The Experts below are selected from a list of 186 Experts worldwide ranked by ideXlab platform
A Tsafriri - One of the best experts on this subject based on the ideXlab platform.
-
role of meiosis activating sterols in rat oocyte maturation effects of specific inhibitors and changes in the expression of lanosterol 14α demethylase during the Preovulatory Period
Biology of Reproduction, 2001Co-Authors: Karen M Vaknin, Shlomi Lazar, Malka Popliker, A TsafririAbstract:In vitro studies on mouse oocytes have shown that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on the resumption of meiosis. These sterols are synthesized by cytochrome P(450) lanosterol 14alpha-demethylase (LDM), a key enzyme in cholesterol biosynthesis. We have used specific inhibitors of LDM, azalanstat (RS-21607) and RS-21745, to test whether MAS is an obligatory mediator in the resumption of meiosis in the rat. Addition of azalanstat and RS-21745 (1-200 microM) to culture medium of rat isolated cumulus-enclosed oocyte and Preovulatory follicle-enclosed oocyte stimulated by LH/hCG did not allow separation between their inhibition of the resumption of meiosis and the degeneration of oocytes. In both models, doses of the drug that inhibited oocyte maturation also increased oocyte degeneration. The inhibitors only partially suppressed follicular progesterone production. We have examined by reverse transcriptase-polymerase chain reaction, Western blotting, and immunocytochemistry the ovarian expression of LDM mRNA and protein during the Preovulatory Period. We did not find evidence for the stimulation of this enzyme by LH/hCG. The strongest staining by LDM antiserum was obtained in primordial and primary oocytes, and the staining was reduced with oocyte growth. In addition, strong LDM staining could be observed in some of the granulosa cells, especially of the corona radiata localized in close proximity to the oocyte. In conclusion, our results with specific inhibitors and molecular approaches do not reveal evidence to support the hypothesis that MAS is an obligatory step in the stimulation of the resumption of meiosis. Specific inhibitors of MAS synthesis did not prevent spontaneous or LH-stimulated meiosis at doses that have previously been shown to effectively suppress LDM activity. Much higher concentrations of the inhibitors, which affected meiosis, were detrimental to oocytes, leading to their degeneration. The timing of LDM expression in the ovary was incompatible with a role for MAS in meiosis. Finally, the preferential localization of LDM protein to the oocytes suggests MAS production in oocytes rather than its transport from the somatic compartment as implied by the proposed role of MAS as a cumulus-oocyte signal molecule.
-
role of meiosis activating sterols in rat oocyte maturation effects of specific inhibitors and changes in the expression of lanosterol 14α demethylase during the Preovulatory Period
Biology of Reproduction, 2001Co-Authors: Karen M Vaknin, Shlomi Lazar, Malka Popliker, A TsafririAbstract:Abstract In vitro studies on mouse oocytes have shown that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on the resumption of meiosis. These sterols are synthesized by cytochrome P450 lanosterol 14α-demethylase (LDM), a key enzyme in cholesterol biosynthesis. We have used specific inhibitors of LDM, azalanstat (RS-21607) and RS-21745, to test whether MAS is an obligatory mediator in the resumption of meiosis in the rat. Addition of azalanstat and RS-21745 (1–200 μM) to culture medium of rat isolated cumulus-enclosed oocyte and Preovulatory follicle-enclosed oocyte stimulated by LH/hCG did not allow separation between their inhibition of the resumption of meiosis and the degeneration of oocytes. In both models, doses of the drug that inhibited oocyte maturation also increased oocyte degeneration. The inhibitors only partially suppressed follicular progesterone production. We have examined by reverse transcriptase-polymer...
Karen M Vaknin - One of the best experts on this subject based on the ideXlab platform.
