Characteristics of mitotic cells in developing and adult testes with observations on cell lineages

Pancreatic lipase-related protein 2 is selectively expressed by peritubular myoid cells in the murine testis and sustains long-term spermatogenesis

Spermatogenesis is a complicated process of germ cell differentiation that occurs within the seminiferous tubule in the testis. Peritubular myoid cells (PTMCs) produce major components of the basement membrane that separates and ensures the structural integrity of seminiferous tubules. These cells secrete niche factors to promote spermatogonial stem cell (SSC) maintenance and mediate androgen signals to direct spermatid development. However, the regulatory mechanisms underlying the identity and function of PTMCs have not been fully elucidated. In the present study, we showed that the expression of pancreatic lipase-related protein 2 (Pnliprp2) was restricted in PTMCs in the testis and that its genetic ablation caused age-dependent defects in spermatogenesis. The fertility of Pnliprp2 knockout animals (Pnliprp2-/-) was normal at a young age but declined sharply beginning at 9 months. Pnliprp2 deletion impaired the homeostasis of undifferentiated spermatogonia and severely disrupted the development and function of spermatids. Integrated analyses of single-cell RNA-seq and metabolomics data revealed that glyceride metabolism was changed in PTMCs from Pnliprp2-/- mice. Further analysis found that 60 metabolites were altered in the sperm of the Pnliprp2-/- animals; notably, lipid metabolism was significantly dysregulated. Collectively, these results revealed that Pnliprp2 was exclusively expressed in PTMCs in the testis and played a novel role in supporting continual spermatogenesis in mice. The outcomes of these findings highlight the function of lipid metabolism in reproduction and provide new insights into the regulation of PTMCs in mammals.

Leydig cell stem cells: Identification, proliferation and differentiation

Adult Leydig cells develop from undifferentiated mesenchymal-like stem cells (stem Leydig cells, SLCs) present in the interstitial compartment of the early postnatal testis. Putative SLCs also have been identified in peritubular and perivascular locations of the adult testis. The latter cells, which normally are quiescent, are capable of regenerating new Leydig cells upon the loss of the adult cells. Recent studies have identified several protein markers to identify these cells, including nestin, PDGFRα, COUP-TFII, CD51 and CD90. We have shown that the proliferation of the SLCs is stimulated by DHH, FGF2, PDGFBB, activin and PDGFAA. Suppression of proliferation occurred with TGFβ, androgen and PKA signaling. The differentiation of the SLCs into testosterone-producing Leydig cells was found to be regulated positively by DHH (Desert hedgehog), lithium-induced signaling and activin; and negatively by TGFβ, PDGFBB, FGF2, Notch and Wnt signaling. DHH, by itself, was found to induce SLC differentiation into LH-responsive steroidogenic cells, suggesting that DHH plays a critical role in the commitment of SLC into the Leydig lineage. These studies, taken together, address the function and regulation of low turnover stem cells in a complex, adult organ, and also have potential application to the treatment of androgen deficiency.

Transplantation of alginate-encapsulated seminiferous tubules and interstitial tissue into adult rats: Leydig stem cell differentiation in vivo?

In vivo and in vitro studies were conducted to determine whether testosterone-producing Leydig cells are able to develop from cells associated with rat seminiferous tubules, interstitium, or both. Adult rat seminiferous tubules and interstitium were isolated, encapsulated separately in alginate, and implanted subcutaneously into castrated rats. With implanted tubules, serum testosterone increased through two months. Tubules removed from the implanted rats and incubated with LH produced testosterone, and cells on the tubule surfaces expressed steroidogenic enzymes. With implanted interstitial tissue, serum levels of testosterone remained undetectable. However, co-culture of interstitium plus tubules in vitro resulted in the formation of Leydig cells by both compartments. These results indicate that seminiferous tubules contain both cellular and paracrine factors necessary for the differentiation of Leydig cells, and that the interstitial compartment contains precursor cells capable of forming testosterone-producing Leydig cells but requires stimulation by paracrine factors from the seminiferous tubules to do so.

