Production of fertile offspring from genetically infertile male mice

How to improve the clinical outcome of round spermatid injection (ROSI) into the oocyte: Correction of epigenetic abnormalities

Background

First successful human round spermatid injection (ROSI) was conducted by Tesarik et al. in 1996 for the sole treatment of nonobstructive azoospermic men whose most advanced spermatogenic cells were elongating round spermatids. Nine offsprings from ROSI were reported between 1996 and 2000. No successful deliveries were reported for 15 years after that. Tanaka et al. reported 90 babies born after ROSI and their follow-up studies in 2015 and 2018 showed no significant differences in comparison with those born after natural conception in terms of physical and cognitive abilities. However, clinical outcomes remain low.

Method

Clinical and laboratory data of successful cases in the precursor ROSI groups and those of Tanaka et al. were reviewed.

Results

Differences were found between the two groups in terms of identification of characteristics of round spermatid and oocyte activation. Additionally, epigenetic abnormalities were identified as underlying causes for poor ROSI results, besides correct identification of round spermatid and adequate oocyte activation. Correction of epigenetic errors could lead to optimal embryonic development.

Conclusion

Correction of epigenetic abnormalities has a probability to improve the clinical outcome of ROSI.

Production of mouse offspring from zygotes fertilized with freeze-dried spermatids

Mouse cloning by nuclear transfer using freeze-drying (FD) somatic cells is now possible, but the success rate is significantly lower than that of FD spermatozoa. Because spermatozoa, unlike somatic cells, are haploid cells with hardened nuclei due to protamine, the factors responsible for their tolerance to FD treatment remain unclear. In this study, we attempt to produce offspring from FD spermatid, a haploid sperm progenitor cell whose nuclei, like somatic cells, have not yet been replaced by protamine. We developed a method for collecting FD spermatids from testicular suspension. Despite the significantly lower success rate than that of FD spermatozoa, healthy offspring were obtained when FD spermatids were injected into oocytes. Offspring were also obtained from FD spermatids derived from immature male mice that had not yet produced spermatozoa. These results suggest that nuclear protaminization, rather than haploid nuclei, is one of the key processes responsible for tolerance to FD treatment.

Oviducal gland transcriptomics of Octopus maya through physiological stages and the negative effects of temperature on fertilization

Background

Elevated temperatures reduce fertilization and egg-laying rates in the octopus species. However, the molecular mechanisms that control the onset of fertilization and egg-laying in the octopus' oviducal gland are still unclear; and the effect of temperature on the expression of key reproductive genes is unknown. This study aims to better understand the molecular bases of octopus fertilization and egg-laying, and how they are affected by elevated temperatures.

Method

RNA-seq of oviducal glands was performed for samples before, during, and after fertilization and their transcriptomic profiles were compared. Also, at the fertilization stage, the optimal and thermal-stress conditions were contrasted. Expression levels of key reproductive genes were validated via RT-qPCR.

Results

In mated females before egg-laying, genes required for the synthesis of spermine, spermidine, which may prevent premature fertilization, and the myomodulin neuropeptide were upregulated. Among the genes with higher expression at the fertilization stage, we found those encoding the receptors of serotonin, dopamine, and progesterone; genes involved in the assembly and motility of the sperm flagellum; genes that participate in the interaction between male and female gametes; and genes associated with the synthesis of eggshell mucoproteins. At temperatures above the optimal range for reproduction, mated females reduced the fertilization rate. This response coincided with the upregulation of myomodulin and APGW-amide neuropeptides. Also, genes associated with fertilization like LGALS3, VWC2, and Pcsk1 were downregulated at elevated temperatures. Similarly, in senescent females, genes involved in fertilization were downregulated but those involved in the metabolism of steroid hormones like SRD5A1 were highly expressed.

Clinical values and advances in round spermatid injection (ROSI)

Azoospermia is defined as the complete absence of sperm cells in the ejaculate. Approximately 10-15 % of infertile men display azoospermia. Azoospermia can be subdivided into two types, obstructive azoospermia (OA) and non-obstructive azoospermia (NOA). NOA azoospermia might be the result due to primary testicular damage, secondary testicular damage, or incomplete testicular development. NOA azoospermia accounts for a considerable proportion of male infertility. A significant percentage of men with NOA azoospermia have foci of active spermatogenesis up to the stage of round spermatid. Round spermatid injection (ROSI) is a technique of assisted in-vitro fertilization (IVF) in assisted reproductive technology (ART). ROSI technique involves the injection of haploid germ cells derived from testicular biopsies into the recipient oocytes. The present study demonstrates that more participants and long-term follow-up studies are required to assess the reliability of the ROSI technique. In order to increase the success rate of the ROSI technique, round spermatids should be correctly evaluated and selected. Our study refers to the clinical values, challenges, and innovations in round spermatid injection (ROSI).

Production of offspring by intracytoplasmic sperm injection using sperm from deceased transgenic mice at different postmortem intervals

Successful fertilization by intracytoplasmic sperm injection (ICSI) is possible as long as the sperm genome is intact, even in the context of defective sperm or sustained adverse treatment. However, there are few reports on rescuing gene-modified mouse lines after accidental death. To investigate whether sperm from a dead transgenic mouse can fertilize an oocyte and enable embryo development into a pup, Nestin-GFP transgenic male mice were sacrificed, and sperm was collected 14 h, 24 h, and 48 h after death. The collected sperm was injected into oocytes from hybrid B6D2F1 or inbred C57BL/6 N mice. The results showed that the sperm in the three groups activated oocytes from B6D2F1 and supported embryo development to the blastocyst stage. For ICSI embryos derived from B6D2F1 mice, the cleavage and blastocyst rates were significantly lower in the three experimental groups than in the control group (0 h) (P < 0.05), and the birth rate in the 24 h and 48 h groups was significantly lower than that in the 14 h and control groups (0 h). For C57BL/6N-derived ICSI embryos, the cleavage rates were significantly lower at 24 h and 48 h than at 14 h and 0 h (control group), and the birth rate in the three experimental groups was significantly lower than that in the control group (0 h). The F0 mice derived from B6D2F1 and C57BL/6 N oocytes had normal reproductive ability, and F1 mice were successfully obtained. The characteristics of the GFP gene were preserved and inherited. The histone H2AX phosphorylation assay showed that the proportion of focus-negative embryos was markedly and significantly lower in the 14 h, 24 h, and 48 h groups than in the control group (0 h). The proportion of focus-negative embryos was significantly lower at 48 h than at 14 h or 24 h. The number of foci was significantly higher in the three experimental groups than in the control group (0 h), indicating that sperm DNA sustained more damage after death and that few sperm had an intact genome. In summary, sperm obtained from mice 14 h, 24 h, and 48 h after death is capable of activating an oocyte and supporting complete embryo development into a pup. This study provides an effective way to rescue accidently died mouse strains.

