Regulation of spermatogenesis: the shark testis model

Functional characterization of follicle-stimulating hormone and luteinizing hormone receptors in cloudy catshark, Scyliorhinus torazame

The follicle-stimulating hormone receptor (FSHR) and luteinizing hormone receptor (LHR) in cloudy catshark were cloned, and recombinant FSHR and LHR were expressed for characterization. Ventral lobe extract (VLE) from the pituitary contains homologous FSH and LH, and it stimulated the cAMP signaling of FSHR and LHR dose-dependently. Two transcript variants of LHR (LHR-L with exon 10 and LHR-S without) were identified, and LHR-S was the dominant form with higher basal cAMP activity without VLE stimulation. Among various developmental stages of follicles, FSHR expression was mainly associated with the pre-vitellogenic and early white follicles. When follicles were recruited into vitellogenesis, the expression of FSHR decreased while of LHR was upregulated reciprocally, suggesting that LHR may also be responsible for the control of vitellogenesis in chondrichthyans. The expression of LHR-L was upregulated among maturing follicles before ovulation, indicating LHR-L could have a specific role in receiving the LH surge signal for final maturation. Plasma LH-like activity was transiently increased prior to the progesterone (P4)-surge and testosterone-drop at the beginning of P4-phase, supporting a pituitary control of follicle-maturation via LH signaling in chondrichthyans. The expression of follicular LHR was downregulated during the P4-phase when LH-like activity was high, indicating that the LH-dependent downregulation of LHR is conserved in chondrichthyans as it is in other vertebrate lineages. (213 words).

In vitro and in vivo gene transfer in the cloudy catshark Scyliorhinus torazame

Cartilaginous fishes have various unique physiological features such as a cartilaginous skeleton and a urea-based osmoregulation strategy for adaptation to their marine environment. Also, because they are a sister group of bony vertebrates, understanding their unique features is important from an evolutionary perspective. However, genetic engineering based on gene functions as well as cellular behavior has not been effectively utilized in cartilaginous fishes. This is partly because their reproductive strategy involves internal fertilization, which results in difficulty in microinjection into fertilized eggs at the early developmental stage. Here, to identify efficient gene transfer methods in cartilaginous fishes, we examined the effects of various methods both in vitro and in vivo using the cloudy catshark, a candidate model cartilaginous fish species. In all methods, green fluorescent protein (GFP) expression was used to evaluate exogenous gene transfer. First, we examined gene transfer into primary cultured cells from cloudy catshark embryos by lipofection, polyethylenimine (PEI) transfection, adenovirus infection, baculovirus infection, and electroporation. Among the methods tested, lipofection, electroporation, and baculovirus infection enabled the successful transfer of exogenous genes into primary cultured cells. We then attempted in vivo transfection into cloudy catshark embryos by electroporation and baculovirus infection. Although baculovirus-injected groups did not show GFP fluorescence, electroporation successfully introduced GFP into muscle cells. Furthermore, we succeeded in GFP transfer into adult tissues by electroporation. The in vitro and in vivo gene transfer methods that worked in this study may open ways for genetic manipulation including knockout experiments and cellular lineage analysis in cartilaginous fishes.

Steroid hormones and chondrichthyan reproduction: physiological functions, scientific research, and implications for conservation

The study of the reproductive aspects of chondrichthyans through the analysis of steroid hormones has been carried out for more than five decades in several species around the world. This scientific knowledge constitutes the basis of the reproductive endocrinology of chondrichthyans, which has provided information regarding their sexual maturation, gametogenesis, mating seasons, gestation periods, and parturition. The present review summarises the existing literature on steroid hormones in chondrichthyan reproduction and identifies future research directions addressing critical knowledge gaps in the reproductive physiology of this taxon. A total of 59 peer reviewed scientific papers from 1963 to 2020 were reviewed and the following parameters analysed: species, steroid hormones, biological matrix, field sampling (year, location), and methodology (assays, sample size, precision, and recoveries). We provided a summary of the methods, biological matrices, and the functions of up to 19 hormones on the biology of 34 species of chondrichthyans that have been analysed to date. The majority of the studies used radioimmunoassay as the main methodology (76.3%; n = 45/49); while the most frequent biological matrix used was plasma (69.5%; n = 41/49). A Kernel’s heat map was generated to present the scientific effort according to geographic location and evidenced a lack of research in high biodiversity areas for chondrichthyans worldwide. The implications of the study of steroid hormones for the conservation of chondrichthyans are discussed, as only 2.9% of the species of this group have been analysed and most of the scientific effort (93.2%; n = 55/59 papers) has focused on the analysis of less than six hormones.

