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

Long-term monitoring of egg-laying cycle using ultrasonography reveals the reproductive dynamics of circulating sex steroids in an oviparous catshark, Scyliorhinus torazame

The many diverse reproductive strategies of elasmobranchs (sharks, skates and rays) from lecithotrophic oviparity to matrotrophic viviparity have attracted significant research attention. However, the endocrine control of elasmobranch reproduction is less well-documented largely due to their reproductive characteristics, such as a long reproductive cycle, and/or repeated internal fertilization using stored sperm in oviparous species. In the present study, for the first time, we succeeded in non-invasive monitoring of the continuing egg-laying cycle of the cloudy catshark Scyliorhinus torazame using portable ultrasound devices. Furthermore, long-term simultaneous monitoring of the egg-laying cycle and measurement of plasma sex steroids revealed cycling patterns of estradiol-17β (E2), testosterone (T) and progesterone (P4). In particular, a decline in T followed by a reciprocal surge in plasma P4 were consistently observed prior to the appearance of the capsulated eggs, implying that P4 is likely associated with the ovulation and/or egg-case formation. While the cycling pattern of E2 was not as apparent as those of T and P4, threshold levels of E2 (>5 ng/mL) and T (>1 ng/mL) appeared to be crucial in the continuation of egg-laying cycle. The possibility to trace the dynamics of plasma sex steroids in a single individual throughout the reproductive cycles makes the catshark a useful model for regulatory and mechanistic studies of elasmobranch reproduction.

Assessing reproductive status in elasmobranch fishes using steroid hormones extracted from skeletal muscle tissue

Elasmobranch fishes (sharks, skates, and rays) are particularly susceptible to anthropogenic threats, making a thorough understanding of their life history characteristics essential for proper management. Historically, elasmobranch reproductive data have been collected by lethal sampling, an approach that is problematic for threatened and endangered species. However, recent studies have demonstrated that non-lethal approaches can be as effective as lethal ones for assessment of the reproductive status of an animal. For example, plasma has been used to examine concentrations of steroid hormones. Additionally, skeletal muscle tissue, which can be obtained non-lethally and with minimal stress, can also be used to quantify concentrations of steroid hormones. Skeletal muscle progesterone, testosterone, and estradiol concentrations were determined to be statistically significant indicators of reproductive status in the oviparous Leucoraja erinacea, the yolk-dependent viviparous Squalus acanthias, and the yolk-sac placental viviparous Rhizoprionodon terraenovae. The results of the present study demonstrate that steroid hormones present in non-lethally harvested skeletal muscle tissue can be used as reliable indicators of reproductive status in elasmobranchs.

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.

Effect of 17beta-estradiol and progesterone on vitellogenesis in the spotted ray Torpedo marmorata Risso 1810 (Elasmobranchii: Torpediniformes): studies on females and on estrogen-treated males

The influence of 17beta-estradiol (E(2)) on vertebrate vitellogenesis is well ascertained. The aim of the present paper is to study the involvement of E(2) and progesterone (P) in the induction and regulation of vitellogenesis in females and experimental E(2)-treated males of Torpedo marmorata. We analyzed females in various stages of the reproductive cycle and E(2) experimentally treated males. The presence of vitellogenin was investigated in the plasma and in the liver by western blot and immunohistochemistry; its site of synthesis was investigated by in situ hybridization. The steroid levels in the plasma were measured by Enzyme Immunoassay. In treated males, E(2) induces in the liver the synthesis of VTG which is then secreted into the bloodstream as a 205-kDa polypeptide, the same that is found in the plasma of non-pregnant vitellogenic females. In females, E(2) is naturally present in the plasma and its level is correlated with VTG synthesis in the liver and with the female reproductive cycle. Indeed, large amounts of E(2) are only found in mature vitellogenic females, whose liver is involved in VTG synthesis and secretion. By contrast, small amounts of E(2) are evident in juveniles whose ovaries are lacking in vitellogenic follicles and in females preparing for ovulation. Low titers are also found in gravid females, whose liver is not engaged in VTG synthesis. We show that P, which is absent in untreated males and juvenile females, is evident in the blood serum of E(2)-treated males and sexually mature females. Interestingly, in treated males P appears in the plasma just 24h after the first injection of E(2) and its titer increases; a week after the last injections, the P level is similar to that recorded in non-gravid vitellogenic females. Finally, it is noteworthy that the highest titer of P was recorded in pregnant females. We demonstrate that in Torpedo vitellogenin synthesis, as in other vertebrates, is under the control of E(2) but also that this synthesis is probably under the control of progesterone.

An androgen receptor in the brain of the green frog Rana esculenta

An androgen receptor (AR) has been detected in both the hypothalamic and extra-hypothalamic area of the brain of the male of the green frog Rana esculenta. 3H-T binding activity was detected separately in the hypothalamic and extra-hypothalamic areas. Experiments of binding assay showed 3H-T binding activity in the nuclear extract but not in the cytosol of both the hypothalamic and the extra-hypothalamic areas. The androgen binding moiety was not strictly specific for androgens, binding also 17 beta-estradiol, although to a lesser extent. 3H-testosterone binding activity fluctuated in both the hypothalamic and the extra-hypothalamic areas throughout the reproductive cycle, and paralleled androgen plasma levels.