TBC1D20 deficiency induces Sertoli cell apoptosis by triggering irreversible endoplasmic reticulum stress in mice

Male 'blind sterile' mice with the causative TBC1 domain family member 20 (TBC1D20) deficiency are infertile with excessive germ cell apoptosis and spermatogenesis arrest at the spermatid stage. Sertoli cells are characterised as 'nurse cells' essential for normal spermatogenesis, but the role and corresponding molecular mechanisms of TBC1D20 deficiency in Sertoli cells of mice are not clear to date. In the present study, the histopathology of the testis and Sertoli cell proliferation and apoptosis were determined, and the corresponding molecular mechanisms were investigated by western blotting. Our data showed that TBC1D20 exhibits a testis-abundant expression pattern, and its expression level is positively associated with spermatogenesis. TBC1D20 is assembled in the Golgi and endoplasmic reticulum and is widely expressed by various germ cell subtypes and Sertoli cells. TBC1D20 deficiency in Sertoli cells led to an excessive apoptosis ratio and G1/S arrest. The increased apoptosis of TBC1D20-deficient Sertoli cells resulted from caspase-12 activation. TBC1D20-deficient Sertoli cells had an abnormal Golgi-endoplasmic reticulum structure, which led to endoplasmic reticulum stress, resulting in cell cycle arrest and excessive apoptosis. It suggested that TBC1D20 deficiency triggers irreversible endoplasmic reticulum stress resulting in G1/S arrest and excessive apoptosis in TBC1D20-deficient Sertoli cells, and TBC1D20 deficiency in Sertoli cells may also contribute to the infertility phenotype in 'blind sterile' male mice.

Improvement of a twice collection method of mouse oocytes by surgical operation

Mouse oocytes are generally collected after euthanasia. However, if oocytes were collected without euthanasia, then mice could be used to collect oocytes again after recovery. This condition is especially useful for mice that are genotypically rare. In this study, we examined the reusability of mice after collecting oocytes via a surgical operation. When oocytes were collected using medetomidine/midazolam/butorphanol combination anesthesia and examined for the quality of oocytes after in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI), they could develop to full term at the same rate as controls. When oocytes were collected from those mice a second time, the average number of oocytes was reduced by nearly 1/3. However, the blastocyst and offspring rates of those oocytes after IVF or ICSI were the same as those of the control regardless of the recovery day period. Although germinal vesicle (GV) oocytes can be collected from all reused mice, the final number of offspring did not increase. Interestingly, when oocytes were collected from the front position of the ampulla, 76% of the oviducts possessed oocytes after reuse, and the average number of oocytes significantly increased to a level comparable to that of the control. Finally, we examined whether reused mice can be used as recipient females, and then healthy offspring were obtained similarly as the control recipients. In conclusion, we provide a new method to collect a sufficient number of oocytes from reused mice without concern.

Increasing associations between defects in phospholipase C zeta and conditions of male infertility: not just ICSI failure?

PURPOSE

Oocyte activation is a fundamental event at mammalian fertilization. In mammals, this process is initiated by a series of characteristic calcium (Ca²⁺) oscillations, induced by a sperm-specific phospholipase C (PLC) termed PLCzeta (PLCζ). Dysfunction/reduction/deletion of PLCζ is associated with forms of male infertility where the sperm is unable to initiate Ca²⁺ oscillations and oocyte activation, specifically in cases of fertilization failure. This review article aims to systematically summarize recent advancements and controversies in the field to update expanding clinical associations between PLCζ and various male factor conditions. This article also discusses how such associations may potentially underlie defective embryogenesis and recurrent implantation failure following fertility treatments, alongside potential diagnostic and therapeutic PLCζ approaches, aiming to direct future research efforts to utilize such knowledge clinically.

METHODS

An extensive literature search was performed using literature databases (PubMed/MEDLINE/Web of Knowledge) focusing on phospholipase C zeta (PLCzeta; PLCζ), oocyte activation, and calcium oscillations, as well as specific male factor conditions.

RESULTS AND DISCUSSION

Defective PLCζ or PLCζ-induced Ca²⁺ release can be linked to multiple forms of male infertility including abnormal sperm parameters and morphology, sperm DNA fragmentation and oxidation, and abnormal embryogenesis/pregnancies. Such sperm exhibit absent/reduced levels, and abnormal localization patterns of PLCζ within the sperm head.

CONCLUSIONS

Defective PLCζ and abnormal patterns of Ca²⁺ release are increasingly suspected a significant causative factor underlying abnormalities or insufficiencies in Ca²⁺ oscillation-driven early embryogenic events. Such cases could potentially strongly benefit from relevant therapeutic and diagnostic applications of PLCζ, or even alternative mechanisms, following further focused research efforts.

TBC1D20 Is Essential for Mouse Blood-Testis Barrier Integrity Through Maintaining the Epithelial Phenotype and Modulating the Maturation of Sertoli Cells

Sertoli cells are important for spermatogenesis not only by directly interacting with germ line cells in the seminiferous epithelium but also by constituting the blood-testis barrier (BTB) structure to create a favorable environment for spermatogenesis. Blind sterile (bs) male mice are infertile, with excessive germ cell apoptosis and spermatogenesis arrest. TBC1D20 (TBC1 domain family member 20) deficiency has been identified as the causative mutation in bs mice. However, whether TBC1D20 loss of function also impairs BTB integrity, which further contributes to the failed spermatogenesis of bs male mice, remains unclear. In the present study, biotin tracer assay and transmission electron microscopy showed severely disrupted BTB integrity in bs testes. Compared to the wild-type Sertoli cells, BTB components of cultured bs Sertoli cells in vitro was perturbed with downregulation of E-cadherin, ZO-1, β-catenin, and Claudin 11. The obvious rearrangement of F-actin indicated disrupted epithelial-mesenchymal balance in TBC1D20-deficient Sertoli cells. The ability of bs Sertoli cells to maintain the clone formation of spermatogonia stem cells was also obviously limited. Furthermore, the decreasing of SOX9 (sex-determining region Y box 9) and WT1 (Wilms' tumor 1) and increasing of vimentin in bs Sertoli cells indicated that TBC1D20 loss of function attenuated the differentiation progression of bs Sertoli cells. In summary, TBC1D20 loss of function impedes the maturation of adult Sertoli cells and resulted in impaired BTB integrity, which is further implicated in the infertile phenotype of bs male mice.

