The Sertoli cell: one hundred fifty years of beauty and plasticity

It has been one and a half centuries since Enrico Sertoli published the seminal discovery of the testicular 'nurse cell', not only a key cell in the testis, but indeed one of the most amazing cells in the vertebrate body. In this review, we begin by examining the three phases of morphological research that have occurred in the study of Sertoli cells, because microscopic anatomy was essentially the only scientific discipline available for about the first 75 years after the discovery. Biochemistry and molecular biology then changed all of biological sciences, including our understanding of the functions of Sertoli cells. Immunology and stem cell biology were not even topics of science in 1865, but they have now become major issues in our appreciation of Sertoli cell's role in spermatogenesis. We end with the universal importance and plasticity of function by comparing Sertoli cells in fish, amphibians, and mammals. In these various classes of vertebrates, Sertoli cells have quite different modes of proliferation and epithelial maintenance, cystic vs. tubular formation, yet accomplish essentially the same function but in strikingly different ways.

Transplantation of bovine germinal cells into mouse testes

To develop techniques for spermatogonial transplantation in bulls, it is essential to have an effective bioassay procedure to evaluate the transplantation efficiency of spermatogonial stem cell collection, purification, and culture techniques. The objective of the present study was to develop a mouse bioassay model to evaluate transplantation efficiency of fresh and cultured bovine germ cells. Bull calves of four ages (1, 2, 3, and 4 mo) were used as a source of donor testes cells. Two calves were used for each age point, one calf was experimentally made cryptorchidistic at 1 wk of age and the other left normal. A STO (mouse fibroblast) feeder cell line was used to culture bovine testes cells for 2 wk preceding transfer into recipient testes. Immunodeficient nude mice (nu/nu) in which endogenous spermatogenesis had been abolished by busulfan treatment served as recipient animals for transplantation. Donor bovine germ cells were microinjected into mouse seminiferous tubules. Mouse testes were analyzed 2 wk after transplant with the use of a bovine-specific antibody and whole-mount immunohistochemistry for the presence of bovine donor germ cells. Bovine testis cells were present in all recipient mouse testes analyzed. Fresh bovine testes cells were observed as colonies of round cells within mouse seminiferous tubules, indicating spermatogonial expansion and colonization; however, cultured bovine testes cells appeared as fibrous tissue and not as spermatogenic colonies. The average number of colonies resulting from donor cryptorchid testes was not different (P > 0.05) from noncryptorchid, 56+/-4 and 78+/-7, respectively. Fresh donor cells from calves older than 1 mo gave rise to a greater average number of colonies within recipient testes (P <0.05) (1 mo, 33+/-4; 2 mo, 70+/-8; 3 mo, 63+/-6; 4 mo, 87+/-9). Fresh bovine germ cells are capable of colonization in the busulfan-treated nude mouse testis, making it a suitable model for evaluation and development of spermatogonial transplant techniques in bulls.

Intrinsically disordered protein

Proteins can exist in a trinity of structures: the ordered state, the molten globule, and the random coil. The five following examples suggest that native protein structure can correspond to any of the three states (not just the ordered state) and that protein function can arise from any of the three states and their transitions. (1) In a process that likely mimics infection, fd phage converts from the ordered into the disordered molten globular state. (2) Nucleosome hyperacetylation is crucial to DNA replication and transcription; this chemical modification greatly increases the net negative charge of the nucleosome core particle. We propose that the increased charge imbalance promotes its conversion to a much less rigid form. (3) Clusterin contains an ordered domain and also a native molten globular region. The molten globular domain likely functions as a proteinaceous detergent for cell remodeling and removal of apoptotic debris. (4) In a critical signaling event, a helix in calcineurin becomes bound and surrounded by calmodulin, thereby turning on calcineurin's serine/threonine phosphatase activity. Locating the calcineurin helix within a region of disorder is essential for enabling calmodulin to surround its target upon binding. (5) Calsequestrin regulates calcium levels in the sarcoplasmic reticulum by binding approximately 50 ions/molecule. Disordered polyanion tails at the carboxy terminus bind many of these calcium ions, perhaps without adopting a unique structure. In addition to these examples, we will discuss 16 more proteins with native disorder. These disordered regions include molecular recognition domains, protein folding inhibitors, flexible linkers, entropic springs, entropic clocks, and entropic bristles. Motivated by such examples of intrinsic disorder, we are studying the relationships between amino acid sequence and order/disorder, and from this information we are predicting intrinsic order/disorder from amino acid sequence. The sequence-structure relationships indicate that disorder is an encoded property, and the predictions strongly suggest that proteins in nature are much richer in intrinsic disorder than are those in the Protein Data Bank. Recent predictions on 29 genomes indicate that proteins from eucaryotes apparently have more intrinsic disorder than those from either bacteria or archaea, with typically > 30% of eucaryotic proteins having disordered regions of length > or = 50 consecutive residues.

Clusterin, a binding protein with a molten globule-like region

Clusterin is a heterodimeric glycoprotein found in many tissues of the body and is the most abundant protein secreted by cultured rat Sertoli cells. The function of clusterin is unknown, but it has been associated with cellular injury, lipid transport, apoptosis, and it may be involved in the clearance of cellular debris caused by cell injury or death. Consistent with this last idea, clusterin has been shown to bind to a variety of molecules with high affinity including lipids, peptides, and proteins and the hydrophobic probe 1-anilino-8-naphthalenesulfonate (ANS). Given this variety of ligands, clusterin must have specific structural features that provide the protein with its promiscuous binding activity. Using sequence analyses, we show that clusterin likely contains three long regions of natively disordered or molten globule-like structures containing putative amphipathic alpha-helices. These disordered regions were highly sensitive to trypsin digestion, indicating a flexible nature. The effects of denaturation on the fluorescence of the clusterin-ANS complex were compared between proteins with structured binding pockets and molten globular forms of proteins. Clusterin bound ANS in a manner that was very similar to that of molten globular proteins. Furthermore, we found that, when bound to ANS, at least one cleavage site within the protease-sensitive disordered regions of clusterin was protected from trypsin digestion. In addition, we show that clusterin can function as a biological detergent that can solubilize bacteriorhodopsin. We propose that natively disordered regions with amphipathic helices form a dynamic, molten globule-like binding site and provide clusterin the ability to bind to a variety of molecules.

Identification of a novel retrovirus expressed in rat Sertoli cells and granulosa cells

Differential display reverse transcriptase-polymerase chain reaction (DDRT-PCR) was used to identify a novel retrovirus, designated SC1, that is expressed at high levels in rat granulosa cells and prepubertal Sertoli cells. The initial DDRT-PCR screen was performed using RNA from cultured prepubertal rat Sertoli cell, liver, and brain samples. SC1 was detected in the prepubertal rat Sertoli cell samples but not in those from liver and brain. SC1 cDNA was 6 kilobases in length and contained regions encoding for the gag, pol, and env retroviral proteins. Northern blot analysis failed to detect expression of the SC1 gene in total RNA isolated from adult brain, heart, spleen, lung, liver, skeletal muscle, kidney, prostate, and epididymis. Similarly, Northern blot analysis of testes from rats at various ages of development showed that high-level expression of the SC1 gene was limited to prepubertal testis samples. In situ hybridization analysis localized the SC1 mRNA to the seminiferous tubules of prepubertal testes and at a much lower level in Sertoli cells of adult testes. Northern blot analysis of total RNA isolated from Sertoli cells from 20-, 27-, and 35-day-old rat Sertoli cells and type A spermatogonia, pachytene spermatocytes, and round spermatids showed expression of the SC1 gene to be restricted to 20- and 27-day-old Sertoli cells, with no expression detected in germ cells. Furthermore, Northern blot analysis also showed expression of the SC1 gene in rat ovaries, and the level of expression was affected during eCG/hCG-induced ovulation. Expression of SC1 mRNA was localized by in situ hybridization of eCG-treated ovaries to the granulosa cell layer in developing follicles. Southern blot analysis showed SC1 to be endogenous in the rat and absent in mouse and human cell genomes. Transient transfection assays using the SC1 promoter region showed high promoter activity in MSC-1 and cultured prepubertal rat Sertoli cells, and no activity in 3T3 or MCF-7 cell lines.