Immunological evidence for progesterone and estradiol receptors in the freshwater crayfish Austropotamobius pallipes

In this article, we present evidence for progesterone and estradiol receptors (PR and ER, respectively) in the female of the crayfish Austropotamobius pallipes. To our knowledge, this is the first report of sex steroid receptors in crustaceans. By using immunohistochemistry and Western blotting approaches and employing three different antibodies against PR (human PR, chicken PR-hinge region, and chicken PR A/B domain) and antibodies against human ER, we showed the presence of PR in the ovary and hepatopancreas and ER in the hepatopancreas of the freshwater crayfish A. pallipes. The immunological characteristics and the tissue localization suggest a relatedness with both PR and ER in vertebrates along with their involvement in the modulation of reproductive functions in this crustaceans.

Progesterone receptor in the liver and oviduct of the lizard Podarcis sicula

In this paper we report the presence of a (3)H-Progesterone ((3)H-P) binding moiety, which has the characteristics of a true receptor, in the liver of the female of the lizard Podarcis sicula. (3)H-P binding studies show the presence of one type of binding site with an average Kd value of 6.2 +/- 2.0 nM in the cytoplasm and 6.3 +/- 1.1 nM in the nucleus. Competition experiments showed that progesterone (P) was the best competitor, while testosterone, deoxycorticosterone (DOC), corticosterone, 17 alpha-hydroxyprogesterone; R5020; RU486 and RU26988-5 were poor competitors. We have also investigated the immunological characteristics of progesterone receptor (PR) in both the liver and the oviduct of Podarcis sicula, by Western blotting using the monoclonal antibody PR22 raised against the PR isoforms A and B of chicken. One imunoreactive band of about 70 kDa was detected in cytoplasmic and nuclear extracts of both the liver and the oviduct. PR immunoreactivity was present in the liver during the quiescent phase. In the oviduct PR immunoreactivity increased from the recovery to the full grown phase. P treatment of estrogen-primed females did not affect the presence of PR in the liver, while brought about a PR increase in the oviduct. This study suggests that PR is expressed differently in the liver and the oviduct of Podarcis sicula throughout the reproductive cycle. PR might fulfill different requirements in relation to the different physiological functions of the tissue during the reproductive cycle.

Evidence of a progesterone receptor in the liver of the green frog Rana esculenta and its down-regulation by 17 beta estradiol and progesterone

Progesterone is a versatile hormone showing an ample variety of effects. One of the numerous functions attributed to progesterone is the modulation of vitellogenesis in oviparous vertebrates. As a prerequisite for the possible involvement of progesterone in vitellogenesis modulation, we investigated the presence of a progesterone receptor (PR) in the liver of the female green frog Rana esculenta. 3H-Progesterone (3H-P) binding activity was found in both cytosol and nuclear extract of the liver of Rana esculenta. The progesterone-binding moiety showed the typical characteristics of a true receptor, such as high affinity, low capacity, and specificity for progesterone. It also bound to DNA-cellulose and was eluted with a linear salt gradient at a concentration of 0.05 M of NaCl. The progesterone-binding moiety was down regulated by steroid hormones, in that ovariectomy resulted in a significant increase, in both cytosol and nuclear extract, of 3H-P binding activity with respect to intact females. On the contrary, 3H-P binding activity was almost undetectable after estradiol and/or progesterone treatment. The progesterone binding moiety of Rana esculenta was analyzed by Western blotting with the aid of a monoclonal antibody raised against the subunits A and B of the chicken PR. An immunoreactive band of about 67 kDa was observed in the liver of both intact and treated females. The 67 kDa band showed an increased intensity in ovariectomized animals, while it was faint following treatment with estradiol and/or progesterone. This is the first report on the presence of a progesterone receptor (PR) in the liver of an amphibian. PR of Rana esculenta is down regulated by estradiol and/or progesterone and shows peculiar immunological and biochemical characteristics, which make it rather different from the PR of other vertebrates.

Progesterone receptor in the reproductive system of the female of Octopus vulgaris: characterization and immunolocalization

In this study for the first time we have characterized a progesterone receptor in the reproductive system of the female of Octopus vulgaris. Scatchard analysis revealed that one binding component with high affinity and low capacity for the ligand was present only in the nuclear extract. Competition experiments showed that the progesterone receptor was strictly specific for progesterone. DNA-cellulose binding and DEAE-Sephacel both confirmed the presence of one 3H-progesterone binding component which eluted at a salt concentration of 0.14 +/- 0.05 M NaCl and 0.15 +/- 0.05 M NaCl respectively. By using monoclonal antibodies against chicken progesterone receptor (subunits A and B), we have localized on Western Blot one band of about 70 kDa. Immunoreactivity for progesterone binding molecules has been localized in the nuclei of the follicle cells of the ovary, of the proximal portion of the oviduct and of the outer region of the nidimental gland. These data, taken together, provide evidence that in Octopus vulgaris the progesterone receptor has biochemical and immunohistochemical characteristics resembling those of progesterone receptor in vertebrates.