-
role of meiosis activating sterols in rat oocyte maturation effects of specific inhibitors and changes in the expression of lanosterol 14α demethylase during the Preovulatory Period
Biology of Reproduction, 2001Co-Authors: Karen M Vaknin, Shlomi Lazar, Malka Popliker, A TsafririAbstract:In vitro studies on mouse oocytes have shown that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on the resumption of meiosis. These sterols are synthesized by cytochrome P(450) lanosterol 14alpha-demethylase (LDM), a key enzyme in cholesterol biosynthesis. We have used specific inhibitors of LDM, azalanstat (RS-21607) and RS-21745, to test whether MAS is an obligatory mediator in the resumption of meiosis in the rat. Addition of azalanstat and RS-21745 (1-200 microM) to culture medium of rat isolated cumulus-enclosed oocyte and Preovulatory follicle-enclosed oocyte stimulated by LH/hCG did not allow separation between their inhibition of the resumption of meiosis and the degeneration of oocytes. In both models, doses of the drug that inhibited oocyte maturation also increased oocyte degeneration. The inhibitors only partially suppressed follicular progesterone production. We have examined by reverse transcriptase-polymerase chain reaction, Western blotting, and immunocytochemistry the ovarian expression of LDM mRNA and protein during the Preovulatory Period. We did not find evidence for the stimulation of this enzyme by LH/hCG. The strongest staining by LDM antiserum was obtained in primordial and primary oocytes, and the staining was reduced with oocyte growth. In addition, strong LDM staining could be observed in some of the granulosa cells, especially of the corona radiata localized in close proximity to the oocyte. In conclusion, our results with specific inhibitors and molecular approaches do not reveal evidence to support the hypothesis that MAS is an obligatory step in the stimulation of the resumption of meiosis. Specific inhibitors of MAS synthesis did not prevent spontaneous or LH-stimulated meiosis at doses that have previously been shown to effectively suppress LDM activity. Much higher concentrations of the inhibitors, which affected meiosis, were detrimental to oocytes, leading to their degeneration. The timing of LDM expression in the ovary was incompatible with a role for MAS in meiosis. Finally, the preferential localization of LDM protein to the oocytes suggests MAS production in oocytes rather than its transport from the somatic compartment as implied by the proposed role of MAS as a cumulus-oocyte signal molecule.
-
role of meiosis activating sterols in rat oocyte maturation effects of specific inhibitors and changes in the expression of lanosterol 14α demethylase during the Preovulatory Period
Biology of Reproduction, 2001Co-Authors: Karen M Vaknin, Shlomi Lazar, Malka Popliker, A TsafririAbstract:Abstract In vitro studies on mouse oocytes have shown that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on the resumption of meiosis. These sterols are synthesized by cytochrome P450 lanosterol 14α-demethylase (LDM), a key enzyme in cholesterol biosynthesis. We have used specific inhibitors of LDM, azalanstat (RS-21607) and RS-21745, to test whether MAS is an obligatory mediator in the resumption of meiosis in the rat. Addition of azalanstat and RS-21745 (1–200 μM) to culture medium of rat isolated cumulus-enclosed oocyte and Preovulatory follicle-enclosed oocyte stimulated by LH/hCG did not allow separation between their inhibition of the resumption of meiosis and the degeneration of oocytes. In both models, doses of the drug that inhibited oocyte maturation also increased oocyte degeneration. The inhibitors only partially suppressed follicular progesterone production. We have examined by reverse transcriptase-polymer...
Malka Popliker - One of the best experts on this subject based on the ideXlab platform.
