Changes in ovarian follicles and in vitro sex hormone release in the lizard Podarcis sicula sicula

Hormonal control of seasonal color change in female spiny-footed lizards: an observational and experimental approach

Breeding coloration of females often signals aspects of their reproductive status, suggesting a link between color and sex steroid hormones. In this study, we examined the relationships between 2 sex steroid hormones (progesterone and β-estradiol) and reproductive coloration in female spiny-footed lizards Acanthodactylus erythrurus. We first explored natural variation in female plasma hormone levels and coloration during their reproductive cycle. β-estradiol was negatively related to brightness and positively related to red saturation, whereas progesterone was not significantly related to coloration. After identifying key relationships, plasma hormone concentrations were manipulated by creating 3 experimental female groups (β-estradiol-treated, progesterone-treated, and control), and the effects on coloration were monitored. β-estradiol-treated females, in which there was a rise in both β-estradiol and progesterone levels, lost their red coloration earlier than females in the other 2 experimental groups, whereas progesterone treatment had no significant effect on female coloration. Our results suggest that high levels of either β-estradiol alone or β-estradiol together with progesterone trigger the loss of red coloration in female spiny-footed lizards, and that progesterone alone does not affect coloration. We hypothesize that changes in female breeding color might be regulated by β-estradiol in species in which conspicuous coloration is displayed before ovulation, and by progesterone in species in which this color is displayed during gravidity.

The maturation of oocyte follicular epithelium of Podarcis s. sicula is promoted by D-aspartic acid

We investigated whether the maturation of oocyte follicular epithelium of lizard is affected by d-aspartic acid (d-Asp). Our results demonstrated that d-Asp is endogenously present in the oocytes, and its distribution varies during the reproductive cycle and following intraperitoneal administration. At previtellogenesis, it is observed in the cytoplasm and nucleus of pyriform cells, in intermediate cells, in some small cells of the granulosa, in the ooplasm, and in some thecal elements. At vitellogenesis, d-Asp is localized in the proximity of the zona pellucida, in the theca, and in the ooplasm. Injected d-Asp is mainly captured by pyriform cells and ooplasm of previtellogenic oocytes, but a moderate accumulation is evident in the cytoplasm of some small granulosa cells and in the theca. d-Asp also increases the ovarian and plasmatic levels of 17β-estradiol and decreases those of testosterone. As a direct and/or indirect consequence of d-Asp, previtellogenic oocytes grow up and mature, resulting in a higher accumulation of carbohydrates in the granulosa, zona pellucida, and ooplasm, but also a reduction in the thickness of the granulosa layer and an increase of the theca stratum. Taken together, our results show that d-Asp may be related to the synchrony of reproduction, either enhancing the growth and maturation of follicular epithelium or influencing its endocrine functions.

Immunolocalization of hepatic estrogen and progesterone receptors in the female lizard Uromastyx acanthinura

The hormonal regulation of hepatic synthesis of vitellogenin during the annual reproductive cycle was performed for the first time in the deserticole, oviparous, diurnal and herbivorous Uromastyx acanthinura, a lizard belonging to the Agamidae family. In order to elucidate what kind of estrogen receptor is involved in this process, an immunohistochemical study was performed. Changes were obtained in the labeling and cellular distribution of the estrogen and progesterone receptors according to the period of the reproductive cycle and the experimental administration of 17β-estradiol. Only the ERβ subtype was present; it was found in all phases of the cycle with a variable localization: nuclear and cytosolic during vitellogenesis, mainly cytosolic in the female with egg retention (luteal phase) and strictly cytosolic in females at sexual rest. The progesterone receptors were present only at the luteal phase and during sexual rest and disappeared completely from females after 17β-estradiol treatment in sexual rest. Our data suggested that mediation of action of the 17β-estradiol in the vitellogenin synthesis in the lizard U. acanthinura occured via ERβ. PRA and PRB could both be necessary for the negative effect of progesterone on the hepatic synthesis of vitellogenin.

Localization of c-kit and stem cell factor (SCF) in ovarian follicular epithelium of a lizard, Podarcis s. sicula

We performed an immunohistochemical study to determine the immunolocalization of c-kit and stem cell factor (SCF) in ovarian follicles during the reproductive cycle of the lizard, Podarcis s. sicula. Follicles were serially cut and used for histological and histochemical characterization and also for immunohistochemical detection of both c-kit and SCF. C-kit and SCF were localized in the follicles with a differing pattern with regard to the stage of sexual cycle or the cell type forming the follicular epithelium (granulosa). In pre-reproductive follicles, where the granulosa consists of three main different cytotypes, the c-kit receptor was prevalently localized on the plasmalemma of small cells, although some pyriform and intermediate cells also appeared positive. C-kit was also localized in the theca. In pre-reproductive follicles, SCF was markedly observed in the cytoplasm of some pyriform cells. Small cells and theca also stained moderately positive, whereas the intermediate cells were mostly negative. In reproductive follicles, where granulosa cells are morphologically rearranged, c-kit was observed in small cells and in some thecal elements, while SCF was weakly immunostained. At the site of follicular layer invaginations evident c-kit/SCF immunostaining was observed in the granulosa epithelium and in the theca. These observations suggest that the expression of c-kit and SCF changes as a function of follicular development and may reflect the involvement of this system in the maturation of the oocyte.

In vitro progesterone production by maternal and embryonic tissues during gestation in the southern snow skink (Niveoscincus microlepidotus)

The southern snow skink, Niveoscincus microlepidotus, has a protracted gestation, lasting approximately one year. Ovulation occurs in spring (November) and embryonic development is completed by early autumn (March); however, birth does not occur until the following spring. Previous studies have shown that plasma progesterone concentration peaks in preovulatory females (spring, October), remains high during early gestation, and decreases to basal by autumn. In vitro progesterone production by corpora lutea, non-luteal ovary, anterior oviduct, placental tissues, muscle, and embryonic adrenal-gonads from N. microlepidotus was assessed throughout gestation. Tissues were incubated with or without the precursor pregnenolone for 3h at 24 degrees C; the resulting media were analysed for progesterone using radioimmunoassay. In vitro progesterone production by corpora lutea in media only was high during early gestation, dropping to basal by autumn. Maternal adrenal glands produced progesterone in vitro in media only throughout gestation; however, the pattern of production did not correlate with plasma concentrations and may represent steroid that is normally converted to corticosterone. Non-luteal ovary, anterior oviduct, placental tissues, muscle, and embryonic adrenal-gonads produced minimal progesterone in media only, but were able to convert pregnenolone to progesterone; this suggests steroid metabolic capability within these tissues. Further research is needed to address the possible endocrine role(s) of placental and embryonic tissues during gestation in viviparous squamates.

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.