Lipovitellin constitutes the protein backbone of glycoproteins involved in sperm-egg interaction in the amphibian Discoglossus pictus

Our knowledge of the molecules that interact with sperm at the egg membrane is restricted to a short list. In the eggs of Discoglossus pictus, fusion with sperm is limited to a differentiated structure, the dimple, offering several advantages for detecting molecules involved in fertilization. Previous studies have identified fucosylated glycoproteins of 200, 260, and 270 kDa located at the surface of the dimple that are able to bind sperm in vitro. Here, we show that dimple glycoproteins and a protein represented by a 120-kDa band released following gel-into-gel SDS-PAGE of both glycoproteins share the same N-terminal amino acid sequence, which itself is similar to the N-termini of Xenopus liver-synthesized vitellogenin (VTG) and the lipovitellin 1. MALDI/MS mass spectrometry indicated that the 120-kDa band is part of both gps 200 and 270/260. A 117-kDa major protein of the egg lysate exhibits the same MALDI/MS spectrum, and LC-MSMS indicates that this is a lipovitellin 1 (DpLIV) that coincides with the 120-kDa band and is responsible for the formation of the 200-270-kDa dimers. Therefore, lipovitellin 1 constitutes the protein backbone of the dimple glycoconjugates. In vitro assays using polystyrene beads coated with DpLIV or with its dimers indicate that significant sperm binding occurs only with DpLIV dimers. In amphibians, VTG is taken up by the oocyte, where it releases lipovitellins destined to form yolk. In Discoglossus, our data suggest that yolk proteins are also synthesized by the oocyte. The dimple forms in the ovulated oocyte following the exocytosis of vesicles that likely expose DpLIVs at their membrane. Indeed, in whole mounts of immunostained eggs, anti-vitellogenin antibodies label only the surface of the dimple.

Occurrence of beta-endorphin binding sites in the pituitary of the frog Rana esculenta: effect of beta-endorphin on luteinizing hormone secretion

The possible effect of proopiomelanocortin-derived peptide, beta-endorphin on frog gonadotrope cells was investigated. Binding and internalization of beta-endorphin to pituitary pars distalis cultured cells were visualized by immunofluorescence and analyzed by means of confocal laser scanning microscopy. Using biotinylated endorphin, the time-course of beta-binding showed that this opioid was internalized through receptor-mediated endocytosis, the mechanism in which actin and clathrin were involved; then, the lysosomal degradation program occurred at later stages. The beta-endorphin binding was well antagonized by Naloxone, the opiate receptor antagonist, and up-regulated since more rapid response was obtained in the previously primed cells. The double immunostaining reaction for beta-endorphin and LH beta-subunit revealed that half the beta-endorphin labeled cell population was positively immunostained for LH beta-subunit, and beta-endorphin was able to induce an increasing trend of LH secretion in cultured pars distalis cells. Therefore, it seems that beta-endorphin acts directly on pituitary pars distalis and influences gonadotropin secretion through the interaction with its own receptor.

Molecular components related to egg viability in the gilthead sea bream, Sparus aurata

In pelagic egg spawners, the production of large numbers of sinking eggs, unable to develop into embryos, represents one of the major limiting factors in controlled reproduction. The aim of this study is to elucidate the molecular differences between floating and nonfloating eggs at cytoplasmic and nuclear level. Comparison of analyses between floating and nonfloating sea bream Sparus aurata eggs evidenced differences in vitelline envelope protein components, such differences being probably related with the hydration process but not with fertilization as supported by the assessment of DNA that doubled after in vitro insemination. These data clearly indicated that the absence of embryo development in nonfloating eggs is not due to lack of fertilization. The cytoplasmic composition was also different, the number of protein components being higher in floating eggs, and these extra components may generate the appropriate osmotic pressure at the base of the hydration process. Some lysosomal enzymes, such as cathepsin D and L both involved in yolk proteolysis, in virgin nonfloating eggs were significantly higher with respect to floating ones; the levels of these two enzymes significantly increased in the latter after fertilization. On the contrary, in nonfloating eggs cathepsin L significantly decreased after fertilization. These changes may be related with a series of metabolic processes vital for the production of viable offspring. The capacity of egg transcription and the protein synthesis in these two types of eggs, indicated by the RNA/DNA and RNA/protein ratios, evidenced that the status of cell transcription rate and protein synthesis capacity is significantly higher in floating eggs. This, in turn, suggested that the lack of embryo development may be due to low levels of proteins involved in cell cycle regulation.