Transient Sperm Starvation Improves the Outcome of Assisted Reproductive Technologies

To become fertile, mammalian sperm must undergo a series of biochemical and physiological changes known as capacitation. These changes involve crosstalk between metabolic and signaling pathways and can be recapitulated in vitro. In this work, sperm were incubated in the absence of exogenous nutrients (starved) until they were no longer able to move. Once immotile, energy substrates were added back to the media and sperm motility was rescued. Following rescue, a significantly higher percentage of starved sperm attained hyperactivated motility and displayed increased ability to fertilize in vitro when compared with sperm persistently incubated in standard capacitation media. Remarkably, the effects of this treatment continue beyond fertilization as starved and rescued sperm promoted higher rates of embryo development, and once transferred to pseudo-pregnant females, blastocysts derived from treated sperm produced significantly more pups. In addition, the starvation and rescue protocol increased fertilization and embryo development rates in sperm from a severely sub-fertile mouse model, and when combined with temporal increase in Ca²⁺ ion levels, this methodology significantly improved fertilization and embryo development rates in sperm of sterile CatSper1 KO mice model. Intracytoplasmic sperm injection (ICSI) does not work in the agriculturally relevant bovine system. Here, we show that transient nutrient starvation of bovine sperm significantly enhanced ICSI success in this species. These data reveal that the conditions under which sperm are treated impact post-fertilization development and suggest that this “starvation and rescue method” can be used to improve assisted reproductive technologies (ARTs) in other mammalian species, including humans.

The evolution and patterning of male gametophyte development

The reproductive adaptations of land plants have played a key role in their terrestrial colonization and radiation. This encompasses mechanisms used for the production, dispersal and union of gametes to support sexual reproduction. The production of small motile male gametes and larger immotile female gametes (oogamy) in specialized multicellular gametangia evolved in the charophyte algae, the closest extant relatives of land plants. Reliance on water and motile male gametes for sexual reproduction was retained by bryophytes and basal vascular plants, but was overcome in seed plants by the dispersal of pollen and the guided delivery of non-motile sperm to the female gametes. Here we discuss the evolutionary history of male gametogenesis in streptophytes (green plants) and the underlying developmental biology, including recent advances in bryophyte and angiosperm models. We conclude with a perspective on research trends that promise to deliver a deeper understanding of the evolutionary and developmental mechanisms of male gametogenesis in plants.

Transcription factor DUO1 generated by neo-functionalization is associated with evolution of sperm differentiation in plants

Evolutionary mechanisms underlying innovation of cell types have remained largely unclear. In multicellular eukaryotes, the evolutionary molecular origin of sperm differentiation is unknown in most lineages. Here, we report that in algal ancestors of land plants, changes in the DNA-binding domain of the ancestor of the MYB transcription factor DUO1 enabled the recognition of a new cis-regulatory element. This event led to the differentiation of motile sperm. After neo-functionalization, DUO1 acquired sperm lineage-specific expression in the common ancestor of land plants. Subsequently the downstream network of DUO1 was rewired leading to sperm with distinct morphologies. Conjugating green algae, a sister group of land plants, accumulated mutations in the DNA-binding domain of DUO1 and lost sperm differentiation. Our findings suggest that the emergence of DUO1 was the defining event in the evolution of sperm differentiation and the varied modes of sexual reproduction in the land plant lineage.

Production of inbred offspring by intracytoplasmic sperm injection of oocytes from juvenile female mice

The aim of the present study was to determine whether the use of oocytes from juvenile female mice would improve the efficiency of intracytoplasmic sperm injection (ICSI). In the present study, 15 adult and 14 juvenile C57BL6/J female mice were superovulated, with 17.8 oocytes per mouse harvested from adults, significantly lower than the 40.2 harvested from juveniles (P<0.01). Sixty and 233 oocytes were harvested from C57BL/6J adult and juvenile mice respectively, activated in 10mM SrCl2+5μgmL-1 cytochalasin B for 5-6h and cultured in potassium simplex optimisation medium (KSOM) for 3.5 days, with no differences in morula and blastocyst rates between groups (91.7% vs 96.6%; P>0.05). Twelve hours after injection of human chorionic gonadotrophin, oocytes were harvested from C57BL/6J juvenile mice into KSOM, randomly divided into groups and activated with the same method mentioned above at 0, 2, 4 or 6h and then cultured in KSOM for 3.5 days. There was no significant difference in morula and blastocyst rates among the different groups (P>0.05). Oocytes from juvenile mice activated in 10mM SrCl2 for 2h were subjected to ICSI and the rates of pronuclear formation and Day 1 cleavage were significantly improved compared with the control group (P<0.01). ICSI combined with activation of oocytes from inbred mouse strains (C57BL/6J, C57BL/6N and 129Svev) successfully produced pups. The fertility of some these mice resulting from ICSI was tested, and the animals proved fertile. In conclusion, superovulated juvenile mice can yield more useable oocytes than adult mice, but additional activation is essential for full development of ICSI oocytes harvested from juvenile inbred mice.

Effects of different kinds of essentiality on sequence evolution of human testis proteins

We asked if essentiality for either fertility or viability differentially affects sequence evolution of human testis proteins. Based on murine knockout data, we classified a set of 965 proteins expressed in human seminiferous tubules into three categories: proteins essential for prepubertal survival (“lethality proteins”), associated with male sub- or infertility (“male sub-/infertility proteins”), and nonessential proteins. In our testis protein dataset, lethality genes evolved significantly slower than nonessential and male sub-/infertility genes, which is in line with other authors’ findings. Using tissue specificity, connectivity in the protein-protein interaction (PPI) network, and multifunctionality as proxies for evolutionary constraints, we found that of the three categories, proteins linked to male sub- or infertility are least constrained. Lethality proteins, on the other hand, are characterized by broad expression, many PPI partners, and high multifunctionality, all of which points to strong evolutionary constraints. We conclude that compared with lethality proteins, those linked to male sub- or infertility are nonetheless indispensable, but evolve under more relaxed constraints. Finally, adaptive evolution in response to postmating sexual selection could further accelerate evolutionary rates of male sub- or infertility proteins expressed in human testis. These findings may become useful for in silico detection of human sub-/infertility genes.

