Cografting of hamster (Phodopus sungorus) and marmoset (Callithrix jacchus) testicular tissues into nude mice does not overcome blockade of early spermatogenic differentiation in primate grafts

The ectopic xenotransplantation of testicular tissues into nude mice is a tool to generate sperm from immature testes. Immunodeficient mice as recipients of xenografts offered an appropriate microenvironment for differentiation of testicular tissue from hamsters, goats, pigs, and macaques. One exception is the neotropical primate Callithrix jacchus. Spermatogenesis in testicular grafts from marmosets does not proceed beyond the spermatogonial stage. The most likely cause for the poor graft development of marmosets is a deletion of exon 10 in the luteinizing hormone-receptor (LHR) gene, which renders this species insensitive to LH but responsive to chorionic gonadotropin (CG). We investigated whether cografting of testicular tissue from Djungarian hamsters would overcome the blockade in marmoset graft development. We also tested if exogenous administration of human CG (hCG) to the recipient would stimulate development of the marmoset tissue. No difference in graft survival was noted between hamster and monkey tissue. Seminiferous lumina were present in marmoset and hamster grafts but were significantly larger in hamster grafts. In the hamster grafts, a high proportion of the tubules contained meiotic and postmeiotic germ cells. In contrast, the marmoset tubules were populated with gonocytes and premeiotic spermatogonia. These results indicate that neither normal serum androgen levels nor the high local testosterone levels were sufficient to initiate marmoset spermatogenesis, nor was administration of hCG successful in overcoming the developmental blockade in marmoset tissue. Our results indicate that the conditions needed for initiation of spermatogenesis in the marmoset are remarkably different from those present in most other mammals.     

Interleukin-6 expression during normal maturation of the mouse testis

In this study, we examined the cellular origin and the expression levels of interleukin-6 (IL-6) during normal maturation of mouse testis. The levels of IL-6 (protein and mRNA) were higher in testicular homogenates of sexually immature than mature mice. Immunohistochemical staining of testicular tissues of sexually immature and adult mice show that testicular germ cells, at different stages of differentiation, Leydig cells/interstitial cells and peritubular cells express IL-6. Our results demonstrate, for the first time, overexpression of IL-6 in testicular tissues of immature mice, as compared to mature mice, as well as the expression of IL-6 in germ cells of testicular tissues of adult and sexually immature mice. Thus, our results may indicate the involvement of the endocrine system (gonadotropins and testosterone) in the regulation of IL-6, which is involved in the regulation of testicular development, functions and spermatogenesis.     

Over-expression of IL-18, ICE and IL-18 R in testicular tissue from sexually immature as compared to mature mice

In this study we examined the cellular origin and the expression levels of interleukin-18 (IL-18), IL-18 receptor (IL-18R) and IL-1beta-converting enzyme (ICE), which activates pro-IL-18, during normal maturation of murine testis. The levels of IL-18, IL-18R and ICE were significantly higher in testicular tissues and homogenates (but not in the spleen or liver) from sexually immature than mature mice. Immunohistochemical staining of testicular tissues from sexually immature and mature mice shows that testicular germ cells and Leydig cells/interstitial cells express higher levels of IL-18, as compared to other testicular cells. Peritubular cells of sexually immature and mature mice also expressed IL-18. Our results demonstrate, for the first time, over-expression of the IL-18 family in testicular tissues of sexually immature mice, as compared to mature mice, as well as the expression of IL-18 in the different stages of differentiation of testicular germ cells. Thus, our results may indicate involvement of the endocrine system (gonadotropins and testosterone) in the regulation of the testicular IL-18 family, which could be involved in the regulation of testicular functions, development and spermatogenesis under physiological conditions.     