Detection and localization of gonadotrophin-releasing hormone (GnRH)-like material in the frog, Rana esculenta, ovary

GnRH-like material has been identified using HPLC followed by RIA in the ovary of Rana esculenta. During the reproductive cycle three immunoreactive GnRH peaks were eluted. One of them coeluted with s-GnRH, the other two forms between GnRH and cII-GnRH. During the recovery phase s-GnRH immunoreactivity disappears. By immunocytochemistry, cII-GnRH immunostaining was localized to granulosa cells while s-GnRH was present in the perinuclear zone of the oocytes.

Opioid peptide modulation of stress-induced plasma steroid changes in the frog Rana esculenta

The present paper aims to evaluate whether a neuroendocrine system including opioids accounts for the effects of stress in the frog, Rana esculenta. Using an acute-stress paradigm, the involvement of hypothalamic opioid peptides was investigated biochemically as well as by in vivo studies. HPLC and RIA investigations confirm the presence of beta-endorphin-like peptides in the brain of this frog. Several immunoreactive peaks are present, two of them coeluting with beta-endorphin and acetyl beta-endorphin reference peptides. Quantitative evaluation revealed that the beta-EP content of 24-hr captured animals was higher than that in fresh captured ones. The stress paradigm applied here was consistent with the measurement of plasma androgens and corticosterone levels in females after short-captivity confinement. In comparison with fresh-captured animals, a sharp decrease of these levels was found within 10-24 hr after capture. These effects were reversed by naltrexone, a long-acting opioid antagonist, after 24 hr of treatment. In fact, in the captive animals injected with 100 ng of naltrexone, the plasma androgen titers remained low at the 10th hour postcapture, but rose to the control levels within 24 hr. A similar effect was found for the plasma corticosterone levels. These data demonstrate that, in this anuran, endogenous opioids could mediate the stress-induced inhibition of gonadal function, and perhaps the inhibition of the hypothalamus-pituitary-adrenal axis.

Presence and steroidogenetic activity of beta-endorphin in the ovary of the lizard, Podarcis s. sicula raf

In mammals, proopiomelanocortin (POMC)-related peptides are involved in reproductive processes at both the hypothalamopituitary and ovarian levels. Through immunocytochemical and physiological in vitro studies, evidence for a diffuse POMC-related opioid system in the lizard Podarcis s. sicula is provided. In the lizard ovary, beta-endorphin (beta-EP)-like immunoreactive cells were observed within the granulosa layer; the immunoresponse showed seasonal variation, being most pronounced in the winter ovary. HPLC followed by immunoassay showed that acetyl beta-EP is the main form of POMC-related peptide in both pituitary and ovary. In vitro studies showed that picomolar amounts of beta-EP stimulate follicular estrogen production during both the reproductive and winter phases; induction was found to be higher in the reproductive phase. The data reported here provide evidence for the physiological role played by beta-EP in the reproductive function of Podarcis s. sicula via induction of ovarian production of estradiol-17 beta, which is the main factor responsible for the vitellogenic process.