Paternal pachytene piRNAs are not required for fertilization, embryonic development and sperm-mediated epigenetic inheritance in mice

Pachytene piRNAs are MIWI-/MILI-bound small RNAs abundantly expressed in pachytene spermatocytes and round spermatids in adult mouse testes. Miwi knockout (KO) male mice are sterile due to spermiogenic arrest. In Caenorhabditis elegans, sperm-borne piRNAs appear to have an epigenetic role during fertilization and development because progeny of individuals with piRNA-deficient gametes display a progressive loss of fertility after several generations. In mice, it remains unknown whether pachytene piRNA-deficient round spermatids can produce offspring, and whether the progeny of Miwi mutants also exhibits transgenerational, progressive fertility loss. Here, we report that Miwi KO round spermatids could fertilize both wild-type (WT) and Miwi KO oocytes through round spermatid injection, and could produce healthy and fertile offspring despite the global downregulation of both MIWI-/MILI-bound pachytene piRNAs. Progeny of ROSI-derived heterozygotes, both male and female, displayed normal fertility for at least three generations when bred with either WT or Miwi KO females. Our data indicate that aberrant MIWI-/MILI-bound pachytene piRNA profiles in spermatids do not affect fertilization, early embryonic development, or fertility of the offspring, suggesting that pachytene piRNAs might not be required for paternal transgenerational epigenetic inheritance in mice.

Transcriptional Framework of Male Gametogenesis in the Liverwort Marchantia polymorpha L

In land plants, there are two types of male gametes: one is a non-motile sperm cell which is delivered to the egg cell by a pollen tube, and the other is a motile sperm cell with flagella. The molecular mechanism underlying the sexual reproduction with the egg and pollen-delivered sperm cell is well understood from studies using model plants such as Arabidopsis and rice. On the other hand, the sexual reproduction with motile sperm has remained poorly characterized, due to the lack of suitable models. Marchantia polymorpha L. is a model basal land plant with sexual reproduction involving an egg cell and bi-flagellated motile sperm. To understand the differentiation process of plant motile sperm, we analyzed the gene expression profile of developing antheridia of M. polymorpha. We performed RNA-sequencing experiments and compared transcript profiles of the male sexual organ (antheridiophore and antheridium contained therein), female sexual organ (archegoniophore) and a vegetative organ (thallus). Transcriptome analysis showed that the antheridium expresses nearly half of the protein-coding genes predicted in the genome, but it also has unique features. The antheridium transcriptome shares some common features with male gamete transcriptomes of angiosperms and animals, and homologs of genes involved in male gamete formation and function in angiosperms and animals were identified. In addition, we showed that some of them had distinct expression patterns in the spermatogenous tissue of developing antheridia. This study provides a transcriptional framework on which to study the molecular mechanism of plant motile sperm development in M. polymorpha as a model.

Sperm-borne miRNAs and endo-siRNAs are important for fertilization and preimplantation embryonic development

Although it is believed that mammalian sperm carry small noncoding RNAs (sncRNAs) into oocytes during fertilization, it remains unknown whether these sperm-borne sncRNAs truly have any function during fertilization and preimplantation embryonic development. Germline-specific Dicer and Drosha conditional knockout (cKO) mice produce gametes (i.e. sperm and oocytes) partially deficient in miRNAs and/or endo-siRNAs, thus providing a unique opportunity for testing whether normal sperm (paternal) or oocyte (maternal) miRNA and endo-siRNA contents are required for fertilization and preimplantation development. Using the outcome of intracytoplasmic sperm injection (ICSI) as a readout, we found that sperm with altered miRNA and endo-siRNA profiles could fertilize wild-type (WT) eggs, but embryos derived from these partially sncRNA-deficient sperm displayed a significant reduction in developmental potential, which could be rescued by injecting WT sperm-derived total or small RNAs into ICSI embryos. Disrupted maternal transcript turnover and failure in early zygotic gene activation appeared to associate with the aberrant miRNA profiles in Dicer and Drosha cKO spermatozoa. Overall, our data support a crucial function of paternal miRNAs and/or endo-siRNAs in the control of the transcriptomic homeostasis in fertilized eggs, zygotes and two-cell embryos. Given that supplementation of sperm RNAs enhances both the developmental potential of preimplantation embryos and the live birth rate, it might represent a novel means to improve the success rate of assisted reproductive technologies in fertility clinics.

Fourteen babies born after round spermatid injection into human oocytes

During the human in vitro fertilization procedure in the assisted reproductive technology, intracytoplasmic sperm injection is routinely used to inject a spermatozoon or a less mature elongating spermatid into the oocyte. In some infertile men, round spermatids (haploid male germ cells that have completed meiosis) are the most mature cells visible during testicular biopsy. The microsurgical injection of a round spermatid into an oocyte as a substitute is commonly referred to as round spermatid injection (ROSI). Currently, human ROSI is considered a very inefficient procedure and of no clinical value. Herein, we report the birth and development of 14 children born to 12 women following ROSI of 734 oocytes previously activated by an electric current. The round spermatids came from men who had been diagnosed as not having spermatozoa or elongated spermatids by andrologists at other hospitals after a first Micro-TESE. A key to our success was our ability to identify round spermatids accurately before oocyte injection. As of today, all children born after ROSI in our clinic are without any unusual physical, mental, or epigenetic problems. Thus, for men whose germ cells are unable to develop beyond the round spermatid stage, ROSI can, as a last resort, enable them to have their own genetic offspring.

mir-34b/c and mir-449a/b/c are required for spermatogenesis, but not for the first cleavage division in mice

Mammalian sperm are carriers of not only the paternal genome, but also the paternal epigenome in the forms of DNA methylation, retained histones and noncoding RNAs. Although paternal DNA methylation and histone retention sites have been correlated with protein-coding genes that are critical for preimplantation embryonic development, physiological evidence of an essential role of these epigenetic marks in fertilization and early development remains lacking. Two miRNA clusters consisting of five miRNAs (miR-34b/c and miR-449a/b/c) are present in sperm, but absent in oocytes, and miR-34c has been reported to be essential for the first cleavage division in vitro. Here, we show that both miR-34b/c- and miR-449-null male mice displayed normal fertility, and that intracytoplasmic injection of either miR-34b/c- or miR-449-null sperm led to normal fertilization, normal preimplantation development and normal birth rate. However, miR-34b/c and miR-449 double knockout (miR-dKO) males were infertile due to severe spermatogenic disruptions and oligo-astheno-teratozoospermia. Injection of miR-dKO sperm into wild-type oocytes led to a block at the two-pronucleus to zygote transition, whereas normal preimplantation development and healthy pups were obtained through injection of miR-dKO round spermatids. Our data demonstrate that miR-34b/c and miR-449a/b/c are essential for normal spermatogenesis and male fertility, but their presence in sperm is dispensable for fertilization and preimplantation development.