Constitutive expression of IL-18 binding protein in murine testicular tissues and cells

In the present study, we examined the cellular origin and the expression levels of interleukin-18 binding protein (IL-18 BP), during normal maturation of murine testis. Immunohistochemical staining of testicular tissues from sexually mature mice, shows that testicular germ cells, at different stages of differentiation, express IL-18 BP. Leydig cells/interstitial cells and peritubular cells express higher levels of IL-18 BP, as compared to other testicular cells. The levels of IL-18 BP were similar in testicular tissues and homogenates from sexually immature and mature mice, as examined by western blot, ELISA and real time PCR analysis. Our results demonstrate, for the first time, the expression of IL-18 BP in murine testicular tissues and cells. Together with our previous studies, which showed over-expression of IL-18 in testicular tissues of immature mice as compared with mature mice, these results may indicate a role for IL-18 in testicular development, and also in the regulation of testicular functions under physiological conditions.     

Estimation of Steroids and Steroid Metabolism in a Lower Vertebrate (Lampetra planeri Bloch)

Pregnenolone, androstenedione and testosterone were identified by RIA in tissue homogenates of the pronephric region, the opisthonephros, the gonads and in plasma samples from male and female immature and mature adult brook lampreys. Additionally, hydroxysteroid dehydrogenase activity was determined spectrophotometrically in homogenates from the same tissues of mature and spent adult brook lampreys employing pregnenolone, testosterone or 3β,17β-dihydroxy-5β-androstane as substrates. The steroid levels show differences corresponding to developmental stages, tissues and sex. Remarkable quantities of testosterone were measured in the testicular tissue homogenates, in homogenates obtained from the pronephric region and in the serum.     

Generation of Live Piglets for the First Time Using Sperm Retrieved from Immature Testicular Tissue Cryopreserved and Grafted into Nude Mice

Cryopreservation of immature testicular tissues is essential for increasing the possibilities of offspring generation by testicular xenografting for agricultural or medical purposes. However, successful production of offspring from the sperm involved has never been reported previously. In the present study, therefore, using intracytoplasmic sperm injection (ICSI), we examined whether xenogeneic sperm obtained from immature pig testicular tissue after cryopreservation would have the capacity to produce live piglets. Testicular fragments from 9- to 11-day-old piglets were vitrified after 10- or 20-min immersion in vitrification solution containing ethylene glycol (EG), polyvinyl pyrrolidone (PVP) and trehalose as cryoprotectants, and then stored in liquid nitrogen for more than 140 days. Thirty nude mice were assigned to each immersion-time group. Testicular fragments were transplanted under the back skin of castrated mice immediately after warming and removal of the cryoprotectants. Blood and testicular grafts were then recovered from the recipient mice on days 60, 120, 180 and 230−350 (day 0 =  grafting). Histological assessment of the testicular grafts and analyses of inhibin and testosterone production revealed no significant differences between the two immersion-time groups, indicating equal growth activity of the cryopreserved tissues. A single sperm obtained from a mouse in each group on day 230−350 was injected into an in vitro-matured porcine oocyte, and then the ICSI oocytes were transferred to the oviducts of estrus-synchronized recipient gilts. One out of 4 gilts that had received oocytes fertilized using sperm from the 10-min immersion group delivered 2 live piglets, and one of another 4 gilts from the 20-min group delivered 4 live piglets. Thus, we have successfully generated porcine offspring utilizing sperm from immature testicular tissues after cryopreservation and transplantation into nude mice. The present model using pigs will be applicable to many large animals, since pigs are phylogenetically distant from the murine recipients.     

Over expression of interleukin-1alpha,interleukin-1beta and interleukin-1 receptor antagonist in testicular tissues from sexually immature mice as compared to adult mice