Comparison of the Morphology and Histomorphometry of Spermatogenic Cyst of Three Sharks Species With Diametric Testes

Characterization of the reproductive anatomy of elasmobranchs (sharks, skates, rays, and sawfish) offers unique insights into the evolution of reproductive traits in animals due to their phylogenetic position at the base of the vertebrate tree of life. Yet, despite advances in our understanding of male elasmobranch reproductive physiology and testes histology, very little is known about how testes histomorphometrics varies with male maturation. In this study, we characterize and contrast testes morphology and histomorphology of males at different maturation stages in three shark species with diametric testes development: Prionaceglauca, Rhizoprionodon lalandii, and Mustelus canis. All stages of spermatogenesis were observed in P. glauca and R. lalandii, while for M. canis, only males at early stages of maturation were examined and therefore all the spermatogenesis cells lineage were not present. The number of Sertoli cells increased with cell development by six times in R. lalandii and roughly four times in P. glauca, and were statistically different among stages of spermatogenesis cysts in both species. Statistical differences in cyst diameter and Sertoli cell numbers were observed between P. glauca and R. lalandii. The increase of spermatocyte II cell diameter described for R. Lalandii in this study was not usual to elasmobranch species as compared, for example, to P. glauca. This information proves the importance of studying the testicular development and the process of spermatogenesis is necessary for understanding the reproductive biology of the species, including life cycles and history, variation of reproductive morphology. Anat Rec, 299:759-768, 2016. © 2016 Wiley Periodicals, Inc.

Reproductive endocrinology in chondrichthyans: the present and the future

The class Chondrichthyes, that includes Elasmobranchii and Holocephali, is a diverse group of fish occupying a key position at the base of vertebrate evolution. Their evolutionary success is greatly attributed to their wide range of reproductive strategies controlled by different endocrine mechanics. As in other vertebrates, hormonal control of reproduction in chondrichthyans is mediated by the neuropeptide gonadotropin-releasing hormone (GnRH) that regulates the brain control of gonadal activity via a hypothalamus-pituitary-gonadal (HPG) axis. Chondrichthyans lack of a direct vascular supply from the hypothalamus to the zone of the pituitary where the gonadotropic activity resides, thus transport between these two zones likely occurs via the general circulation. In the brain of elasmobranchs, two groups of GnRH, GnRH-I and GnRH-II were identified, and the presence of two immunoreactive gonadotropins similar to the luteinising (LH) and follicle stimulating (FSH) hormones was identified in the pituitary. In holocephalans, only GnRH-II has been confirmed, and while gonadotropin activity has been found in the buccal pituitary lobe, the presence of gonadotropin receptors in the gonads remains unknowns. The diversity of reproductive strategies display by chondrichthyans makes it difficult to generalize the control of gametogenesis and steroidogenesis; however, some general patterns emerge. In both sexes, androgens and estrogens are the main steroids during gonadal growth; while progestins have maturational activity. Androgens also form the precursors for estrogen steroid production. Estrogens stimulate the hepatic synthesis of yolk and stimulate the development of different part of the reproductive tract in females. The role of other gonadal steroids may play in chondrichthyan reproduction remains largely unknown. Future work should concentrate in filling the gaps into the current knowledge of the HPG axis regulation, and the use of reproductive endocrinology as a non-lethal technique for management of chondrichthyan populations.

Effects of larval exposure to estradiol on spermatogenesis and in vitro gonadal steroid secretion in African clawed frogs, Xenopus laevis