Steroidogenic factor 1 differentially regulates fetal and adult leydig cell development in male mice

The nuclear receptor steroidogenic factor 1 (SF-1, AD4BP, NR5A1) is a key regulator of the endocrine axes and is essential for adrenal and gonad development. Partial rescue of Nr5a1(-/-) mice with an SF-1-expressing transgene caused a hypomorphic phenotype that revealed its roles in Leydig cell development. In contrast to controls, all male rescue mice (Nr5a1(-/-);tg(+/0)) showed varying signs of androgen deficiency, including spermatogenic arrest, cryptorchidism, and poor virilization. Expression of various Leydig cell markers measured by immunohistochemistry, Western blot analysis, and RT-PCR indicated fetal and adult Leydig cell development were differentially impaired. Whereas fetal Leydig cell development was delayed in Nr5a1(-/-);tg(+/0) embryos, it recovered to control levels by birth. In contrast, Sult1e1, Vcam1, and Hsd3b6 transcript levels in adult rescue testes indicated complete blockage in adult Leydig cell development. In addition, between Postnatal Days 8 and 12, peritubular cells expressing PTCH1, SF-1, and CYP11A1 were observed in control testes but not in rescue testes, indicating SF-1 is needed for either survival or differentiation of adult Leydig cell progenitors. Cultured prepubertal rat peritubular cells also expressed SF-1 and PTCH1, but Cyp11a1 was expressed only after treatment with cAMP and retinoic acid. Together, data show SF-1 is needed for proper development of fetal and adult Leydig cells but with distinct primary functions; in fetal Leydig cells, it regulates differentiation, whereas in adult Leydig cells it regulates progenitor cell formation and/or survival.

Chronic stress induces ageing-associated degeneration in rat Leydig cells

Several studies have suggested that stress and ageing exert inhibitory effects on rat Leydig cells. In a pattern similar to the normal process of Leydig cell ageing, stress-mediated increases in glucocorticoid levels inhibit steroidogenic enzyme expression that then results in decreased testosterone secretion. We hypothesized that chronic stress accelerates the degenerative changes associated with ageing in Leydig cells. To test this hypothesis, we established a model of chronic stress to evaluate stress-induced morphological and functional alterations in Brown Norway rat Leydig cells; additionally, intracellular lipofuscin levels, reactive oxygen species (ROS) levels and DNA damage were assessed. The results showed that chronic stress accelerated ageing-related changes: ultrastructural alterations associated with ageing, cellular lipofuscin accumulation, increased ROS levels and more extensive DNA damage were observed. Additionally, testosterone levels were decreased. This study sheds new light on the idea that chronic stress contributes to the degenerative changes associated with ageing in rat Leydig cells in vivo.

Stem Leydig cells: from fetal to aged animals

Leydig cells are the testosterone-producing cells of the testis. The adult Leydig cell (ALC) population ultimately develops from undifferentiated mesenchymal-like stem cells present in the interstitial compartment of the neonatal testis. Distinct stages of ALC development have been identified and characterized. These include stem Leydig cells (SLCs), progenitor Leydig cells, immature Leydig cells, and ALCs. This review describes our current understanding of the SLCs in the fetal, prenatal, peripubertal, adult, and aged rat testis, as well as recent studies of the differentiation of steroidogenic cells from the stem cells of other organs.

Leydig cell aging and the mechanisms of reduced testosterone synthesis

In males, serum testosterone levels decline with advancing age. Though part of a complex process, this age-related decline in testosterone appears to occur, in part, due to a significant decline in the ability of aged Leydig cells to produce testosterone maximally in response to luteinizing hormone (LH). The structure of the molecular machinery responsible for the synthesis of testosterone is described, and placed in the context of Leydig cell biology. Multiple parameters related to the synthesis of testosterone by the Leydig cell have been observed to change with age. Relationships among these changes are reviewed. A discussion of potential causes of the age-related decline in Leydig cell steroidogenic capacity presents a model in which the inability of aged cells to adequately respond to hormonal stimulation results in cellular regression with concomitant decline in maximal testosterone output.

Efeito do uso de pentoxifilina no período neonatal sobre a produção espermática em ratos Wistar adultos

Utilizaram-se doses crescentes de pentoxifilina em ratos Wistar neonatos visando aumentar a produção espermática em animais adultos. Trinta e sete animais foram distribuídos de acordo com os tratamentos: não tratados (n=10) e tratados com 1mg/kg (n=10), 5mg/kg (n=9) e 10mg/kg (n=8) de pentoxifilina (IP). Aos 90 dias, os animais foram anestesiados e perfundidos intracardiacamente com solução fixadora. Os testículos foram processados rotineiramente para inclusão em resina plástica à base de glicol metacrilato. Cortes histológicos de 4µm de espessura foram corados em azul de toluidina/borato de sódio a 1% e analisados histometricamente. O número de células de Sertoli por secção transversal diminuiu nos grupos tratados com 5mg/kg e 10mg/kg em relação aos grupos controle e tratado com 1mg/kg. O índice de células de Sertoli aumentou nos animais tratados com 5mg/kg em comparação aos do grupo-controle. A utilização da pentoxifilina não foi capaz de induzir aumento na população das células de Sertoli e produção espermática em ratos adultos.