The levels of IL-1alpha, IL-1beta and IL-1Ra were higher in homogenates of testicular tissue from sexually immature than those from mature mice. Immunohistochemical staining of testicular tissues from sexually immature and adult mice show that differentiated germ cells express higher levels of IL-1alpha compared to Sertoli cells and Leydig cells/interstitial cells. Peritubular cells of sexually immature and adult mice did not express IL-1alpha. Testicular tissue cells of adult mice showed high levels of expression of IL-1beta, mainly in the cytoplasm and nucleus of the spermatogonia and in spermatocytes. Sertoli cells and Leydig/interstitial cells were also highly stained for IL-1beta. However, peritubular cells did not express IL-1beta. On the other hand, testicular tissue cells from sexually immature mice, showed high levels of IL-1beta, mainly in spermatocytes. Spermatogonia showed low levels of IL-1beta expression. Also, high levels of IL-1beta expression were detected in Leydig/interstitial cells. Peritubular cells clearly showed IL-1beta expression. Testicular tissue cells from adult mice, showed IL-1Ra expression in spermatogonia, Sertoli and Leydig/interstitial cells. IL-1Ra expression was clearly present in the Golgi apparatus of spermatogonia and Sertoli cells. However, peritubular cells did not show IL-1Ra expression. Testicular tissue cells from sexually immature mice, also showed high levels of IL-1Ra expression mainly in the cytoplasm and nucleus of the spermatogonia and Sertoli cells. In addition, Leydig/interstitial cells and peritubular cells also expressed IL-1Ra. Our results demonstrate, for the first time, the expression of IL-1beta in germ and Sertoli cells, and IL-1Ra in Leydig/interstitial cells of testicular tissues from adult and sexually immature mice, under in vivo conditions. In addition, the relative elevated levels of the IL-1 system in the testis of immature mice compared to mature mice may indicate its involvement in the spermatogenesis.     

Establishment of spermatogenesis in neonatal bovine testicular tissue following ectopic xenografting varies with donor age

Ectopic testicular xenografting can be used to investigate spermatogenesis and as an alternative means for generating transgenic spermatozoa in many species. Improving the efficiency of spermatogenesis in xenografted testicular tissue will aid in the application of using this approach. The present study was conducted to evaluate age-related differences in the establishment of spermatogenesis in grafted testicular tissue from bulls between 2 and 16 wk of life. Testicular tissue was ectopically xenografted under the skin on the backs of castrated nude mice and subsequently evaluated for growth, testosterone production, and establishment of spermatogenesis 24 wk after grafting. The greatest weight increases occurred in donor tissue from calves of the ages 2, 4, and 8 wk compared with the ages of 12 and 16 wk. Recipient mouse serum testosterone concentration was at normal physiological levels 24 wk after grafting and no significant differences were detected between recipients grafted with testicular tissue from bull calves of different ages. The development of germ cells to elongated spermatids were observed in seminiferous tubules of grafts from donor calves of the ages 4, 8, 12, and 16 wk but not observed in grafts from 2-wk donors, which contained round spermatids as the most advanced germ cell stage. Grafts from 8-wk donors contained a significantly higher (10-fold) average percentage of seminiferous tubules with elongated spermatids than all other donor ages. These data demonstrate differences in the ability of testicular tissue from donor animals of different ages to establish spermatogenesis following ectopic testicular xenografting.     

Proteomic changes in rat spermatogenesis in response to in vivo androgen manipulation; impact on meiotic cells

The production of mature sperm is reliant on androgen action within the testis, and it is well established that androgens act on receptors within the somatic Sertoli cells to stimulate male germ cell development. Mice lacking Sertoli cell androgen receptors (AR) show late meiotic germ cell arrest, suggesting Sertoli cells transduce the androgenic stimulus co-ordinating this essential step in spermatogenesis. This study aimed to identify germ cell proteins responsive to changes in testicular androgen levels and thereby elucidate mechanisms by which androgens regulate meiosis. Testicular androgen levels were suppressed for 9 weeks using testosterone and estradiol-filled silastic implants, followed by a short period of either further androgen suppression (via an AR antagonist) or the restoration of intratesticular testosterone levels. Comparative proteomics were performed on protein extracts from enriched meiotic cell preparations from adult rats undergoing androgen deprivation and replacement in vivo. Loss of androgenic stimulus caused changes in proteins with known roles in meiosis (including Nasp and Hsp70-2), apoptosis (including Diablo), cell signalling (including 14-3-3 isoforms), oxidative stress, DNA repair, and RNA processing. Immunostaining for oxidised DNA adducts confirmed spermatocytes undergo oxidative stress-induced DNA damage during androgen suppression. An increase in PCNA and an associated ubiquitin-conjugating enzyme (Ubc13) suggested a role for PCNA-mediated regulation of DNA repair pathways in spermatocytes. Changes in cytoplasmic SUMO1 localisation in spermatocytes were paralleled by changes in the levels of free SUMO1 and of a subunit of its activating complex, suggesting sumoylation in spermatocytes is modified by androgen action on Sertoli cells. We conclude that Sertoli cells, in response to androgens, modulate protein translation and post-translational events in spermatocytes that impact on their metabolism, survival, and completion of meiosis.     

