-seq analyses of pre-implantation SCNT embryos revealed complete loss of H3K27me3 imprinting, which may account for the postnatal developmental defects observed in SCNT embryos. Together, these results provide an efficient method for mouse cloning while paving the way for further improving SCNT efficiency.

Reproductive technologies for the generation and maintenance of valuable animal strains

Many types of mutant and genetically engineered strains have been produced in various animal species. Their numbers have dramatically increased in recent years, with new strains being rapidly produced using genome editing techniques. In the rat, it has been difficult to produce knockout and knock-in strains because the establishment of stem cells has been insufficient. However, a large number of knockout and knock-in strains can currently be produced using genome editing techniques, including zinc-finger nuclease (ZFN), transcription activator-like effector nuclease (TALEN), and the clustered regularly interspaced short palindromic repeats (CRISPR) and CRISPR-associated protein 9 (Cas9) system. Microinjection technique has also contributed widely to the production of various kinds of genome edited animal strains. A novel electroporation method, the “Technique for Animal Knockout system by Electroporation (TAKE)” method, is a simple and highly efficient tool that has accelerated the production of new strains. Gamete preservation is extremely useful for maintaining large numbers of these valuable strains as genetic resources in the long term. These reproductive technologies, including microinjection, TAKE method, and gamete preservation, strongly support biomedical research and the bio-resource banking of animal models. In this review, we introduce the latest reproductive technologies used for the production of genetically engineered animals, especially rats, using genome editing techniques and the efficient maintenance of valuable strains as genetic resources. These technologies can also be applied to other laboratory animals, including mice, and domestic and wild animal species.

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.

Effects of the histone deacetylase inhibitor 'Scriptaid' on the developmental competence of mouse embryos generated through round spermatid injection

STUDY QUESTION

Can the histone deacetylase inhibitor Scriptaid improve the efficiency of the development of round spermatid injection (ROSI)-fertilized embryos in a mouse model?

SUMMARY ANSWER

Treatment of ROSI mouse zygotes with Scriptaid increased the expression levels of several development-related genes at the blastocyst stage, resulting in more efficient in vitro development of the blastocyst and an increased birth rate of ROSI-derived embryos.

WHAT IS KNOWN ALREADY

The full-term development of embryos derived through ROSI is significantly lower than that following ICSI in humans and other species.

STUDY DESIGN, SIZE, DURATION

Oocytes, spermatozoa and round spermatids were collected from BDF1 (C57BL/6 × DBA/2) mice. For in vitro development experiments, mouse ROSI-derived zygotes were treated with Scriptaid at different concentrations (0, 125, 250, 500 and 1000 nM) and for different exposure times (0, 6, 10, 16 or 24 h). Next, blastocysts of the optimal Scriptaid-treated group and the non-treated ROSI group were separately transferred into surrogate ICR mice to compare in vivo development with the ICSI group (control). Each experiment was repeated at least three times.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Metaphase II (MII) oocytes, spermatozoa and round spermatids were obtained from sexually mature BDF1 female or male mice. The developmental potential of embryos among the three groups (the ICSI, ROSI and optimal Scriptaid-treated ROSI groups) was assessed based on the rates of obtaining zygotes, two-cell stage embryos, four-cell stage embryos, blastocysts and full-term offspring. In addition, the expression levels of development-related genes (Oct4, Nanog, Klf4 and Sox2) were analysed using real-time PCR, and the methylation states of imprinted genes (H19 and Snrpn) in these three groups were detected using methylation-specific PCR (MS-PCR) sequencing following bisulfite treatment.

MAIN RESULTS AND THE ROLE OF CHANCE

The in vitro experiments revealed that treating ROSI-derived zygotes with 250 nM Scriptaid for 10 h significantly improved the blastocyst formation rate (59%) compared with the non-treated group (38%) and further increased the birth rates of ROSI-derived embryos from 21% to 40% in vivo. Moreover, in ROSI-derived embryos, the expression of the Oct4, Nanog and Sox2 genes at the blastocyst stage was decreased, but the optimal Scriptaid treatment restored expression to a level similar to their ICSI counterparts. In addition, Scriptaid treatment moderately repaired the abnormal DNA methylation pattern in the imprinting control regions (ICRs) of H19 and Snrpn.