Leydig cell re-generation and expression of cell signaling molecules in the germ cell-free testis

Leydig cells in the rat testis can be specifically ablated with ethane dimethane sulfonate (EDS) and will subsequently re-generate. In this study, we have characterized Leydig cell re-generation and expression of selected cell-signaling molecules in a germ cell-free model of EDS action. This model offers the advantage that re-generation occurs on a stable background without confounding changes from the regressing and repopulating germ cell population. Adult rats were treated with busulfan to remove the germ cell population and Leydig cells were then ablated with EDS. Testicular testosterone levels declined markedly within 24 h of EDS treatment and started to recover after 8 days. After EDS treatment there were marked declines in levels of Leydig cell-specific mRNA transcripts coding for steroidogenic enzymes cytochrome P450 11a1 (Cyp11a1), cytochrome P450 17a1 (Cyp17a1), 3beta-hydroxysteroid dehydrogenase type 1 (Hsd3b1), 17beta-hydroxysteroid dehydrogenase type 3 (Hsd17b3) and the LH receptor. Levels of all transcripts recovered within 20 days of EDS treatment apart from Hsd17b3, which remained undetectable up to 20 days. Immunohistochemical localization of CYP11A1 during the phase of early Leydig cell re-generation showed that the Leydig cell precursors are spindle-shaped peritubular cells. Studies on factors which may be involved in Leydig cell re-generation showed there were significant but transient increases in platelet-derived growth factor A (Pdgfa), leukemia inhibitory factor (Lif), and neurofilament heavy polypeptide (Nefh) after EDS, while desert hedgehog (Dhh) levels declined sharply but recovered by 3 days. This study shows that the Leydig cell precursors are peritubular cells and that expression of Pdgfa and Lif is increased at the start of the re-generation process when precursor proliferation is likely to be taking place.

Neuroendocrine regulation of Leydig cell development

During development in the mouse, two populations of Leydig cells arise sequentially. The fetal Leydig cell population arises shortly after testicular differentiation and functions primarily to produce androgens that are essential for masculinization of the fetus. The origin of the fetal Leydig stem cells remains uncertain, but it has been suggested that adrenocortical cells and fetal Leydig cells may share a common origin in an adrenogenital primordium. The fetal Leydig cells require an intact pituitary for normal development and are sensitive to both luteinizing hormone (LH) and adrenocorticotrophic hormone (ACTH). Loss of either one of these hormones does not, however, affect fetal androgen production, suggesting that both LH and ACTH may act to maintain fetal Leydig cell function in vivo in a redundant fashion. The adult Leydig cell population starts to develop soon after birth in the mouse. Initial differentiation does not appear to require gonadotropin input, but subsequent development and function are completely dependent upon LH. The adult Leydig cells do not require circulating follicle-stimulating hormone, provided that LH is present, but androgen stimulation, through the androgen receptor, is required for normal Leydig cell development in the mouse. It is likely that the effects of androgen are mediated directly in the Leydig cells or indirectly through the peritubular cells.

Enhancing tyrosine hydroxylase expression and survival of fetal ventral mesencephalon neurons with rat or porcine Sertoli cells in vitro

Sertoli cells (SCs) are testis-derived cells that secrete trophic factors important for the development of germ cells. Both porcine and rat SCs have been used as graft facilitators - neonatal porcine SCs to support islets in diabetes and 15-day-old rat SCs to enhance dopaminergic neuron transplants in Parkinson's disease models. However, there has never been a study examining the optimal SCs preparation to enhance tyrosine hydroxylase expression in the ventral mesencephalon (VM) neuron. The aim of this study was to compare the ability of both rat and porcine SCs to enhance tyrosine hydroxylase expression (TH) and neuronal survival at the same postnatal developmental ages. The SCs were isolated from 1-, 9-, or 15-day-old rat, or neonate (2-5 days), 2-month, or 4-month-old pig, and co-cultured with VM tissue from 13.5-day-old embryos. Our results showed that VM neurons co-cultured with SCs dispersed over the culture plate and had extensive neuritic outgrowth, while VM neurons cultured alone tended to cluster together forming a mass of cells with limited neurite outgrowth. TH expression was significantly increased when VM neurons were co-cultured with 15-day rat SCs or 2-month pig SCs but not when the cells were co-cultured with other ages of SCs. This suggests that secretion of trophic factors by SCs varies according to the developmental age, and it is critical for the success of graft facilitation that SCs from the appropriate age and species be used.

