Regulation of ovarian follicle atresia

The majority of ovarian follicles undergo atresia, a hormonally controlled apoptotic process. Monitoring apoptotic DNA fragmentation provides a quantitative and sensitive endpoint to study the hormonal regulation of atresia in ovarian follicles. During follicle development, gonadotropins, together with local ovarian growth factors (IGF-I, EGF/TGF-alpha, basic FGF) and cytokine (interleukin-1 beta), as well as estrogens, activate different intracellular pathways to rescue follicles from apoptotic demise. In contrast, TNF-alpha, Fas ligand, presumably acting through receptors with a death domain, and androgens are atretogenic factors. These diverse hormonal signals probably converge on selective intracellular pathways (including genes of the bcl-2 and ICE families) to regulate apoptosis. With a constant loss of follicles from the original stockpile, the ovary provides a unique model for studying the hormonal regulation of apoptosis.

Bok is a pro-apoptotic Bcl-2 protein with restricted expression in reproductive tissues and heterodimerizes with selective anti-apoptotic Bcl-2 family members

In the intracellular death program, hetero- and homodimerization of different anti- and pro-apoptotic Bcl-2-related proteins are critical in the determination of cell fate. From a rat ovarian fusion cDNA library, we isolated a new pro-apoptotic Bcl-2 gene, Bcl-2-related ovarian killer (Bok). Bok had conserved Bcl-2 homology (BH) domains 1, 2, and 3 and a C-terminal transmembrane region present in other Bcl-2 proteins, but lacked the BH4 domain found only in anti-apoptotic Bcl-2 proteins. In the yeast two-hybrid system, Bok interacted strongly with some (Mcl-1, BHRF1, and Bfl-1) but not other (Bcl-2, Bcl-xL, and Bcl-w) anti-apoptotic members. This finding is in direct contrast to the ability of other pro-apoptotic members (Bax, Bak, and Bik) to interact with all of the anti-apoptotic proteins. In addition, negligible interaction was found between Bok and different pro-apoptotic members. In mammalian cells, overexpression of Bok induced apoptosis that was blocked by the baculoviral-derived cysteine protease inhibitor P35. Cell killing induced by Bok was also suppressed following coexpression with Mcl-1 and BHRF1 but not with Bcl-2, further indicating that Bok heterodimerized only with selective anti-apoptotic Bcl-2 proteins. Northern blot analysis indicated that Bok was highly expressed in the ovary, testis and uterus. In situ hybridization analysis localized Bok mRNA in granulosa cells, the cell type that underwent apoptosis during follicle atresia. Identification of Bok as a new pro-apoptotic Bcl-2 protein with restricted tissue distribution and heterodimerization properties could facilitate elucidation of apoptosis mechanisms in reproductive tissues undergoing hormone-regulated cyclic cell turnover.

Stage-specific expression of nucleoprotein mRNAs during rat and mouse spermiogenesis

The expression of mRNAs for a transition protein (TP1) and two variants of protamines (P1 and P2) during rat and mouse spermiogenesis was investigated using cDNA hybridization techniques. Slot-blot analyses from 1-mm segments of seminiferous tubules and in situ hybridization from testis sections showed that the levels of mRNA for TP1 increased in step-7 round spermatids at substage VIIb of the seminiferous epithelial cycle, earlier than that of P1 and P2 at substage VIIc. The mRNA levels of all transcripts remained high during steps 8-13 in both species. In the rat, the mRNA of TP1 disappeared during step 14 between substages XIVa and XIVb. The P1 mRNA levels decreased during steps 15-16 (stages I-III) and the P2 mRNA during step 15 (stage I). In the mouse, TP1 mRNA disappeared during step 13 (stage I). The P1 mRNA level decreased before P2 in step 14 (stage II), whereas P2 was detected up to step 15 (stage V). Northern-blot analyses with all three cDNA probes revealed two sizes of mRNA and their stage-specific expression. The shorter transcripts appeared later than the longer ones, at the steps of spermiogenesis where translation is known to begin. The results suggest that transcription of TP1, P1, and P2 mRNAs starts at specifically defined times during spermiogenesis and that the temporal translational regulation of these mRNAs is different.

Tumor necrosis factor-alpha and its second messenger, ceramide, stimulate apoptosis in cultured ovarian follicles