-
role of meiosis activating sterols in rat oocyte maturation effects of specific inhibitors and changes in the expression of lanosterol 14α demethylase during the Preovulatory Period
Biology of Reproduction, 2001Co-Authors: Karen M Vaknin, Shlomi Lazar, Malka Popliker, A TsafririAbstract:In vitro studies on mouse oocytes have shown that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on the resumption of meiosis. These sterols are synthesized by cytochrome P(450) lanosterol 14alpha-demethylase (LDM), a key enzyme in cholesterol biosynthesis. We have used specific inhibitors of LDM, azalanstat (RS-21607) and RS-21745, to test whether MAS is an obligatory mediator in the resumption of meiosis in the rat. Addition of azalanstat and RS-21745 (1-200 microM) to culture medium of rat isolated cumulus-enclosed oocyte and Preovulatory follicle-enclosed oocyte stimulated by LH/hCG did not allow separation between their inhibition of the resumption of meiosis and the degeneration of oocytes. In both models, doses of the drug that inhibited oocyte maturation also increased oocyte degeneration. The inhibitors only partially suppressed follicular progesterone production. We have examined by reverse transcriptase-polymerase chain reaction, Western blotting, and immunocytochemistry the ovarian expression of LDM mRNA and protein during the Preovulatory Period. We did not find evidence for the stimulation of this enzyme by LH/hCG. The strongest staining by LDM antiserum was obtained in primordial and primary oocytes, and the staining was reduced with oocyte growth. In addition, strong LDM staining could be observed in some of the granulosa cells, especially of the corona radiata localized in close proximity to the oocyte. In conclusion, our results with specific inhibitors and molecular approaches do not reveal evidence to support the hypothesis that MAS is an obligatory step in the stimulation of the resumption of meiosis. Specific inhibitors of MAS synthesis did not prevent spontaneous or LH-stimulated meiosis at doses that have previously been shown to effectively suppress LDM activity. Much higher concentrations of the inhibitors, which affected meiosis, were detrimental to oocytes, leading to their degeneration. The timing of LDM expression in the ovary was incompatible with a role for MAS in meiosis. Finally, the preferential localization of LDM protein to the oocytes suggests MAS production in oocytes rather than its transport from the somatic compartment as implied by the proposed role of MAS as a cumulus-oocyte signal molecule.
-
role of meiosis activating sterols in rat oocyte maturation effects of specific inhibitors and changes in the expression of lanosterol 14α demethylase during the Preovulatory Period
Biology of Reproduction, 2001Co-Authors: Karen M Vaknin, Shlomi Lazar, Malka Popliker, A TsafririAbstract:Abstract In vitro studies on mouse oocytes have shown that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on the resumption of meiosis. These sterols are synthesized by cytochrome P450 lanosterol 14α-demethylase (LDM), a key enzyme in cholesterol biosynthesis. We have used specific inhibitors of LDM, azalanstat (RS-21607) and RS-21745, to test whether MAS is an obligatory mediator in the resumption of meiosis in the rat. Addition of azalanstat and RS-21745 (1–200 μM) to culture medium of rat isolated cumulus-enclosed oocyte and Preovulatory follicle-enclosed oocyte stimulated by LH/hCG did not allow separation between their inhibition of the resumption of meiosis and the degeneration of oocytes. In both models, doses of the drug that inhibited oocyte maturation also increased oocyte degeneration. The inhibitors only partially suppressed follicular progesterone production. We have examined by reverse transcriptase-polymer...
Shlomi Lazar - One of the best experts on this subject based on the ideXlab platform.
-
role of meiosis activating sterols in rat oocyte maturation effects of specific inhibitors and changes in the expression of lanosterol 14α demethylase during the Preovulatory Period
Biology of Reproduction, 2001Co-Authors: Karen M Vaknin, Shlomi Lazar, Malka Popliker, A TsafririAbstract:In vitro studies on mouse oocytes have shown that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on the resumption of meiosis. These sterols are synthesized by cytochrome P(450) lanosterol 14alpha-demethylase (LDM), a key enzyme in cholesterol biosynthesis. We have used specific inhibitors of LDM, azalanstat (RS-21607) and RS-21745, to test whether MAS is an obligatory mediator in the resumption of meiosis in the rat. Addition of azalanstat and RS-21745 (1-200 microM) to culture medium of rat isolated cumulus-enclosed oocyte and Preovulatory follicle-enclosed oocyte stimulated by LH/hCG did not allow separation between their inhibition of the resumption of meiosis and the degeneration of oocytes. In both models, doses of the drug that inhibited oocyte maturation also increased oocyte degeneration. The inhibitors only partially suppressed follicular progesterone production. We have examined by reverse transcriptase-polymerase chain reaction, Western blotting, and immunocytochemistry the ovarian expression of LDM mRNA and protein during the Preovulatory Period. We did not find evidence for the stimulation of this enzyme by LH/hCG. The strongest staining by LDM antiserum was obtained in primordial and primary oocytes, and the staining was reduced with oocyte growth. In addition, strong LDM staining could be observed in some of the granulosa cells, especially of the corona radiata localized in close proximity to the oocyte. In conclusion, our results with specific inhibitors and molecular approaches do not reveal evidence to support the hypothesis that MAS is an obligatory step in the stimulation of the resumption of meiosis. Specific inhibitors of MAS synthesis did not prevent spontaneous or LH-stimulated meiosis at doses that have previously been shown to effectively suppress LDM activity. Much higher concentrations of the inhibitors, which affected meiosis, were detrimental to oocytes, leading to their degeneration. The timing of LDM expression in the ovary was incompatible with a role for MAS in meiosis. Finally, the preferential localization of LDM protein to the oocytes suggests MAS production in oocytes rather than its transport from the somatic compartment as implied by the proposed role of MAS as a cumulus-oocyte signal molecule.