Caspase 2 Activity Contributes to the Initial Wave of Germ Cell Apoptosis During the First Round of Spermatogenesis1

Early in postnatal life the first phase of spermatogenesis is accompanied by an initial wave of germ cell apoptosis. This wave of germ cell death is thought to reflect an adjustment of germ cell numbers that can be adequately maintained by Sertoli cells. Caspase 2 is an initiator caspase whose activation has been found to stimulate apoptosis through the mitochondria. The present study investigates if germ cell apoptosis during the first phase of spermatogenesis involves activation of caspase 2. Germ cell apoptosis was found to peak at Postnatal Days (pnds) 15 and 16 in male C57BL/6 mice. Western blot analysis revealed that caspase 2 also increased in the testes at pnd 16. Immunolocalization of total caspase 2 showed staining of germ cells in the periphery of the seminiferous tubules as well as germ cells more centrally located in an area where apoptotic germ cells were observed. Cytoplasmic as well as nuclear staining was observed. Western blot analysis of cytoplasmic and nuclear proteins from pnd 16 testis revealed pro-caspase 2 in both fractions. Further Western blot analysis for caspase 2 detected an increase in the activation of caspase 2 at pnd 16 in proteins isolated from the cytoplasm but not from the nucleus. Proteins isolated from mitochondria from pnd 16 testes revealed an increase in pro-caspase 2 as well as activated caspase 2 corresponding with an increase in cytochrome c in cytoplasmic fractions. Injection of the caspase 2-specific inhibitor z-VDVAD-fmk directly into the testis significantly reduced the observed germ cell apoptosis at pnds 15 and 16. These results suggest that caspase 2 is present in germ cells in the murine testis in early postnatal life and increases in expression in correspondence to the initial wave of germ cell apoptosis. Caspase 2 also localizes to mitochondria, where it is correlated with a release of cytochrome c and germ cell apoptosis. Blockade of caspase 2 activation reduced the number of apoptotic germ cells in the initial wave of germ cell apoptosis, indicating that caspase 2 plays an important role upstream of the mitochondria in germ cell apoptosis during the first phase of spermatogenesis.

Stimulation of TM3 Leydig cell proliferation via GABA(A) receptors: a new role for testicular GABA

The neurotransmitter gamma-aminobutyric acid (GABA) and subtypes of GABA receptors were recently identified in adult testes. Since adult Leydig cells possess both the GABA biosynthetic enzyme glutamate decarboxylase (GAD), as well as GABA(A) and GABA(B) receptors, it is possible that GABA may act as auto-/paracrine molecule to regulate Leydig cell function. The present study was aimed to examine effects of GABA, which may include trophic action. This assumption is based on reports pinpointing GABA as regulator of proliferation and differentiation of developing neurons via GABA(A) receptors. Assuming such a role for the developing testis, we studied whether GABA synthesis and GABA receptors are already present in the postnatal testis, where fetal Leydig cells and, to a much greater extend, cells of the adult Leydig cell lineage proliferate. Immunohistochemistry, RT-PCR, Western blotting and a radioactive enzymatic GAD assay evidenced that fetal Leydig cells of five-six days old rats possess active GAD protein, and that both fetal Leydig cells and cells of the adult Leydig cell lineage possess GABA(A) receptor subunits. TM3 cells, a proliferating mouse Leydig cell line, which we showed to possess GABA(A) receptor subunits by RT-PCR, served to study effects of GABA on proliferation. Using a colorimetric proliferation assay and Western Blotting for proliferating cell nuclear antigen (PCNA) we demonstrated that GABA or the GABA(A) agonist isoguvacine significantly increased TM3 cell number and PCNA content in TM3 cells. These effects were blocked by the GABA(A) antagonist bicuculline, implying a role for GABA(A) receptors. In conclusion, GABA increases proliferation of TM3 Leydig cells via GABA(A) receptor activation and proliferating Leydig cells in the postnatal rodent testis bear a GABAergic system. Thus testicular GABA may play an as yet unrecognized role in the development of Leydig cells during the differentiation of the testicular interstitial compartment.