LARGE SCALE DATA

N/A LIMITATIONS, REASONS FOR CAUTION: Because of the ethics regarding the use of human gametes for ROSI studies, the mouse model was used as an approach to explore the effects of Scriptaid on the developmental potential of ROSI-derived embryos. However, to determine whether these findings can be applied to humans, further investigation will be required.

WIDER IMPLICATIONS OF THE FINDINGS

Scriptaid treatment provides a new means of improving the efficiency and safety of clinical human ROSI.

STUDY FUNDING/COMPETING INTERESTS

The study was financially supported through grants from the National Key Research Program of China (No. 2016YFC1304800); the National Natural Science Foundation of China (Nos: 81170756, 81571486); the Natural Science Foundation of Shanghai (Nos: 15140901700, 15ZR1424900) and the Programme for Professor of Special Appointment (Eastern Scholar) at Shanghai Institutions of Higher Learning. There are no conflicts of interest to declare.

Transgenic mouse offspring generated by ROSI

The production of transgenic animals is an important tool for experimental and applied biology. Over the years, many approaches for the production of transgenic animals have been tried, including pronuclear microinjection, sperm-mediated gene transfer, transfection of male germ cells, somatic cell nuclear transfer and the use of lentiviral vectors. In the present study, we developed a new transgene delivery approach, and we report for the first time the production of transgenic animals by co-injection of DNA and round spermatid nuclei into non-fertilized mouse oocytes (ROSI). The transgene used was a construct containing the human CMV immediate early promoter and the enhanced GFP gene. With this procedure, 12% of the live offspring we obtained carried the transgene. This efficiency of transgenic production by ROSI was similar to the efficiency by pronuclear injection or intracytoplasmic injection of male gamete nuclei (ICSI). However, ICSI required fewer embryos to produce the same number of transgenic animals. The expression of Egfp mRNA and fluorescence of EGFP were found in the majority of the organs examined in 4 transgenic lines generated by ROSI. Tissue morphology and transgene expression were not distinguishable between transgenic animals produced by ROSI or pronuclear injection. Furthermore, our results are of particular interest because they indicate that the transgene incorporation mediated by intracytoplasmic injection of male gamete nuclei is not an exclusive property of mature sperm cell nuclei with compact chromatin but it can be accomplished with immature sperm cell nuclei with decondensed chromatin as well. The present study also provides alternative procedures for transgene delivery into embryos or reconstituted oocytes.

Uniparental embryos in the study of genomic imprinting

Nuclear transplantation has been used to study genomic imprinting. Available nuclear transfer methods include pronuclear transfer (PNT), intracytoplasmic sperm injection, and round spermatid injection. By generating uniparental embryos that have exclusively paternal or maternal genomes, it is possible to study the functions of the parental genomes separately. It is possible to compare functions in haploid and diploid states. In addition, nuclear transfer allows the effects of the ooplasm, including mitochondria, to be distinguished from effects of the maternally inherited chromosomes. PNTs can also be used to study epigenetic modifications of the parental genomes by the ooplasm. This chapter reviews the methods employed to generate uniparental embryonic constructs for these purposes.

Fertilization studies and assisted fertilization in mammals: their development and future

Studies of mammalian fertilization progressed very slowly in the beginning because of difficulties in obtaining a large quantity of fully mature eggs at one time. With progression of techniques to collect and handle eggs and spermatozoa, research in mammalian fertilization advanced rapidly. Today, far more papers are published on mammalian gametes and fertilization than those of all other animals combined. The development of assisted fertilization and related technologies revolutionized basic research as well as human reproductive medicine and animal husbandry. Reproduction is fundamental to human and animal lives. The author lists a few subjects of his personal interest for further development of basic and applied research of gametes and fertilization. Each reader will probably have more exciting subjects of future investigation.

Long-term preservation of freeze-dried mouse spermatozoa

Many genetically engineered mice strains have been generated worldwide and sperm preservation is a valuable method for storing these strains as genetic resources. Freeze-drying is a useful sperm preservation method because it requires neither liquid nitrogen nor dry ice for preservation and transportation. We report here successful long-term preservation at 4 °C of mouse spermatozoa freeze-dried using a simple buffer solution (10mM Tris, 1mM EDTA, pH 8.0). Offspring with fertility were obtained from oocytes fertilized with freeze-dried spermatozoa from C57BL/6 and B6D2F1 mouse strains stored at 4 °C for 3 years. This freeze-drying method is a safe and economical tool for the biobanking of valuable mouse strains.