Distribution of type A spermatogonia in the mouse is not random

The distribution of type A spermatogonia was studied using drawings of cross-sectioned tubules at various stages of the spermatogenic cycle of perfusion-fixed, epoxy-embedded mouse testis. Spermatogonia were classified as either positioned opposite the interstitium or opposite the region where two tubules make contact or in a defined, intermediate region at which the two tubules diverged. At stage V, the population of type A spermatogonia, comprised of A(s) through A(al) cells, is randomly positioned around the periphery of the seminiferous tubule. The A(s) through A(al) population becomes nonrandomly distributed beginning at stage VI, being located primarily in regions where the tubule opposes the interstitium, and remains nonrandom through stage III of the next cycle. The A(1) spermatogonia of stage VII, derived from most A(pr) and A(al) spermatogonia, and the A(2) spermatogonia of stage IX, derived from the A(1) spermatogonia, are also nonrandomly positioned opposing the interstitium. However, the A(3) population of stage XI becomes randomly distributed around the tubule. To our knowledge, these are the first data to show that the more primitive spermatogonial types (A(s) to A(al)) move to specific sites within the seminiferous tubule. Division of the regularly spaced, more primitive spermatogonia (A(s) to A(al)) leads to the spread of their progeny (A(1) to A(4)) laterally along the base of the seminiferous tubule. The lateral spread from more or less evenly spaced foci ensures that spermatogenesis is conducted uniformly around the entire tubule. The data also suggest that the position of a seminiferous tubule in the mouse is stabilized in relationship to other seminiferous tubules.

E2F and GATA-1 are required for the Sertoli cell-specific promoter activity of the follicle-stimulating hormone receptor gene

The follicle-stimulating hormone receptor (FSHR) gene is expressed in Sertoli cells in males and in granulosa cells in females. Cis-acting sequences and associated binding factors responsible for the transcription of the TATA-less FSHR gene in Sertoli cells were analyzed with dimethylsulfate (DMS) footprinting assays and electrophoretic mobility shift assay (EMSA). In vivo footprints in the core promoter using nuclear proteins from Sertoli cells identified several protected sequences, including an inverted GATA (TATC, -88/-85), and an E2F (TTTCGCG, -45/-39) motif. EMSA showed the presence of one or more sequence-specific proteins interacting with these potential regulatory elements. Antibody-supershift assays as well as competition assays further revealed that testis-specific GATA-1 recognized the inverted GATA element. The functional role of the potential cis-acting elements was analyzed by transient transfection assays with and without mutations of the putative elements. The mutational analysis indicated that the GATA and E2F elements were each required for optimal promoter activity. The effects of each of the promoter elements was examined in transfections in which mutations were made in each of the known regulatory sites, including the E box, GATA, and E2F sites in various combinations. All of these sites contribute to the maximum promoter activity such that mutations of the E box, GATA, and E2F sites eliminated nearly all promoter activity.

Murine germ cells do not require functional androgen receptors to complete spermatogenesis following spermatogonial stem cell transplantation

The spermatogonial stem cell transplantation technique was employed to determine if murine germ cells require functional androgen receptors to complete qualitatively normal spermatogenesis. Testicular cells from testicular feminized mice were injected into the seminiferous tubules of azoospermic mice expressing functional androgen receptors. Recipient testes were analyzed between 110 and 200 days following transplantation. Multiple colonies of complete and qualitatively normal donor-derived spermatogenesis were seen within the seminiferous tubules of each recipient testis, demonstrating that murine germ cells do not require functional androgen receptors to complete spermatogenesis.

A fragment of prosaposin (SGP-1) from rooster sperm promotes sperm-egg binding and improves fertility in chickens

A protein isolated from the supernatant of cryopreserved rooster sperm was found to increase the capability of cryopreserved rooster sperm to bind in vitro to the perivitelline membrane of a chicken egg and substantially raise fertility after artificial insemination (AI). That activity was partially purified and termed universal primary sperm-egg binding protein (UPSEBP). Insufficient protein remained from 6 x 10(11) sperm, despite retention of bioactivity, to allow sequencing. We deduced that the protein may be related to prosaposin (also termed SGP-1, for sulfated glycoprotein-1), and we used published amino acid sequences of prosaposin as a guide for synthesis of peptides. Certain peptides were found to increase in vitro sperm-egg binding and increase fertility of frozen-thawed or fresh rooster sperm, in a manner similar to semipurified UPSEBP. Active epitopes were in a 60 amino acid sequence, reflecting the intervening sequence between saposins A and B, plus short extensions into saposins A and B. Highest activity was found when this synthetic peptide was oxidized to form a disulfide bond between terminal cysteines. Antibody against a synthetic peptide consisting of 58 of these 60 amino acids bound to a 7-9 kilodalton protein in UPSEBP. Collectively, the data support the conclusion that UPSEBP is a fragment of prosaposin. Because prosaposin is in semen in humans and animals, these observations have broad implications for possible cause and therapy of one type of subfertility.

Mechanisms involved in the homologous down-regulation of transcription of the follicle-stimulating hormone receptor gene in Sertoli cells

The action of follicle-stimulating hormone (FSH) in spermatogenesis is regulated at a fundamental level by controlling the number of competent receptors present at the surface of Sertoli cells. By controlling the number of receptors, the cell is able to modulate the timing and magnitude of subsequent signal transduction in response to FSH. One mechanism of control is the down-regulation of the steady state levels of the FSH receptor gene after exposure to FSH or agents that stimulate or prolong the cAMP signal transduction cascade (homologous down-regulation) in Sertoli cells. The goals of this study were to examine possible mechanisms involved in the down-regulation of mRNA levels of this gene. Analysis of transcription and processing by a PCR-based assay showed that treatment of Sertoli cells with FSH caused at least a 50% reduction of hnRNA for the FSH receptor gene. Reporter genes controlled by 5' flanking sequences of the FSH receptor gene that were transiently transfected into Sertoli cells were not down-regulated. In electrophoretic mobility shift assays (EMSA), cAMP-inducible nuclear protein complex containing c-Fos formed on the activator protein-1/cAMP responsive element-like site located at -216 to -210 in the promoter of the rat FSH receptor gene. We concluded from this study that there was no evidence for the putative role of ICER in the down-regulation of the FSH receptor promoter. In addition, the FSH-induced down-regulation of the transcription of the FSH receptor gene in Sertoli cells was prevented by the treatment of Sertoli cells with trichostatin A prior to the addition of FSH. This experiment coupled with other observations suggested that the down-regulation may be mediated by changes in chromatin structure.

Site-specific methylation of the promoter alters deoxyribonucleic acid-protein interactions and prevents follicle-stimulating hormone receptor gene transcription

In the male gonad, the FSH receptor (FSHR) gene is expressed only in Sertoli cells. To date, the mechanism(s) responsible for Sertoli cell-specific expression of the FSHR gene are unknown. In this study, DNA methylation at specific sites in the promoter are shown to lead to changes in the DNA-protein interactions at those sites and, subsequently, to transcriptional repression of the gene. The extent of methylation of cytosine residues within the core promoter region of genomic DNA isolated from cells/tissues that expressed, or did not express, the FSHR gene was analyzed by the sodium bisulfite conversion technique. All seven cytosine residues in CpG dinucleotides within the core promoter region were found to be unmethylated in primary cultured rat Sertoli cells that were actively expressing FSHR mRNA. In contrast, in tissues not expressing FSHR the same region of the gene was methylated at each of the CpG dinucleotides examined. In addition, DNA-protein interactions in three primary regulatory regions of the promoter were examined by electrophoretic mobility shift assays (EMSA) with synthetic oligonucleotides containing selectively methylated cytosine residues. Methylation of a CpG sequence within a consensus E box element (CACGTG, -124/-119) decreased the binding affinity of USF1/2 transcription factors for this element. Methylation of the CpG sequence in the Inr region (CCGG, -85/-82) allowed the formation of an additional DNA-protein complex. Methylation at both cytosine residues in the E2F element ((m)CG(m)CG) generated a new methylcytosine-specific DNA-protein complex. The core FSHR promoter region of a mouse Sertoli cell line (MSC-1) that does not express FSHR was shown to be methylated at four CpG dinucleotides. The demethylation of these four sites by treatment of the MSC-1 cells with 5-aza-2'-deoxycytidine (5-azaCdR) activated the transcription of the FSHR gene. Taken together, these results suggest that cytosine methylation is a major factor in the repression of the expression of the FSHR gene.