Thyroid hormone, glucocorticoids, and prolactin at the nexus of physiology, reproduction, and toxicology

A symposium at the 2003 Annual Meeting of the Society of Toxicology brought together an expert group of endocrinologists to review how non-reproductive hormones can affect the endocrine system. This publication captures the essence of those presentations. Paul Cooke and Denise Holsberger recapitulate the evidence of how thyroid hormones affect male and female reproduction, and reproductive development. Ray Witorsch summarizes the many effects of glucocorticoids on the reproductive system. Finally, Paul Sylvester reviews the mechanism of action of prolactin, and reminds us that this ancient hormone has many functions beyond lactation.

Cell biology of Leydig cells in the testis

This article reviews results on differentiation, structure, and regulation of Leydig cells in the testes of rodents and men. Two different populations-fetal and adult Leydig cells-can be recognized in rodents. The cells in these two populations are different in ultrastructure, life span, capacity for androgen synthesis, and mechanisms of regulation. A brief survey on the origin, ontogenesis, characterization of precursors, ultrastructure, and functional markers of fetal and adult Leydig cells is presented, followed by an analysis of genes in Leydig cells and the role of luteinizing hormone and its receptor, steroidogenic acute regulatory protein, hydroxysteroid dehydrogenases, androgen and its receptor, anti-Müllerian hormone, estrogens, and thyroid hormones. Various growth factors modulate Leydig cell differentiation, regeneration, and steroidogenic capacity, for example, interleukin 1alpha, transforming growth factor beta, inhibin, insulin-like growth factors I and II, vascular endothelial growth factor, and relaxin-like growth factor. Retinol and retinoic acid increase basal testosterone secretion in adult Leydig cells, but decrease it in fetal Leydig cells. Resident macrophages in the interstitial tissue of the testis are important for differentiation and function of Leydig cells. Apoptosis of Leydig cells is involved in the regulation of Leydig cell number and can be induced by cytotoxins. Characteristics of aging Leydig cells in rodents seem to be species specific. 11beta-hydroxysteroid dehydrogenase protects testosterone synthesis in the Leydig cells of stressed rats. Last, the following aspects of human Leydig cells are briefly described: origin, differentiation, triphasic development, aging changes, pathological changes, and gene mutations leading to infertility.

Bax-dependent spermatogonia apoptosis is required for testicular development and spermatogenesis

Bax is a multidomain, proapoptotic member of the Bcl-2 family that is required for normal spermatogenesis in mice. Despite its proapoptotic function, previous results found that Bax-deficient mature male mice demonstrate increased cell death and dramatic testicular atrophy. The present study examined the role of Bax during the normal development of the testis to determine whether the increased cell death in mature mice could be explained by decreased apoptosis earlier in development. Consistent with this hypothesis, testicular atrophy is preceded by increased testicular weight and hypercellular tubules in immature Bax-deficient mice. TUNEL staining at Postnatal Day (P) 7 and morphological quantitation between P5 and P15 demonstrates decreased germ cell apoptosis in Bax-deficient mice. By P15, increased numbers of type A spermatogonia, and at P12 and P15, an increase in intermediate type spermatogonia were noted in Bax-deficient animals. By P25, the number of basal compartment cells was greatly increased in Bax-deficient animals compared with controls such that four or five layers of preleptotene spermatocytes were routinely present within the basal compartment of the testis. Although the Sertoli cell barrier was significantly removed from the basement membrane, it appeared intact as judged by the hypertonic fixation test. During late pubertal development, massive degeneration of germ cells took place, including many of those cell types that previously survived in the first wave of spermatogenesis. The data indicate that Bax is required for normal developmental germ cell death in the type A spermatogonia, specifically dividing (A(2), A(3), and A(4)) spermatogonia, at a time at which the number of spermatogonia is regulated in a density-dependent manner. The massive hyperplasia that occurs in Bax-deficient mice subsequently results in Bax independent cell death that may be triggered by overcrowding of the seminiferous epithelium.

