Germ line stem cell competition in postnatal mouse testes

Niche is believed to affect stem cell behavior. In self-renewing systems for which functional transplantation assays are available, it has long been assumed that stem cells are fixed in the niche and that ablative treatments to remove endogenous stem cells are required for successful donor engraftment. Our results demonstrate that enriched populations of donor stem cells can produce long-lasting spermatogenic colonies in testes of immature and mature, nonablated mice, albeit at a lower frequency than in ablated mice. Colonization of nonablated recipient testes by neonate, pup, and cryptorchid adult donor spermatogonial stem cells demonstrates that competition for niche begins soon after birth and that endogenous stem cells influence the degree and pattern of donor cell colonization. Thus, a dynamic relationship between stem cell and niche exists in the testis, as has been suggested for hematopoiesis. Therefore, similar competitive properties of donor stem cells may be characteristic of all self-renewing systems.     

睾丸生殖细胞的凋亡及其调控

睾丸生殖细胞在分化过程中存在自发性和诱发性凋亡,这是清除过量或异常生殖细胞的一种重要途径。生殖细胞的凋亡涉及内分泌、细胞社会组成和基因等多因素的调控。深入了解生殖细胞凋亡的调控机制,明确决定睾丸生殖细胞（Ｇｅｒｍ ｃｅｌｌｓ,Ｇｃ）凋亡机制的分子组成,将为治疗男性不育和开发男性避孕药物奠定理论基础。     

Germ cell transplantation from large domestic animals into mouse testes

Donor-derived spermatogenesis after spermatogonial transplantation to recipient animals could serve as a novel approach to manipulate the male germ line in species where current methods of genetic modification are still inefficient. The objective of the present study was to investigate germ cell transplantation from boars, bulls, and stallions, which are economically important domestic animals, to mouse recipients. Donor testis cells (fresh, cryopreserved, or cultured for 1 month) were transplanted into testes of immunodeficient recipient mice in which endogenous spermatogenesis had been destroyed. Recipient testes were analyzed from 1 to > 12 months after transplantation for the presence of donor germ cells by donor-specific immunohistochemistry. Donor cells were present in most recipient testes with species-dependent differences in pattern and extent of colonization. Porcine donor germ cells formed chains and networks of round cells connected by intercellular bridges but later stages of donor-derived spermatogenesis were not observed. Transplanted bovine testis cells initially appeared similar but then developed predominantly into fibrous tissue within recipient seminiferous tubules. Few equine germ cells proliferated in mouse testes with no obvious difference between cells recovered from a scrotal or a cryptorchid donor testis. The pattern of colonization after transplantation of cultured cells did not resemble spermatogonial proliferation. These results indicate that fresh or cryopreserved germ cells from large animals can colonize the mouse testis but do not differentiate beyond the stage of spermatogonial expansion. Species-specific differences in the compatibility of large animal donors and mouse recipients were detected which cannot be predicted solely on the basis of phylogenetic distance between donor and recipient species.     

Germ cell suicide: new insights into apoptosis during spermatogenesis

Mature sperm are the product of a precisely regulated developmental sequence in which germ cell proliferation, differentiation, self-renewal and apoptosis are carefully controlled. The control of germ cell apoptosis during spermatogenesis is especially important. It is mediated by signals derived from the Sertoli cells with which each germ cell is closely associated, as well as by signals originating outside the testis. A greater understanding of these signals is emerging from studies of the spermatogenic defects of genetically modified animals. In particular, the intracellular signaling cascades which ultimately determine germ cell fate are being illuminated by recent studies of the Bcl-2 protein family. This review summarises the crucial role which stringently regulated apoptosis plays in the production of male gametes.     

Androgens and oestrogens in normal and cryptorchid stallions.

Total androgens, testosterone and total oestrogens were measured in twenty-one intact, nine unilaterally cryptorchid, three bilaterally cryptorchid stallions and four geldings. Total oestrogens were significantly higher (P less than 0-005) and total androgens significantly lower (P less than 0-05) in the bilateral cryptorchid compared to other groups. There was a significant (P less than 0-025) day and night variation in total androgen levels. Thyroidectomized and intact animals showed a marked decrease in total androgen as well as testosterone levels during the winter period thus showing an effect of season on androgenic function of the testis. Disappearance rate of total and androgens following castration was extremely rapid and levels were undectable within 12 hr. Sexual stimulation appeared to increase total androgen levels. Testosterone, androstenedione, dihydrotestosterone, androstandiols, and androstenediol were identified in spermatic vein blood. Dihydrotestosterone was measured in fluid from the cauda epididymidis.     