Germ cell transplantation and the study of testicular function

Spermatogonial stem cell transplantation is a novel technique in which donor testicular cells are transferred into recipient testes. A population of germ cells from a transgenic or mutant donor is introduced into the seminiferous tubules of recipient testes by microinjection. Following injections, spermatogonial stem cells can colonize the recipient testis, initiate spermatogenesis and produce sperm capable of fertilization. This technique will allow scientists to: (1) investigate fundamental aspects of spermatogenesis; (2) provide a method to regenerate spermatogenesis in infertile individuals; and (3) genetically manipulate spermatogonial stem cells to develop transgenic animals.

Clusterin gene in rat sertoli cells is regulated by a core-enhancer element

Clusterin is a ubiquitous glycoprotein that is promiscuously expressed at a low basal level but can be highly induced by a variety of stress conditions. In contrast, in some secretory cells associated with tissue-fluid interfaces such as the Sertoli cells in the testis, clusterin demonstrates high constitutive expression. In this study, we address the mechanisms that regulate the constitutive expression of the clusterin gene by using primary cultures of immature rat Sertoli cells. We have identified a region of the rat clusterin gene promoter that activated transcription only in Sertoli cells and that mapped between positions -426 and -311. Sequence analysis of this region revealed a high concentration of potential regulatory elements. Using gel-shift assays combined with hydroxyl radical footprinting, we identified the elements recognized by the Sertoli cell nuclear factors. Comparison of the interactions with this region of the nuclear factors from different cell types demonstrated that recognition of the core-enhancer element is specific for the Sertoli cells, and in vitro, the core region was recognized by the transcription factor CBF. Transient transfections showed that a core enhancer is responsible for more than a half of the total promoter activity and is an essential element for the cell-specific activity of the Sertoli-specific region. In addition to the core enhancer, tandem Sp1 sites are also required for maximal activity of this region.

Juvenile spermatogonial depletion (jsd) mutant seminiferous tubules are capable of supporting transplanted spermatogenesis

In mice, the juvenile spermatogonial depletion (jsd) mutation results in a single wave of spermatogenesis followed by failure of type A spermatogonial stem cells to repopulate the testis, rendering male animals sterile. It is not clear whether the defect in jsd resides in a failure of the somatic component to support spermatogenesis or in a failure that is intrinsic to the mutant's germ cells. To determine if the jsd intratesticular environment is capable of supporting spermatogenesis, germ cell transplantation experiments were performed in which C57BL/6 ROSA germ cells were transplanted into jsd recipients. To determine if jsd spermatogonia are able to develop in a permissive seminiferous environment, jsd germ cells were transplanted into W/W(v) and busulfan-treated C57BL/6 animals. The data demonstrate that up to 7 mo after transplantation of normal germ cells, jsd seminiferous tubules are capable of supporting spermatogenesis. In contrast, when jsd germ cells were transplanted into busulfan-treated C57BL/6 testis, or into testis of W/W(v) mice, no jsd-derived spermatogenesis was observed. The data support the hypothesis that the jsd phenotype is due to a defect in the germ cells themselves, and not in the intratubular environment.

Advances in spermatogonial stem cell transplantation

Spermatogonial stem cell transplantation was first reported by Ralph Brinster's laboratory in 1994. It has proven to be a technological breakthrough in the study of both stem cells and Sertoli cell-germ cell interactions. This technique can be used to transfer testicular stem cells successfully from one animal to another of the same species (referred to as syngeneic transplants) and sometimes to an animal of a different species (xenogeneic transplants). This transfer technique, combined with developments in cryopreservation, long-term culture, and the enrichment of stem cell populations makes more significant breakthroughs likely in the near future. Ultimately, the application of spermatogonial stem cell transfer will allow transplantation of cultured stem cells manipulated genetically in vitro to give rise to functional male gametes with an altered genotype. This achievement will have applications in basic science, human medicine, and domestic and wild animal reproduction. Although progress toward this goal has been swift, potentially significant barriers, such as the stable incorporation of genetic material into stem cells and immunological responses to the introduced germ cells, remain to be overcome. This article is a review of the scientific advances made since the initial report of successful transplantation in 1994.

E-MAP-115, encoding a microtubule-associated protein, is a retinoic acid-inducible gene required for spermatogenesis

Cell type-specific microtubules, such as the Sertoli cell microtubules and the manchette and flagellum microtubules of the spermatids, play essential roles in spermatogenesis. We identified the gene encoding E-MAP-115 (epithelial microtubule-associated protein of 115 kD) as a retinoic acid-inducible gene using gene trap mutagenesis in mouse embryonic stem cells. The gene trap insertion led to a null allele of the E-MAP-115 gene and, in agreement with its high expression in the testis, male mice homozygous for the mutation were sterile because of deformation of spermatid nuclei and subsequent gradual loss of germ cells. Consistent with a possible role for E-MAP-115 in stabilizing microtubules, microtubule associations in the mutant were morphologically abnormal in the manchette of spermatids and in Sertoli cells. We hypothesize that the abnormal microtubules in these two cell types are responsible for deformation of spermatid nuclei and germ cell loss, respectively, and indicate an essential role for E-MAP-115 in microtubule functions required for spermatogenesis.

Identification of INSL6, a new member of the insulin family that is expressed in the testis of the human and rat

A new member of the insulin gene family (INSL6) was identified from an Expressed Sequence Tag database through a search for proteins containing the insulin family B-chain cysteine motif. Human and rat INSL6 encoded polypeptides of 213 and 188 amino acids, respectively. These orthologous sequences contained the B-chain, C-peptide, and A-chain motif found in other members of the insulin family. Human INSL6 was 43% identical to human relaxin H2 in the B- and A-chain regions. As with other family members, human and rat INSL6 had predicted dibasic sequences at the junction of the C-peptide and A-chain. Human INSL6 sequence had an additional dibasic site near the C-terminus of the A-chain. The presence of a single basic residue at the predicted junction of the B-chain and C-peptide suggests that multiple prohormone convertases are required to produce the fully mature hormone. INSL6 was found to be expressed at high levels in the testis as determined by Northern blot analysis and specifically within the seminiferous tubules in spermatocytes and round spermatids as detected by in situ hybridization analysis. Radiation hybrid mapping placed the human INSL6 locus at chromosome 9p24 near the placenta insulin-like homologue INSL4 and the autosomal testis-determining factor (TDFA) locus.

Spermatogonial transplantation - an update for the millennium

Spermatogonial transplantation as developed in the laboratory of Ralph Brinster has been a technological breakthrough in the study of Sertoli-germ cell interactions. For the first time, germ cells can be transferred from one animal to another and from one species to another. The transfer technology combined with developments in freezing germ cells, long-term culture of germ cells, and enrichment of stem cell populations portend even more significant breakthroughs in the new millennium. The ultimate application of germ cell transfer would allow the in vitro genetic manipulation of cultured stem cells that could then be transplanted into recipient syngeneic or xenogeneic recipients and give rise to functional male gametes. Clearly, this achievement would have applications in basic science, human medicine, and domestic and wild animal reproduction. While progress in this direction has been significant and swift, significant barriers such as immunological response and mechanisms for introducing genetic material into the stem cells remain to be examined. This report is a chronological review of the technological advances made and conceptual insights gained since the first report of successful transplantation in 1994.

