Male reproductive hormones in patients treated with pretomanid.

BACKGROUND: Pretomanid (Pa) is a nitroimidazole-class drug recently approved by the US Food and Drug Administration and other regulatory authorities as part of a regimen for treating highly drug-resistant pulmonary Mycobacterium tuberculosis infections. Studies in rodents identified the testis as a target organ of concern, which led to monitoring of reproductive hormones in >800 male patients enrolled in four clinical trials of Pa-containing regimens and the HRZE (isoniazid+rifampin+pyrazinamide+ethambutol) control regimen.METHODS: Serum hormone levels relevant to male reproductive health - follicle stimulating hormone (FSH), luteinizing hormone (LH), inhibin B (InhB) and total testosterone (T) - from the four clinical trials were summarized numerically and analyzed by repeated-measures modeling.RESULTS: Hormone levels generally behaved similarly in Pa-containing and HRZE arms. Relative to baseline, serum T and InhB levels generally increased at the end of treatment and follow-up. FSH and LH levels were variable, but were generally at or below baseline levels by follow-up. Before treatment, many patients were borderline hypogonadal, with T levels near the lower limits of the normal range.CONCLUSION: Changes in male hormones in four clinical trials studying patients with TB indicate that Pa-containing treatment was not associated with testicular toxicity but rather led to improvement in the underlying hypogonadism.

Paving the way for application of next generation risk assessment to safety decision-making for cosmetic ingredients.

Next generation risk assessment (NGRA) is an exposure-led, hypothesis-driven approach that has the potential to support animal-free safety decision-making. However, significant effort is needed to develop and test the in vitro and in silico (computational) approaches that underpin NGRA to enable confident application in a regulatory context. A workshop was held in Montreal in 2019 to discuss where effort needs to be focussed and to agree on the steps needed to ensure safety decisions made on cosmetic ingredients are robust and protective. Workshop participants explored whether NGRA for cosmetic ingredients can be protective of human health, and reviewed examples of NGRA for cosmetic ingredients. From the limited examples available, it is clear that NGRA is still in its infancy, and further case studies are needed to determine whether safety decisions are sufficiently protective and not overly conservative. Seven areas were identified to help progress application of NGRA, including further investments in case studies that elaborate on scenarios frequently encountered by industry and regulators, including those where a 'high risk' conclusion would be expected. These will provide confidence that the tools and approaches can reliably discern differing levels of risk. Furthermore, frameworks to guide performance and reporting should be developed.

Toxicity testing in the 21st century: progress in the past decade and future perspectives.

Advances in the biological sciences have led to an ongoing paradigm shift in toxicity testing based on expanded application of high-throughput in vitro screening and in silico methods to assess potential health risks of environmental agents. This review examines progress on the vision for toxicity testing elaborated by the US National Research Council (NRC) during the decade that has passed since the 2007 NRC report on Toxicity Testing in the 21st Century (TT21C). Concomitant advances in exposure assessment, including computational approaches and high-throughput exposomics, are also documented. A vision for the next generation of risk science, incorporating risk assessment methodologies suitable for the analysis of new toxicological and exposure data, resulting in human exposure guidelines is described. Case study prototypes indicating how these new approaches to toxicity testing, exposure measurement, and risk assessment are beginning to be applied in practice are presented. Overall, progress on the 20-year transition plan laid out by the US NRC in 2007 has been substantial. Importantly, government agencies within the United States and internationally are beginning to incorporate the new approach methodologies envisaged in the original TT21C vision into regulatory practice. Future perspectives on the continued evolution of toxicity testing to strengthen regulatory risk assessment are provided.

High-quality human and rat spermatozoal RNA isolation for functional genomic studies.