Optimization of a protocol for cryopreservation of mouse spermatozoa using cryotubes

The rapid increase in the number of genetically modified mouse strains has produced a high demand for their frozen spermatozoa from laboratories and mouse banking facilities. Historically, plastic straws have been used preferentially as containers for frozen mammalian spermatozoa because spermatozoa frozen in plastic straws have a high survival rate after thawing. However, plastic straws are more fragile and are used less often than the cryotubes used for conventional cell freezing. In this study, we sought to develop a new protocol for sperm freezing using cryotubes as the container to increase the accessibility of mouse sperm cryopreservation. Epididymal spermatozoa were collected from mature ICR or C57BL/6J (B6) males and were suspended in 18% raffinose and 3% skim milk solution. We then optimized the following conditions using the sperm survival rate as an index: 1) distance of cryotubes from the surface of the liquid nitrogen at freezing, 2) volume of the sperm suspension in the cryotube and 3) temperature of warming sperm during thawing. The best result was obtained when cryotubes containing 10 µl of sperm suspension were immersed 1 cm below the surface of the liquid nitrogen and then thawed at 50 C. The fertilization rates using spermatozoa frozen and thawed using this method were 63.1% in ICR mice and 28.2% in B6 mice. The latter rate was increased to 62.3% by adding reduced glutathione to the fertilization medium. After embryo transfer, 68% and 62% of the fertilized oocytes developed into normal offspring in the ICR and B6 strains, respectively. These results show that cryotubes can be used for cryopreservation of mouse spermatozoa under optimized conditions. This protocol is easy and reproducible, and it may be used in laboratories that do not specialize in sperm cryopreservation.

Birth of normal mice following round spermatid injection without artificial oocyte activation

For fertilization using round spermatid injection (ROSI) in mice, oocytes need to be artificially preactivated because of the lack of oocyte-activating capacity in round spermatids of this species. However, when round spermatids were frozen-thawed before microinjection, 11-71% of injected oocytes developed into 2-cell embryos without any artificial activation. After being transferred into recipient females, 5-27% of these embryos reached term. At least some of the injected oocytes showed intracellular Ca(2+) oscillations, which normally occur after fertilization by mature spermatozoa. Thus, these round spermatids could transmit a sperm-borne oocyte-activating factor, which might have been released from spermatozoa and elongated spermatids in the same suspension by freezing and thawing. This possibility was further supported by activation of intact oocytes following transplantation of the pronuclei from ROSI-generated embryos. Thus, one-step ROSI can be achieved in mice simply by injecting frozen-thawed round spermatids into intact oocytes. Clearly, there is a need for careful interpretation of microinjection experiments when assessing the oocyte-activating capacity of spermatogenic cells, especially when they are derived from frozen-thawed stocks.

The effect on intracytoplasmic sperm injection outcome of genotype, male germ cell stage and freeze-thawing in mice

Background

Intracytoplasmic sperm injection (ICSI) has been widely used to study the mechanisms of mammalian fertilization and to rescue male-factor infertility in humans and animals. However, very few systematic analyses have been conducted to define factors affecting the efficiency of ICSI. In this study, we undertook a large-scale series of ICSI experiments in mice to define the factors that might affect outcomes.

Methodology/Principal Findings

We used a 5×3×2 factorial design with the following factors: mouse genotype (ICR, C57BL/6, DBA/2, C3H/He, and 129/Sv strains), type of male germ cells (epididymal sperm, elongated or round spermatids), and their freeze–thawing treatment. The efficiencies (parameters) of each developmental step were analyzed by three-way ANOVA (significance level P<0.01). The type of male germ cells affected all the four parameters observed: oocyte survival after injection, cleavage of oocytes, implantation, and birth of offspring. Genotype affected the oocyte survival, cleavage and birth rates, whereas freeze–thawing had no effects on any of the parameters. There were significant genotype/cell type interactions for oocyte survival and cleavage, indicating that they were determined by a combination of strain and germ cell maturity. Multiple comparisons revealed that spermatozoa and elongated spermatids gave better implantation and birth rates than did round spermatids, while spermatozoa and elongated spermatozoa were indistinguishable in their ability to support embryonic development. The best overall efficiency (birth rate per oocytes injected) was obtained with frozen–thawed DBA/2 strain elongated spermatids (23.2±4.2%).

Conclusions/Significance

The present study provides the first comprehensive information on ICSI using the mouse as a model and will contribute to the efficient use of materials, time, and efforts in biomedical research and clinics involving ICSI.