Premeiotic Origin of Teratomas: Is Meiosis Required for Differentiation into Mature Tissues?

By virtue of meiotic cell division, primordial germ cells with heterozygous alleles develop into postmeiotic germ cells with homozygous alleles. Female and male germ cells may develop tumors - so-called teratomas - with a unique co-existence of a variety of histological elements from all three embryonic germ layers. In particular, mature teratomas consist exclusively of developmentally mature tissues whereas immature teratomas contain variable amounts of mature and immature tissues. In this study, we report genetic analysis of individual tissue components from mature and immature teratomas. The majority of mature teratomas showed consistent and concordant homozygous alleles in all selectively procured tissue components. In a small subset of mature teratomas, we observed discordant homozygous alleles. In contrast, immature teratomatous tissue revealed a heterozygous genotype. Remarkably, mature tissue components within immature teratoma revealed homozygosity. The findings suggest that immature teratomas and at least a subset of mature teratomas may originate from premeiotic cells, and implicate that meiosis may be required for differentiation into mature tissues.     

Testicular interleukin-6 response to systemic inflammation

Spermatogenesis is a highly controlled process of proliferation, meiosis, and differentiation. Systemic infection and chronic inflammation can impair testicular steroidogenesis and spermatogenesis. In this study, we examined the effect of systemic infection--intraperitoneal (i.p.) injection of lipopolysaccharide (LPS)--on the expression levels of IL-6 in the testis of sexually immature and adult mice. IL-6 levels in testicular homogenates of immature mice were significantly higher than in mature mice (both protein and RNA levels), before and after LPS injection. Injection of LPS (i.p.) into mature mice over 3 hours, significantly increased testicular IL-6 protein and mRNA levels (as demonstrated by ELISA and RT-PCR respectively) compared to the control group. Injection of LPS over 24 hours significantly increased IL-6 mRNA expression, but it did not significantly affect IL-6 protein levels in the homogenates. In contrast, stimulation of immature mice with LPS (2, 20 or 100 microg/mL) over 3 hours or LPS (2 or 20 microg/mL) over 24 hours, significantly increased testicular IL-6 (both protein and mRNA expression). The levels of testicular IL-6 (protein) in the homogenates were not significantly increased after stimulation with 100 microg/mL over 24 hours, but they were significantly increased at the mRNA level. Our results demonstrate, for the first time, the over-expression of IL-6 in testicular homogenates of mature and immature mice following systemic inflammation (i.p. injection of LPS). These results suggest the possibility of the involvement of systemic infection/inflammation, through the elevation of testicular IL-6, in testicular functions, which may affect male fertility. Also, high levels of IL-6 during pathological conditions, could play a role in protecting testicular tissue.     

Cryoconservation du tissue testiculaire chez l’enfant: comment préserver la fertilité chez le jeune garçon?

Survival rates for almost all types of childhood cancer have improved over the last 30 years. Estimates suggest that, in 2010, 1 out of 715 adolescents and young adults will be a long-term survivor of childhood cancer. With current therapy, 70% of children are cured. The increased number of survivors has focused attention on the many long-term or late sequelae of treatment. Most of the effects cannot be detected at the end of therapy, but only become apparent with puberty, growth and the normal aging process. Among the various sequelae, gonadal dysfunction is observed and the degree of gonadal damage depends on the type and total doses of chemotherapy and/or radiotherapy. The male gonald is also more sensitive to cancer therapy than the female gonad. Cryopreservation of ejaculated spermatozoa should be proposed for sexually mature boys. However, when ejaculated semen samples cannot be collected, or in the case of prepubertal boys who are not yet able to produce spermatozoa, another strategy must be used: testicular biopsy associated with cryopreservation of (i) testicular tissue, or (ii) isolated testicular spermatozoa or (iii) immature germ cells. The future use of immature testicular tissue will depend on the development of novel technologies in humans such as germ cellin vitro maturation, or autologous or xenogeneic germ cell transplantation.     