Sperm RNA is a sensitive monitoring endpoint for male reproductive toxicants, and a potential biomarker to assess male infertility and sperm quality. However, isolation of sperm RNA is a challenging procedure due to the heterogeneous population of cells present in the ejaculate, the low yield of RNA per spermatozoon, and the absence of 18S and 28S ribosomal RNA subunits. The unique biology of spermatozoa has created some uncertainty in the field about RNA isolation methods, indicating the need for rigorous quality control checks to ensure reproducibility of data generated from sperm RNA. Therefore, we developed a reliable and effective protocol for RNA isolation from rat and human spermatozoa that delivers highly purified and intact RNA, verified using RNA-specific electrophoretic chips and molecular biology approaches such as RT-PCR and Western blot analysis. The sperm RNA isolation technique was optimized using rat spermatozoa and then adapted to human spermatozoa. Three steps in the sperm isolation procedure, epididymal fluid collection, sperm purification, and spermatozoon RNA extraction, were evaluated and assessed. The sperm RNA extraction methodology consists of collection of rat epididymal fluid with repeated needle punctures of the epididymis, somatic cell elimination using detergent-based somatic cell lysis buffer (SCLB) and the use of RNA isolation Kit. Rat sperm heads are more resistant to disruption than human spermatozoa, necessitating the addition of mechanical lysis with microbeads and heat in the rat protocol, whereas the human sperm protocol only required lysis buffer. In conclusion, this methodology results in reliable and consistent isolation of high-quality sperm RNA. Using this technique will aid in translation of data collected from animal models, and reproducibility of clinical assessment of male factor fertility using RNA molecular biomarkers.

Intra- and inter-individual differences in human sperm DNA methylation.

There is growing evidence that sperm DNA methylation is important in maintaining proper sperm health and function. Previous studies have associated sperm DNA methylation levels with sperm quality and function, however, little is known regarding the intra- and inter-individual variability in sperm methylation levels. This study characterizes this variation. Sperm epigenetic differences between successive semen samples from 12 patients were examined to identify the intra- and inter-individual differences globally across the genome, and in specifically defined genomic regions using the Illumina Infinium HumanMethylation450 BeadChips. Methylation analysis identified a bimodal distribution in the methylation levels that were non-uniformly distributed across the different genomic regions. The methylation levels were highly correlated in both the intra- and inter-individual comparisons. The intra-individual methylation levels were more highly correlated than the inter-individual comparison both globally and across the defined genomic regions, demonstrating that sperm DNA methylation levels are relatively stable between semen sample collections.

Functional modulation of choroid plexus epithelial clusters in vitro for tissue repair applications.

One of the primary obstacles in the restoration or repair of damaged tissues is the temporospatial orchestration of biological and physiological events. Cellular transplantation is an important component of tissue repair as grafted cells can serve as replacement cells or as a source of secreted factors. But few, if any, primary cells can perform more than a single tissue repair function. Epithelial cells, derived from the choroid plexus (CP), are an exception to this rule, as transplanted CP is protective and regenerative in animal models as diverse as CNS degeneration and dermal wound repair. They secrete a myriad of proteins with therapeutic potential as well as matrix and adhesion factors, and contain responsive cytoskeletal components potentially capable of precise manipulation of cellular and extracellular niches. Here we isolated CP from neonatal porcine lateral ventricles and cultured the cells under a variety of conditions to specifically modulate tissue morphology (2D vs. 3D) and protein expression. Using qRT-PCR analysis, transmission electron microscopy, and gene microarray studies we demonstrate a fine level of control over CP epithelial cell clusters opening further opportunities for exploration of the therapeutic potential of this unique tissue source.

Secreted products from the porcine choroid plexus accelerate the healing of cutaneous wounds.

The choroid plexus (CP), located at the blood-brain interface, is partially responsible for maintaining the composition of cerebrospinal fluid. Epithelial cell clusters isolated from the CP secrete numerous biologically active molecules, and are neuroprotective when transplanted in animal models of Huntington's disease and stroke. The transcriptomic and proteomic profiles of CP may extend beyond CNS applications due to an abundance of trophic and regenerative factors, including vascular endothelial growth factor, transforming growth factor-beta, and others. We used microarray to investigate the transcriptome of porcine CP epithelium, and then assessed the in vitro and in vivo regenerative capability of secreted CP products in cell monolayers and full-thickness cutaneous wounds. In vitro, CP reduced the void area of fibroblast and keratinocyte scratch cultures by 70% and 33%, respectively, compared to empty capsule controls, which reduced the area by only 35% and 6%, respectively. In vivo, after 10 days of topical application, CP conditioned medium lyophilate dispersed in antibiotic ointment produced a twofold improvement in incision tensile strength compared to ointment containing lyophilized control medium, and an increase in the regeneration of epidermal appendages from roughly 50-150 features per wound. Together, these data identify the CP as a source of secreted regenerative molecules to accelerate and improve the healing of superficial wounds and potentially other similar indications.