[Causes and clinical implications of sperm DNA damages]

Numerous recent studies involve DNA damages associated with poor fertilization rates, early embryo development defect, and poor quality of conceptus following Assisted Reproductive Technologies (ART). The authors denounce a particularly high rate of miscarriages and childhood cancer or dominant genetic mutations such as achondroplasia, Apert syndrome or aberrant gene imprinting such as Angelman and Beckwith Wiedeman syndromes. Gametes DNA defects have numerous origins which are difficult to determine; they are known to involve hypomethylation, oxydative stress and environmental factors.(adducts formation). DNA defect is also linked to a more or less delayed apoptotic phenomenon. Exposure to radiations or radiofrequency electromagnetic emissions can also induce DNA alterations into the spermatozoa of infertile men. Although the underlying mechanisms are unclear, these DNA defects have obvious consequences on reproduction of mammalian species. Detection of such anomalies before ART, are an important step toward developing strategies for clinical management according to the aetiology.

Efficient production of intersubspecific hybrid mice and embryonic stem cells by intracytoplasmic sperm injection

Recently, mice and embryonic stem (ES) cells with allelic polymorphisms have been used extensively in the field of genetics and developmental biology. In this study, we examined whether intersubspecific hybrid mice and ES cells with these genotypes can be efficiently produced by intracytoplasmic sperm injection (ICSI). Frozen-thawed spermatozoa from wild-derived strains, JF1 (Mus musculus molossinus), MSM (M. m. molossinus), HMI (M. m. castaneus), and SWN (M. m. spp.), were directly injected into mature oocytes from laboratory mice ([C57BL/6 x DBA2]F1; M. m. domesticus). The in vitro and in vivo developmental capacity of F1 embryos was not significantly different among the groups (P > 0.05), and term offspring were efficiently obtained in all groups (27%-34% of transferred embryos). However, the mean body and placental weights of the offspring differed significantly with genotype (P < 5 x 10(-10)), with the HMI hybrid greatest in both body and placental weights. In an application study using these F1 offspring, we analyzed their mitochondrial DNA using intersubspecific polymorphisms and found the consistent disappearance of sperm mitochondrial DNA in the F1 progeny. In a second series of experiments, we generated F1 blastocysts by injecting MSM spermatozoa into C57BL/6 oocytes and used them to generate hybrid ES cell lines. The ES cell lines were established at a high efficiency (9 lines from 20 blastocysts) and their allelic polymorphisms were confirmed. Thus, ICSI using cryopreserved spermatozoa allows the efficient and immediate production of a number of F1 hybrid mice and ES cell lines, which can be used for polymorphic analysis of mouse genetics.

Offspring derived from oocytes injected with rat sperm, frozen or freeze-dried without cryoprotection

Sperm preservation is a valuable technique for maintaining genetic resources in biomedical research. In the present study, 10mM Tris-HCl and 1mM EDTA (TE buffer; a simple solution without cryoprotection), was used to freeze or freeze-dry rat sperm. The results were compared with rat sperm frozen using a solution containing Equex STM and egg yolk. Sperm from Wistar and Sprague-Dawley (SD) rats were evaluated by injecting them individually into oocytes derived from the same strain. Of the oocytes that survived after sperm injection, more than 94% were fertilized in all treatments of both strains. In the Wistar rat, 27, 20, 43, and 30% of 2-cell embryos developed to blastocysts, and 35, 9, 11, and 14% of 2-cell embryos developed to offspring from oocytes injected with fresh, frozen (Equex STM/egg yolk), frozen (TE buffer), and freeze-dried sperm, respectively. Using the analagous sources of sperm in the SD rat, 45, 14, 27, and 7% of 2-cell embryos developed to blastocysts, and 22, 0, 14, and 4% of 2-cell embryos developed to offspring. These results demonstrated that rat sperm could be frozen or freeze-dried using TE buffer. We concluded that this simple preservation method, in which cryoprotection was not required, allowed sperm to be preserved efficiently with maintenance of their fertilizing ability.