Differentiation of the adult Leydig cell population in the postnatal testis

Five main cell types are present in the Leydig cell lineage, namely the mesenchymal precursor cells, progenitor cells, newly formed adult Leydig cells, immature Leydig cells, and mature Leydig cells. Peritubular mesenchymal cells are the precursors to Leydig cells at the onset of Leydig cell differentiation in the prepubertal rat as well as in the adult rat during repopulation of the testis interstitium after ethane dimethane sulfonate (EDS) treatment. Leydig cell differentiation cannot be viewed as a simple process with two distinct phases as previously reported, simply because precursor cell differentiation and Leydig cell mitosis occur concurrently. During development, mesenchymal and Leydig cell numbers increase linearly with an approximate ratio of 1:2, respectively. The onset of precursor cell differentiation into progenitor cells is independent of LH; however, LH is essential for the later stages in the Leydig cell lineage to induce cell proliferation, hypertrophy, and establish the full organelle complement required for the steroidogenic function. Testosterone and estrogen are inhibitory to the onset of precursor cell differentiation, and these hormones produced by the mature Leydig cells may be of importance to inhibit further differentiation of precursor cells to Leydig cells in the adult testis to maintain a constant number of Leydig cells. Once the progenitor cells are formed, androgens are essential for the progenitor cells to differentiate into mature adult Leydig cells. Although early studies have suggested that FSH is required for the differentiation of Leydig cells, more recent studies have shown that FSH is not required in this process. Anti-Müllerian hormone has been suggested as a negative regulator in Leydig cell differentiation, and this concept needs to be further explored to confirm its validity. Insulin-like growth factor I (IGF-I) induces proliferation of immature Leydig cells and is associated with the promotion of the maturation of the immature Leydig cells into mature adult Leydig cells. Transforming growth factor alpha (TGFalpha) is a mitogen for mesenchymal precursor cells. Moreover, both TGFalpha and TGFbeta (to a lesser extent than TGFalpha) stimulate mitosis in Leydig cells in the presence of LH (or hCG). Platelet-derived growth factor-A is an essential factor for the differentiation of adult Leydig cells; however, details of its participation are still not known. Some cytokines secreted by the testicular macrophages are mitogenic to Leydig cells. Moreover, retarded or absence of Leydig cell development has been observed in experimental models with impaired macrophage function. Thyroid hormone is critical to trigger the onset of mesenchymal precursor cell differentiation into Leydig progenitor cells, proliferation of mesenchymal precursors, acceleration of the differentiation of mesenchymal cells into Leydig cell progenitors, and enhance the proliferation of newly formed Leydig cells in the neonatal and EDS-treated adult rat testes.

Mesenchymal cell precursors of peritubular smooth muscle cells of the mouse testis can be identified by the presence of the p75 neurotrophin receptor

In the mouse embryo, at approximately 11.5 days postcoitum (dpc), cells migrate from the mesonephros into the developing testis to contribute to the somatic population of the interstitial compartment (i.e., peritubular myoid cells, Leydig cells, and endothelial cells). Studies from this laboratory have shown that the interstitial population of mesenchymal cells in fetal and newborn mouse testis express the p75 neurotrophin receptor (p75NTR, formerly known as the low-affinity nerve growth factor receptor); part of the cell population progressively congregates around testis cords, later to be replaced by contractile peritubular myoid cells, which express smooth muscle cell markers. In the present study, we show that the migrating cells and the p75NTR-expressing cells are the same population. We also show that the neurotrophin receptor is a useful endogenous marker to follow cell migration within the urogenital ridge and to identify and isolate mesenchymal precursors of myoid cells. A time-course immunolocalization study of the location of p75NTR-bearing cells within the urogenital ridge of mouse embryos between 10.5 and 12.5 dpc showed that the interstitium of the fetal testis was progressively occupied by p75NTR+ cells. The progressive increase of p75NTR expression within the developing testis was confirmed by immunoblot analysis of proteins isolated from the fetal gonads. Organ cultures of isolated testes or testis-mesonephros grafts confirmed that p75NTR+ cells do not appear in the testis unless a mesonephros is attached to it. Cells bearing the p75NTR receptor, purified from 12.5-dpc male mouse mesonephroi by immunomagnetic sorting, were able to differentiate in vitro into myoid cells. Immunofluorescence analysis of postnatal testis sections confirmed the presence around the tubules of cells coexpressing p75NTR and alpha-smooth muscle actin. The ability to identify and purify precursors of myoid cells may be of considerable help for studying the mechanisms regulating their differentiation.