Continuously proliferative stem germ cells partially repopulate the aged, atrophic rat testis after gonadotropin-releasing hormone agonist therapy.

Aging in the male human is accompanied by testicular atrophy, although relatively little is known about the mechanisms underlying germ cell loss. Testicular atrophy in the aged Brown Norway rat, an animal model for studies of aging in the human, has been attributed to a loss of spermatogonial stem cells. However, examination of testicular cross-sections from 27-mo-old Brown Norway rats indicated that approximately 14% of type A spermatogonia were stem cells. Furthermore, using bromodeoxyuridine labeling, we found that approximately 47% of these stem cells were actively dividing, with a cell cycle time of approximately 12.6 days. Both serum and testicular interstitial fluid testosterone levels were depressed in the aged rat. Therapy with the GnRH agonist, leuprolide, which has been empirically shown to reverse testicular atrophy in other models of germ cell loss, also partially restored spermatogenesis in the aged Brown Norway rat. The extent of testicular atrophy varied considerably, not only within the control and leuprolide-treatment groups but also between the left and right testes of the same animals. No significant difference was found between the mean percentage of populated tubules in 31-mo-old control animals (16.2 +/- 28%, mean +/- SD) and 31-mo-old leuprolide-treated animals (20.9 +/- 19.8%), but categorical comparisons showed that significantly fewer leuprolide-treated animals and testes contained < or = 1% populated tubules, indicating that GnRH agonist therapy stimulates differentiation of type A spermatogonia. An increase in the ratio of soluble to membrane stem cell factor mRNA levels was present in aged rats and partially reversed following leuprolide therapy.

Spermatogenesis by Sisyphus: proliferating stem germ cells fail to repopulate the testis after 'irreversible' injury.

2,5-Hexanedione is the toxic metabolite resulting from oxidation of the commonly used solvents n-hexane and methyl n-butyl ketone. Exposure to 2,5-hexanedione or its precursors results in a slowly progressive peripheral polyneuropathy and testicular injury. The chemical basis of the injury involves reaction of 2,5-hexanedione with protein amines, such as the epsilon-amine of lysine, to form pyrroles which further react to form protein-protein crosslinks. The target cell of injury in the testis is the supportive cell in the seminiferous epithelium, the Sertoli cell. A major function of the Sertoli cell is to nurture the dependent germ cell population by secreting seminiferous tubule fluid. 2,5-Hexanedione-induced crosslinking of the microtubule subunit protein, tubulin, leads to altered Sertoli cell microtubule-dependent transport and deficient formation of seminiferous tubule fluid, compromising germ cell viability. In an established model of testicular injury, rats are exposed to 1% 2,5-hexanedione in the drinking water for a period of 3-5 weeks. Three weeks after initiating exposure, decreased seminiferous tubule fluid secretion initiates a wave of germ apoptosis which peaks during the 5th week. The germ cell content of the injured testis continues to decline after cessation of the exposure, reaching a nadir during the 12th week. From this time onward, the testis is severely atrophic with less than 1% of seminiferous tubules in a testicular cross section containing germ cells more advanced than spermatogonia. Interestingly, this persistent state of post-injury 'irreversible' atrophy in the rat is characterized by the presence of a proliferating stem germ cell population which produces differentiating spermatogonia which then die by apoptosis. Serial cross sections of bromodeoxyuridine-labeled testis were analyzed to determine the kinetics of stem germ cell proliferation. Approximately 40% of stem cells (identified as single cells in the seminiferous epithelium) were actively proliferating with a cell cycle time of 8-14 days. Analysis of the total germ cell population present and modeling using the known cell cycle times of differentiating spermatogonia indicated a block in differentiation at the level of type A3/A4 spermatogonia. Quantitation of the frequency of apoptosis indicated that all of the germ cells died prematurely by this mechanism. Leuprolide is a gonadotropin-releasing hormone agonist which produces a profound suppression of testosterone levels with chronic administration. When delivered as a series of 3 depot injections 24 days apart, leuprolide resulted in a partial reversal of the 2,5-hexanedione-induced persistent atrophy. The reinitiation of spermatogenesis follows a lowering of the intratesticular testosterone concentration, indicating that intratesticular testosterone is at least partially responsible for the persistent atrophy. The efficacy of leuprolide-induced reversal of the persistent atrophy decreases with time after injury, suggesting that atrophic seminiferous tubules are initially capable of recovery and then enter a state of irreversible injury. Injection of ethane dimethane sulfonate at the beginning of leuprolide treatment eliminated Leydig cells during therapy and ablated the recovery of spermatogenesis, indicating that a Leydig cell-associated paracrine factor is required to restart spermatogenesis. The rat, therefore, has multiple states of testicular germ cell proliferation: normal spermatogenesis and at least two forms of persistent atrophy (leuprolide reversible and leuprolide non-reversible). Partial reversal of the persistent atrophy can be achieved by lowering intratesticular testosterone. Ongoing experiments are designed to address the role of the Leydig cell in post-injury recovery, and to further characterize the molecular events contributing to the different states of persistent atrophy.