-
role of meiosis activating sterols in rat oocyte maturation effects of specific inhibitors and changes in the expression of lanosterol 14α demethylase during the Preovulatory Period
Biology of Reproduction, 2001Co-Authors: Karen M Vaknin, Shlomi Lazar, Malka Popliker, A TsafririAbstract:Abstract In vitro studies on mouse oocytes have shown that two closely related sterols, subsequently named meiosis-activating sterols (MAS), can overcome the inhibitory effect of hypoxanthine on the resumption of meiosis. These sterols are synthesized by cytochrome P450 lanosterol 14α-demethylase (LDM), a key enzyme in cholesterol biosynthesis. We have used specific inhibitors of LDM, azalanstat (RS-21607) and RS-21745, to test whether MAS is an obligatory mediator in the resumption of meiosis in the rat. Addition of azalanstat and RS-21745 (1–200 μM) to culture medium of rat isolated cumulus-enclosed oocyte and Preovulatory follicle-enclosed oocyte stimulated by LH/hCG did not allow separation between their inhibition of the resumption of meiosis and the degeneration of oocytes. In both models, doses of the drug that inhibited oocyte maturation also increased oocyte degeneration. The inhibitors only partially suppressed follicular progesterone production. We have examined by reverse transcriptase-polymer...
Silvia N. Fernández - One of the best experts on this subject based on the ideXlab platform.
-
analysis of bufo arenarum oviductal secretion during the sexual cycle
Zygote, 2009Co-Authors: Claudia A. Crespo, Inés Ramos, Marcela Fátima Medina, Silvia N. FernándezAbstract:SummaryBufo arenarum oocytes are oviposited surrounded by jelly coats, one component of the extracellular matrix required for fertilization. The secretion, released to the oviductal lumen, was analysed by SDS-PAGE. The coomassie blue staining evidenced an electrophoretic pattern with molecules ranging between 300 and 19 kDa that showed variations in their secretion profiles during the sexual cycle. In the Preovulatory Period the densitometric analysis showed the presence of nine peaks with marked predominance of the 74 kDa molecule. Once ovulation has occurred, the jelly coats become arranged around the oocytes during their transit throughout the oviductal pars convoluta (PC), revealing the addition of three proteins only observed during this Period, which suggests a differential secretion. Some of these proteins could not diffuse under any extraction treatment, indicating for them a structural or in situ function. Proteins of low molecular mass diffused totally while others showed a partial diffusing capacity. After ovulation a marked decrease in the relative amount of all the proteins released to the lumen, especially the 74 kDa protein, could be detected. During this Period, unlike the other stages of the sexual cycle, a differential secretion pattern was observed along the PC. The histochemical analysis performed during the ovulatory Period showed the presence of glycoconjugates including both acidic and neutral groups. The present results are in agreement with previous ultrastructural and histochemical studies that describe the role of Bufo arenarum jelly coats in fertilization.