Annual cycle of the Sertoli cell population in adult stallions

Stereological methods were employed in two experiments with adult stallions: to confirm seasonal variation in number of Sertoli cells and to characterize the annual cycle of the Sertoli cell population. In the first experiment, testes from 28 adult (4-20 years old) horses obtained in the non-breeding season (December-January) were compared to testes from 28 adult horses in the breeding season (June-July). Sertoli cell numbers were calculated from the nuclear volume density, parenchymal volume, and volume of an individual Sertoli cell nucleus determined by reconstruction of serial sections or from average height and width measurements. The number of Sertoli cells per testis was significantly greater in the breeding season. In a second experiment involving 43-48 adult horses in each 3-month period, the Sertoli cell population was higher (P less than 0.05) in May-July than other periods and higher (P less than 0.01) than in November-January. These combined studies confirm seasonal differences in the Sertoli cell numbers per testis and define the annual cycle of the Sertoli cell population in adult stallions.     

Morphology of spermatozoa in semen from stallions of normal fertility.

Semen samples were collected from 3 fertile stallions by means of an 'open' artificial vagina and examined under scanning and transmission electron microscopy. The stallion spermatozoon has many features in common with that of other mammals but differs specifically in that it has an asymmetric head, an abaxial position of the tail and an acrosome of small volume. The presence of microtubules in the neck is also a characteristic of stallion spermatozoa.     

Sexual behavior and serum concentrations of reproductive hormones in normal stallions

Recently, it has been reported that impotence in the stallion has a physiological basis that involves decreased serum concentrations of luteinizing hormone (LH) and estradiol-17beta, but not testosterone. We have found such a hormonal profile in two of nine stallions studied during an ongoing investigation of the endocrinology of the normal stallion. Nevertheless, both of these stallions possessed vigorous libido and normal seminal characteristics. We conclude that the hormonal profile of low LH, low estradiol and normal testosterone, although it may accompany impotence in the stallion, is not predictive of, or causally related to, abnormalities in sexual behavior.     

Fas-Fas ligand system as a possible mediator of spermatogenic cell apoptosis in human maturation-arrested testes

To elucidate the mechanism of maturation arrest, known as one of the male infertility, we addressed whether germ cell apoptosis occurs during maturation arrest, and if so, whether Fas and Fas ligand expressions are involved in the apoptosis. By electron microscopy and terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labeling (TUNEL), typical apoptotic features were frequently found around the spermatocytic stage in maturation arrest, compared to that in normal testes. When paraffin-embedded sections reacted with anti-Fas antiserum, staining for Fas was found in the plasma membranes of spermatocytes in the maturation-arrested testes, while no positive spermatogenic cells were seen in the normal testes. On the other hand, positive immunostaining for Fas ligand was restricted to Sertoli cells in the maturation-arrested testes as well as in the normal testes, although the intensity of staining for Fas ligand in normal testicular Sertoli cells was much weaker than that of maturation-arrested ones. Thus, these findings demonstrate that "maturation arrest" is characterized by frequent apoptosis of spermatocytes, and that Fas and Fas ligand staining are associated with a high frequency of apoptosis.     

Germ cell transplantation in goats

Transplantation of spermatogonial stem cells provides a unique approach for the study of spermatogenesis and manipulation of the male germ line. This technique may also offer an alternative to the currently inefficient methods of producing transgenic domestic animals. We have recently established the technique of spermatogonial transplantation, originally developed in laboratory rodents, in pigs, and this study was aimed to extend the technique to the goat. Isolated donor testis cells were infused into the seminiferous tubules of anesthetized recipient goats through an ultrasonographically-guided catheter inserted into the rete testis. Donor cells were obtained by enzymatic digestion of freshly collected testes from immature goats (either from the recipients' contralateral testis or from unrelated donors). Prior to transplantation, testis cells were labeled with a fluorescent marker to allow identification after transplantation. Recipient testes were examined for the presence and localization of labeled donor cells at 3-week intervals up to 12 weeks after transplantation. Labeled donor cells were found in the seminiferous tubules of all testes, comprising 10-35% of the examined tubules. Histological examination of the recipient testes did not reveal evident tissue damage, except for limited fibrotic changes at the site of needle insertion. Likewise there were no detectable local or systemic signs of immunologic reactions to the transplantations. These results indicate that germ cell transplantation is technically feasible in immature male goats and that donor-derived cells are retained in the recipient testis for at least three months and through puberty. This study represents the first report of germ cell transplantation in goats.     