A mutation study of sperm head shape and motility in the mouse: lessons for the clinic

Mouse mutants that show effects on sperm head shape, the sperm tail (flagellum), and motility were analysed in a systematic way. This was achieved by grouping mutations in the following classes: manchette, acrosome, Sertoli cell contact, chromatin remodelling, and mutations involved in complex regulations such as protein (de)phosphorylation and RNA stability, and flagellum/motility mutations. For all mutant phenotypes, flagellum function (motility) was affected. Head shape, including the nucleus, was also affected in spermatozoa of most mouse models, though with considerable variation. For the mutants that were categorized in the flagellum/motility group, generally normal head shapes were found, even when the flagellum did not develop or only poorly so. Most mutants are sterile, an occasional one semi-sterile. For completeness, the influence of the sex chromosomes on sperm phenotype is included. Functionally, the genes involved can be categorized as regulators of spermiogenesis. When extrapolating these data to human sperm samples, in vivo selection for motility would be the tool for weeding out the products of suboptimal spermiogenesis and epididymal sperm maturation. The striking dependency of motility on proper sperm head development is not easy to understand, but likely is of evolutionary benefit. Also, sperm competition after mating can never act against the long-term multi-generation interest of genetic integrity. Hence, it is plausible to suggest that short-term haplophase fitness i.e., motility, is developmentally integrated with proper nucleus maturation, including genetic integrity to protect multi-generation fitness. We hypothesize that, when the prime defect is in flagellum formation, apparently a feedback loop was not necessary as head morphogenesis in these mutants is mostly normal. Extrapolating to human-assisted reproductive techniques practice, this analysis would supply the arguments for the development of tools to select for motility as a continuous (non-discrete) parameter.

Reduced pachytene piRNAs and translation underlie spermiogenic arrest in Maelstrom mutant mice

Pachytene piRNAs are a class of Piwi-interacting small RNAs abundant in spermatids of the adult mouse testis. They are processed from piRNA primary transcripts by a poorly understood mechanism and, unlike fetal transposon-derived piRNAs, lack complementary targets in the spermatid transcriptome. We report that immunopurified complexes of a conserved piRNA pathway protein Maelstrom (MAEL) are enriched in MIWI (Piwi partner of pachytene piRNAs), Tudor-domain proteins and processing intermediates of pachytene piRNA primary transcripts. We provide evidence of functional significance of these complexes in Mael129 knockout mice that exhibit spermiogenic arrest with acrosome and flagellum malformation. Mael129-null mutant testes possess low levels of piRNAs derived from MAEL-associated piRNA precursors and exhibit reduced translation of numerous spermiogenic mRNAs including those encoding acrosome and flagellum proteins. These translation defects in haploid round spermatids are likely indirect, as neither MAEL nor piRNA precursors associate with polyribosomes, and they may arise from an imbalance between pachytene piRNAs and MIWI.

In vivo serial sampling of epididymal sperm in mice

This study was undertaken to refine the techniques of in vivo collection of sperm in the mouse. The principal objective was to offer a viable, safe and reliable method for serial collection of in vivo epididimary sperm through the direct puncture of the epididymis. Six C57Bl/6J males were subjected to the whole experiment. First we obtain a sperm sample of the right epididymis, and perform a vasectomy on the left side. This sample was used in an in vitro fertilization (IVF) experiment while the males were individually housed for 10 days to let them recover from the surgery, and then their fertility was tested with natural matings until we obtained a litter of each one. After that, the animals were subjected another time to the same process (sampling, recover and natural mating). The results of these experiments were a fertilization average value of 56.7%, and that all the males had a litter in the first month after the natural matings. This study documented the feasibility of the epididimary puncture technique to in vivo serial sampling of sperm in the mouse.

Loss-of-function mutations in TBC1D20 cause cataracts and male infertility in blind sterile mice and Warburg micro syndrome in humans

blind sterile (bs) is a spontaneous autosomal-recessive mouse mutation discovered more than 30 years ago. Phenotypically, bs mice exhibit nuclear cataracts and male infertility; genetic analyses assigned the bs locus to mouse chromosome 2. In this study, we first positionally cloned the bs locus and identified a putative causative mutation in the Tbc1d20 gene. Functional analysis established the mouse TBC1D20 protein as a GTPase-activating protein (GAP) for RAB1 and RAB2, and bs as a TBC1D20 loss-of-function mutation. Evaluation of bs mouse embryonic fibroblasts (mEFs) identified enlarged Golgi morphology and aberrant lipid droplet (LD) formation. Based on the function of TBC1D20 as a RABGAP and the bs cataract and testicular phenotypes, we hypothesized that mutations in TBC1D20 may contribute to Warburg micro syndrome (WARBM); WARBM constitutes a spectrum of disorders characterized by eye, brain, and endocrine abnormalities caused by mutations in RAB3GAP1, RAB3GAP2, and RAB18. Sequence analysis of a cohort of 77 families affected by WARBM identified five distinct TBC1D20 loss-of-function mutations, thereby establishing these mutations as causative of WARBM. Evaluation of human fibroblasts deficient in TBC1D20 function identified aberrant LDs similar to those identified in the bs mEFs. Additionally, our results show that human fibroblasts deficient in RAB18 and RAB3GAP1 function also exhibit aberrant LD formation. These findings collectively indicate that a defect in LD formation/metabolism may be a common cellular abnormality associated with WARBM, although it remains unclear whether abnormalities in LD metabolism are contributing to WARBM disease pathology.

Bioinformatic identification of novel elements potentially involved in messenger RNA fate control during spermatogenesis

In eukaryotic cells, 3' untranslated regions (3' UTRs) of mRNA transcripts contain conserved sequence elements (motifs), which, once bound by RNA-binding proteins, can affect mRNA stability and translational efficacy. Despite abundant sequences contained within the 3' UTRs, only a limited number of motifs are known to interact with RNA-binding proteins and have a role in mRNA fate control. Spermatogenesis represents an excellent in vivo model for studying posttranscriptional regulation of gene expression because numerous mRNAs are transcribed in late pachytene spermatocytes and/or round spermatids, but their translation will not occur until many hours or even days later, when they have developed into elongated spermatids, in which transcription has long been shut off because of the increasingly condensed chromatin. Translationally suppressed mRNAs are sequestered and confined to ribonuclear protein particles, and their loading onto the ribosomes marks their translation. By bioinformatic sequence analyses of the 3' UTRs of translationally suppressed mRNAs during spermatogenesis, we identified numerous novel sequence elements overrepresented in the transcripts subject to posttranscriptional regulation than in the unregulated transcripts. These include AU(U/A)(U/A)UGAGU and (A/U)AUUA(U/C/G) for genes translationally upregulated in early spermiogenesis, and (G/A)GUACG(U/C/A)(A/U)(A/U) and UGUAGC for genes translationally upregulated in late spermiogenesis. The bioinformatic approach reported in this study can be adapted for rapid discovery of novel regulatory elements involved in mRNA fate control in a wide range of tissues or organs.

Molecular analysis of the PArkin co-regulated gene and association with male infertility

OBJECTIVE

To investigate the potential role of PArkin co-regulated gene (PACRG) in human male infertility.

