The regulation of male fertility by the PTPN11 tyrosine phosphatase.

PTPN11 (also known as SHP2) is a ubiquitously expressed non-receptor tyrosine phosphatase that regulates cell survival, proliferation, differentiation, migration and adhesion. Naturally occurring mutations in the PTPN11 gene cause Noonan and LEOPARD syndromes, two genetic disorders that are characterized by a spectrum of defects including male infertility. This review summarizes four cellular and molecular mechanisms by which PTPN11 acts to support male fertility.

Mouse Spermatogenesis Requires Classical and Nonclassical Testosterone Signaling.

Testosterone acts though the androgen receptor in Sertoli cells to support germ cell development (spermatogenesis) and male fertility, but the molecular and cellular mechanisms by which testosterone acts are not well understood. Previously, we found that in addition to acting through androgen receptor to directly regulate gene expression (classical testosterone signaling pathway), testosterone acts through a nonclassical pathway via the androgen receptor to rapidly activate kinases that are known to regulate spermatogenesis. In this study, we provide the first evidence that nonclassical testosterone signaling occurs in vivo as the MAP kinase cascade is rapidly activated in Sertoli cells within the testis by increasing testosterone levels in the rat.

Restoration of spermatogenesis and male fertility using an androgen receptor transgene.

Androgens signal through the androgen receptor (AR) to regulate male secondary sexual characteristics, reproductive tract development, prostate function, sperm production, bone and muscle mass as well as body hair growth among other functions. We developed a transgenic mouse model in which endogenous AR expression was replaced by a functionally modified AR transgene. A bacterial artificial chromosome (BAC) was constructed containing all AR exons and introns plus 40 kb each of 5' and 3' regulatory sequence.

Endocrine control of spermatogenesis: Role of FSH and LH/ testosterone.

Evaluation of testicular functions (production of sperm and androgens) is an important aspect of preclinical safety assessment and testicular toxicity is comparatively far more common than ovarian toxicity. This chapter focuses (1) on the histological sequelae of disturbed reproductive endocrinology in rat, dog and nonhuman primates and (2) provides a review of our current understanding of the roles of gonadotropins and androgens. The response of the rodent testis to endocrine disturbances is clearly different from that of dog and primates with different germ cell types and spermatogenic stages being affected initially and also that the end-stage spermatogenic involution is more pronounced in dog and primates compared to rodents.

The transition from stem cell to progenitor spermatogonia and male fertility requires the SHP2 protein tyrosine phosphatase.

SHP2 is a widely expressed protein tyrosine phosphatase required for signal transduction from multiple cell surface receptors. Gain and loss of function SHP2 mutations in humans are known to cause Noonan and LEOPARD syndromes, respectively, that are characterized by numerous pathological conditions including male infertility. Using conditional gene targeting in the mouse, we found that SHP2 is required for maintaining spermatogonial stem cells (SSCs) and the production of germ cells required for male fertility.

The tyrosine phosphatase SHP2 regulates Sertoli cell junction complexes.

The blood-testis barrier (BTB) is a large junctional complex composed of tight junctions, adherens junctions, and gap junctions between adjacent Sertoli cells in the seminiferous tubules of the testis. Maintenance of the BTB as well as the controlled disruption and reformation of the barrier is essential for spermatogenesis and male fertility. Tyrosine phosphorylation of BTB proteins is known to regulate the integrity of adherens and tight junctions found at the BTB.

Autologous ectopic grafting of cryopreserved testicular tissue preserves the fertility of prepubescent monkeys that receive sterilizing cytotoxic therapy.

Boys faced with future sterility as a result of the need of a sterilizing cancer therapy might avoid this fate by engraftment of cryopreserved immature testicular tissue after therapy is completed. Efforts to address this important survivorship issue have been encouraged by reports of the long-term survival and proliferation of human spermatogonia after xenotransplant of cryopreserved immature testicular tissue into immunocompromised murine hosts. However, spermatogenic arrest at the pachytene spermatocyte stage that occurs in this situation has been associated with a failure in sperm production.