In the mammalian ovary, only a small fraction of follicles fully mature and ovulate, while most of them die via apoptosis. Multiple factors promoting follicle survival have been identified, but intraovarian mediators of apoptosis are poorly known. Tumor necrosis factor-alpha (TNF alpha) is a cytokine capable of inducing apoptosis in diverse cell types, and the apoptotic effect of TNF alpha is, partially, coupled to the sphingomyelin signaling pathway with ceramide as a second messenger. Because TNF alpha has been localized in the rat ovary, and TNF alpha treatment increases granulosa cell ceramide production, we studied the effect of treatment with TNF alpha and ceramide on follicle apoptosis. Immature rats were implanted with diethylstilbestrol to stimulate the development of early antral follicles. Follicles were isolated and cultured in a serum-free medium for 24 h with or without hormone treatments. During culture, spontaneous follicle apoptosis occurred (10-fold increase in DNA fragmentation), which was partially blocked by 100 ng/ml FSH (60% suppression). The effect of FSH was counteracted by TNF alpha in a dose-dependent manner, with the maximal effect at 100 ng/ml TNF alpha (90% reversal of FSH action). In situ analysis indicated that the granulosa cell is the follicle cell type undergoing DNA fragmentation. A membrane-permeable ceramide analog, C2-ceramide N-acetyl sphingosine, mimicked the effect of TNF alpha and was able to completely abolish the action of FSH at 50 microM. In contrast, another ceramide analog, C2-dihydroceramide N-acetyl dihydrosphingosine, did not alter the effect of FSH, verifying the specificity of ceramide action. To study the mechanism of TNF alpha and ceramide action, the effect of sodium aurathiomalate (ATM), an inhibitor of interleukin-1 beta-converting enzyme/ced-3-related cystine proteases known to be essential in the execution of mammalian cell apoptosis, was studied. Treatment with ATM (1 mM) prevented the apoptosis-inducing effect of both TNF alpha and ceramide, suggesting a role for cysteine proteases in mediating follicle apoptosis. Treatment with either TNF alpha or ceramide increased both basal and FSH-stimulated progesterone production by cultured follicles. Concomitant treatment by ATM did not alter the stimulatory effect of TNF alpha or ceramide on progesterone production, ruling out nonspecific toxic effect of the inhibitor and indicating that the apoptotic and steroidogenic pathways are independent. In summary, treatment with TNF alpha or its second messenger, ceramide, stimulates apoptosis of early antral follicles in culture, suggesting a potential role for TNF alpha as an intraovarian regulator of follicle atresia by acting through the ceramide signaling pathway.

Modulation of basal and FSH-dependent cyclic AMP production in rat seminiferous tubules staged by an improved transillumination technique

The stage-dependent action of follicle-stimulating hormone (FSH) in the rat seminiferous epithelium was investigated in microdissected 1 mm tubule segments, where the precise stage of the cycle was identified by a rapid screening method of live cell squash preparations. For distinction of stages I and II and the substages of VII, new criteria were used. The step 16 spermatids with rapid assembly of outer dense fibers leading to marked increase of flagellar thickness were used for distinction of stages I and II. The form and density of the cytoplasmic lobes of step 19 spermatids was used for recognition of substages of VII. Highest basal production of cyclic AMP (cAMP, measured by radioimmunoassay) was found in stage II of the cycle and stages XIV-I-VI had higher values than did stages VII-XIII. A decline occurred during stage VII and an increase at stage XIV. When stimulated with FSH, highest cAMP secretion was found in stage IV of the cycle; again, stages XIV-I-VI had higher values than did other stages. A small but significant (P less than .01) stimulation was found at substage VIId. FSH-stimulated and basal cAMP productions of different stages were compared, highest values were found at stages IV and XIII, and lowest, at stages VIIa-c and IX of the cycle. Since the FSH-dependent cAMP production is confined to Sertoli cells, and the number of these cells is constant per unit length of seminiferous tubules, the Sertoli cells are obviously under a stage-specific paracrine control by the surrounding spermatogenic cells. Specific steps in cell differentiation, such as spermatogonial proliferation, final maturation of the spermatids (stages I-VII), onset of meiosis (substage VIId), and completion of meiotic divisions (stage XIV) may be involved in this interaction.

Expression of beta-nerve growth factor and its receptor in rat seminiferous epithelium: specific function at the onset of meiosis

beta-Nerve growth factor (NGF) is expressed in spermatogenic cells and has testosterone-downregulated low-affinity receptors on Sertoli cells suggesting a paracrine role in the regulation of spermatogenesis. An analysis of the stage-specific expression of NGF and its low affinity receptor during the cycle of the seminiferous epithelium in the rat revealed NGF mRNA and protein at all stages of the cycle. Tyrosine kinase receptor (trk) mRNA encoding an essential component of the high-affinity NGF receptor was also present at all stages. In contrast, expression of low affinity NGF receptor mRNA was only found in stages VIIcd and VIII of the cycle, the sites of onset of meiosis. The low-affinity NGF receptor protein was present in the plasma membrane of the apical Sertoli cell processes as well as in the basal plasma membrane of these cells at stages VIIcd to XI. NGF was shown to stimulate in vitro DNA synthesis of seminiferous tubule segments with preleptotene spermatocytes at the onset of meiosis while other segments remained nonresponsive. We conclude that NGF is a meiotic growth factor that acts through Sertoli cells.