Seasonal changes in plasma growth hormone and prolactin concentrations of the frog Rana esculenta

Plasma growth hormone (GH), prolactin (PRL), and vitellogenin (VTG) concentrations were determined during the annual reproductive cycle of the frog Rana esculenta. Plasma GH and PRL were measured using a RIA that employed purified bullfrog (Rana catesbeiana) GH and PRL as standards and radioligand, and their respective antibodies. Using ELISA, plasma VTG titers were related to ovarian weight. GH, PRL, and VTG displayed different trends related to season and sex. In male frogs the GH and PRL trends have been found parallel, showing the highest concentrations (35 and 85 ng/ml, respectively) during the winter months. In the female frogs, the GH trend behaved differently from that in males; in fact, plasma GH changed during the annual reproductive cycle, showing two main peaks occurring during the reproductive period and the autumn ovarian recrudescence that are well correlated with the vitellogenesis as well as with the main changes in ovarian weight.

Opioids and testicular activity in the frog, Rana esculenta

The presence and activity of brain, pituitary and testicular beta-endorphin (beta-EP)-like material have been studied in the frog, Rana esculenta, using reverse-phase high-pressure liquid chromatography, coupled with radioimmunoassay and immunocytochemistry. In-vivo and in-vitro treatments with naltrexone were carried out to assess the putative physiological activity of opioid peptides. beta-EP(1-31) and (1-27), together with their acetylated forms, have been identified in brain, pituitary and testis. In particular, beta-EP(1-31) concentrations peaked during July in the brain and pituitary, whilst in testes maximum concentrations were found in April and November. beta-EP immunoreactivity was present in the brain within the nucleus preopticus and nucleus infundibularis ventralis while positive fibres in the retrochiasmatic regions projected to the median eminence. In the testis, interstitial cells, canaliculi of the efferent system, spermatogonia and spermatocytes showed positive immunostaining for beta-EP. In intact animals, naltrexone treatment increased plasma and testicular androgen levels and this effect was confirmed in in-vitro incubations of minced testes. Naltrexone also induced a significant increase in germ cell degeneration. Our results indicated that an opioid system modulates the hypothalamus-pituitary-gonadal axis in the frog, Rana esculenta and, for the first time, we have shown that the testicular activity of a non-mammalian species may be regulated by opiates locally.

Occurrence of immunoreactive Met- and Leu-enkephalin-like peptides in the ovary of the green frog, Rana esculenta

In the present study, we have localized for the first time Met- and Leu-enkephalin-like material in the ovary of the anuran, Rana esculenta, using the indirect immunofluorescence method. The ovaries were sampled during the main representative phases of the annual reproductive cycle of the frog, living in a mountain pond (Colfiorito, Umbria at 820 m a.s.l.). Strong immunoreactivity to Met- and Leu-enkephalin antisera was observed in the follicle cells of the granulosa layer of vitellogenic oocytes; moreover, during this phase, immunofluorescent materials were also radially localized in the cytoplasm and in the perinuclear zone. The mature oocytes showed Met- and Leu-enkephalin-like immunostaining in the thecal layer and in several granules scattered in the peripheral zone of the yolk. The different pattern of Leu- and Met-enkephalin-like immunoreactivity in the frog ovary parallels and complements the changes occurring in the reproductive (May) and in the vitellogenetic (September) phases during the ovarian cycle. Consequently, these findings strongly support the hypothesis for a local synthesis of these peptides in the ovary and suggest their possible involvement in the control of ovarian function.

Ovarian opioids and the reproductive cycle of the frog Rana esculenta

In mammals, proopiomelanocortin-related peptides are involved in reproductive processes both at the hypothalamo-pituitary and ovarian levels. Using immunocytochemical, biochemical and physiological "in vitro" studies, we provide here evidence for a diffuse POMC-related opioid system in the frog Rana esculenta. Ovarian beta-endorphin (beta-EP) is expressed in thecal cells and changes during the reproductive cycle in an inverse relationship with follicular development. Seasonal changes in the ovary are different to those in the brain or in the pituitary. The ratio of acetylated vs native beta-EP in the ovary also changes over the reproductive period, affecting the biological activity of the peptide. During both the reproductive spring period and the summer post-reproductive phase pMol amounts of beta-EP stimulate follicular androgen secretion in vitro, in a naloxone-reversible way. In either period, an inhibition of estradiol, possibly mediated via other factors, is the result of opioid action. In conclusion, these data demonstrate for the first time the widespread presence of beta-EP-related peptides in the frog Rana esculenta. Both immunocytochemical and biochemical evidence, as well as in vitro responses, support a physiological role for beta-EP in ovarian seasonality during the reproductive cycle of this amphibian.