Ultrastructure of testicular biopsy from an XX male

Ultrastructural study of testicular biopsy specimens from an XX male showed hyalinized seminiferous tubules and tubules containing only mature Sertoli cells. These cells possessed large lipid inclusions as well as microfilament bundles which were perpendicular to the basement membrane and parallel to one another. The basal lamina was thickened and composed of several parallel layers with myofibroblast layers between them. The interstitium showed nodular to diffuse Leydig cell hyperplasia. Four types of Leydig cells were found: 1) normal Leydig cells with crystals of Reinke; 2) cells with abundant microcrystalline inclusions as well as microfilaments and concentric cisternae of smooth endoplasmic reticulum; 3) vacuolated cells containing numerous large lipid droplets; 4) immature Leydig cells. The different ultrastructural abnormalities found in the Sertoli and Leydig cells might be considered as the histological expression of a tubular-interstitial dysgenesis which is reflected in the high levels of gonadotropins and low levels of testosterone.     

Effects of different numbers of ectopic pituitary transplants on regulation of testicular LH/hCG and prolactin receptors in the hamster (Mesocricetus auratus)

Adult male hamsters were given transplants of 1/2, 1, 2, 3 or 4 pituitaries under the kidney capsule and were killed 4 weeks later. Pituitary transplants produced a significant, dose-related increase in plasma prolactin levels, no changes in plasma LH and an increase in plasma FSH. Concentration of LH/hCG receptors in the testes was significantly increased in animals with 2 or 3 transplants and concentration of testicular prolactin receptors was significantly increased in those given 2 transplants. The apparent stimulatory effects of 1/2, 1 or 4 transplants on testicular LH/hCG and prolactin binding were not statistically significant. Some of the animals were injected with 0.3 i.u. hCG/g body weight 24 h before being killed. This produced a significant reduction in the levels of prolactin receptors and an apparent reduction in the levels of LH/hCG receptors in the testes. Elevation of plasma testosterone concentrations in response to hCG was significantly greater in animals given 3 or 4 pituitary transplants than in the remaining groups. These results provide further evidence that prolactin increases the number of LH/hCG and prolactin receptors in the hamster testis and suggest that changing the number of ectopic pituitary transplants may result in biphasic effects on the testis, with 2 or 3 transplants being maximally stimulatory.     

Location of enzymes of androgen and estrogen biosynthesis in the testis of the ground squirrel (Citellus lateralis)

The intratesticular localization of enzymes of androgen and estrogen biosynthesis was studied in the ground squirrel (Citellus lateralis). In mature animals, interstitium and tubules were isolated by manual dissection. Microsomes were prepared and enzymes assayed by analysis of product formation after incubation with appropriate 3H-labeled substrates. In the immature testis, tubules and interstitium are not readily separable; thus, distribution was inferred after analysis of whole testicular microsomes from control, follicle-stimulating hormone (FSH)-treated, and luteinizing hormone (LH)-treated animals. To verify the cellular composition of tissues and the status of steroidogenic organelles in Leydig and Sertoli cells, samples were also analyzed by light and electron microscopy. In mature squirrels, enzymes of androgen biosynthesis were concentrated in the interstitium; however, levels present in the tubules were sufficient to account for a substantial fraction of whole testicular activity (1/3 to 1/5). By contrast, virtually all of the testicular aromatase was accounted for by that in the seminiferous tubules. The purity of these fractions was checked by light microscopy; they showed little cross-contamination. In whole testicular microsomes of immature squirrels, androgen biosynthetic enzymes had a much lower specific activity than in mature animals; however, the opposite was true for aromatase, its activity being approximately 5-fold higher in prepubertal animals. Luteinizing hormone treatment markedly stimulated hydroxylase and lyase but not aromatase. Luteinizing hormone also induced an increase in Leydig cell size and a dramatic proliferation of smooth endoplasmic reticulum. These changes were correlated with increased serum testosterone. As shown previously in rats, 3 beta-hydroxysteroid dehydrogenase was independent of LH control. Follicle-stimulating hormone had no effect on any of the enzymes studied, but induced some increase of agranular reticulum in Sertoli cells. Results from immature squirrels thus corroborate data from mature animals, showing a predominant interstitial location of androgen biosynthetic enzymes. While we cannot explain the absence of FSH stimulation of aromatase activity, the data do not refute the findings in mature animals showing a predominant tubular location of this enzyme. We conclude that the distribution of steroidogenic enzymes in the testis of squirrels differs in several important respects from rats, although both are members of the order Rodentia.     