Estrogen or eco-estrogenic chemicals can disrupt normal gonadal sex differentiation, causing intersex formation and feminization in amphibians. The cellular basis for estrogen-induced sex reversal is not well understood. In the present study, we investigated the concentration- and stage-dependent effects of estradiol (E(2)) exposure during the larval period on histological characteristics of gonadal sex differentiation and gonadal sex steroid secretion in vitro in the African clawed frog, Xenopus laevis. Embryos were exposed to E(2) (1, 10, or 100 microg/L) or vehicle control through metamorphosis and then allowed to develop in untreated medium for 2-mo post-metamorphosis. To investigate gonadal sex differentiation and development during and after exposure, gonadal samples were collected at different developmental stages. Gonadal sex differentiation did not occur before NF stage 52 in any group. At NF stage 54-55 primordial germ cells (PGCs) were observed in both cortical and medullary regions of developing tadpoles gonads in the control, 1 and 10 microg/L E(2) treatments, but were observed only in the cortical region of tadpoles exposed to 100 microg/L E(2). E(2) increased the percent of spermatocytes, spermatids, and spermatozoa compared to controls. Larval E(2) exposure did not alter hCG-induced gonadal testosterone secretion in vitro but significantly increased E(2) secretion from ovaries of juvenile frogs. Our results indicate that E(2) exposure during larval development appears to prevent PGC migration to the medulla of developing gonads in a concentration-dependent manner. The degree of PGC migration to the medulla may be related to the degree of E(2)-induced intersex formation and feminization in X. laevis. E(2) exposure during the larval period accelerates spermatogenesis and can increase ovarian E(2) secretion in juvenile frogs.

Immunolocalization of 3beta-HSD and 17beta-HSD in the testis of the spotted ray Torpedo marmorata

Using polyclonal antibodies, we examined the localization of 3beta-hydroxysteroid dehydrogenase (3beta-HSD) and 17beta-hydroxysteroid dehydrogenase (17beta-HSD) as markers of the site of steroidogenetic activity during the spermatogenesis of Torpedo marmorata. These enzymes play a central role in the biosynthesis of steroid hormones, including androgen and oestrogen production. We demonstrated that in the spotted ray testis, Sertoli and Leydig cells, as well as spermatogonia, show a positive reaction to anti 3beta-HSD and 17beta-HSD antibodies. In particular, we demonstrated that Sertoli cells show a positive reaction to anti 3beta-HSD and 17beta-HSD antibodies in cysts containing spermatogonia and spermatozoa, while Leydig cells present a positive reaction only when they are located between cysts containing meiotic cells. This study strongly suggests that, as hypothesised in our previous study [Prisco, M., Liguoro, A., D'Onghia, B., Ricchiari, L., Andreuccetti, P., Angelini, F., 2002. Fine structure of Leydig and Sertoli cells in the testis of immature and mature spotted ray Torpedo marmorata. Mol. Reprod. Dev. 63, 192-201.], Sertoli and Leydig cells are differently involved in the hormonal control of spermatogenesis: Sertoli cells before the beginning of meiosis and after spermiation, Leydig cells only during meiosis phase. Moreover, the present paper deals with the possibility that also spermatogonia are engaged in the production of androgen hormones, as they are characterized by the presence of 3beta-HSD and 17beta-HSD enzymes, and show the ultrastructural features of steroid hormone-producing cells.

Distribution of terminal sugar residues in the testis of the spotted rayTorpedo marmorata

Lectins represent a class of proteins/glycoproteins binding specifically to terminal sugar residues. The present investigation aims to identify lectin-binding sites in testis of Torpedo marmorata. Using a panel of lectins coupled with fluoresceine isothiocyanate, we demonstrated that germ and somatic cells present in Torpedo testis contain glycoconjugates, whose distribution at the level of the surface, the cytoplasm and the nucleus changes during germ cell differentiation. Moreover our observations demonstrate that the germ cells undergoing apoptosis (Prisco et al., 2003a: Mol Reprod Dev 64:341-348) overexpress a residual sugar recognised by WFA lectin that can be considered a specific marker for apoptotic germ cells. Finally, our results indicate that there is a progressive increase in glycosilation during spermatogenesis, especially at the level of the acrosome in the spermatocyte-spermatid step, and that Leydig cells are differently stained in relation to the spermatogenetic cycle.

Evolutionary aspects of cellular communication in the vertebrate hypothalamo-hypophysio-gonadal axis

This review emphasizes the comparative approach for developing insight into knowledge related to cellular communications occurring in the hypothalamus-pituitary-gonadal axis. Indeed, research on adaptive phenomena leads to evolutionary tracks. Thus, going through recent results, we suggest that pheromonal communication precedes local communication which, in turn, precedes communication via the blood stream. Furthermore, the use of different routes of communication by a certain mediator leads to a conceptual change related to what hormones are. Nevertheless, endocrine communication should leave out of consideration the source (glandular or not) of mediator. Finally, we point out that the use of lower vertebrate animal models is fundamental to understanding general physiological mechanisms. In fact, different anatomical organization permits access to tissues not readily approachable in mammals.