Interference of BAD (Bcl-xL/Bcl-2-associated death promoter)-induced apoptosis in mammalian cells by 14-3-3 isoforms and P11

Apoptosis and survival of diverse cell types are under hormonal control, but intracellular mechanisms regulating cell death are unclear. The Bcl-2/Ced-9 family of proteins contains conserved Bcl-2 homology regions that mediate the formation of homo- or heterodimers important for enhancing or suppressing apoptosis. Unlike most other members of the Bcl-2 family, BAD (Bcl-xL/Bcl-2 associated death promoter), a death enhancer, has no C-terminal transmembrane domain for targeting to the outer mitochondrial membrane and nuclear envelope. We hypothesized that BAD, in addition to binding Bcl-xL and Bcl-2, may interact with proteins outside the Bcl-2 family. Using the yeast two-hybrid system to search for BAD-binding proteins in an ovarian fusion cDNA library, we identified multiple cDNA clones encoding different isoforms of 14-3-3, a group of evolutionally conserved proteins essential for signal transduction and cell cycle progression. Point mutation of BAD in one (S137A), but not the other (S113A), putative binding site found in diverse 14-3-3 interacting proteins abolished the interaction between BAD and 14-3-3 without affecting interactions between BAD and Bcl-2. Because the S137A BAD mutant presumably resembles an underphosphorylated form of BAD, we used this mutant to screen for additional BAD-interacting proteins in the yeast two-hybrid system. P11, a nerve growth factor-induced neurite extension factor and member of the calcium-binding S-100 protein family, interacted strongly with the mutant BAD but less effectively with the wild type protein. In Chinese hamster ovary (CHO) cells, transient expression of wild type BAD or its mutants increased apoptotic cell death, which was blocked by cotransfection with the baculovirus-derived cysteine protease inhibitor, P35. Cotransfection with 14-3-3 suppressed apoptosis induced by wild type or the S113A mutant BAD but not by the S137A mutant incapable of binding 14-3-3. Furthermore, cotransfection with P11 attenuated the proapoptotic effect of both wild type BAD and the S137A mutant. For both 14-3-3 and P11, direct binding to BAD was also demonstrated in vitro. These results suggest that both 14-3-3 and P11 may function as BAD-binding proteins to dampen its apoptotic activity. Because the 14-3-3 family of proteins could interact with key signaling proteins including Raf-1 kinase, protein kinase C, and phosphatidyl inositol 3 kinase, whereas P11 is an early response gene induced by the neuronal survival factor, nerve growth factor, the present findings suggest that BAD plays an important role in mediating communication between different signal transduction pathways regulated by hormonal signals and the apoptotic mechanism controlled by Bcl-2 family members.

Effects of activin-A, inhibin-A, and transforming growth factor-beta 1 on stage-specific deoxyribonucleic acid synthesis during rat seminiferous epithelial cycle

Activin and inhibin are members of the transforming growth factor-beta (TGF beta) gene family. They are expressed in various organ systems, where they possess regulatory functions. Inhibin, activin, and TGF beta have been reported to also be expressed in the adult rat testis. We studied in vitro the action of these growth factors on premitotic and premeiotic DNA synthesis during the rat seminiferous epithelial cycle. Two-millimeter rat seminiferous tubule segments were isolated by transillumination-assisted microdissection from stages V, VIIa, VIII-IX, and I of the cycle and incubated in vitro in the presence of activin-A, inhibin-A, or TGF beta 1. During 24-, 48-, and 72-h incubation spontaneous progression of spermatogenesis was noted. The staged samples allowed us to selectively quantitate DNA synthetic activity of specific germ cell types. At the end of the culture, the tubules were pulse labeled with [3H]thymidine, and DNA synthesis was quantified by liquid scintillation counting, and the activated cells were detected by autoradiography. Activin-A stimulated preleptotene spermatocyte DNA synthesis in a dose-dependent manner. DNA synthesis of intermediate spermatogonia was also stimulated by activin-A, whereas inhibin-A inhibited DNA synthesis of these cells. TGF beta 1 had a small, but significant, stimulatory effect on DNA synthetic activity at stage VII. These results support the view that activin-A, inhibin-A, and TGF beta 1 take part in the regulation of DNA synthesis during rat spermatogenesis.

Expression of inhibin beta A and beta B, follistatin and activin-A receptor messenger ribonucleic acids in the rat seminiferous epithelium

The expression of inhibin beta A and beta B subunits, follistatin, and activin-A receptor messenger RNA (mRNAs) in different stages of rat seminiferous epithelial cycle was analyzed by in situ hybridization in order to understand their role in the regulation of spermatogenesis. Inhibin beta A mRNA was expressed in Sertoli cells in a highly stage-specific manner. The mRNA levels started to accumulate in Sertoli cells at stage VIII of the cycle and were highly expressed during stages IX-XI. Follistatin mRNA expression was identical to that of inhibin beta A, while inhibin beta B mRNA was maximally expressed in Sertoli cells at stages XIII-III. Low expression was found in stages VII-VIII. Activin-A receptor mRNA was localized mainly in spermatogenic cells. Maximal expression was seen in late primary spermatocytes at stages XIII-XIV and in early round spermatids at stages I-IV. A low even expression by Sertoli cells was also seen. Inhibin beta A and follistatin mRNAs were coexpressed in stage IX-XI Sertoli cells, suggesting close interplay between these molecules. The pattern of inhibin beta B mRNA expression was similar to that of inhibin alpha-mRNA. Localization of activin-A receptor mRNA in spermatogenic cells suggests that activin may influence meiotic divisions and early spermiogenesis.