DESIGN

Case-control study.

SETTING

Academic reproductive biology department.

PATIENT(S)

Blood samples were obtained from 610 patients and 156 normal control subjects.

INTERVENTION(S)

Genomic DNA was used as template for polymerase chain reaction amplification of the PACRG promoter and coding exons. The amplified fragments were tested for DNA sequence variations by direct sequencing and restriction enzyme analysis.

MAIN OUTCOME MEASURE(S)

Gene structure and sequence alterations of PACRG in infertile male patients.

RESULT(S)

The structure of PACRG was determined to comprise 5 coding exons, generating a single transcript in the testis which encoded a predicted protein of 257 amino acids. No pathogenic mutations were identified; however, a variant in the promoter of PACRG was shown to be significantly associated with azoospermia, but not oligospermia, in the case-control cohort.

CONCLUSION(S)

Mutation of PACRG was not identified as a cause of male infertility, but variation in the promoter was demonstrated to be a risk factor associated with azoospermia.

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.

Lack of Spem1 causes aberrant cytoplasm removal, sperm deformation, and male infertility

We identified a previously uncharacterized gene, spermatid maturation 1 (Spem1), encoding a protein exclusively expressed in the cytoplasm of steps 14-16 elongated spermatids in the mouse testis. This protein contains no known functional domains and is highly conserved across mammalian species. Male mice deficient in Spem1 were completely infertile because of deformed sperm characterized by a bent head wrapped around by the neck and the middle piece of the tail. We show that lack of Spem1 causes failure of the cytoplasm to become loose and detach from the head and the neck region of the developing spermatozoa. Retained cytoplasmic components mechanically obstruct the straightening of the sperm head and the stretching of the growing tail, leading to the bending of the head in the neck, followed by the wrapping of the head by the neck or the middle piece of the sperm tail. Our study reveals that proper cytoplasm removal is a genetically regulated process requiring the participation of Spem1 and that lack of Spem1 causes sperm deformation and male infertility.

Preservation of ejaculated mouse spermatozoa from fertile C57BL/6 and infertile Hook1/Hook1 mice collected from the uteri of mated females

Methods routinely used to preserve mouse spermatozoa require that the male be killed to recover spermatozoa from the epididymides. Here we obtained multiple samples of ejaculated spermatozoa from normal fertile C57BL/6 and infertile Hook1/Hook1 (formerly known as azh/azh) mutant males from uteri after mating, thus avoiding termination of the males. Ejaculated sperm were preserved by conventional cryopreservation or by rapid freezing without cryoprotection, and were injected into the oocytes by intracytoplasmic sperm injection (ICSI). The proportions of oocytes that survived, became activated, and developed into two-cell embryos were similar when comparing the two preservation methods in wild-type versus Hook1/Hook1 mice and tested mice versus controls (fresh and rapid-frozen epididymal and fresh ejaculated sperm). Two-cell embryos were transferred into the oviducts of pseudopregnant females, and fetal development was examined at Day 15 of gestation. A total of 39%-54% of transferred embryos produced with preserved ejaculated sperm implanted. Live, normal fetuses (11%-17%) were obtained in all examined groups and from all males included in the study. More implants (71%-82%) and fetuses (28%-31%) were noted in controls. Lower developmental potentials of embryos produced with preserved ejaculated sperm might be due to their capacitation status; the majority of sperm retrieved from the uterus were capacitated. This study bears significance for the maintenance and distribution of novel mouse strains. The method is applicable for all types of mice, including those with male infertility syndromes. The sole requirement is that the male of interest is able to copulate and its ejaculate contains spermatozoa.

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.

The relationship between sperm morphology and in vitro fertilization ability in mice

In vitro fertilization (IVF) is widely used in reproduction research, but the sperm of some inbred strains of mice yield low fertilization rates in IVF. To determine the cause of this problem, we examined the effect of epididymal sperm morphology, in particular, tail bending and the presence and type of cytoplasmic droplet (CD), on fertilizability in vitro. Sperm suspensions were obtained from the following five strains: C57BL/6J, BALB/cA, C3H/HeN, DBA/2J, and 129 x 1/SvJ. The sperm were fixed in 10% formalin and three parts of the sperm, namely the head, tail, and CD, were examined. We recorded the proportion of abnormal sperm heads and hairpins at the neck; tails were categorized as straight, proximal bent, or distal bent; and the CDs were categorized as none, light-type, and heavy-type. Based on these parameters, we determined the correlations between sperm morphology and fertilizability in vitro, as judged by IVF using ICR oocytes. The proportion of sperm with a hairpin neck was higher in strain C57BL/6J, while abnormal head morphology occurred significantly more often in strain BALB/cA. The percentage of sperm with a proximal bent tail was highest in strain DBA/2J and lowest in strain 129 x 1/SvJ. A heavy-type CD was observed more frequently in the 129 x 1/SvJ and C57BL/6J strains than in the other three strains in which a light-type CD predominated. The rank order of the fertilization rates was 129 x 1/SvJ < C57BL/6J < C3H/HeN < BALB/cA < DBA/2J. In addition, fertilization rate was positively correlated with a proximal bent tail, but negatively correlated with a heavy-type CD and distal bent tail. This new classification system establishes that the morphological characteristics of epididymal sperm differ among inbred strains of mice and that tail and CD morphology are closely related to fertilization ability in IVF. Thus, our results provide a novel method for assessing the quality of mouse sperm used for IVF.

Knockout mouse models of sperm flagellum anomalies

To date, 21 knockout mouse models are known to bear specific anomalies of the sperm flagellum structures leading to motility disorders. In addition, genes responsible for flagellar defects of two well-known spontaneous mutant mice have recently been identified. These models reveal genetic factors, which are required for the proper assembly of the axoneme, the annulus, the mitochondrial sheath and the fibrous sheath. Many of these genetic factors follow unexpected cellular pathways to act on sperm flagellum morphogenesis. These mouse models may bear anomalies which are restricted to the spermatozoa or display more complex phenotypes that often include neuropathies and/or cilia-related diseases. In human, several structural disorders of the sperm flagellum found in brothers or consanguineous men probably have a genetic origin, but the genes involved have not yet been identified. The mutant mice we present in this review are invaluable models, which can be used to identify potential candidate genes for infertile men with specific sperm flagellum anomalies.