Desert hedgehog (Dhh) gene is required in the mouse testis for formation of adult-type Leydig cells and normal development of peritubular cells and seminiferous tubules

Testes from adult and prepubertal mice lacking the Desert hedgehog (DHH:) gene were examined in order to describe further the role of Dhh in spermatogenesis because, in a previous report, DHH:-null male mice were shown to be sterile. Dhh is a signaling molecule expressed by Sertoli cells. Its receptor, patched (Ptc), has been previously localized to Leydig cells and is herein described as being localized also to peritubular cells. Two phenotypes of the mice were observed: masculinized (7.5% of DHH:-null males) and feminized (92.5%), both of which displayed abnormal peritubular tissue and severely restricted spermatogenesis. Testes from adult feminized animals lacked adult-type Leydig cells and displayed numerous undifferentiated fibroblastic cells in the interstitium that produced abundant collagen. The basal lamina, normally present between the myoid cells and Sertoli cells, was focally absent. We speculate that the abnormal basal lamina contributed to other characteristics, such as extracordal gonocytes, apolar Sertoli cells, and anastomotic seminiferous tubules. The two DHH:-null phenotypes described have common peritubular cell defects that may be indicative of the essential role of peritubular cells in development of tubular morphology, the differentiation of Leydig cells, and the ultimate support of spermatogenesis.

Studies on the onset of Leydig precursor cell differentiation in the prepubertal rat testis

Leydig cells of the adult rat testis differentiate postnatally from spindle-shaped cells in the testis interstitium during the neonatal-prepubertal period. Which spindle-shaped cell types are the precursor for Leydig cells and the stimulus for initiation of their differentiation are, however, two unresolved issues. In the present study, our objectives were to identify unequivocally which spindle-shaped cells are the precursors to Leydig cells and to test whether the initiation of their differentiation into Leydig cells depends on LH. Testes from fifteen groups of Sprague-Dawley rats (n = 4 per group) from 7-21 days of age were fixed in Bouin solution and embedded in paraffin. Immunoexpression of 3beta-hydroxysteroid dehydrogenase (3betaHSD), cytochrome P450 side-chain cleavage (P450(scc)), 17alpha-hydroxylase cytochrome P450 (P450(c17)), and LH receptors (LHR) in interstitial cells (other than fetal Leydig cells) was observed using the avidin biotin method. Of all spindle-shaped cell types in the testis interstitium, only the peritubular mesenchymal cells showed positive immunolabeling for all three steroidogenic enzymes, beginning from the 11th postnatal day. All three enzymes were expressed simultaneously in these cells, and their numbers increased significantly thereafter. Immunoexpression of LHR in a few of these cells was just evident for the first time on postnatal Day 12 (i.e., after acquiring the steroidogenic enzyme activity). Their numbers gradually increased with time. The number of immunolabeled cells per 1000 interstitial cells (excluding fetal Leydig cells and capillary endothelial cells) was not significantly different for the three steroidogenic enzymes tested at all ages; however, a lower value was observed for LHR at each time-point. Based on these observations, we suggest that 1) the precursor cell type for the adult generation of Leydig cells in the postnatal rat testis is the peritubular mesenchymal cells, 2) precursor cells acquire 3beta-HSD, P450(scc), and P450(c17) enzyme activity simultaneously during Leydig cell differentiation, and 3) onset of precursor cell differentiation during Leydig cell development does not depend on LH.

Absence of correlation between in situ expression of cytochrome P450 17alpha hydroxylase/lyase and 3beta-hydroxysteroid dehydrogenase/(Delta5-4) isomerase messenger ribonucleic acids and steroidogenesis during pubertal development in the rat testis

Changes in expression of Leydig cell 3beta-hydroxysteroid dehydrogenase (3betaHSD) and 17alpha-hydroxylase/C17-20 lyase (P450(17alpha)) messenger RNA (mRNA) during pubertal development have not been well characterized in the rat. In the present study, expression of 3betaHSD and P450(17alpha) were determined in frozen sections of testes of immature (days 21 and 28), pubertal (days 45 and 60) and adult (day 90) rats by in situ hybridization using digoxigenin-labeled riboprobes and quantified densitometrically. Measures of steroidogenesis in this study, 3betaHSD and P450(17alpha) enzyme activities per testis and plasma testosterone concentration, increased during pubertal development, peaking at 45-60 days of age. Expression of 3betaHSD protein, a marker for Leydig cell function, was abundantly immunolocalized to the interstitial compartment of the testis. Quantified densitometrically, the amount of 3betaHSD protein did not vary significantly during pubertal development. Transcripts of 3betaHSD and P450(17alpha) were expressed abundantly by clusters of immature Leydig cells in immature animals. However, in contrast to measures of steroidogenesis during pubertal development, mRNA of 3betaHSD and P450(17alpha) decreased to undetectable levels at the age of 45 and 60 days, respectively. The decline in mRNA of 3betaHSD and P450(17alpha) was confirmed by Northern analysis. Expression of 3betaHSD and P450(17alpha) transcripts rebounded in the adult at 90 days and were comparable to levels of expression observed in immature animals. These results show that during pubertal development the steady-state accumulation of mRNA of 3betaHSD and P450(17alpha) are not correlated with accumulation of 3betaHSD protein, enzyme activities of 3betaHSD and P450(17alpha), or testosterone secretion. Possible explanations of the depletion of transcripts during pubertal development include: specific inhibition of transcription, increased mRNA instability, or high translational activity.