Follicle-stimulating hormone inhibits all-trans-retinoic acid-induced retinoic acid receptor alpha nuclear localization and transcriptional activation in mouse Sertoli cell lines

The regulation of retinoic acid receptor alpha (RARalpha) signal transduction has not been well characterized. In this study, we determined whether all-trans-retinoic acid (tRA) and follicle-stimulating hormone (FSH) modulate RARalpha receptor subcellular localization, leading to changes in its transcriptional activity and protein expression in mouse Sertoli cell lines. We found that tRA induced the nuclear localization of RARalpha within 30 min and that longer term exposure increased the receptor transcriptional activity and RARalpha protein expression. Conversely, FSH suppressed the tRA-induced nuclear localization, transcriptional transactivation, and protein expression of RARalpha. Treatment with two different protein kinase A-selective antagonists reversed the inhibitory actions of FSH on tRA-dependent RARalpha nuclear localization and transcriptional activity. These results are consistent with the involvement of protein kinase A in mediating the inhibitory effects of FSH. For the first time, we demonstrate a unique signaling convergence between the RARalpha and the FSH-mediated signaling pathways, which may have significant implications in the testis because both are critical regulators of testis physiology.

Clusterin in the male reproductive system: localization and possible function

Clusterin is a glycoprotein that was initially isolated from the male reproductive system. Subsequently, clusterin has been found to be widely distributed in a variety of tissues in mammals. One characteristic of the expression of clusterin is that it is induced as a result of cellular injury, death, or pathology. Despite the efforts of many laboratories working in diverse biological systems, the function of clusterin remains unknown. Recent studies have revealed a 'heat-shock element' in the promoter of the gene that may account for the inducible nature of the clusterin gene. Overall, the evidence suggests that function of clusterin is to protect surviving cells after damage. This protection may result from a detergent-like action of the protein.

The central role of Sertoli cells in spermatogenesis

Sertoli cells are the somatic cells of the testis that are essential for testis formation and spermatogenesis. Sertoli cells facilitate the progression of germ cells to spermatozoa via direct contact and by controlling the environment milieu within the seminiferous tubules. The regulation of spermatogenesis by FSH and testosterone occurs by the action of these hormones on the Sertoli cells. While the action of testosterone is necessary for spermatogenesis, the action of FSH minimally serves to promote spermatogenic output by increasing the number of Sertoli cells.

Androgen regulation of the Pem homeodomain gene in mice and rat Sertoli and epididymal cells

Although the role of homeodomain transcription factors during embryogenesis is well known, their developmental function in postnatal animals is only beginning to be understood. We examined the regulation and expression pattern of Pem, a homeodomain protein that may regulate androgen-dependent events in the testis and epididymis. Immunohistochemical analysis showed that Pem protein is expressed selectively in the nuclei of Sertoli cells during the androgen-dependent stage of the seminiferous epithelium cycle in vivo. RNase protection analysis revealed that a proximal promoter was responsible for androgen-dependent mouse Pem expression in testis and epididymis in vivo, whereas a distal promoter was used in placenta. The mouse Pem gene was expressed at approximately 10-fold higher levels in the testis than in the epididymis; conversely, the rat Pem gene was expressed at >10-fold higher levels in the epididymis than in the testis. Because androgen-binding protein has been proposed to transport androgens from the testis to the epididymis, we tested whether the > or = 20-fold higher levels of androgen-binding protein expression in the rat, compared to that of mouse, are responsible for the differential expression of Pem in these two rodent species. Studies with androgen-binding protein transgenic mice demonstrated that the species-specific difference in androgen-binding protein expression is unlikely to be responsible for the species-specific difference in Pem expression. We found that androgen is necessary but not sufficient for Pem expression, since purified Sertoli cells rapidly down-regulated Pem transcripts in culture, regardless of the presence of testosterone. We conclude that Pem gene expression in Sertoli cells requires other cell types or cellular factors in addition to androgen.

Accumulation of clusterin/sulfated glycoprotein-2 in degenerating pachytene spermatocytes of adult rats treated with methoxyacetic acid

Clusterin is a ubiquitous glycoprotein that is produced constitutively by Sertoli cells at relatively high amounts. Its association with apoptosis, damage, disease, and repair in nongonadal tissues led us to investigate whether clusterin could be part of a damage-induced response in Sertoli cells brought on by apoptosis of an adjacent cell type. Therefore, the objective of this study was to treat adult rats with methoxyacetic acid (MAA) to selectively destroy pachytene spermatocytes, examine the localization and expression of testicular clusterin, and relate this to the timing of DNA fragmentation, a hallmark of apoptosis. Clusterin protein was localized to the cytoplasm of pachytene spermatocytes at 6 h post-MAA, whereas clusterin mRNA was localized to Sertoli cells. Morphological degeneration of dying cells and DNA fragmentation were not seen until 12 h. Thus, Sertoli cell-derived clusterin had accumulated in the cytoplasm of degenerating spermatocytes early in the apoptotic process. On the basis of these results and the known binding of clusterin to hydrophobic macromolecules, we hypothesize that clusterin is produced by Sertoli cells as a mechanism to "clear" potentially harmful cellular components during the degeneration of germ cells and remodeling of their membranes that occur normally during spermatogenesis.

Specific testicular cellular localization and hormonal regulation of the PKIalpha and PKIbeta isoforms of the inhibitor protein of the cAMP-dependent protein kinase

We have previously demonstrated that there exist two distinct genes for the thermostable inhibitor protein of the cAMP-dependent protein kinase, PKIalpha and PKIbeta (Van Patten, S. M., Howard, P., Walsh, D. A., and Maurer, R. A. (1992) Mol. Endocrinol. 6, 2114-2122). We have also shown that in the testis, at least eight forms of PKIbeta exist, differing as a result of at least post-translational modification and alternate translational initiation (Kumar, P., Van Patten, S. M., and Walsh, D. A. (1997) J. Biol. Chem. 272, 20011-20020). We now report that in the testis, there is a unique cellular distribution of protein kinase inhibitor forms, with PKIbeta being essentially (if not exclusively) a germ cell protein and PKIalpha being expressed primarily in Sertoli cells. Furthermore, there is a progressive change in the forms of PKIbeta that are present within germ cells with development that is initiated in testis tubules and continues as the germ cells migrate through the epididymis. These conclusions are derived from studies with isolated cell populations and with the at/at germ cell-deficient mouse line, by in situ hybridization, and by following the developmental expression of these proteins in both testis and epididymis. We have also shown that follicle-stimulating hormone (FSH) can increase the expression of both PKIalpha and PKIbeta. The FSH-regulated expression of PKIalpha in the Sertoli cell likely occurs via the normal route of second messenger signal transduction. In contrast, the FSH-dependent PKIbeta expression must arise by some form of Sertoli cell-germ cell intercommunication.

Follicle-stimulating hormone (FSH) regulates the expression of FSH receptor messenger ribonucleic acid in cultured Sertoli cells and in hypophysectomized rat testis

FSH acts on Sertoli cells via interaction with a transmembrane receptor (FSHr). Control of expression of the receptor is surely a factor in the regulation of the action of FSH. The regulation of FSHr by FSH and testosterone was studied both in culture and in vivo. Sertoli cells from 18- to 20-day-old male rats were cultured in the presence of 25 ng/ml ovine (o) FSH. At 8 h after addition of FSH, expression of FSHr mRNA decreased significantly. Addition of FSH and actinomycin D to cells did not result in a further decrease in FSHr mRNA levels, suggesting that FSH does not alter turnover of FSHr mRNA. Treatment of cells with 40 ng/ml testosterone did not have any significant effect on the expression of FSHr mRNA. Hypophysectomy of 20-day-old male rats resulted in an increase in expression of FSHr mRNA as compared to that in sham-hypophysectomized animals. This increase was measured at 24 h posthypophysectomy and was maintained at 72 h after surgery. Injection of rats with 0.2 U oFSH at 48 h posthypophysectomy resulted in a reduction in FSHr mRNA when compared to the levels in hypophysectomized rats. Treatment with 2 mg testosterone propionate had no effect on FSHr mRNA levels. The findings confirm that FSH plays an important role in regulating mRNA expression of the FSHr in Sertoli cells in culture and show for the first time that FSHr mRNA is regulated in vivo by FSH in the immature rat testis.