The effects of deletions of the mouse Y chromosome long arm on sperm function--intracytoplasmic sperm injection (ICSI)-based analysis

In mouse and man, Y chromosome deletions are frequently associated with spermatogenic defects. XY(Tdy)(m1)qdelSry males have an extensive Yq deletion that almost completely abolishes the expression of two gene families, Ssty and Sly, located within the male-specific region of the mouse Y long arm. These males exhibit severe sperm defects and sterility. XY(RIII)qdel males have a smaller interstitial Yq deletion, removing approximately two thirds of Ssty/Sly gene copies, and display an increased incidence of mild sperm head anomalies with impairment of fertility and an intriguing distortion in the sex ratio of offspring in favor of females. Here we used intracytoplasmic sperm injection (ICSI) to investigate the functional capacity of sperm from these Yq deletion males. Any selection related to the ability of sperm to fertilize in vitro is removed by ICSI, and we obtained two generations of live offspring from the infertile males. Genotyping of ICSI-derived offspring revealed that the Y(Tdym1)qdel deletion does not interfere with production of Y chromosome-bearing gametes, as judged from the frequency of Y chromosome transmission to the offspring. ICSI results for XY(RIII)qdel males also indicate that there is no deficiency of Y sperm production in this genotype, although the data show an excess of females following in vitro fertilization and natural mating. Our findings suggest that 1) Yq deletions in mice do not bias the primary sex ratio and 2) Y(RIII)qdel spermatozoa have poorer fertilizing ability than their X-bearing counterparts. Thus, a normal complement of the Ssty and/or Sly gene families on mouse Yq appears necessary for normal sperm function.

SUMMARY

ICSI was successfully used to reproduce infertile mice with Yq deletions, and the analysis of sperm function in obtained offspring demonstrated that gene families located within the deletion interval are necessary for normal sperm function.

Reproductive and neurological Quaking(viable) phenotypes in a severe combined immune deficient mouse background

The quaking(viable) (qkv) mutation, a spontaneous deletion of a multigenic region encompassing roughly 1 Mb at 5.9 cM on the proximal end of mouse chromosome 17, causes severe trembling in all homozygous animals and infertility in all homozygous males. Physiologically, quaking mice exhibit dysmyelination and postmeiotic spermatogenic arrest. Molecular defects in Qkv mice occur in the affected tissues, indicating the primary causes of these pathologies are cell autonomous. However, because both the reproductive and neurological defects are in immune-privileged sites and because some similar pathologies at both sites have been shown to be immune mediated, we tested whether the immune system participates secondarily in manifestation of Qkv phenotypes. The qkv mutation was bred into a severe combined immune-deficient mouse line (SCID; devoid of mature B and T cells) and penetrance of the neurological and the male sterile phenotypes was measured. Results showed that neither defect was ameliorated in the immune-deficient background. We conclude that the Qkv pathologies do not likely involve a B- or T-cell-dependent response against these immune-privileged sites.

Alkylated Imino Sugars, Reversible Male Infertility-Inducing Agents, Do Not Affect the Genetic Integrity of Male Mouse Germ Cells During Short-Term Treatment Despite Induction of Sperm Deformities1

Reversible infertility can be induced in male mice by oral administration of the alkylated imino sugars N-butyldeoxynojirimycin (NB-DNJ) and N-butyldeoxygalactonojirimycin (NB-DGJ). Spermatozoa of these mice have grossly misshapen heads and reduced motility. Because NB-DNJ and related compounds may hold promise as nonhormonal male contraceptives, a comprehensive examination of their effects on male reproduction is necessary. To this end, we further examined reproductive properties of the dysmorphic spermatozoa that are produced after short-term imino sugar administration at the minimal dose that completely abolishes the ability of male C57BL/6 mice to produce offspring by natural mating. Here, we report that, in vitro, the abnormal spermatozoa from the NB-DNJ- and NB-DGJ-treated mice were unable to fertilize oocytes. In addition, we investigated whether the imino sugars damage the genetic integrity of spermatozoa. To test this, we microsurgically injected deformed spermatozoa from imino sugar-treated males into oocytes. The deformed spermatozoa from the testis were able to activate oocytes very efficiently, but those from the cauda epididymis often failed to do so. This problem was overcome when the sperm-injected oocytes were treated with a parthenogenetic agent, Sr(2+). Oocytes injected with the misshapen spermatozoa from NB-DNJ- and NB-DGJ-treated mice developed (with or without Sr(2+) treatment) into live offspring that grew normally and were normally fertile. This indicates that during short-term administration, alkylated imino sugars alter sperm morphology and physiology but do not diminish the genetic potential of spermatozoa.

Intracytoplasmic sperm injection effects in infertile azh mutant mice

Several reports in the literature describe men with infertility resulting from abnormal sperm head shape or decapitation defects of their spermatozoa. These defects are similar to those shown for the spermatozoa from azh (abnormal spermatozoon head shape) mice. The present study examines the efficiency and effects of intracytoplasmic sperm injection (ICSI) in successive generations of azh mice generated with this method. Three successive generations of azh mice were produced with ICSI. In all three ICSI series, more than 80% of 2-cell embryos were obtained, and more than 35% of embryos transferred gave rise to normal live offspring. In addition, ICSI was used to cross homozygous azh/azh males with homozygous azh/azh females, and live offspring were obtained. The ICSI-derived males were tested for their fecundity and abnormalities of sperm morphology. Spermatozoa from ICSI-derived azh/+ males did not show any impairment of fecundity in in vitro fertilization. These spermatozoa successfully fertilized oocytes from both C57BL/6 and B6D2F1 females, with fertilization rates ranging from 70%- 92%. The proportion of morphologically normal spermatozoa was similar in azh/+ males from three successive generations of ICSI (57.8%, 54.8%, and 49.0%, respectively), and no differences were noted when comparing ICSI-derived males with males derived by mating (57.6%) and with wild-type controls (61.6%). Detailed analysis differentiating between specific types of anomalies of sperm morphology did not reveal significant differences among the examined groups. The results of the present study demonstrate that ICSI does not enhance the azh mutation phenotype in the offspring and brings no risks when applied continuously. Moreover, serial (successive generations) ICSI is highly efficient in maintaining valuable mice with fertility problems.

Propagation of an infertile hermaphrodite mouse lacking germ cells by using nuclear transfer and embryonic stem cell technology

Animals generated by systematic mutagenesis and routine breeding are often infertile because they lack germ cells, and maintenance of such lines of animals has been impossible. We found a hermaphrodite infertile mouse in our colony, a genetic male with an abnormal Y chromosome lacking developing germ cells. We tried to clone this mouse by conventional nuclear transfer but without success. ES cells produced from blastocysts, which had been cloned by using somatic cell nuclear transfer (ntES cells) from this mouse, were also unable to produce offspring when injected into enucleated oocytes. Although we were able to produce two chimeric offspring using these ntES cells by tetraploid complementation, they were infertile, because they also lacked developing germ cells. However, when such ntES cells were injected into normal diploid blastocysts, many chimeric offspring were produced. One such male offspring transmitted hermaphrodite mouse genes to fertile daughters via X chromosome-bearing sperm. Thus, ntES cells were used to propagate offspring from infertile mice lacking germ cells.