Identification, ontogeny, and regulation of an interleukin-6-like factor in the rat seminiferous tubule

The present study's aims are to search for the presence of interleukin-6 bioactivity (IL-6) in medium conditioned by various testicular cell types and to investigate the cellular and hormonal regulation of testicular IL-6 production. Sertoli cells prepared from rats of increasing ages (20, 35, and 45 days) secreted IL-6 in vitro, whereas medium conditioned by pachytene spermatocytes, early spermatids, and peritubular cells showed no activity. Lipopolysaccharide (LPS) and latex beads, two known stimulators of monocyte/macrophage IL-6 production, markedly stimulated IL-6 secretion by Sertoli cells at all the ages investigated. Maximum levels of IL-6 were reached after 6 h of culture of Sertoli cells with LPS and after 24 h with latex beads. When Sertoli cells were cocultured with pachytene spermatocytes, early spermatids, or fractions containing residual bodies and cytoplasts from elongated spermatids, only the latter significantly stimulated IL-6 levels. Maximum levels of IL-6 were attained by adding 2 x 10(6) residual bodies to Sertoli cells; a significant increase in IL-6 secretion was seen after 6 h, and maximum levels were observed after 24 h. The levels of IL-6 varied throughout different stages of the seminiferous epithelium cycle; highest levels were observed in stages II-VI and lowest in stages VII-VIII. IL-6 bioactivities induced by LPS and residual bodies and cytoplasts from elongated spermatids could be totally neutralized with a specific monoclonal antibody at all of the ages studied. FSH, phorbol myristate acetate, and IL-1 alpha augmented Sertoli cell IL-6 secretion in a dose-dependent manner. Furthermore, FSH and (Bu)2cAMP differentially stimulated IL-6 secretion during the seminiferous epithelial cycle. It is concluded that the release of IL-6 from Sertoli cells is regulated by a complex interplay between residual bodies and humoral factors.

Ontogeny of luteinizing hormone receptor gene expression in the rat testis

The ontogeny of expression of the LH receptor (LHR) gene was studied in rat testis between day 12.5 of fetal life and adulthood. Specific hybridization of testicular mRNA with a LHR cRNA probe encoding the extracellular domain of the receptor was found from day 16.5 of fetal life onward in Northern hybridization. Transcripts of 6.8, 4.2, and 2.7 kilobases were present at all ages, and a 1.8-kilobase species was present mainly in the adult testes. Hybridization was most intensive in day 21.5 fetuses, decreased after birth, and increased again by adulthood. The LHR mRNA was also analyzed by the reverse transcriptase-polymerase chain reaction technique, with primers multiplying either the full-length LHR mRNA or its extracellular domain. The specificity of the DNA species generated was verified by Southern hybridization using a nested 32P-labeled oligonucleotide. The results indicated that a truncated mRNA form, encoding the extracellular part of LHR, appears 1 day before the full-length LHR mRNA, i.e. on fetal days 14.5 and 15.5, respectively. This is in striking contrast to the rat fetal ovary, in which a difference of more than 10 days is found in the appearance of these two LHR mRNAs (17.5 days of fetal and 7 days of postnatal age, respectively). The appearance of the full-length LHR mRNA coincides in both sexes with the developmental onset of LHR binding observed in earlier studies. In situ hybridization using an antisense cRNA probe demonstrated that the LHR mRNA was confined to Leydig cells at all fetal and postnatal ages studied. In conclusion, there is good correlation in the developing rat testes between the onset of LHR gene expression and LHR binding, as observed in earlier studies. The findings in the fetal testis are at striking variance with those in the ovary, which starts expressing the extracellular domain of the LHR mRNA at roughly the same age as the testis. However, the appearance of full-length LHR mRNA and the functional receptor are delayed until day 7 postpartum.

Cell death and survival during ovarian follicle development

Mammalian germ cells arise in the yolk sac endoderm at the caudal aspect of the embryo and migrate to the mesodermally-derived gonadal ridge early in development. After the oogonia reach the gonadal ridge, the process of meiosis begins which coincides with the first major wave of apoptosis of female germ cells (Coucouvanis et al., 1993). Subsequently, oocytes progress to the dictyate stage of prophase I where they remain arrested until ovulation.

Expression and function of a proapoptotic Bcl-2 family member Bcl-XL/Bcl-2-associated death promoter (BAD) in rat ovary