Expression of clusterin/sulfated glycoprotein-2 under conditions of heat stress in rat Sertoli cells and a mouse Sertoli cell line

Clusterin is the major protein produced by rat Sertoli cells and is deposited onto sperm membranes; however, its function is unknown. In order to gain insight into the regulation of clusterin in Sertoli cells, the objective of the present study was to develop a model where the expression of clusterin could be affected in Sertoli cells in vitro. Rat Sertoli cells and mouse Sertoli cells (MSC1) were cultured under heat stress conditions (41 degrees C) for up to 48 hours. The mRNA for clusterin in Sertoli cells was compared to that in human epitheliod cancer cells (A431) to determine if clusterin expression was regulated in a lestis-specific manner. The mRNA for heat shock protein 70 (HSP70) was also examined as it is a known stress-regulated gene. Expression of HSP70 mRNA was increased in all three cell types by 4 hours after the start of heat stress. Clusterin mRNA was increased over that of controls by 4 hours in heat-stressed A431 cells but did not significantly increase in MSC1 or Sertoli cells until 12 hours (P < 0.05). The induction of clusterin mRNA in MSC1 cells continued for at least 48 hours and required the sustained exposure of cells to the 41 degrees C temperature. The increase in the amount of clusterin mRNA was not due to an increase in transcript half-life, as determined by the addition of actinomycin D to the media of control vs. heat-stressed MSC1 cells. From the development of this in vitro model, we have seen that the timing of induction of clusterin by heat stress is Sertoli cell specific and is different than that of HSP70. This response in surviving cells during heat stress may be protective in that clusterin would bind to toxic compounds or solubilize cellular debris released by degenerating cells.

Decreased spermatogenesis as the result of an induced autoimmune reaction directed against the gonadotropin receptors in male rats

The presence of luteinizing hormone (LH) and testosterone is considered critical for the maintenance of spermatogenesis in the rat. However, the role and importance of follicle-stimulating hormone (FSH) in the initiation and maintenance of spermatogenesis has been a subject of debate for some time. The objective of this study was to examine the role of FSH and LH in vivo in the developing and adult rat by inducing an autoimmune reaction against the receptors to these gonadotropins. Sperm numbers were reduced in animals immunized against either the FSH or LH receptor (FSHR/LHR). In animals immunized against both FSHR and LHR there was also a significant reduction in sperm number although spermatogenesis was never completely ablated. These results were seen in male rats immunized either prepubertally (18 days of age) or as adults (80 days of age). To examine the requirements for FSH in early postnatal-testicular development, pregnant females were also immunized against either FSHR, LHR, or both of the receptors, and the male offspring were examined at 30 days of age. Again, germ-cell number was decreased with the greatest effect in those pups whose mothers were immunized against both FSHR and LHR. Radioligand-receptor-binding assays revealed that the antibody produced in the rats against FSHR was able to compete with FSH for binding sites in receptor-membrane preparations. Therefore, the mechanism of disruption of spermatogenesis is probably due to suppression of hormone to receptor binding. The results of this study support a role for FSH in spermatogenesis not only during neonatal and early postnatal development but also in the adult animal.

Expression of apolipoprotein E mRNA in the epithelium and interstitium of the testis and the epididymis

Apolipoprotein E (apo E) is an important constituent of plasma lipoproteins and is believed to be involved in the regulation of lipid transport and distribution between tissues. The production of this apolipoprotein in extra-hepatic tissues such as the testis and epididymis could facilitate specific local functions. Apo E mRNA was detected in testis, epididymis, seminal vesicles, and prostate. In the epididymis, apo E was detected using in situ hybridization in epithelial cells and in some cells in the interstitium throughout the organ (i.e., caput, corpus, and cauda). Northern blot analysis showed that apo E mRNA is present in Sertoli cells and germ cells, but not peritubular myoid cells. Interstitial cells of the testis displayed the most intense signal for apo E message using in situ hybridization. Messenger RNA for apo E was also detected in the interstitium of rat testes at 3 and 6 days after animals were treated with ethylene dimethanesulfonate (EDS) to eliminate Leydig cells. Thus, in addition to Leydig cells, other cell types within the interstitium are capable of producing apo E message. Levels of testicular apo E mRNA increased between 30 and 60 days pc during which the germ cell population is increasing. As determined by northern blot analysis of RNA from stage synchronized testes, the levels of apo E mRNA fluctuate in relation to the cycle of the seminiferous epithelium. The cells responsible for this stage-specific variation in message could not be identified by in situ hybridization. Apolipoprotein Al (apo Al) mRNA was also found to be expressed in the epididymis but not in the testis of adult rats. The role of apolipoproteins in spermatogenesis and sperm maturation has not been elucidated. The results of this study demonstrate the specific tissues and cells types which play a role in the production and possible regulation of apo E mRNA in the male reproductive tract. These data will help in the elucidation of the function of apo E in spermatogenesis and sperm maturation.

Role of E box and initiator region in the expression of the rat follicle-stimulating hormone receptor

The promoter for the rat follicle-stimulating hormone receptor (FSHR) gene contains a conserved consensus E box sequence and an initiator-like region (InR) sequence. Deletion analysis and transient transfections showed that a 114-base pair region (-143 to -30) that encompasses the E box and the InR was sufficient for greater than 75% of promoter function. DNase I footprint analysis showed that the E box and InR were protected by nuclear proteins from rat Sertoli cells, and the E box region was shown by electrophoretic mobility shift assays (EMSA) to be a site of Sertoli protein interactions. Mutations in the E box disrupted these interactions and reduced FSHR promoter activity. Co-transfection of the inhibitor of DNA binding (Id) with an FSHR/luciferase construct into mouse Sertoli 1 cells reduced FSHR promoter activity. Using EMSA, the upstream stimulatory factor was shown to be a component of the complexes that interacted with the E box in the FSHR promoter. Binding of proteins from rat Sertoli cells to the InR was demonstrated using EMSA. Also, an oligonucleotide that represented the sequence of the terminal deoxynucleotidyltransferase InR displaced the complexes at the FSHR InR. Mutations in the InR resulted in a significant reduction of FSHR promoter activity.

Steady-state luteinizing hormone receptor messenger ribonucleic acid levels and endothelial cell composition in bovine normal- and short-lived corpora lutea

The short-lived corpus luteum (CL) contributes to reproductive inefficiency during the postpartum period in beef cows. The cause for the early demise of the short-lived CL is not fully understood but is believed to involve a premature release of prostaglandin F2 alpha. The objectives of this study were to evaluate norgestomet-hCG-induced normal-lived CL and hCG-induced short-lived CL in postpartum cows with respect to serum progesterone (P4) and 13,14-dihydro-15-keto, prostaglandin F2 alpha (PGFM) concentrations and luteal LH receptor (LH-R) concentrations, LH-R mRNA levels, and vascularity. Although serum P4 profiles from the time of hCG administration (Day 0) until luteectomy (Day 6, 7, or 8) were similar between CL life span groups, PGFM concentrations were elevated (p < 0.05) on Day 8 in cows expected to have short-lived CL compared to normal-lived CL. The LH-R concentrations were similar between normal- and short-lived CL on all days measured. Irrespective of luteal life span and day of luteectomy, all CL possessed a 4.4-kb LH-R transcript. Actin-normalized LH-R mRNA levels were similar between normal- and short-lived CL on Days 6 and 7; however, Day 8 short-lived CL contained less (p < 0.05) LH-R mRNA than Day 8 normal-lived CL. Although the area of luteal tissue occupied by capillaries in normal- and short-lived CL was similar on Days 6 and 7, the area occupied by capillaries in short-lived CL was lower (p < 0.05) than that for normal-lived CL on Day 8. Collectively, these results indicate that there is a decrease in steady-state LH-R mRNA and a reduction in luteal vascularity in CL expected to be short-lived. These changes occur concomitantly with a rise in serum PGFM, but prior to a decline in serum P4.