Testicular cell differentiation in fetal mouse ovaries following transplantation into adult male mice

Testicular development is a complicated process involving differentiation and arrangement of several cell types. To analyze the process of testicular organization we examined the sequence of the appearance of testicular structures induced in fetal ovaries following transplantation. Fetal mouse ovaries on the twelfth day of gestation were transplanted beneath the kidney capsules of adult male mice. They continued to develop morphologically as ovaries until the eleventh day after transplantation, when seminiferous cord formation and testosterone production began in addition to follicle development (ovotestes). Between the eleventh and fourteenth day after transplantation, ovarian grafts frequently contained transitional structures consisting of Sertoli cells, pregranulosa cells, a third type of cells which show intermediate characteristics between Sertoli and pregranulosa cells, and oocytes enclosed by common basal lamina. Leydig cells or peritubular myoid cells were not found in the transitional area, whereas these cells were present around seminiferous cords composed only of Sertoli cells. Oocytes were absent or degenerated in the well-developed seminiferous cords. The present findings suggest that, in ovarian grafts, pregranulosa cells can differentiate into Sertoli cells, which are responsible for the organization of the seminiferous cords, degeneration of oocytes, and differentiation of other testicular somatic cell types.     

Functional Activity of Substantia Nigra Grafts Reinnervating the Striatum: Neurotransmitter Metabolism and [14C]2-Deoxy-d-glucose Autoradiography

Dopaminergic innervation of the caudate nucleus in adult rats can be partially restored by the grafting of embryonic substantia nigra into the overlying parietal cortex with concomitant compensation of certain behavioral abnormalities. In this study the function of such grafts was investigated neurochemically by quantification of transmitter metabolism and glucose utilization in the reinnervated target. Rats with unilateral 6-hydroxydopamine lesions of the nigrostriatal bundle received a single graft to the dorsal caudate-putamen and were screened for rotational behavior following 5 mg/kg methamphetamine. The grafts restored dopamine concentrations in the caudate-putamen from initially less than 0.5% to an average of 13.6% of normal in rats with behavioral compensation. The ratio of 3,4-dihydroxyphenylacetic acid to dopamine, which is a measure of the rate of transmitter turnover, were equivalent in transplanted and normal control rats. Moreover, measurements of DOPA accumulation for a 30-min period after DOPA decarboxylase inhibition indicated similar fractional dopamine turnover rates in normal and transplant-reinnervated tissues. Correlations between rotational behavior and dopamine concentrations showed that reinnervation to only 3% of normal was sufficient to counterbalance the motor asymmetry. Measurements of glucose utilization by [14C]deoxyglucose autoradiography indicated equivalent metabolic rates for the grafted tissue and the intact substantia nigra. 6-Hydroxydopamine denervation of the caudate-putamen had no significant effect on neuronal metabolism in that region, nor did subsequent reinnervation from a graft. Grafts, however, were associated with a 16% reduction of glucose uptake in the ipsilateral globus pallidus, indicating a significant transsynaptic influence of the nigral transplants on neuronal metabolism in the host brain. Overall the results indicate that behaviorally functional neuronal grafts spontaneously metabolize dopamine and utilize glucose at rates characteristic of the intact nigrostriatal system. This provides further evidence that ectopic intracortical nigral transplants can reinstate dopaminergic neurotransmission in regions of the host brain initially denervated by the 6-hydroxydopamine lesion.     