Bcl-2-related anti- and proapoptotic proteins are important in the decision step of the intracellular death program upstream from the caspase proteases. Targeted overexpression of Bcl-2 in ovarian somatic cells of transgenic mice leads to decreased apoptosis of granulosa cells and is associated with higher ovulation rate, increased litter size, and ovarian teratoma formation. The ability of exogenous Bcl-2 proteins to promote follicle cell survival suggests that the transgene can bind to endogenous ovarian Bcl-2 family members and modulate the intracellular apoptosis process in favor of cell survival. We used the yeast two-hybrid system to search for ovarian Bcl-2 interacting proteins. The screening of an ovarian fusion complementary DNA library yielded several clones encoding for the death agonist Bcl-XL/Bcl-2-associated death promoter (BAD). Dimerization of Bcl-2-related proteins mediated by the consensus Bcl-2 homology (BH) domains is essential for their apoptosis-regulating function. Consistent with these observations, yeast two-hybrid assays indicated that the interaction of Bcl-2 with BAD is dependent on both BH4 and BH2 domains of Bcl-2. Northern blot analysis showed a wide distribution of BAD messenger RNA (mRNA) in diverse tissues with highest levels in the lung, ovary, uterus, and brain. In situ hybridization analysis indicated BAD mRNA expression in granulosa cells of different sizes of follicles and also in the theca and interstitial cells. BAD mRNA was expressed in the ovaries between postnatal 15-27 days and did not alter during the developmentally occurring apoptosis found about postnatal day 18 when the first group of early antral follicles were formed. Similarly, BAD mRNA levels did not change during follicle atresia induced by estrogen withdrawal in immature rats. To study the role of BAD in the ovary, BAD complementary DNA was transfected into primary cultures of granulosa cells and in a gonadal tumor cell line. Overexpression of BAD induced apoptosis in both cell types, and the effect of BAD was reversed by a membrane-permeable caspase inhibitor, indicating that BAD induces apoptosis via the activation of caspase cysteine proteases. In summary, the death agonist BAD was identified as a Bcl-2-interacting protein in the ovary, and BAD mRNA is constitutively expressed in granulosa cells, suggesting that BAD is an essential part of the ovarian cell death process. Because BAD overexpression in granulosa cells leads to apoptosis, future studies on ovarian BAD binding proteins and hormonal regulation of the interactions among different Bcl-2 family members could provide a better understanding of the cellular mechanism of ovarian follicle atresia.

Derivation of functional antagonists using N-terminal extracellular domain of gonadotropin and thyrotropin receptors

Receptors for the glycoprotein hormones, LH/CG, FSH, and TSH, are a unique subclass of the seven-transmembrane, G protein-coupled proteins with a large N-terminal extracellular (ecto-) domain. Although ecto-domains of gonadotropin receptors confer ligand binding, expression of soluble binding proteins has been difficult. We fused the ecto-domains of LH or FSH receptors to the single-transmembrane domain of CD8 and found that hybrid proteins anchored on the cell surface retained high-affinity ligand binding. Inclusion of a junctional thrombin cleavage site in the hybrids allowed generation of soluble receptor fragments that interfered with gonadotropin binding to their receptors and blocked cAMP production stimulated by gonadotropins. Cross-linking analyses confirmed the formation of high molecular weight complexes between receptor ecto-domains and their specific ligands. A similar approach also generated a soluble TSH receptor fragment capable of blocking TSH-induced signal transduction. When administered to rats, the soluble FSH receptor fragment retarded testis growth and induced testis cell apoptosis. These findings demonstrate the feasibility of generating ligand-binding regions of glycoprotein hormone receptors to selectively neutralize actions of gonadotropins and TSH, thus allowing future design of novel contraceptives and management of different gonadal and thyroid dysfunction. The present study represents the first successful derivation of soluble, ligand-binding domains from glycoprotein hormone receptors as functional antagonists. Similar approaches could allow generation of ecto-domains of related receptors to neutralize actions of ligands or receptor antibodies and to facilitate structural-functional analysis.

Glove perforations in open and laparoscopic abdominal surgery: the feasibility of double gloving

BACKGROUND AND AIMS

According to the traditional view, the glove protects the patient from the bacterial growth of the surgeons' hands and doing so prevents infections. Today, with growing incidences of HIV and Hepatitis B and C, surgical gloves are also important as protection for the surgeon. We compared the safety of double indicator gloves to standard single surgical gloves by investigating how often surgical gloves are punctured in laparoscopic and open gastrointestinal surgery.

STUDY

As study material we gathered all gloves that had been used in gastrointestinal surgery in Satakunta Central Hospital during two months. 814 gloves from 274 operations were tested by using standardized water filling test method.

RESULTS

In open surgery 67 gloves out of 694 had been punctured (9.6 percent). Puncture occurred in 22.5 percent of operations (53 out of 236). During open surgery 24 holes out of 35 were undetected with single gloves (69 percent). With double indicator gloves, only 3 out of 31 holes were unnoticed (10 percent). Long duration of operation increased the risk of puncture. In laparoscopic operations 4 gloves out of 120 had been perforated (3.3 percent).

CONCLUSION

Double surgical gloves give markedly better protection in surgery. This is important especially in high risk operations.