Apoptosis during spermatogenesis in the spotted ray Torpedo marmorata

This article is a cytological and molecular investigation on the occurrence of apoptosis during spermatogenesis in Torpedo, a cartilaginous fish characterised by a typical cystic testis. Using DNA fragmentation and Bak gene expression, it demonstrated that germ cells undergo apoptosis only at the stages of spermatocyte and spermatid, and degeneration also involves Sertoli but not Leydig cells. In immature cysts, this cellular process probably occurs when the ratio of germ cells to the only Sertoli cell (SC) forming the spermatoblast changes. Apoptosis also takes place in mature cysts after sperm release to eliminate most of the SCs. Few of them, however, become cytoplasts and probably continue secreting androgens so as to control the final events of spermatogenesis, i.e., passage of spermatozoa through the ductus deferentes. Finally, the present investigation demonstrated that, in Torpedo testis, Bak mRNA is expressed during spermatogenesis, thus suggesting that the mitochondrial pathway might be active. This observation in one of the oldest vertebrate classes indicates that, in all vertebrates, the apoptotic process during spermatogenesis is conserved, contributing to testicular homeostasis.

Fine structure of leydig and sertoli cells in the testis of immature and mature spotted ray Torpedo marmorata

An ultrastructural investigation revealed the presence of true Leydig cells in the testis of sexually mature specimens of Torpedo marmorata. They showed the typical organization of steroid-hormone-producing cells, which, however, changed as spermatocysts approached maturity. In fact, they appeared as active cells among spermatocysts engaged in spermatogenesis, while in regions where spermiation occurred, they progressively regressed resuming the fibroblastic organization typically present in the testis of immature specimens. Such observations strongly suggest that these cells might be engaged in steroidogenesis and actively control spermatogenesis. Sertoli cells, too, appeared to play a role in spermatogenesis control, since, like Leydig cells, they showed the typical aspect of steroidogenic cells. In addition, the presence of gap junctions between Sertoli cells suggests that their activity might be coordinated. After sperm release, most Sertoli cells were modified and, finally, degenerated, but few of them changed into round cells (cytoplasts) or round cell remnants, which continued their steroidogenic activity within the spermatocyst and the genital duct lumen. From the present observations, it can be reasonably concluded that, in T. marmorata, spermatogenesis depends on both Leydig and Sertoli cells, and, as postulated by Callard (1991), in cartilaginous fish, the function of the Leydig cells as producers of steroids might be more recent and subsequent to that of Sertoli cells. In this regard, it is noteworthy that, in immature males, when Leydig cells showed a fibroblastic organization, Sertoli cells already displayed the typical organization of a steroidogenic cell.

Characterization of progesterone-binding moieties in the little skate Raja erinacea

In this study we report evidence of a [3H]progesterone-binding moiety in the liver and oviduct of the little skate Raja erinacea. It is characterized by high affinity, low capacity and DNA-cellulose-binding activity. Furthermore Western blot analysis revealed that monoclonal antibodies against the chicken progesterone receptor (PR) subunits A and B cross-reacted with a 110-kDa band in the liver and a 80-kDa band in the oviduct. When analyzed by DEAE-Sepharose ion-exchange column chromatography, [3H]progesterone-binding molecules resolved into two peaks, one nonadherent and one adherent to the column. The liver adherent peak eluted in a linear gradient at a NaCl concentration of about 0.07 M and resolved on Western blot as a single band of a 110 kDa. The oviduct adherent peak eluted at about 0.14 M NaCl and resolved on Western blot as a single band of 80 kDa. Competition studies showed that the progesterone-binding moiety in the cytosol was specific for progesterone. On the contrary, the nuclear component is not specific for progesterone; it also binds testosterone and estradiol 17 beta in the oviduct, and progesterone, testosterone, dihydrotestosterone, estradiol 17 beta, mibolerone, and R5020 in the liver. The [3H]progesterone-binding activity was monitored in both liver and oviduct of females in different reproductive stages. Females were separated into three groups; laying, nonlaying, and immature. [3H]Progesterone-binding activity levels were higher in the liver of immature than of nonlaying skates, and it was undetectable in laying skates. [3H]Progesterone binding was higher in the oviduct of laying and nonlaying skates than of immature skates. This PR-binding moiety has many characteristics of a true receptor: high affinity, low capacity, binds to DNA, and cross-reacts with antibodies against chicken PR. However, while the cytosolic form of this progesterone-binding component was quite specific for P, nuclear extracted material was nonspecific. If these progesterone-binding components are homologous with the PR A and PR B forms of other vertebrates, as we believe, it is clear that there are species differences that probably relate to phylogenetic level and physiology of the organism.