Intracytoplasmic injection of spermatozoa and spermatogenic cells: its biology and applications in humans and animals

Intracytoplasmic sperm injection (ICSI) has become the method of choice to overcome male infertility when all other forms of assisted fertilization have failed. Animals in which ICSI has produced normal offspring include many species. Success rate with normal spermatozoa is well above 50% in the mouse but ICSI success rates in other animals have been low, ranging from 0.3 to 16.5%. Mouse ICSI revealed that spermatozoa that cannot participate in normal fertilization can produce normal offspring by ICSI, provided their nuclei are genomically intact. Human ICSI using infertile spermatozoa has been highly successful perhaps because of the intrinsic instability of human sperm plasma membrane. The health of children born after ICSI and other assisted fertilization techniques is of major concern. Careful analyses suggest that higher incidences of congenital malformations and/or low birth weights after assisted fertilization are largely attributable to parental genetic background and increased incidence of multiple births, rather than to the techniques of assisted fertilization. Since the physiological and nutritional environments of developing embryos may cause persisting alteration in DNA methylation, extreme caution must be exercised in handling gametes and embryos in vitro. In the mouse, round spermatid injection (ROSI) has been routinely successful but its use in humans is controversial. Whether human ROSI and assisted fertilization involving younger spermatogenic cells are medically safe must be the subject of further investigations.

Genetic control of spermiogenesis: insights from the CREM gene and implications for human infertility

Male germ cell differentiation requires a highly cell-specific gene expression programme that is achieved by unique chromatin remodelling, transcriptional control, and the expression of testis-specific genes or isoforms. The regulatory processes governing gene expression in spermatogenesis have fundamentally unique requirements, including meiosis, ongoing cellular differentiation and a peculiar chromatin organization. The signalling cascades and the downstream effectors contributing to the programme of spermatogenesis are currently being unravelled, revealing the unique features of germ cell regulatory circuits. This paper reports on the unique role that CREM exerts as a master regulator. Targeted inactivation of the genes encoding CREM and ACT has been achieved. ACT selectively associates with KIF17b, a kinesin motor protein highly expressed in germ cells. It has been found that KIF17b directly determines the intracellular localization of ACT. Thus, the activity of a transcriptional co-activator is intimately coupled to the function of a kinesin via tight regulation of its intracellular localization. The conservation of these elements and of their regulatory functions in human spermatogenesis indicates that they are likely to provide important insights into understanding the molecular mechanisms of human infertility.

Cloning and assisted reproductive techniques: Influence on early development and adult phenotype

Over the past 40 years, our increased understanding and development of cell and molecular biology has allowed even greater advances in reproductive biology. This is most evident by the development of various aspects of assisted reproductive techniques (ART), generation of transgenic animals, and most recently generation of mammals through somatic cell cloning. To date, cloning from adult somatic cells has been successful in at least 10 mammalian species. Although generating viable cloned mammals from adult cells is technically feasible and the list of successes will only continue to grow with time, prenatal and perinatal mortality is high and live cloned offspring have not been without health problems. The success of many of the proposed applications of the cloning technique obviously depends upon the health and survival of founder animals generated by nuclear transfer. This article summarizes the health consequences of cloning in mice, and discusses possible mechanisms through which these conditions may arise. In addition, we discuss the effects of ART in animal models and in humans. ART also involves some of the same procedures used in cloning, and there are reports that offspring generated by ART sometimes display aberrant phenotypes as well. It is important to point out that although these techniques do sometimes produce abnormalities, the majority of offspring are born apparently normal and survive to adulthood. Additionally, we must emphasize that the effects of ART and cloning observed in animal models do not necessarily indicate that they will occur in humans. In this article, we review studies examining the phenotype of animals generated by cloning and various ART, and discuss clinical implications of these findings.

Microinsemination and Nuclear Transfer Using Male Germ Cells

Microinsemination has been widely used in basic reproductive research and in human-assisted reproductive technology for treating infertility. Historically, microinsemination in mammals started with research on the golden hamster; since then, it has provided invaluable information on the mechanisms of mammalian fertilization. Thanks to advances in animal genetic engineering and germ-cell technologies, microinsemination techniques are now used extensively to identify the biological significance of genes of interest or to confirm the genetic normality of gametes produced by experimental manipulations in vitro. Fortunately, in mice, high rates of embryo development to offspring can be obtained so long as postmeiotic spermatogenic cells are used as male gametes-that is, round spermatids, elongated spermatids, and spermatozoa. For some other mammalian species, using immature spermatogenic cells significantly decreases the efficiency of microinsemination. Physically unstable chromatin and low oocyte-activating capacity are the major causes of fertilization failure. The youngest male germ cells, including primordial germ cells and gonocytes, can be used in the construction of diploid embryos by nuclear-transfer cloning. The cloned embryos obtained in this way provide invaluable information on the erasure and reestablishment of genomic imprinting in germ cells.

Deletion of the Parkin coregulated gene causes male sterility in the quaking(viable) mouse mutant

Quaking(viable) (qk(v)) is a recessive neurological mouse mutation with severe dysmyelination of the CNS and spermiogenesis failure. The molecular lesion in the qk(v) mutant is a deletion of approximately 1 Mb on mouse chromosome 17 that alters the expression of the qk gene in oligodendrocytes. Complementation analysis between the qk(v) mutation and qk mutant alleles generated through chemical mutagenesis showed that the male sterility is a distinctive feature of the qk(v) allele. This observation suggested that the sperm differentiation defect in qk(v) is due to the deletion of a gene(s) distinct from qk. Here, we demonstrate that the deletion of Pacrg is the cause of male sterility in the qk(v) mutant. Pacrg is the mouse homologue of the human PARKIN-coregulated gene (PACRG), which encodes for a protein whose biochemical function remains unclear. We show that Pacrg is highly expressed in the testes in both mice and humans. In addition, the expression pattern of Pacrg during spermiogenesis suggests that it plays a role in sperm differentiation. In support of this hypothesis, we show that transgenic expression of Pacrg in testes restores spermiogenesis and fertility in qk(v) males. This finding provides the first in vivo evidence, to our knowledge, for the function of Pacrg in a model organism. Immunolocalization experiments on isolated spermatozoa show that the Pacrg protein is present in mature sperm. Remarkably, the mammalian Pacrg protein shares significant sequence similarities with gene products from flagellated protozoans, suggesting that Pacrg may be necessary for proper flagellar formation in many organisms.