The molecular biology of the FSH receptor

The actions of follicle stimulating hormone (FSH) mediated through its receptor are necessary for the proper functioning of mammalian gonads. The FSH receptor is localized on granulosa cells of the ovary and Sertoli cells of the testis. The expression of the FSH receptor (FSHR) in Sertoli cells varies in vivo as a function of the stage of the cycle of the seminiferous epithelium and in culture as a result of the addition of exogenous hormones. The gene for the FSH receptor is large and has been shown to be related in structure to the genes for luteinizing hormone (LH) receptor and thyroid stimulating hormone (TSH) receptor. The promoter region of the gene for FSHR does not contain a TATA box and has multiple transcriptional start sites. Less than 280 bp of the promoter are sufficient in transient transfection assays to direct expression of the chloramphenicol acetyl transferase gene (CAT) in a number of different cell types including non-gonadal cells. However, the promoter does direct the expression of a marker gene only into testis and ovary of transgenic mice.

Prevention of cell death induced by tumor necrosis factor alpha in LNCaP cells by overexpression of sulfated glycoprotein-2 (clusterin)

Sulfated glycoprotein-2 (SGP-2) expression has been associated with programmed cell death in the prostate, but its exact role remains unclear. The present study was carried out in an attempt to establish the function of SGP-2 in programmed cell death using tumor necrosis factor (TNF) alpha-induced cytotoxicity in LNCaP cells as the model system. LNCaP is an androgen-sensitive, human prostatic cancer cell line that responds to TNF in culture by undergoing programmed cell death, as determined by the loss of cell number, failure to exclude trypan blue, detection of DNA fragmentation, and increased release of previously incorporated [3H]thymidine. Immunocytochemical staining for SGP-2 was weak but evident in LNCaP cells. Following treatment with TNF alpha, there was a time-dependent increase in SGP-2 staining, the intensity of which peaked at 2 h and declined thereafter. SGP-2 staining in LNCaP cells was undetectable prior to the onset of DNA fragmentation at 6 h of TNF treatment. This observation indicated that TNF-induced cell death in LNCaP cells was characterized by an initial transient elevation of SGP-2, followed by a period of SGP-2 depletion that preceded cell death. Transfection of LNCaP with a 21-base oligonucleotide antisense to SGP-2 resulted in a significant increase in cell death that was sequence specific and was accompanied by a reduction in SGP-2 biosynthesis. These findings supported the concept that SGP-2 depletion, rather than its expression, was associated with cell death. Finally, stable transfection and subsequent overexpression of SGP-2 in LNCaP cells resulted in resistance to the cytotoxic effect of TNF. These results have provided evidence to indicate that SGP-2 plays a role in the protection of TNF-induced cell death in LNCaP cells.

Isolation and culture of Sertoli cells from the testes of adult Siberian hamsters: analysis of proteins synthesized and secreted by Sertoli cells cultured from hamsters raised in a long or a short photoperiod

In the present study, we describe two procedures for isolation and culture of Sertoli cells from the testes of adult Siberian hamsters. In procedure I, collagenase and pancreatin were used for differential enzymatic digestion of the tissue at 32 degrees C, and effects of several attachment factors were examined. Sertoli cells isolated from adult hamsters were not affected by addition of Na selenite, epidermal growth factor, insulin, and transferrin, with or without 5% fetal bovine serum, to Dulbecco's modified Eagle's medium + Ham's F-12. Significant increase in the yield and plating efficiency of Sertoli cells was achieved by developing a novel procedure (procedure II) for Sertoli cell isolation. In this procedure, testicular tissue was exposed to only one enzyme (collagenase I) for two consecutive digestions at 37 degrees C, and the total period of enzymatic exposure was reduced relative to that of procedure I. Another objective of this study was to compare the functions of Sertoli cells isolated from spermatogenetically active and inactive adult testes. Isolated Sertoli cells from 60 +/- 5-day-old hamsters raised in long day conditions (LD, 16L:8D) or in short day conditions (SD, 6L:18D) were stimulated with FSH and testosterone in the presence of 35S-methionine for 24 h on Day 4 of culture. The medium was concentrated, and equal amounts of radioactive proteins from LD and SD hamster Sertoli cell cultures were analyzed by two-dimensional PAGE. Compared to Sertoli cells derived from SD hamsters, Sertoli cells from LD animals produced greater amounts of two secretory proteins and a smaller amount of one.(ABSTRACT TRUNCATED AT 250 WORDS)

Interactions between germ cells and Sertoli cells in the testis

The "nurse cell" function of Sertoli cells in spermatogenesis was originally tacitly assumed on the basis of the anatomical relationships between cells in the testis. In mammals, from very early in prenatal development to the onset of meiosis and to the ultimate production of spermatozoa, the relationship between the germinal cells and the Sertoli cells is important and apparently obligatory. The experimental evidence supports the notion that the primary endocrine regulation of spermatogenesis via FSH and testosterone is manifested through actions on the Sertoli cells. Although diverse strategies are used by Sertoli cells to support germ cell development, one of the most important roles of Sertoli cells is the regulation of the intratubular and intercellular environment adluminal to the tight junctional complexes. The meiotic and post-meiotic germ cells are sequestered by Sertoli-Sertoli junctional complexes in an adluminal compartment that is isolated from the serum or lymph. As a result of this sequestering activity, the secretion products of the Sertoli cells and the meiotic germ cells determine the composition of this local environment that can influence meiosis as well as spermatid and spermatocyte development. Evidence is accumulating that paracrine and autocrine factors from Sertoli and germ cells are important in the functioning of both cell types. While it is important to know what Sertoli cells and germ cells make, it is equally important to know when they make it. Distinct but well-defined groups of germ cells interact with Sertoli cells in a cyclic pattern. These recurring groups of germ cells define the cycle of the seminiferous epithelium during which sperm are produced in an asynchronous fashion.(ABSTRACT TRUNCATED AT 250 WORDS)

The testicular iron shuttle: a "nurse" function of the Sertoli cells

The techniques of cell culture and molecular biology first revealed that Sertoli cells synthesize transferrin. Accumulated biological information led to a plausible model for the role of testicular transferrin in an iron shuttle system designed to transport ferric ions around the cellular tight junctions to the germ cells inside the blood-testis barrier. Experiments done in culture and in vivo have supported many aspects of this model. A mutant mouse model that lacks the ability to synthesize transferrin is defective in spermatogenesis and may help to delineate the nature of the iron requirement by germ cells. The levels of seminal transferrin, possibly of Sertoli cell origin, are proportional to sperm production in humans and cattle and may be an effective indicator of Sertoli cell function. The testicular iron shuttle thus represents an important "nurse cell" function of the Sertoli cells.

Accessibility of rat and human follitropin receptor primary sequence (R265-S296) in situ

The primary sequence of FSH receptor (FSHR) is homologous to LH and TSH receptors (LHR and TSHR). This family of receptors belong to the G-protein-coupled class of membrane-bound receptors. A very large extracellular domain suggests that interaction of ligand with receptor is likely to be complex. Secondary structure analysis of the FSHR R265-S296 primary sequence, which has little homology to LHR, predicted a helix-turn-helix motif. An objective of these studies was to test directly the hypothesis that FSHR R265-S296 is accessible in FSHR and plays a role in hormone binding. Rat FSHR (rFSHR) was expressed in insect cells and used as a source of receptor for binding studies. Recombinant receptor had a Kd in the picomolar range with about 200,000 receptors/cell and appeared as two forms (180 and 75 kilodaltons) by Western blot analysis. Functional coupling of the rat FSHR to adenylate cyclase in insect cells was demonstrated. Antipeptide antibodies against FSHR R265-S296 inhibited binding of radiolabeled hFSH to insect cell rat FSHR. In contrast, neither nonimmune rabbit serum nor antipeptide antibodies against FSHR G150-L183 inhibited the binding of radiolabeled hFSH to rat FSHR in insect cells. Similar results were obtained with recombinant human FSHR in Y1 cells, measuring progesterone production as an end point. Confocal microscopy using antihuman FSHR R265-S296 demonstrated that recombinant human FSHR on Chinese hamster ovary cells existed as discrete patches on the surface. In summary, the data offer compelling evidence that portions of the peptide sequence FSHR R265-S296 are accessible to the antipeptide antibodies and may be involved in hormone binding.