Testosterone signaling and the regulation of spermatogenesis.

Spermatogenesis and male fertility are dependent upon the presence of testosterone in the testis. In the absence of testosterone or the androgen receptor, spermatogenesis does not proceed beyond the meiosis stage. The major cellular target and translator of testosterone signals to developing germ cells is the Sertoli cell.

Upstream stimulatory factor induces Nr5a1 and Shbg gene expression during the onset of rat Sertoli cell differentiation.

Within the testis, each Sertoli cell can support a finite number of developing germ cells. During development, the cessation of Sertoli cell proliferation and the onset of differentiation establish the final number of Sertoli cells and, thus, the total number of sperm that can be produced. The upstream stimulatory factors 1 and 2 (USF1 and USF2, respectively) differentially regulate numerous Sertoli cell genes during differentiation.

Testicular recovery after irradiation differs in prepubertal and pubertal non-human primates, and can be enhanced by autologous germ cell transplantation.

Background: Although infertility is a serious concern in survivors of pediatric cancers, little is known about the influence of the degree of sexual maturation at the time of irradiation on spermatogenic recovery after treatment. Thus, we address this question in a non-human primate model, the rhesus monkey (Macaca mulatta).

Methods: Two pubertal (testis size 3 and 6.

Regulation of Sertoli-germ cell adhesion and sperm release by FSH and nonclassical testosterone signaling.

Testosterone and FSH act in synergy to produce the factors required to maximize the production of spermatozoa and male fertility. However, the molecular mechanisms by which these hormones support spermatogenesis are not well established. Recently, we identified a nonclassical mechanism of testosterone signaling in cultured rat Sertoli cells.

Follicle-stimulating hormone (FSH) transiently blocks FSH receptor transcription by increasing inhibitor of deoxyribonucleic acid binding/differentiation-2 and decreasing upstream stimulatory factor expression in rat Sertoli cells.

FSH acts through the FSH receptor (FSHR) to modulate cell processes that are required to support developing spermatozoa. Within the testis, only Sertoli cells possess receptors for FSH and are the major targets for this regulator of spermatogenesis. FSH stimulation of Sertoli cells for 24-48 h is known to induce Fshr mRNA expression through an E-box motif (CACGTG) located 25 bp upstream of the transcription start site.

Testicular stem cells for fertility preservation: preclinical studies on male germ cell transplantation and testicular grafting.

Spermatogonial stem cells open novel strategies for preservation of testicular tissue and fertility preservation in boys and men exposed to gonadotoxic therapies. This review provides an update on the physiology of spermatogonial stem cells in rodent and primate testes. Species-specific differences must be considered when new technologies on testicular stem cells are considered.

A re-examination of proliferation and differentiation of type A spermatogonia in the adult rhesus monkey (Macaca mulatta).

Background: Companion studies using an experimental non-human primate paradigm known as a testicular clamp indicated that the behavior of undifferentiated type A spermatogonia did not conform fully to earlier classical models. This issue was therefore re-examined in normal monkeys.

Methods: Adult male rhesus monkeys (n = 4) received an i.

A selective monotropic elevation of FSH, but not that of LH, amplifies the proliferation and differentiation of spermatogonia in the adult rhesus monkey (Macaca mulatta).

Background: Unilateral orchidectomy in monkeys increases spermatogenesis in the remaining testis in association with elevated follicle-stimulating hormone (FSH) secretion and testicular testosterone. The present study examined the relative importance of FSH and testosterone in driving the primate testis toward its spermatogenic ceiling.

Methods: Adult male rhesus monkeys were treated with a gonadotropin-releasing hormone receptor antagonist to inhibit endogenous FSH and luteinizing hormone (LH) secretion.

Molecular mechanisms of testosterone action in spermatogenesis.

Testosterone is required for the maturation of male germ cells, the production of sperm and thus male fertility. However, the mechanisms by which testosterone regulates spermatogenic processes have not been well defined. In this review, classical and non-classical pathways of testosterone signaling in the Sertoli cells of the testis are discussed in relation to testosterone-regulated processes that are required for spermatogenesis.