Analysis of testes and semen from rabbits treated by intravenous injection with a retroviral vector encoding the human factor VIII gene: no evidence of germ line transduction.

In a phase 1 clinical trial, we are evaluating a murine leukemia virus (MuLV)-based retroviral vector encoding the human factor VIII gene [hFVIII(V)], administered intravenously, as a therapy for hemophilia A. Preclinical biolocalization studies in adult rabbits revealed vector-specific PCR signals in testis tissue at low levels. In follow-up animal studies we used PCR to (1) estimate the frequency with which a given cell in testis tissue is transduced, and (2) determine whether a positive PCR signal could be detected in semen samples from animals treated with hFVIII(V). Using the 99% confidence bound, results indicate that the probability that a given cell within the testis was transduced is less than 1/709,000 (97 days after treatment). This probability decreased with time after hFVIII(V) administration. Moreover, the rate of provector sequence detection in semen samples collected weekly throughout two cycles of spermatogenesis was 3/4281 reactions (0.07%), which is lower than the rate of false positives (1/800, 0.125%) observed for control animals. Using PCR assays with single-copy sensitivity, we have shown that the small number of transduced cells present in testis tissue does not give rise to detectable transduced cells in semen.

Role of Sertoli cells in injury-associated testicular germ cell apoptosis.

This review examines experimental models of Sertoli cell injury resulting in germ cell apoptosis. Since germ cells exist in an environment created by Sertoli cells, paracrine signaling between these intimately associated cells must regulate the process of germ cell death. Germ cell apoptosis may be signaled by a decrease in Sertoli cell pro-survival factors, an increase in Sertoli cell pro-apoptotic factors, or both. The different models of Sertoli cell injury indicate that spermatogenesis is susceptible to disruption, and that targeting critical Sertoli cell functions can lead to rapid and massive germ cell death.

Transmembrane versus soluble stem cell factor expression in human testis.

The interaction between stem cell factor (SCF), a ligand produced by Sertoli cells, and its c-kit receptor on germ cells is necessary for successful spermatogenesis in animal models. SCF can be alternatively spliced into soluble and transmembrane forms, and it is the transmembrane form that is required for spermatogenesis in rodents. c-Kit receptors are also present on Leydig cells, and soluble SCF has been implicated in the regulation of testosterone production. This study had two goals: To test the hypothesis that the extent of germ cell production in human males is correlated with the expression of transmembrane SCF, and to examine the relationship between testosterone production and the expression of soluble SCF in humans. Reverse transcriptase polymerase chain reaction was used to determine the ratio of transmembrane-to-soluble SCF in testicular tissue. Clinical analysis, hormonal measurements, and histological methods were used to evaluate the causes of infertility and to seek correlations with the pattern of SCF expression. SCF was preferentially expressed as the transmembrane type in all testicular samples, regardless of the state of germ cell production. Furthermore, the percent of transmembrane SCF expression was independent of clinical and histopathological diagnosis (r(s) = 0.111, n = 28) and unrelated to the extent of spermatogenesis. This contrasts with rat models of testicular injury that exhibit a decreased proportion of transmembrane SCF with atrophy. A significant correlation (r(s) = 0.665, P < .02, n = 16) was found between testosterone levels and percent soluble SCF, which suggests that, in humans, there may be a regulatory interaction between soluble SCF and testosterone.

Multiple cadherin superfamily members with unique expression profiles are produced in rat testis.