Relationship of a mouse Sertoli cell line (MSC-1) to normal Sertoli cells

Recently, a mouse Sertoli cell line (MSC-1) was established from transgenic mice carrying a fusion gene composed of human Müllerian inhibitory substance transcriptional regulatory sequences linked to the SV40 T-antigen gene. This cell line contained a morphologically heterogeneous population of cells that expressed characteristic Sertoli cell mRNAs such as transferrin, the beta-subunit for inhibin, and sulfated glycoprotein-2 (SGP-2). In this study, we compared various characteristics of MSC-1 cells to primary cultures of Sertoli cells from immature rats or adult mice. Our observations indicated that: 1) These cells were ultrastructurally similar to mouse Sertoli cells in culture; 2) MSC-1 cells expressed mRNA for androgen-binding protein (ABP) and SGP-1, but not the receptor for FSH; 3) The expression of SGP-2 mRNA and secretion of SGP-2 increased approximately 2-fold when cells were cultured at 41 degrees C, the nonpermissive temperature for the SV40 virus, while SGP-1 and transferrin mRNA levels and secretion were unaffected; 4) Proliferation of these cells was serum-dose dependent and temperature dependent and could be inhibited by incubating MSC-1 cells at 41 degrees C; 5) Proliferation was also significantly reduced after cells were incubated in the presence of dibutyryl cAMP (dbcAMP) for 6 days; 6) Fifteen subcultures produced from single MSC-1 cells displayed similar levels of mRNA expression for transferrin or SGP-1. Together these data indicate that the MSC-1 cell line is composed of a single cell type displaying numerous characteristics of Sertoli cells. This cell line may provide a unique source of tissue for studying various aspects of Sertoli cell behavior.

Activity and form of sulfated glycoprotein 2 (clusterin) from cultured Sertoli cells, testis, and epididymis of the rat

Sulfated glycoprotein 2 (SGP 2) is a 73-kDa highly glycosylated disulfide-linked heterodimer. It is a major secreted protein of Sertoli cells, is found in high abundance within the seminiferous tubule fluid (STF) and epididymal fluid (EPF), and can be found on the surface of spermatozoa. Due to its high abundance and location it is believed to play a major role in the development of spermatozoa; however, its specific function(s) within the reproductive tract is not known. Purified and renatured SGP 2 were found to have the ability to inhibit complement activity with a mean concentration of 66 mg/ml for 50% inhibition. Extraction of epididymal sperm with various reagents showed that a major fraction of the SGP 2 in EPF was free or was loosely associated with the spermatozoa whereas a smaller fraction was more tightly associated and disruption of the lipid bilayer was required for its complete removal. Ultracentrifugation techniques and gel permeation chromatography revealed that SGP 2 in plasma, STF, and EPF formed complexes with other proteins and/or lipids but was not specifically associated with the apolipoprotein-like particles containing apolipoprotein A1 (apo A1).

Sertoli cell and germ cell cystatin C: stage-dependent expression of two distinct messenger ribonucleic acid transcripts in rat testes

Sertoli cells were shown to synthesize and secrete cystatin C, a potent inhibitor of cysteine proteases. The evidence for this observation was obtained from protein sequencing. Western analysis using antiserum specific to cystatin C, and immunoprecipitation of 35S protein secreted by cultured cells. The Western analysis with an antiserum to human cystatin C showed that cultured Sertoli cells secrete three previously reported immunoreactive forms of cystatin C: a predominant pair of proteins at 13-14 kDa and a less abundant 20-kDa protein. Immunohistochemical localization of cystatin C in sections of rat testes showed intense staining in Sertoli cells; no immunoreactivity was observed in spermatogonia or spermatocytes. A cDNA fragment for rat cystatin C was obtained by use of the polymerase chain reaction and was used as a probe in Northern analyses to examine the steady-state levels of cystatin C mRNA in intact testes and in Sertoli and spermatogenic cells. Sertoli cells contained a 700-nucleotide cystatin C transcript, and a mixed population of spermatids and spermatocytes contained a 550-nucleotide transcript. Analysis of RNA from purified spermatogenic cells revealed that round and condensing spermatids contained the 550-nucleotide transcript, while pachytene spermatocytes contained a smaller 500-nucleotide transcript. The 700-nucleotide transcript was present in testes isolated from rats of 5-79 days of age, the 500-nucleotide transcript was detected initially in testes from 24-day-old rats, and the 550-nucleotide transcript was detected initially at 35 days of age. Both the 500- and 550-nucleotide transcripts increased in abundance until 50 days of age. RNA from stage-synchronized testes showed that steady-state levels of both the 550- and 700-nucleotide transcripts were lowest in stages VI-VII of the cycle. These data suggest that the role of cystatin C in the testis may be to inhibit the proteolytic activity of the cysteine protease cathepsin L in all stages except stages VI-VII.

Localization and molecular heterogeneity of sulfated glycoprotein-2 (clusterin) among ventral prostate, seminal vesicle, testis, and epididymis of rats

In the rat reproductive tract, sulfated glycoprotein 2 (SGP-2) is present in the ventral prostate, seminal vesicle, testis, and epididymis. In the ventral prostate, SGP-2 is associated with the process of programmed cell death, while in the testis and epididymis a role for SGP-2 in sperm maturation has been proposed. Available information suggests that there are both inter- and intra-organ variations in SGP-2 localization, molecular forms, and response to androgen ablation. In the present study, localization of SGP-2 within the ventral prostate, seminal vesicle, and epididymis was compared by immunohistochemistry. In the ventral prostate of intact rats, immunoreactive SGP-2 was confined to a discrete population of epithelial cells lining the proximal ducts. Epithelial cells in other regions of the ventral prostate did not stain for SGP-2. A similar staining pattern was observed for the seminal vesicle; a small population of SGP-2-expressing epithelial cells was found in epithelium that did not stain for SGP-2. The epididymis also demonstrated a non-uniform staining pattern. The caput displayed strong immunoperoxidase reaction over the apical membrane and stereocilia of all principal cells. Principal cells also showed variable degrees of cytoplasmic staining ranging from weak to strongly positive. The corpus and cauda showed a similar staining pattern. After castration, all epithelial cells in the ventral prostate and seminal vesicle became intensely positive for SGP-2 staining. In the caput and cauda epididymis there was an increase in the number of principal cells demonstrating strong intracellular staining for SGP-2. These results suggest that as observed previously in the regressing ventral prostate, increased intracellular SGP-2 staining may also be associated with the regressing epididymis and seminal vesicle. Differences in molecular forms of SGP-2 were investigated by two-dimensional Western and lectin blots. Molecular forms of SGP-2 differed between testis and epididymis but were similar between ventral prostate and seminal vesicle. Prostate and seminal vesicle forms of SGP-2 differed from those of both testis and epididymis. Analysis of terminal carbohydrate present on the various SGP-2 molecular forms also confirmed the existence of heterogeneity. These results demonstrate the presence of multiple molecular forms of SGP-2 in various organs of the male reproductive tract in rats and suggest a possible variation in functional activity and/or half-life of SGP-2 in these organs.