Isolation and characterization of the cDNA encoding the spiny dogfish shark (Squalus acanthias) form of cytochrome P450c17

Cytochrome P450c17 is a key steroidogenic enzyme for the production of sex steroids in gonadal tissue and for cortisol production in adrenal tissue. This protein possesses two enzymatic activities. The 17 alpha-hydroxylase activity results in the introduction of a hydroxyl group at the 17 alpha-position. The resultant 17 alpha-hydroxylated, C21 pregnene is converted to a C19 androgen by the C17,20-lyase activity. A cDNA library was constructed from poly(A)-enriched mRNA isolated from spiny dogfish shark (Squalus acanthias) testis and ligated into EcoRI-cut lambda arms. The amplified library was screened using a bovine P450c17 cDNA probe and five positive clones were isolated. The described cDNA encompasses 23 bp of the 5'-untranslated region, a 1,527 bp open reading frame, and 414 bp of the 3'-untranslated region. A putative polyadenylation signal (AATAAA) is 18 bp from the poly(A) tail. Northern blot analysis showed a single transcript of 1.9 kb, thus indicating the isolated clone is a full-length cDNA. The deduced amino acid sequence of the shark form of P450c17 is 59% and 57% identical to the rainbow trout and chicken forms, respectively. The shark form is 43% to 46% identical to mammalian forms (rat, human, mouse, bovine, and porcine). There are large regions of extremely high identity shared among all the forms. The deduced shark 17 alpha-hydroxylase protein is 509 residues in length with a predicted weight of 57.2 kDa. Non-steroidogenic COS cells, transfected with the shark P450c17 cDNA, was capable of 17 alpha-hydroxylase and C17,20-lyase activities using both pregnenolone and progesterone as initial substrates.

Detection of c-mos related products in the dogfish (Scyliorhinus canicula) testis

The objective of the present paper was to do a comparative study to assess somatic versus germ cell localization of c-mos products in the testis. In mouse and amphibian oocytes, c-mos activity is necessary for meiotic maturation. Lack of c-mos expression has been reported in somatic cells of male and female gonads while transcripts have been found in germ cells of testis and ovary. Using a v-mos probe, we report here the detection of a c-mos related transcript (1.7 kb) in the dogfish Scyliorhinus canicula testis. Western blot analysis detects two proteins of 106 and 32 kDa. A specific immunostaining was exclusively localized in the interstitial tissue while the germinal compartment was completely negative. In conclusion, our results indicate for the first time the presence of c-mos products in an elasmobranch species and, moreover, their presence in somatic testicular cells rather than germ cells. Therefore, this finding in an ancient vertebrate indicates that c-mos activity does not have a direct universal role in the regulation of spermatogenesis.

In vitro approach to the control of spermatogonia proliferation in the trout

When spermatogonia and primary spermatocytes (G(o) + CI), uncontaminated by somatic testicular cells, were prepared from trout testes at various maturation stages and cultured alone, basal tritiated thymidine (3H-Tdr) incorporation decreased throughout the reproductive cycle. It was unchanged by salmon gonadotropin (sGtH II), trout growth hormone (rhGH), testosterone, estradiol and 17 alpha, 20 beta-dihydroprogesterone. Conversely, it was dose-dependently stimulated by rhIGF-I, with a mean ED50 of 5.2 ng/ml and a mean maximum stimulation of 3.2-fold above control. When Go + CI were cultured either in the presence of Sertoli cells or in Sertoli cell-conditioned medium (SCCM), basal 3H-Tdr incorporation was always decreased when the Sertoli cells were from spermatogenetic testes, but it was stimulated when they were from testes which were to resume spermatogenesis soon. Whatever the origin of the Sertoli cells, they always partly inhibited IGF-I stimulation. When present during either the co-cultures or the preparation of SCCM, sGtH II and rtGH had no effect when Sertoli cells were from spermatogenetic testes. In conclusion, IGF-I is a direct efficient stimulator of the proliferation of trout male germ cells, the effect of which is partly counteracted by Sertoli cells. sGtH II, rtGH and the 3 tested steroids are not directly active. While sGtH II has no Sertoli cell-mediated activity, further investigation is necessary to clarify whether the other tested molecules have such an activity.