Adhesion between germ and Sertoli cells is thought to be crucial for spermatogenesis. Cadherin superfamily proteins, including classic cadherins and protocadherins, are important mediators of cell-cell adhesion. Using a degenerate PCR cloning strategy, we surveyed the expression of cadherin superfamily members in rat testis. Similar to brain, testis expressed a large number of cadherin superfamily members: 7 classic cadherins of both types I and II, 14 protocadherins, 2 protocadherin-related cadherins, and 1 cadherin-related receptorlike protein. All three protocadherin families (alpha, beta, and gamma) were found in testis. Using a semiquantitative RT-PCR assay, messenger RNA expression was determined for each cadherin superfamily member during a postnatal developmental time-course and following ablation of specific testis cell types by ethanedimethanesulfonate, methoxyacetic acid, and 2,5-hexanedione. Diverse expression patterns were observed among the cadherins, suggesting that cadherin expression is cell type-specific in testis. The large number and variety of cadherin superfamily members found in testis supports a critical function for cadherin-mediated cell-cell adhesion in spermatogenesis.

Sensitivity of testicular germ cells to toxicant-induced apoptosis in gld mice that express a nonfunctional form of Fas ligand.

Germ cell apoptosis in testis is essential for functional spermatogenesis. Recent evidence suggests that the Fas signaling system is critical for the regulation of testicular germ cell apoptosis. To further evaluate the Fas signaling system in testis, we examined the incidence of germ cell apoptosis in gld mice that lack a functional Fas-signaling pathway. gld mice have a small, but significant, increase in testis weight and numbers of spermatid heads per testis compared with wild-type mice. In addition, gld mice have a small increase in the spontaneous incidence of germ cell apoptosis, as indicated by characteristic DNA fragmentation via the terminal deoxynucleotidyl-transferase-mediated deoxy-UTP nick end labeling assay. To test the role of the Fas system in toxicant-induced germ cell apoptosis, mice were exposed to either a Sertoli cell- or germ cell-specific toxicant [mono-(2-ethylhexyl)phthalate (MEHP; 1 g/kg) or 5 Gy radiation, respectively]. These two exposure paradigms induced extensive increases in germ cell apoptosis in wild-type mice. However, exposure of gld mice to MEHP caused only a minimal increase in germ cell apoptosis, whereas they were as sensitive as wild-type mice to radiation exposure. These data indicate that the Fas signaling pathway is 1) involved in regulating the numbers of germ cells in the testis, 2) crucial for the initiation of germ cell apoptosis after MEHP-induced Sertoli cell injury, and 3) differentially active in the cell-specific regulation of germ cell apoptosis that occurs as a consequence of Sertoli cell vs. germ cell injury.

The Fas system, a regulator of testicular germ cell apoptosis, is differentially up-regulated in Sertoli cell versus germ cell injury of the testis.

Sertoli cells, the supportive cells in the seminiferous epithelium, orchestrate spermatogenesis by providing structural and nutritional support to germ cells. In the rat, physiological apoptosis occurs continuously to limit the size of the germ cell population to numbers that can be adequately supported. This form of germ cell death is exaggerated after testicular insults such as toxicant treatment, radiation, and heat exposure. The Fas system has been proposed as a key regulator of the activation of germ cell apoptosis. According to this model, Fas ligand (FasL) and Fas, expressed by Sertoli cells and germ cells, respectively, respond to environmental conditions and initiate germ cell death. To assess the role of the Fas system in various testicular injury models, a semiquantitative RT-PCR technique was used to evaluate the expression kinetics of both FasL and Fas after induction of massive germ cell death. Radiation exposure, which targets actively dividing germ cells, produced an up-regulation of Fas gene expression, but not FasL gene expression. However, administration of mono-(2-ethylhexyl)phthalate and 2,5-hexanedione, two widely studied Sertoli cell toxicants, resulted in up-regulated expression of both FasL and Fas. These data support the following hypotheses: 1) up-regulation of Fas is a common and critical step for initiating germ cell death in vivo; and 2) if Sertoli cells are injured, Sertoli cells up-regulate FasL to eliminate Fas-positive germ cells, which cannot be supported adequately.

Spermiogenesis is impaired in mice bearing a targeted mutation in the protein phosphatase 1cgamma gene.