Expression of prohibitin in rat seminiferous epithelium

Subtractive hybridization was used to isolate cDNAs highly expressed in stages IX-XI of the cycle of the seminiferous epithelium in the rat. One of the cloned cDNAs was sequenced and shown to be homologous to a previously described cDNA encoding rat prohibitin. Northern blot analyses showed that 1.9- and 1.2-kb transcripts were present in Sertoli cells whereas 1.5-, 1.2-, and 0.7-kb transcripts were expressed in germ cells. Western blot analyses with anti-peptide antibody to prohibitin revealed only a single 30-kDa protein in testis. Immunocytochemistry demonstrated that prohibitin protein was expressed constitutively in adult Leydig cells and Sertoli cells at all stages. Immunoreactivity of prohibition was very low in preleptotene spermatocytes, very high in leptotene spermatocytes, and very low in zygotene spermatocytes. In pachytene spermatocytes, immunoreactivity was very high in stages VII-XI and was minimal during stages XII and XIV. No protein was detected in spermatogonia and spermatocytes undergoing mitotic and meiotic divisions, respectively. These studies show that the prohibitin gene is expressed differentially in testis. The expression pattern of the prohibitin gene in rat testis appears to correlate with a proposed antiproliferative role of prohibitin.

Basic fibroblast growth factor is a testicular germ cell product which may regulate Sertoli cell function

Previously, a proteinacious factor secreted by a mixture of rat testicular spermatocytes and round spermatids was shown to stimulate transferrin mRNA and protein levels in Sertoli cells. To identify the germ cell-secreted proteins which affect Sertoli cell functions, concentrated germ cell-conditioned medium was fractionated by reverse-phase HPLC. The fraction which eluted at 35% acetonitrile increased transferrin secretion in Sertoli cell cultures 2.4-fold above the basal level. Both the active fraction and a protein extract from cultured germ cells were positive for basic fibroblast growth factor (bFGF) as determined by Western blot analysis and immunoprecipitation. The apparent molecular sizes of the immunoreactive proteins were 30, 27, and 24 kilodaltons (kDa). By immunohistochemistry, bFGF was shown to be present in pachytene spermatocytes and Leydig cells. The bFGF receptor was also examined by immunohistochemistry and found to be present in Leydig cells, round and elongated spermatids, and Sertoli cells. The presence of receptors was more pronounced in stages I-VIII. Western blot analysis confirmed that the receptors were expressed in isolated round spermatids, elongated spermatids, and Sertoli cells. Two major receptor species with apparent molecular sizes of 120 and 145 kDa were detected in the rat testis. Germ cells contained both of these receptors, but Sertoli cells possessed only the 120-kDa receptor. From these experiments, it is evident that bFGF is a germ cell product which may regulate Sertoli cell function. The expression of bFGF and its receptor may be an important component of germ cell-Sertoli cell and/or germ cell-germ cell communication during spermatogenesis.

CFTR expression is regulated during both the cycle of the seminiferous epithelium and the oestrous cycle of rodents

Severely reduced fertility is a common finding in cystic fibrosis (CF). We used in situ hybridization to examine the cell-specific expression of CFTR in the reproductive organs of rodents. In males CFTR mRNA is found in the round spermatids (spermatogenic stages V-X) and in the principal cells that line the initial segment of the epididymis. In both the testis and the epididymis, CFTR expression is developmentally regulated suggesting that the defect in the genital tract of male CF patients is of developmental origin. CFTR expression in the luminal and glandular epithelium of the uterus is regulated during the oestrous cycle and is maximal at pro-oestrus. Our results provide a biological rationale for the reduced fertility of CF patients, and suggest a possible cause for the comparatively poorer prognosis for women with CF.

Expression of the FSH receptor in the testis

FSH has multiple and changing roles in the regulation of spermatogenesis. The first function of FSH is to increase the number of Sertoli cells by stimulation of their mitotic activity. During the prepubertal phase of development, FSH is important for the maturation of the Sertoli cells. Hormonal stimulation of tight junction formation and specific protein secretion are essential. In the adult rat, some of the functions carried out by FSH in prepubertal animals are assumed by testosterone. However, there is evidence that even in the adult rat, FSH is important for quantitatively normal spermatogenesis. The gene for the FSH receptor is large (greater than 85 kb) and complex (10 introns) and is structurally similar to the genes for the LH and TSH receptor. The promoter region of the FSHR gene has been identified and is active in the expression of transgenes in transfected Sertoli cells. We have shown that the FSH receptor mRNA is present in the testes of the adult rat and that the levels of this mRNA are changing during the cycle of the seminiferous epithelium. The presence of relatively high levels of FSHR mRNA in stages XIV-II of the cycle and the relatively low levels in stages VII-VIII suggest that the FSH receptor is carefully regulated in adult rats and presumably has an important function in spermatogenesis. The levels of FSHR mRNA in cultured Sertoli cells are immediately reduced in the presence of FSH or phorbol esters, but the levels soon return to normal.

Isolation, immunolocalization, and sperm-association of three proteins of 18, 25, and 29 kilodaltons secreted by the mouse epididymis

Three murine epididymal secretory proteins have been characterized by their site of synthesis, sperm association, and tissue localization by use of polyclonal antisera and immunochemistry. Mouse epididymal protein 7 (MEP 7) was localized initially within the supranuclear regions of some principal epithelial cells in the proximal corpus while other cells remained unstained. In the mid-proximal corpus, all principal cells and stereocilia were stained, and luminal staining increased from corpus to cauda. Some clear cells in the distal corpus and cauda also showed immunoperoxidase staining. Sequential extraction of caudal spermatozoa indicated that MEP 7 was predominantly loosely associated with spermatozoa and that only a small amount of MEP 7 required detergent to extract it from spermatozoa. Examination of other rodent caudal fluids revealed a related protein in rat caudal fluid of 32 kDa, and amino acid sequence analysis of MEP 7 showed a 68% sequence similarity with rat proteins AEG and D/E. MEP 9 immunolocalized within the cytoplasm of all principal cells of the distal caput. In a transition zone between the distal caput and the corpus, some principal cells were stained while others were not. Distal to the corpus, the principal cell staining gradually decreased. In the distal caput and proximal corpus, large heavily stained droplets associated with spermatozoa were seen in the lumen. The staining intensity of these droplets also decreased from corpus to cauda. The clear cells of the distal corpus and cauda did not stain with the antibody to MEP 9. Sequential extraction of caudal spermatozoa showed that some MEP 9 was extractable under low-salt conditions, whereas extraction with 0.1% Triton X-100 was required to remove all MEP 9, indicating it was firmly associated with spermatozoa. The antibody to MEP 9 cross-reacted with a 25-kDa protein present in rat caudal fluid. MEP 10 was localized within the cytoplasm of the principal cells, the stereocilia, and the lumen of the epididymis at the junction of the distal caput and corpus. In the distal corpus, a large number of clear cells were stained, but very few of these cells stained in the cauda. MEP 10 dissociated completely from caudal spermatozoa under low-salt conditions, indicating that it was not firmly bound to spermatozoa. The antiserum to MEP 10 cross-reacted with proteins present in rat and guinea pig caudal fluid. The related rat protein migrated at approximately 20 kDa. Amino acid sequence analysis of MEP 10 revealed an 86% sequence similarity with rat proteins B and C.(ABSTRACT TRUNCATED AT 400 WORDS)

Testicular synchrony: evaluation and analysis of different protocols

Using the vitamin A depletion-replacement rat model to obtain testicular synchrony, we examined the reproducibility and degree of synchronization obtained by two different protocols. In the original protocol (A), synchrony was achieved by use of retinol alone. In protocol B, retinoic acid was used during the final days of vitamin A depletion as a supplement to retinol. With protocol A, a total of 56 rats were analyzed by an adaptation of a previously published method for quantifying synchrony. Animals treated by protocol A demonstrated a reproducible degree of synchrony although variability was high among individual animals. A smaller group of animals treated with protocol B demonstrated a lower degree of synchrony. In contrast, the midpoint of synchrony (point in the cycle at which 50% of the stages are more advanced and 50% are less advanced) was a more constant value and was not different between the two treatments. The midpoints of synchrony obtained from both protocols were used to calculate a cycle duration of 300 h for our strain of Sprague-Dawley rats. Our results indicate that while the use of either protocol can reproducibly provide testicular synchrony, protocol A results in a higher degree of synchrony. The ability to synchronize testes to selected stages provides sufficient experimental material for the study of the molecular and cellular events of spermatogenesis.