Stage-related changes in steroid-converting enzyme activities in Squalus testis: synthesis of biologically active metabolites via 3 beta-hydroxysteroid dehydrogenase/isomerase and 5 alpha-reductase

To investigate the relationship between steroidogenesis and spermatogenesis, two key enzymes of androgen biosynthesis, 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD) and 5 alpha-reductase, were compared at premeiotic (PrM), meiotic (M), and postmeiotic (PoM) stages. Staged tissues were obtained by dissection from the testis of the spiny dogfish Squalus acanthias, in which spermatogenesis is a simple diametric progression. Microsomal 3 beta-HSD activity was measured by conversion of [3H]dehydroepiandrosterone (DHEA) to androstenedione (AE). Reaction constants were: Km = 3.2 microM and Vmax = 243 pmol/min/mg protein. 3 beta-HSD increased progressively with maturation, resulting in three- to four-fold higher levels in PoM than in PrM stages. Absolute values and stage-related differences were the same, whether microsomes were derived from whole testis or from isolated spermatocysts (germ cell/Sertoli cell units), thus supporting microscopic studies showing that Sertoli cells are the primary steroidogenic elements of dogfish testis. In vitro conversion of [3H]testosterone to [3H]dihydrotestosterone (DHT) was used to estimate 5 alpha-reductase activity. Apparent substrate affinity was similar to that of 3 beta-HSD (Km = 2.9 microM), but maximal product yields were two to three orders of magnitude lower (Vmax = 208 fmol/min/mg protein). Also, the stage-related pattern of 5 alpha-reductase activity (PrM > PoM >> M) differed from that of 3 beta-HSD (PoM >> M > PrM).(ABSTRACT TRUNCATED AT 250 WORDS)

Sulfoconjugation of steroids and the vascular pathway of communication in dogfish testis

The zonal testis of the dogfish (Squalus acanthias) has proven advantageous to study biochemical changes in relation to stage of spermatogenesis, including information on steroidogenic enzymes and steroid receptors. To investigate whether sulfotransferase is part of a mechanism regulating the availability of biologically active hormone in close proximity to receptors, we measured in vitro conversion of [3H]estrone (E1) to sulfoconjugated metabolites in cytosolic subfractions of testes grossly dissected according to germ cell composition (premeiotic-PrM, meiotic-M, and postmeiotic-PoM stages). Assays were carried out in the presence of adenosine 3'-phosphate 5'-phosphosulfate (PAPS) at 22 degrees C and optimized for time (60 min) and protein (500 micrograms/ml). Michaelis-Menten kinetics and saturation analysis gave the following reaction constants for [3H]E1: Km = 0.33 microM, Vmax = 2.5 pmol/min/mg; and for PAPS: Km = 33 microM, Vmax = 1.1 pmol/min/mg; competition studies carried out in the absence or presence of 1- or 5-fold excess radioinert steroids indicated that estrogen (E2 > E1) as well as androgens (T = DHEA > 5 alpha dihydrotestosterone, DHT) were effective inhibitors. Sulfotransferase activity was found to be stage-related, being highest in PoM regions (2.31 +/- 0.24 pmol/min/mg protein) when compared to M and PrM regions (1.22 +/- 0.22 and 1.28 +/- 0.21 pmol/min/mg protein, respectively). Sulfoconjugation and the intratesticular distribution of steroid sulfates were also measured in vivo by perfusion of the intact testis with [3H]androgen or -estrogen. The pathway of blood flow via the genital artery was epigonal organ-->PoM-->M-->PrM (mature-->immature). Perfused [3H]E2, T, and DHT were all extensively metabolized in a one-pass, 1 hr perfusion, less than 10% of perfused [3H] steroid being recovered from testicular tissues as unchanged steroid. In general, recovery of polar metabolites was greater than non-polar metabolites from all three substrates. Sequential hydrolysis with glucuronidase and glusulase indicated that sulfoconjugation is a minor component (< 20%) of several "inactivating" pathways, which include glucuronide conjugation, 17-ketosteroid synthesis, and pathways leading to unidentified polar metabolites. No consistent stage-related distribution patterns were observed for any of the metabolite subfractions; however, total recovered radioactive steroid (polar plus non-polar) formed a decreasing concentration gradient from point of entry of perfusate (PoM region) to point of exit (PrM region). These data support the conclusion that access to receptors by steroid ligands may be controlled by a balance between activating and inactivating pathways.(ABSTRACT TRUNCATED AT 400 WORDS)