Origins and consequences of DNA damage in male germ cells

DNA damage in the male germline is associated with poor fertilization rates following IVF, defective preimplantation embryonic development, and high rates of miscarriage and morbidity in the offspring, including childhood cancer. This damage is poorly characterized, but is known to involve hypomethylation of key genes, oxidative base damage, endonuclease-mediated cleavage and the formation of adducts with xenobiotics and the products of lipid peroxidation. There are many possible causes of such DNA damage, including abortive apoptosis, the oxidative stress associated with male genital tract infection, exposure to redox cycling chemicals, and defects of spermiogenesis associated with the retention of excess residual cytoplasm. Physical factors such as exposure to radiofrequency electromagnetic radiation or mild scrotal heating can also induce DNA damage in mammalian spermatozoa, although the underlying mechanisms are unclear. Ultimately, resolving the precise nature of the DNA lesions present in the spermatozoa of infertile men will be an important step towards uncovering the aetiology of this damage and developing strategies for its clinical management.

Spermatozoa and spermatids retrieved from frozen reproductive organs or frozen whole bodies of male mice can produce normal offspring

Cryopreservation of male germ cells is a strategy to conserve animal species and strains of animals valuable to biomedical research. We tested whether mouse male germ cells could be cryopreserved without cryoprotection by simply freezing epididymides, testes, or whole bodies. The reproductive organs were isolated from killed mice and frozen for 1 week to 1 year at -80 degrees C before spermatozoa and spermatids were collected and injected into mature oocytes. Normal pups were born irrespective of strains tested (ICR and C57BL/6). Epididymides and testes frozen and transported internationally to another laboratory by air could produce pups of inbred C57BL/6 mice. Testicular spermatozoa retrieved from the bodies of male mice (BALB/c nude and C3H/He strains) that had been kept frozen (-20 degrees C) for 15 years could also produce normal offspring by microinsemination. Thus, freezing of either male reproductive organs or whole bodies is the simplest way to preserve male germ cells. Restoration of extinct species could be possible if male individuals are found in permafrost.

Clonal Origin of Germ Cell Colonies after Spermatogonial Transplantation in Mice1

Spermatogenesis originates from a small number of spermatogonial stem cells that can reinitiate spermatogenesis and produce germ cell colonies following transplantation into infertile recipient testes. Although several previous studies have suggested a single-cell origin of germ cell colonies, only indirect evidence has been presented. In this investigation, we tested the clonal origin hypothesis using a retrovirus, which could specifically mark an individual spermatogonial stem cell. Spermatogonial stem cells were infected in vitro with an enhanced green fluorescence protein-expressing retrovirus and subsequently transplanted into infertile recipient mice. Live haploid germ cells were recovered from individual colonies and were microinjected into eggs to create offspring. In total, 45 offspring were produced from five colonies, and 23 (51%) of the offspring were transgenic. Southern blot analysis indicated that the transgenic offspring from the single colony carried a common integration site, and the integration site was different among the transgenic offspring from different colonies. These results provide evidence that germ cell colonies develop from single spermatogonial stem cells.

Improvement of Cumulus-free Oocyte Maturation In Vitro and Its Application to Microinsemination with Primary Spermatocytes in Mice

In micromanipulation experiments using immature oocytes, final ooplasmic maturation is often compromised because the oocytes are usually first freed from their nurturing cumulus cells. This study was undertaken to determine whether cumulus-free in vitro maturation (IVM) in mice could be improved by modifying IVM medium having defined components. Cumulus-free germinal vesicle (GV) stage oocytes were subjected to IVM in either alphaMEM medium, TYH medium, or a 1:1 mixture of the two (termed TaM). TYH medium produced a better maturation rate (181/196; 92.3%) than alphaMEM (184/257; 71.6%). However, alphaMEM supported better embryo development to the morula/blastocyst stage than TYH following in vitro fertilization (93.3% vs. 76.5%) or parthenogenetic activation (82.4% vs. 60.4%). Mitochondrial distribution in MII oocytes was diffuse following IVM in alphaMEM, but was aggregated with TYH. The maturation promoting factor (MPF) activity in MII oocytes was significantly higher in TYH than in alphaMEM (P<0.05). Oocytes cultured in TaM had intermediate characteristics and essentially resembled in vivo matured oocytes, with the mitochondrial distribution pattern being most typical of that condition. The highest rate of development from GV oocytes to full-term fetuses following in vitro fertilization and embryo transfer to foster mothers (23.8%) was obtained using TaM. When this IVM system was applied to MI oocytes injected with spermatocytes, offspring were first obtained without cytoplasmic replacement at MII. Thus, optimization of the culture medium can considerably improve the quality of cumulus-free oocyte IVM in mice.