Conservation de tissu testiculaire et maturation in vitro de la lignée germinale pour préservation du potentiel de reproduction avant traitement anticancéreux chez le garçon pré-pubère

Sperm auto-conservation before chimioradiotherapy allows preservation of future reproductive possibilities in case of malignancy in young adult male. Because of the lack of mature spermatozoa, such possibilities cannot be offered for boys before puberty, even though the rate of cure of childhood malignancies is high. This paper reviewed recent advances in reproductive technology, which open the field of withdrawal of immature germ cells in prepubertal boys for in vitro maturation and cryopreservation for future paternity. It has been shown that the main steps of male meiosis have been driven in vitro, allowing to obtain round spermatids from pachytene spermatocytes in the rat. In mice, cryopreserved round spermatids have been used for oocyte fertilization and gave rise to normal living pups. In humans pregnancies and living babies have been reported after microinjection of round spermatids in cases of azoospermia. One pregnancy has been obtained with a cryopreserved spermatid. Thus the project of withdrawal of testicular tissues before sterilizing treatment, in vitro maturation of spermatogonia into round spermatids and cryopreservation of immature germ cells for future use for assisted fertilization does not seem unrealistic since each step has been done individually. However developing animal models is necessary to study not only the efficiency of the whole procedure but also to check its harmlessness before clinical trials.     

Review on testicular development, structure, function, and regulation in common marmoset

BACKGROUND: The common marmoset (Callithrix jacchus) is a New World primate that has been used increasingly in toxicological evaluations including testing for testicular toxicity of pharmaceutical and environmental chemicals. Information on structural and functional characteristics of the testis in common marmosets ("marmoset" in this review) is critical for designing experiments, interpreting data collected, and determining relevance to humans in risk assessment. METHODS: This study provides a comprehensive review on testicular development, structure, function, and regulation in common marmosets. RESULTS: There is little information regarding testicular formation and development during gestation. Based on the overall pattern of embryonic development in marmosets, it is postulated that gonadal formation and testicular differentiation most likely takes place during gestational Week 6-12. After birth, the neonatal period of the first 2-3 weeks and the pubertal period from Months 6-12 are critical for establishment of spermatogenesis in the adult. In the adult, a nine-stage model has been used to describe the organization of seminiferous epithelium and multiple stages per tubular cross-section have been observed. Seminiferous epithelium is organized in a wave or partial-wave manner. There are on average two stages per cross-section of seminiferous tubules in adult marmoset testis. Sertoli cells in the marmoset have a uniform morphology. Marmoset spermatogenesis has a high efficiency. The prime determinant of germ cell production is proliferation and survival of spermatogonia. Sertoli cell proliferation during the neonatal period is regulated by follicle-stimulating hormone (FSH), but chorionic gonadotropin (CG), instead of luteinizing hormone (LH), is the only gonadotropin with luteinizing function in marmoset. The receptor gene for CG in marmoset is unique in that it does not have exon 10. Marmosets have a "generalized steroid hormone resistance," i.e., relatively high levels of steroid hormones in circulation and relatively low response to exogenous steroids. Blockage of FSH, CG, and testosterone production during the first 3 months after birth does not cause permanent damage to the male reproductive system. Initiation of spermatogenesis in the marmoset requires unique factors that are probably not present in other mammals. Normal male marmosets respond to estradiol injection positively (increased LH or CG levels), a pattern seen in normal females or castrated males, but not usually in normal males of other mammalian species. CONCLUSIONS: It seems that the endocrine system including the testis in marmosets has some unique features that have not been observed in rodents, Old World primates, and humans, but detailed comparison in these features among these species will be presented in another review. Based on the data available, marmoset seems to be an interesting model for comparative studies. However, interpretation of experimental findings on the testicular effects in marmosets should be made with serious caution. Depending on potential mode of testicular actions of the chemical under investigation, marmoset may have very limited value in predicting potential testicular or steroid hormone-related endocrine effects of test chemicals in humans.