Plasma vitellogenin and 17 beta-estradiol levels during the annual reproductive cycle of Podarcis s. sicula Raf

Plasma vitellogenin and 17 beta-estradiol concentration were determined during the annual reproductive cycle of the female lizard Podarcis s. sicula Raf. living around Naples. Plasma vitellogenin was purified from estrogenized males for characterization and to raise specific immune serum. Using ELISA, plasma vitellogenin titers were determined in relation to ovary weight; plasma 17 beta-estradiol was measured by RIA method. Native vitellogenin was present as two polypeptide bands: alpha and beta. The electrophoretic patterns, studied in normal male and estrogenized male and female, showed vitellogenin to be a protein present in female and in estrogenized male plasma but not in normal males. Lizard monomeric VTG, determined by SDS-PAGE, was about 200 kDa. Correlations between seasonal ovarian weight variations and plasma vitellogenin and 17 beta-estradiol suggest that ovarian development in Podarcis depends on plasma vitellogenin synthesis, which in turn relies on plasma estradiol levels. The two ovulatory waves observed in this study coincided with the two peak values of plasma vitellogenin and 17 beta-estradiol.

In vitro steroid production by follicles of frog Rana esculenta: mammalian gonadotropin-releasing hormone effects

The effects of mammalian gonadotropin-releasing hormone on ovarian release of progesterone, androgens and estradiol-17 beta were studied in vitro by a superfusion system carried out on follicles of adult female Rana esculenta, collected at different periods of the annual reproductive cycle. The follicles were superfused with medium alone, pituitary, mammalian gonadotropin-releasing hormone, or pituitary plus mammalian gonadotropin-releasing hormone. For follicles obtained in the prereproductive period, pituitary plus mammalian gonadotropin-releasing hormone increased the estradiol values much more than pituitary alone. In the reproductive period, pituitary alone increased the estradiol values much more than pituitary plus mammalian gonadotropin-releasing hormone. For follicles obtained in the recovery period, mammalian gonadotropin-releasing hormone alone stimulated the highest estradiol production, and pituitary plus mammalian gonadotropin-releasing hormone increased the estradiol values much more than pituitary alone. The results reported here suggest that mammalian gonadotropin-releasing hormone and/or pituitary have a direct effect on ovarian estradiol secretion, and that this effect varies with the annual reproductive cycle.

Sex steroid profile and plasma vitellogenin during the annual reproductive cycle of the crested newt (Triturus carnifex Laur.)

The annual reproductive cycle of the crested newt, Triturus carnifex, has been studied in the field. Temperatures, rainfall, humidity, and photoperiod were recorded throughout the year. Adult male and female newts were sampled monthly; snout vent lengths, crest heights of males, and body ovarian, oviducal, testicular, and abdominal gland weights were recorded. Plasma samples were assayed for androgen, estradiol-17 beta, and progesterone by radioimmunoassay and for vitellogenin by enzyme-linked immunosorbent assay. Air, deep water, water surface, and soil temperatures were low from October to March, but increased in April and May without consistent summer variations. Ovarian and oviducal weights increased in October to reach maximum values between January and March (reproductive period). Crest height and abdominal gland weight in males mirrored the ovarian and oviducal pattern, while testicular weights were maximal in October and November. In females, plasma androgens were high during the reproductive period, and plasma estradiol peaked sharply in March, while plasma progesterone changed little. In the males plasma androgen and estradiol concentrations were similar to those of females, while plasma progesterone was significantly correlated with the cycle in testicular weight. In both sexes androgens showed a significantly negative correlation with air and water surface temperature. Plasma vitellogenin peaked in March but it did not correlate with either ovarian weight or plasma estradiol concentrations. These data support and confirm those previously reported for newts under laboratory conditions. The negative correlation between androgens and temperature suggests that this hormone may trigger the reproductive process. Moreover the correlations between plasma progesterone and testicular weight may indicate that this hormone is involved in male newts reproduction.(ABSTRACT TRUNCATED AT 250 WORDS)