Sry induces cell proliferation in the mouse gonad

Sry is the only gene on the Y chromosome that is required for testis formation in mammals. One of the earliest morphological changes that occurs as a result of Sry expression is a size increase of the rudimentary XY gonad relative to the XX gonad. Using 5′-bromo-2′-deoxyuridine (BrdU) incorporation to label dividing cells, we found that the size increase corresponds with a dramatic increase in somatic cell proliferation in XY gonads, which is not detected in XX gonads. This male-specific proliferation was observed initially in the cells of the coelomic epithelium and occurred in two distinct stages. During the first stage, proliferation in the XY gonad was observed largely in SF1-positive cells and contributed to the Sertoli cell population. During the second stage, proliferation was observed in SF1-negative cells at and below the coelomic epithelium and did not give rise to Sertoli cells. Both stages of proliferation were dependent on Sry and independent of any other genetic differences between male and female gonads, such as X chromosome dosage or other genes on the Y chromosome. The increase in cell proliferation began less than 24 hours after the onset of Sry expression, before the establishment of male-specific gene expression patterns, and before the appearance of any other known male-specific morphological changes in the XY gonad. Therefore, an increase in cell proliferation in the male coelomic epithelium is the earliest identified effect of Sry expression.

Duration-dependent effect of transient neonatal hypothyroidism on sertoli and germ cell number, and plasma and testicular interstitial fluid androgen binding protein concentration

The impact of transient neonatal hypothyroidism on growth and function of puberal testis during different milestones of postnatal testicular development was studied in Wistar rats. Rat pups were made hypothyroid for 10, 15, 30, 40 and 60 days of postnatal age from birth by providing 0.05% (W/V) methimazole (MMI) in the drinking water of the mother, from day 1 postpartum till weaning (25 days postpartum) and thereafter in the drinking water. Control rats were raised without MMI treatment. Sertoli cell number and its function was assessed on day 60 postpartum. Sertoli cell number increased consistently in 10, 15, 30 and 40 days transient hypothyroid rats but decreased in rats subjected to continuous hypothyroidism from birth to 60 days postpartum. Rats subjected to continuous hypothyroidism from birth showed spermatogenic arrest at puberty and had only a single layer of spermatogonia. Transient neonatal hypothyroidism for 10 (or) 15 days from birth increased spermatocytes (pachytene and zygotene), spermatids (elongated and round) whereas, that of 30 and 40 days decreases the number of germ cells. Plasma androgen binding protein (ABP) concentration decreased in puberal rats belonging to all groups, whereas the testicular interstitial fluid (TIF) concentration of ABP increased significantly in 10 and 15 days hypothyroid rats while it decreased in all other groups. These findings indicate that the mitogenic activity of Sertoli cell is increased irrespective of the duration of transient neonatal hypothyroidism. However, the functional activity of Sertoli cells (ABP production) in these puberal rats varies depending upon the postnatal period at which the animals were in hypothyroid state.

Developmentally regulated expression of cyclin D3 and its potential in vivo interacting proteins during murine gametogenesis

To begin to assess the function of the cell cycle regulator cyclin D3 during gametogenesis, the present study examined its expression, interacting partners, and associated kinase activity in the murine testis and ovary. In the early stages of postnatal testicular development, cyclin D3 protein was detected in spermatogonia and Leydig cells. In the adult testis, cyclin D3 was also expressed in terminally differentiating spermatids. In the embryonic ovary, detection of cyclin D3 was limited to somatic cells. In the postnatal ovary, its localization was predominantly in the nuclei of oocytes in primordial and small follicles, a localization that diminished with oocyte growth. Cdk4 and p27 were expressed in a similar subset of testicular and ovarian cells, suggesting that they may regulate cyclin D3 function during testicular and ovarian development in a cell type-specific manner. Cyclin D3-associated kinase activity was detected in immature, but not adult, testes and ovaries. These observations suggest unique roles for cyclin D3 in the control of cell division and differentiation in the germ line and the differential regulation of mitotic and meiotic cell cycles during male and female gametogenesis.