Inhibin gene expression in a large cell calcifying Sertoli cell tumour and serum inhibin and activin levels

Inhibin is a potential tumour suppressor gene product in the gonads. While inhibin gene products may have a role in tumourigenesis, serum inhibin levels can be used as a marker for ovarian tumours derived from granulosa cells. Tumours derived from Sertoli cells, testicular counterparts of granulosa cells, are rare. To assess whether inhibin could be used as a human Sertoli cell tumour marker, serum inhibin and activin levels and inhibin subunit mRNA expression in the testis were studied. Northern blot and in situ hybridization revealed abundant expression of inhibin alpha, beta A, and beta B subunit mRNAs in large cell calcifying Sertoli cell tumours found in a 12-year old boy with Carney complex. The tumours were multifocal and bilateral. Serum inhibin levels were clearly elevated at the time of the diagnosis, decreased by 50% after one of the testes was removed, and were low or undetectable after the second orchidectomy six weeks later. Activin was undetectable before the orchidectomies, while a low concentration of activin-A was measured after them. Follicle stimulating hormone (FSH) concentration increased from normal pubertal value to castration level as expected. Normal seminiferous tubules also showed inhibin subunit alpha and beta B mRNA expression, whereas inhibin beta A mRNA was expressed in normal Leydig cells. These data suggest that serum inhibin reflects Sertoli cell activity and can be used as a human tumour marker.

Stage-specific cellular regulation of inhibin alpha-subunit mRNA expression in the rat seminiferous epithelium

To find out the local regulation of inhibin production and its possible paracrine role in the seminiferous epithelium, inhibin alpha mRNA levels were measured in sequential 1 mm segments of rat seminiferous tubules accurately staged by transillumination technique. Highest levels were found at stages XIV-I-IV of the cycle, and lowest at stages VI-VIIb of the cycle. When dividing spermatogonia were selectively destroyed by 3 Gy of high-energy X-irradiation, stage-specific inhibin alpha mRNA levels remained unchanged until 26 and 38 days after irradiation when stages VII and VIII of the cycle showed 6- and 4-fold increases during a selective reduction of pachytene spermatocyte and round spermatid numbers, respectively. The results suggest that these cells at a strictly stage-specific fashion have a paracrine inhibitory effect on Sertoli cell inhibin alpha gene expression. Inhibin alpha mRNA level also correlates closely to the follicle-stimulating hormone-stimulated cAMP production during the cycle of the seminiferous epithelium, but does not seem to have a correlation to spermatogonial DNA synthesis.

Expression of inhibin alpha, beta A and beta B messenger ribonucleic acids in the normal human ovary and in polycystic ovarian syndrome

We studied the cellular distribution of inhibin alpha, beta A and beta B mRNAs in the normal human ovary and in polycystic ovarian syndrome (PCOS) by in situ hybridization. Our results show that human granulosa cells express inhibin alpha, beta A and beta B subunit mRNAs, and theca cells express inhibin alpha and beta A subunit mRNAs. The co-localization of alpha and beta A mRNAs in theca cells supports the hypothesis that inhibin also has an autocrine function in these cells. We did not detect any inhibin subunit mRNA in the granulosa cells of atretic follicles, while theca cells also expressed alpha subunit mRNA in those follicles. The present findings suggest that the expression of inhibin subunits is regulated differently in human follicular granulosa and theca cells. It has been speculated that inhibin may be involved in the development of PCOS. Our results show that the cellular localization of inhibin subunit mRNAs is not disturbed in PCOS ovaries.

Localization of activin receptor (ActR-IIB2) mRNA in the rat seminiferous epithelium

In situ hybridization was used to localize the mRNA expression of the high affinity activin receptor (ActR-IIB2) in the rat seminiferous epithelium. ActR-IIB2 mRNA was expressed maximally in stages IX-XI of the seminiferous epithelial cycle. The mRNA signal was detected basally in the epithelium in type A1 and A2 spermatogonia and in Sertoli cells. In the pubertal rat testis the expression was localized in Sertoli cells around primary spermatocytes and around meiotically dividing cells. The localization of ActR-IIB2 mRNA in spermatogonia lends support to the hypothesis that activin is a spermatogonial growth factor. The expression of activin receptor mRNA in pubertal rat testis suggests that activin may have a function during meiotic maturation.

Development of luteinizing hormone action in the perinatal rat ovary

The expression of LH receptor (LHR) mRNA was studied in fetal rat gonads using polymerase chain reaction multiplication of reverse-transcribed mRNA. A primer pair corresponding to the extracellular domain of the receptor revealed the expression of LHR mRNA in fetal ovaries and testes as early as embryonic Day 13.5, the earliest age studied. The localization of LHR mRNA was examined in the perinatal rat ovary using in situ hybridization with two antisense probes, one encoding the extracellular and the other encoding the transmembrane domains of LHR. At the age of 4 days, only the extracellular LHR probe gave specific signal over ovarian stromal and follicular cells, excluding the ova. Three days later, similar distribution of specific hybridization was observed with both probes. In the 10- and 30-day-old rat ovaries, clear expression of LHR mRNA was found to be with both probes in theca cells. Gonadotropin-stimulated production of cAMP was studied in cultures of dispersed perinatal rat ovarian cells. When 5-day-old ovarian cells were cultured for 3 days in vitro and then stimulated by either hCG (0.1 mg/L) or FSH (1 mg/L) for 6 h, cAMP production was enhanced only in cells stimulated by FSH. In a similar experiment with 7-day-old ovarian cells, cAMP production was stimulated by both FSH and hCG. Stimulation with hCG (0.1 mg/L) during the 3-day culture caused homologous desensitization of cAMP production, but stimulation with FSH (0.1 mg/L) had no such effect. The desensitization of the LHR was also investigated by treating neonatal rats in vivo with a high dose of hCG (600 IU/kg BW s.c. as a single injection on Day 7) or with a dosage of recombinant human (rec) FSH on Days 3-9 (0.3 IU s.c twice daily). Thereafter, at the age of 10 days, the ovaries were incubated either with recFSH (200 IU/L) or hCG (CR-121; 0.1 mg/L) for 1 h. Homologous desensitization of cAMP production by hCG was observed, but the FSH-mediated cAMP production was not affected. The hCG-induced steroidogenesis (progesterone and testosterone production) was not desensitized. In conclusion, these findings indicate that 1) the expression of the mRNA encoding the extracellular domain of LHR, i.e., truncated receptor, occurs in fetal rat gonads as early as embryonic Day 13.5; 2) the expression of the truncated LHR mRNA occurs uniformly in the differentiating ovarian cells before the appearance of the functional theca cell layer; 3) full-length LHR message appears in the developing ovary concomitantly with appearance of differentiated theca cells; 4) homologous desensitization of cAMP output by hCG, without steroidogenic desensitization, is present in perinatal rat ovaries; and 5) no FSH-evoked desensitization of cAMP production occurs in perinatal ovaries.