Germ cell proliferation and apoptosis during testicular regression in a seasonal breeding fish kept in captivity

Cell proliferation and apoptosis regulate germ cells stock and sperm production, eliminate anomalous gametes, and are essential parameters to consider in fish farming. Herein, spermatogenic activity as well as germ cell proliferation and apoptosis were assessed in Leporinus taeniatus, a seasonal breeding species from the São Francisco River basin, Brazil. Testes of 24 adult fishes from a farming station were sampled between December and July and processed for light and transmission electron microscopy and immunohistochemistry for PCNA and TUNEL assay. The gonadosomatic index and seminiferous tubule diameters presented higher values during the breeding season (December/January and February/March), and then significantly reduced during the regression and resting stages (April/May and June/July). Phagocytosis of spermatozoa by Sertoli cells was evident during gonadal regression, but a significant number (up to 30%) remained at the tubular lumen during the resting stage. A higher PCNA/TUNEL ratio occurred in the breeding period, leading to an elevated proportion (%) of spermatogonia (G_A and G_B) in resting. Moreover, a higher TUNEL/PCNA ratio indicates the contribution of apoptosis to the reduction of germ cells during testicular regression. Together, these results indicate a shift in the balance between cell proliferation and apoptosis that contributes to the regulation of the spermatogenic cycle and germ cells pool of L. taeniatus kept in captivity.     

Germ cell intercellular bridges

Stable intercellular bridges are a conserved feature of gametogenesis in multicellular animals observed more than 100 years ago, but their function was unknown. Many of the components necessary for this structure have been identified through the study of cytokinesis in Drosophila; however, mammalian intercellular bridges have distinct properties from those of insects. Mammalian germ cell intercellular bridges are composed of general cytokinesis components with additional germ cell-specific factors including TEX14. TEX14 is an inactive kinase essential for the maintenance of stable intercellular bridges in gametes of both sexes but whose loss specifically impairs male meiosis. TEX14 acts to impede the terminal steps of abscission by competing for essential component CEP55, blocking its interaction in nongerm cells with ALIX and TSG101. Additionally, TEX14-interacting protein RBM44, whose localization in stabile intercellular bridges is limited to pachytene and secondary spermatocytes, may participate in processes such as RNA transport but is nonessential to the maintenance of intercellular bridge stability.     

Germ cell sex determination

Whether a germ cell embarks on oogenesis, the female gametogenic pathway, or spermatogenesis, the male pathway, may be determined cell-autonomously, by the germ cell's own genes, or by the tissue environment in which it is located. The decision may or may not be associated with the time of entry into meiosis, and this in turn may be controlled wholly by the germ cell's own genes, or in part by the environment. These issues will be explored with reference to Caenorhabditis elegans, Drosophila and the mouse.     

Germ cell sex and cell cycle

Germ cells are the only cells in the body capable of transferring an individual's genetic and epigenetic information to the next generation. However, the developmental processes that provide the foundation for male and female germ line development and later gamete production are complex and poorly understood. In mice the primordial germ cells enter the bipotential gonad at E10.5 and, in response to the testicular or ovarian micro-environment, commit to spermatogenesis or oogenesis. This paper reviews progress in understanding the molecular processes underlying the early stages of male and female germ line development.     

Germ cell kinetics in the neonatal rabbit testis

Summary Germ cells in the developing rabbit testis were found to undergo several distinct changes in the first two weeks after birth. Mitotic activity, which had been high in the late fetal period, reached a peak on the day before birth, then diminished steadily and ceased entirely after five days of age. Extensive germ cell degeneration occurred in the first week after birth resulting in accumulation of pools of degenerating germ cells in the central portions of the seminiferous cords. Following shortly after the peak of mitotic activity, germ cells at various stages of preleptotene could be found in squash preparations. This corresponded to the time when germ cells in the rabbit ovary enter and proceed through meiotic prophase. There was no evidence of entry into leptotene or later stages of meiosis in the neonatal testis. The findings suggest that a similar stimulus for entry into meiosis may exist in both sexes, but a blockage occurs in the male.Technical assistance was provided by Margaret Randolph and David Knibbs