Type 1 protein phosphatases (PP1) are involved in diverse cellular activities, ranging from glycogen metabolism to chromatin structure modification, mitosis, and meiosis. The holoenzymes are composed of two or more subunits, including a catalytic subunit (PP1c) and one or more regulatory subunits. Many eukaryotes possess several catalytic subunit genes which encode highly conserved isoforms. In rodents, one of these isoforms, PP1cgamma2, appears to be expressed predominantly in testes. Whether PP1cgamma2 performs a testis-specific function is unclear. To address this and other questions, the PP1cgamma gene was disrupted by targeted insertion in murine embryonic stem cells. Mice derived from these cells were viable, and homozygous females were fertile. However, males homozygous for the targeted insertion were infertile. Histological examination revealed severe impairment of spermiogenesis beginning at the round spermatid stage. In addition, defects in meiosis were inferred from the presence of polyploid spermatids. Immunohistochemistry revealed the presence of PP1calpha protein on condensing spermatids in both wild-type and mutant testes, suggesting that this closely related isoform is unable to compensate for the loss of PP1cgamma. These defects are discussed in the light of known functions of protein phosphatase 1.

Leuprolide, a gonadotropin-releasing hormone agonist, reestablishes spermatogenesis after 2,5-hexanedione-induced irreversible testicular injury in the rat, resulting in normalized stem cell factor expression.

2,5-Hexanedione (2,5-HD) exposure in the rat produces irreversible testicular atrophy, a model of human male infertility that can be used for mechanistic and therapeutic studies. Following testicular injury by 2,5-HD, stem cell factor (SCF), a Sertoli cell-derived growth factor that binds the c-kit receptor on spermatogonia, is altered in its expression, changing from predominantly membrane SCF to predominantly soluble SCF. The goals of this study were 2-fold: first, evaluate leuprolide, a GnRH agonist, as a therapy for 2,5-HD-induced testicular atrophy, and second, examine changes in SCF expression during testicular injury and following recovery from injury. Rats exposed to 2,5-HD showed a nearly complete testicular atrophy that could be reversed by leuprolide therapy. Using RT-PCR, preferential expression of membrane SCF was associated with spermatogenesis, whereas soluble SCF expression was associated with atrophy. In conclusion, 2,5-HD exposure altered the form of SCF expressed and disrupted spermatogenesis; leuprolide therapy allowed recovery of spermatogenesis, which correlated with a normalization in growth factor expression in an otherwise irreversibly atrophic testis.

Expression of Fas system-related genes in the testis during development and after toxicant exposure.

The Fas system has been identified as a key regulator of testicular germ cell apoptosis. The goal of these experiments was to explore the expression of Fas system-related genes in the testis during development and after toxicant exposure. Both Fas ligand (FasL) and Fas receptor (Fas) were expressed postnatally in rat testis with peak expression associated with the high levels of germ cell apoptosis found during the first wave of spermatogenesis. The testicular expression of RIP and FAP-1, components of the Fas activating complex, increased after exposure to mono-(2-ethylhexyl)phthalate (MEHP), a Sertoli cell toxicant which induces massive germ cell death. Finally, the expression of additional apoptosis-inducing genes, including tumor necrosis factor receptor (TNFR), FADD, TRAIL, and DR5, was detected in mammalian testis. These results provide additional support for the following concepts: (1) Sertoli-germ cell interactions are important in the control of germ cell apoptosis; and (2) the Fas system and similar paracrine systems are important modulators of testicular homeostasis.

Development and characterization of a prepubertal rat Sertoli cell line, 93RS2.

Sertoli cells in the seminiferous epithelium provide both structural and nutritional support to germ cells during spermatogenesis. Primary Sertoli cells in culture are an effective tool for the in vitro study of Sertoli cell function; however, primary cultures are inherently variable, time consuming to prepare, expensive, and wasteful of animals. We therefore developed a Sertoli cell line, called 93RS2, by immortalizing primary Sertoli cells derived from prepubertal rats with SV40 tsA255. This cell line proliferates at the permissive temperature (32 degrees C) and has enhanced expression of a differentiated Sertoli cell phenotype at the nonpermissive temperature (40-41 degrees C). Cytogenetic analysis demonstrated that 93RS2 has 42 chromosomes per cell, the same as a normal rat. mRNA analysis showed that this cell line, when cultured at a nonpermissive temperature, exhibited increased expression of transferrin in the presence of testosterone and enhanced expression of sulfated glycoprotein-2. A tumorigenicity assay showed that 93RS2 cells were temperature-dependent for growth in soft agar and were capable of forming tumors in nude mice. In conclusion, this rat 93RS2 cell line should be useful for the study of Sertoli cell function.