Stage- and cell-specific gene expression and hormone regulation of the seminiferous epithelium

The regulation of spermatogenesis seems to involve complex cell interactions in the testis. Little is known about these cellular communication events. Advances in molecular technology and cell or cell group separation methods have made it possible to analyze function of defined spermatogenic and Sertoli cells, thereby giving some insights into the paracrine regulation of spermatogenesis. In this review we will describe how seminiferous tubule segments with distinct cell associations can be rapidly isolated and how the cell composition can be modified by high-energy X-irradiation. Results of the recent studies performed using these techniques will be briefly summarized. Spermatogenic cells at defined stages of their development can be isolated in living condition for morphological and biochemical studies by the transillumination technique. For accurate identification of the stages of the seminiferous epithelial cycle, phase contrast microscopy of live cell squashes has been used. The criteria described by Leblond and Clermont (Am. NY Acad. Sci., 55:548-573, 1952) can be used for accurate recognition of most of the stages of the cycle. However, stages I and II and substages of VII that are important in several studies are difficult to distinguish. Therefore, in addition to the morphology of early spermatids, development of the flagella at step 16 of spermiogenesis and the changing morphology of the cytoplasmic lobes (residual bodies) at stage VII of the cycle were used as criteria for rapid identification and isolation (preparative) of the seminiferous tubule segments. Expression of nucleoprotein and heat shock protein 70-related protein genes was analyzed with Northern blot, slot blot, and in situ hybridization techniques in accurately staged seminiferous tubules. Accurate stage-dependent timing of the onset of transcription, followed by storage and disappearance of the messages was demonstrated. The chromatoid body (cb) has been proposed to have a specific function in storage of the long-lived mRNAs in the spermatids. It is an actively moving cytoplasmic organelle that interacts with Golgi complex during formation of the acrosomic system. The chromatoid body is apparently also dependent on cytoplasmic microtubules, since its movements are inhibited and its structure becomes abnormal in the presence of vincristin, an inhibitor of tubulin polymerization. Follicle-stimulating hormone (FSH) is an important regulator of Sertoli cell function. Since both basal and FSH-dependent cyclic AMP (cAMP) production by seminiferous tubules showed marked stage dependency, Sertoli cells are apparently influenced by spermatogenic cells. Thus, Sertoli cell function varies cyclically depending on the stage of the seminiferous epithelial cycle to provide an optimal microenvironment for spermatogenesis.(ABSTRACT TRUNCATED AT 400 WORDS)

Cellular regulation of basal and FSH-stimulated cyclic AMP production in irradiated rat testes

Basal and follicle-stimulating hormone (FSH)-stimulated cyclic AMP (cAMP) productions by seminiferous tubular segments from irradiated adult rats were investigated at defined stages of the epithelial cycle when specific spermatogenic cells were low in number. Seven days post-irradiation, depletion of spermatogonia did not influence the basal cAMP production, but FSH response increased in stages II-VIII. Seventeen days post-irradiation when spermatocytes were low in number, there was a small increase in basal cAMP level in stages VII-VIII and FSH-stimulated cAMP production increased in stages VII-XII and XIII-I. At 38 days when pachytene spermatocytes and round spermatids (steps 1-6) were low in number, a decreased basal cAMP production was measured in stages II-VI and IX-XII. FSH-stimulated cAMP output increased in stages VII-XII but decreased in stages II-VI. At 52 days when all spermatids were low in number, basal cAMP levels decreased in all stages of the cycle, whereas FSH response was elevated only in stages VII-XII. All spermatogenic cell types seem to have an effect on cAMP production by the seminiferous tubule in a stage-specific fashion. Germ cells appear to regulate Sertoli cell FSH response in a paracrine way, and a part of cAMP may originate from spermatids stimulated by an unknown FSH-dependent Sertoli cell factor. The FSH-dependent functions may control such phenomena as spermatogonial proliferation, final maturation of spermatids, and onset of meiosis.