In vitro steroid secretion by staged spermatocysts (Sertoli/germ cell units) of dogfish (Squalus acanthias) testis

Using the dogfish shark (Squalus acanthias) testis model in which different germ cell stages are topographically separated, we previously observed that steroidogenic enzyme activities vary qualitatively and quantitatively during spermatogenesis. To determine whether these data, obtained by radiolabeled tracer analysis of testicular microsomes, accurately predict steroid secretion by intact cultured spermatocysts (germ cell/Sertoli cell units), steroids were radioimmunoassayed directly in spent medium. Steroid output in basal medium was low, but after addition of 25-hydroxycholesterol (25-OH chol, 60 microM), large amounts of progestins (P) and testosterone (T) accumulated. Dehydroepiandrosterone (DHEA), androstenedione (A), and estradiol (E2) were low or nondetectable in the presence or absence of 25-OH chol; however, addition of T (1 microM) as substrate elevated E2 above assay limits. T and P contents of media increased progressively over a 24-hr culture period (Day 1). Replacement and analysis of spent media at 24-hr intervals indicated that secretion was continuous up to 6 days after seeding, although secretory rates (T plus P) and T/P ratios changed with time in culture. Spermatocysts in premeiotic (PrM), meiotic (M), and post-meiotic (PoM) stages all secreted T and P; however, absolute values, T/P ratios, and stage-dependent patterns varied from one experiment to another with no obvious seasonal pattern. Also steroid secretion by staged cysts did not consistently agree with predictions based on steroidogenic enzyme activities measured in earlier cell-free assays, whether or not 25-OH chol was present. This discrepancy was not explained by stage-related patterns of steroid secretion vs retention or by addition of putative in vivo regulators. Agents that elevated P and/or T were dibutyryl cyclic AMP, 1-isobutyl-3-methylxanthine (IBMX), and forskolin, whereas ventral lobe extract and Ca2+ ionophore (A23817) were inhibitory. An autoregulatory feedback loop was indicated by a negative relationship between cyst concentration per well and steroid secretion rate. In contrast to T and P, E2 secretion in the presence of substrate (T, 1 microM) was as predicted from previously determined patterns of aromatase activity (M > PrM > PoM) and increased in response to IBMX. Added [3H]P, [3H]T and [3H]E2 all were extensively metabolized to polar products and P metabolism was stage related (PoM > M > PrM). These data indicate that analysis of free P, T, and E2 in static cyst cultures may underestimate true steroidogenic potential. Assuming further characterization of the system, we conclude that cultured spermatocysts from dogfish testis have potential for studying the multifactorial regulation of steroid synthesis and secretion stage-by-stage during spermatogenesis.

Characterization of a specific estrogen receptor in the oviduct of the little skate, Raja erinacea

In this study we report the first estrogen receptor to be characterized in an oviparous elasmobranch. The skate receptor has high affinity for estradiol (Kd = 0.7 nM), binds both estradiol and the synthetic estrogen DES, and exists in low quantities (50-100 fmol/g oviduct). The receptor displays rapid binding kinetics with half-times of 5 min at 22 degrees and 77 min at 4 degrees. DEAE-Sepharose chromatography reveals one receptor moiety which elutes between 0.13 and 0.14 M KCl. By sucrose gradient ultracentrifugation sedimentation coefficients of 3.6 S under high-salt (0.5 M KCl) and 6.0 S under low salt (0.01 M KCl) conditions were obtained. Using Sephadex G200 gel filtration chromatography, a Stokes radius (Rs) of 2.8 nm and an estimated molecular weight of 43 kDa were calculated. DNA-cellulose elution profiles reveal that the receptor elutes as one peak between 0.34 and 0.36 M NaCl (as compared to 0.20-0.22 M NaCl in mammals and birds and 0.55 M for dogfish). Although some differences are noted between the elasmobranch ER and those of other vertebrates (e.g., dissociation kinetics, DNA affinity), in general it can be said that the skate ER is a "classical" ER in most respects. It is suggested that this steroid receptor has played a key role in the reproductive tract functions of nutrient provision, embryo protection, and as a conduit to the external environment since the earliest chordate era, approximately 400 million years ago.