Vitellogenin hormonal control in the green frog, Pana esculenta. interplay between estradiol and pituitary hormones

1. The effect of estradiol and pituitary hormones on the titre of serum vitellogenin has been studied in Rana esculenta by rocket immunoelectrophoresis. 2. Hepatic synthesis of vitellogenin depends on physiological doses of estradiol. 3. Gonadotrophins enhance the uptake, presumably by acting directly on the oocyte plasma membrane. 4. In addition, our data support direct pituitary intervention on liver synthesis and/or release of vitellogenin. 5. Hormonal response, as evaluated by vitellogenin serum titres, tends to increase from November to July. This could be the expression of a modification, throughout the sexual cycle, of liver sensitivity to the hormones.

Plasma sex hormones and post-reproductive period in the green frog, Rana esculenta complex

The plasmatic profiles of androgens, estradiol, and progesterone, together with gonads and SSC modifications, have been followed, throughout the post-reproductive period in two Rana esculenta populations, inhabiting, respectively, a mountain pond (Colfiorito) and a sea level lagoon (Lesina). Testosterone and progesterone progressively decrease in the blood until July, while estradiol shows, in both sexes, an increase in the same month. Testosterone depletion accounts for thumb pad atrophy in the male and probably, in both sexes, for the summer interruption of sexual behavior. The estradiol increase could be linked to the induction of vitellogenin synthesis by the liver or, alternatively, could act through negative feed-back on the brain centers involved in GnRF synthesis and therefore it could be responsible for an inhibition of LH release and, in turn, of androgen synthesis/secretion by the gonads. The last function can be framed in the endocrine regulation of the so-called "refractory period" which interrupts the breeding during the summer. The hematic level of progesterone is higher during the ovulation period and this is consistent with the role assigned to the hormone, i.e., the induction of jelly release from oviductal glands. The hormonal trends in the blood of the two frog populations are very similar, although some differences exist in the levels of testosterone and progesterone.

Variations in the vitellogenin titre during the reproductive cycle of Rana esculenta L

1. Vitellogenin titre has been measured by rocket immunoelectrophoresis in specimens of Rana esculenta L. caught at three different locations in southern Italy. 2. Variations in the serum level of vitellogenin are temporally related to ovarian growth during the reproductive cycle. 3. With the exception of the FL population, vitellogenin titre is low at spawning time but increases prior to ovarian recovery. 4. It eventually levels off, or undergoes a slight decline during winter, when the ovary is in a static phase. 5. The evidence presented in this study is consonant with the experimental model on hormonal control of vitellogenesis. 6. The vitellogenin patterns observed in the populations examined in this study are interpreted as due to different environmental conditions even though the hybridogenetic nature of Rana esculenta has also to be taken into account.

Uptake of labeled mammalian gonadotropins by ovary and oviduct of the lizard, Lacerta s. sicula, in vivo

The uptake of radioactivity by ovary, oviduct and thigh muscles of the lizard, Lacerta s. sicula, after administration of labeled mammalian gonadotropins has been followed. Ovary and oviduct show a significantly higher radioactivity than thigh muscles. The ovarian uptake, moreover, is decreased by the corresponding non-labeled gonadotropin. The meaning of these observations for the physiological regulation of reproductive processes in that lizard, are discussed.