-
changes in serum sex steroid levels throughout the reproductive cycle of bufo arenarum females
General and Comparative Endocrinology, 2004Co-Authors: Marcela Fátima Medina, Claudia A. Crespo, Inés Ramos, Silvia Gonzalezcalvar, Silvia N. FernándezAbstract:Abstract The changes in the serum levels of the sexual steroids estradiol-17β (E2), testosterone (T), dihydrotestosterone (DHT), and progesterone (P) in Bufo arenarum females were determined by radioimmunoassay (RIA) during 3 consecutive cycles (1999–2001). The serum concentrations of T and DHT, which showed a close parallelism during the annual reproductive cycle, exhibited the highest levels during the Preovulatory Period, when oogenesis is advanced, while lowest serum levels of these hormones were found during the ovulatory Period. The data obtained for E2 showed a pattern contrary to that determined for androgens. The maximum E2 concentrations detected in the early postovulatory Period might be associated with vitellogenesis and follicular growth. Lowest E2 concentrations were reached during the Period in which B. arenarum undergoes its final hibernation stage. Serum P showed a peak during the preovulatoy Period, related to the induction of nuclear maturation in full grown oocytes. A strong decrease in the levels of the circulating hormones was observed after ovariectomy. Our results showed that, out of the four hormones examined, T and DHT were the best indicators of ovarian and oviductal stage, as shown by the strong positive correlation found between androgen levels and organ weight, while E2 showed a weak negative correlation with ovarian and oviductal weight.
-
subcellular localization of ca atpase and calcium in bufo arenarum oviducts
Acta Histochemica Et Cytochemica, 2000Co-Authors: Marcela Fátima Medina, Claudia A. Crespo, Inés Ramos, Beatriz C. Winik, Silvia N. FernándezAbstract:The localization of calcium and Ca−ATPase activity in Bufo arenarum oviducts was investigated by ultrahistochemical techniques during the sexual cycle. In the Preovulatory Period prominent calcium deposits were detected in the secretory granules of epithelial and glandular cells as well as in close proximity to the plasma membranes. Furthermore, intense Ca−ATPase activity was found outlining the plasma and secretory granule membranes. Regional differences along the oviduct were observed. Immediately after ovulation the above−mentioned cells exhibited a marked reduction of calcium deposits and Ca−ATPase activity, but during hibernation this situation progressively reverted. These results demonstrate that the most prominent calcium deposits can be detected in the cellular structures that, through different secretion mechanisms, release their products towards the oviductal lumen to form the structural network of the jelly coats. The variations in calcium contents in the oviduct and the animal cycle changes in serum calcium levels are closely related with the fluctuations of estradiol serum levels during the sexual cycle, suggesting hormonal regulation.
-
ultrastructural changes in the oviductal mucosa throughout the sexual cycle in bufo arenarum
Journal of Morphology, 1999Co-Authors: Beatriz C. Winik, Inés Ramos, Claudia A. Crespo, Marcela Fátima Medina, Maria F Alcaide, Silvia N. FernándezAbstract:In Bufo arenarum the oviduct exhibits conspicuous changes throughout the sexual cycle. In the present study, we analyzed the optical and ultrastructural characteristics of the oviductal pars convoluta mucosa, the portion responsible for jelly secretion, during both the Preovulatory and postovulatory Periods. Secretory epithelial cells, ciliated cells, basal cells, and glandular cells are described. Secretory epithelial cells are characterized by the presence of secretory granules, the size, shape and electron density of which vary markedly. Their contents are mainly released by exocytosis into the oviductal lumen. Moreover, in the Preovulatory Period, apocrine, and holocrine secretion processes frequently occur. During the postovulatory Period, these cells exhibit a marked diminution of secretory granules. Ciliated cells show a typical ultrastructural organization. Basal cells are distinguished in the lower part of the epithelium by their heterochromatic nuclei and electron-lucent cytoplasm. These cells, to the best of our knowledge, are reported for the first time in Amphibia. Glandular cells exhibit oval, round, or polyhedric granules, most of them with one or more cores. Our results indicate that the contents of epithelial and glandular secretory cells are partially secreted during the Preovulatory Period. Additional secretion occurs during the transit of the oocytes. J. Morphol. 239:61–73, 1999. © 1999 Wiley-Liss, Inc.