USF1/2 transcription factor DNA-binding activity is induced during rat Sertoli cell differentiation.

Each Sertoli cell can support a finite number of developing germ cells. During development of the testis, the cessation of Sertoli cell proliferation and the onset of differentiation determine the final number of Sertoli cells and, hence, the number of sperm that can be produced. We hypothesize that the transition from proliferation to differentiation is facilitated by E-box transcription factors that induce the expression of differentiation-promoting genes.

Initiation of testicular tubulogenesis is controlled by neurotrophic tyrosine receptor kinases in a three-dimensional Sertoli cell aggregation assay.

The first morphological sign of testicular differentiation is the formation of testis cords. Prior to cord formation, newly specified Sertoli cells establish adhesive junctions, and condensation of somatic cells along the surface epithelium of the genital ridge occurs. Here, we show that Sertoli cell aggregation is necessary for subsequent testis cord formation, and that neurotrophic tyrosine kinase receptors (NTRKs) regulate this process.

Identification and characterization of spermatogonial subtypes and their expansion in whole mounts and tissue sections from primate testes.

The different types of spermatogonia present in the testes of all mammalian species have a series of functions in the adult testis. Some cycle regularly to (1) maintain the spermatogonial population and (2) derive differentiating germ cells to maintain continuous spermatogenesis; other spermatogonia act as a functional reserve, proliferating only very rarely under healthy conditions but repopulating the depleted seminiferous tubules after gonadotoxic insult. The number, appearance, and function of different types of spermatogonia differ greatly between mammalian species, and therefore the precise number of mitotic steps and the number of identifiable stages in spermatogenesis, the sperma-togenic efficiency, and the histological appearance of the seminiferous epithelium show remarkable variation.

Age-related changes in diurnal rhythms and levels of gonadotropins, testosterone, and inhibin B in male rhesus monkeys (Macaca mulatta).

Testosterone shows circadian rhythms in monkeys with low serum levels in the morning hours. The decline relies on a diminished frequency of LH pulses. Inhibin B shows no diurnal patterns.

Testicular morphogenesis: comparison of in vivo and in vitro models to study male gonadal development.

The organogenesis of a functional testis is the basis for male fertility and perpetuation of each species. In mammals, testicular development is dependent on two crucial events during embryonic and pubertal development. First, primary sex determination is initiated by expression of the Sry gene on the Y chromosome and directs the primordial gonad toward testicular development rather than ovarian differentiation.

Effect of cold storage and cryopreservation of immature non-human primate testicular tissue on spermatogonial stem cell potential in xenografts.

Background: Successful cryopreservation of gonadal tissue is an important factor in guaranteeing the fertility preservation via germ cell or testicular tissue transplantation. The aim of this study was to evaluate the effects of cooling and cryopreservation on spermatogonial stem cell survival and function of immature non-human primate testicular tissue xenografted to nude mice.

Methods: Group 1 (control group) received subcutaneous grafts of fresh immature rhesus monkey testes.

A revised model for spermatogonial expansion in man: lessons from non-human primates.

We have recently described a revised scheme for spermatogonial expansion in non-human primates. We proposed that A(pale)-spermatogonia act as self-renewing progenitors and premeiotic germ cells are organized and divide as small clones. Here, we are revisiting the model described for man and propose a modified scheme for spermatogonial expansion.

Testicular xenografts: a novel approach to study cytotoxic damage in juvenile primate testis.

The underlying primary damage to the testis caused by chemotherapeutic regimens during childhood is largely unknown. Xenografting of monkey testes was successfully applied in maturation of juvenile testis to the point of complete spermatogenesis. This allows us to manipulate developing primate testis without direct treatment of patients.

De novo morphogenesis of seminiferous tubules from dissociated immature rat testicular cells in xenografts.

Testicular development is initiated with the differentiation of Sertoli cells in the embryonic gonad. The aggregation of Sertoli cells is crucial for the generation of testicular cords and thus for the first sign of male gonadal development. To date, functional testicular tissue has not yet been generated in vitro.