Developmental and differential expression of the ornithine decarboxylase gene in rodent testis

Ornithine decarboxylase (ODCase) is the first and rate-limiting enzyme in the polyamine biosynthetic pathway and it is androgen regulated in the mouse. The expression of ODCase transcripts during testicular development was examined by Northern blot analysis with a mouse ODCase cDNA probe. Total RNA was isolated from the testes of prepubertal mice at 6, 8, 12, 16, 18, 20, 22, and 30 days of age, from enriched populations of germinal cells obtained from the testis of immature (8 days old) and mature (45 days old) mice and from several mouse somatic tissues. The level of the two ODCase transcripts (2.2 and 2.7 kilobases) was low but detectable in the testes of 6- to 16-day-old mice and increased substantially as the first spermatogenic wave proceeded into spermiogenesis. The low ODCase mRNA levels observed in prepubertal mouse testes were confirmed with RNA samples obtained from enriched germ cell populations of type A and type B spermatogonia and interstitial cells obtained from Day 8 mouse testes. In agreement with the developmental studies, ODCase mRNA levels increased substantially in enriched populations of pachytene spermatocytes, round spermatids, and residual bodies/cytoplasts isolated from mature testes. Similar results were obtained by in situ hybridization of sections of rat testes. Reduced levels of ODCase transcripts were detected in RNA obtained from cultured mouse Sertoli cells obtained from the testes of 21-day-old mice and in RNA from liver, brain, heart, spleen, seminal vesicle, and aorta. In contrast, ODCase transcript levels from kidneys of male mice were as high as those detected in testis RNA. Substantial levels of ODCase mRNAs were also found in the epididymis. Analysis of polysome gradients prepared from total testis extracts revealed a distribution of ODCase mRNA in both nonpolysomal and polysomal fractions of the gradient, suggesting that ODCase is translationally regulated in the mouse testis.

Stage- and cell-specific expression of the ornithine decarboxylase gene during rat and mouse spermatogenesis

Ornithine decarboxylase (ODC) is an enzyme that has been shown to be induced in the growth, differentiation and proliferation of cells. We have used a cDNA probe to determine ODC mRNA levels in different stages of the cycle of rat and mouse seminiferous epithelium. For Northern and slot-blot hybridizations, RNA was isolated from microdissected staged seminiferous tubules. Cell-specific localization of ODC mRNA was studied by in situ hybridization. In the rat, in situ hybridization showed increasing mRNA levels during prophase of meiosis with the highest mRNA levels seen in late pachytene spermatocytes and step 3-5 spermatids. In the mouse, the mRNA levels increased in a similar fashion and the highest mRNA levels were found in step 1-8 spermatids. In the rat, Northern blot hybridizations revealed three molecular sizes of ODC mRNA: 2.2, 2.7 and 1.6 kb. The levels of all molecular sizes were highest in stages VII-VIII, and the lowest mRNA levels were seen in stage I of the seminiferous epithelial cycle. The level of the 2.2 kb transcript was low during stages XIII-I. In the mouse, the Northern blot hybridizations also showed three molecular sizes of ODC mRNA: 2.2 and 2.7 kb and very low levels of 1.6 kb transcript. The levels of the transcripts were steady throughout the cycle. In the mouse, the 2.2 kb transcript was more abundant than the 2.7 kb transcript indicating a species difference between rat and mouse in the usage of the two polyadenylation signals within the ODC gene.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro, follicle-stimulating hormone prevents apoptosis and stimulates deoxyribonucleic acid synthesis in the rat seminiferous epithelium in a stage-specific fashion

The effects of FSH on stage-specific apoptosis and DNA synthesis in the adult rat seminiferous epithelium were studied in vitro. Seminiferous tubular segments from stages I, V, VIIa, and VIII-IX were cultured for 24, 48, and 72 h in different concentrations of FSH. Apoptotic cells were detected by in situ end labeling of DNA strands and quantified from squash preparations. After 48 h of culture, a FSH concentration of 2 ng/ml prevented apoptosis of early (steps 1-3) spermatids. In stage VIII-IX tubules cultured for 72 h, FSH decreased the apoptosis of pachytene spermatocytes. An apoptotic type of cell death of germ cells was confirmed by DNA laddering, electron microscopy, supravital acridine orange staining, and phase contrast microscopy of unstained living cells. The effects of FSH on stage-specific DNA synthesis were studied using the same culture system. FSH increased [3H]thymidine incorporation specifically at stages I and VIII-IX, and autoradiography confirmed stimulation of mitotic and meiotic DNA synthesis in type B spermatogonia and preleptotene spermatocytes, respectively. Increased thymidine incorporation also suggested that FSH stimulated DNA synthesis of type A and intermediate spermatogonia. Most effects exerted by FSH were seen in stages containing high levels of FSH receptors and FSH-stimulated cAMP production. In conclusion, the results suggest that FSH, probably acting via Sertoli cells, has a regulatory function in spermatogenic apoptosis and DNA synthesis in stages previously demonstrated to be preferentially dependent on FSH stimulation.