In vitro inhibition of oocyte and follicular maturation and spawning in starfish (Asterias forbesi) by 2-4-dinitrophenol

The in vitro effects of 2-4-dinitrophenol (DNP) on spawning and follicular and oocyte maturation in starfish ovaries and its various cellular components were investigated. Spawning and oocyte and follicular maturation induced by starfish gonadotropin radial nerve factor (RNF) in isolated ovarian fragments were all inhibited by appropriate doses of DNP. DNP inhibits processes which occur shortly after addition of the gonadotropin; in ovarian fragments insensitivity to DNP inhibition occurred shortly after addition of RNF but prior to initiation of spawning. Spontaneous follicular and oocyte maturation which occurred following release of ovarian follicles into sea water was prevented by DNP. In non-spontaneously maturing follicles released from the ovary, DNP inhibited both follicle and oocyte maturation induced by the secondary stimulator of spawning and maturation, 1-methyladenine (1-MA). DNP also inhibited 1-MA induced meiotic maturation in isolated immature oocytes incubated in the absence of follicle cells. Inhibition of oocyte maturation was not associated with inhibition of 3H-1-MA incorporation by isolated oocytes. Immature oocytes incubated in the presence of DNP underwent maturation following washing and subsequent exposure to 1-MA. Immature oocytes initially exposed to both 1-MA and DNP, however, showed decreased maturation responsiveness following washing and re-exposure to 1-MA. The results suggest that the inhibitory effects of DNP on spawning and oocyte maturation are the result of direct effects on the oocytes and possibly other cells and tissues within the ovary.

Meiotic maturation in Xenopus laevis oocytes initiated by insulin

Insulin can induce meiotic division in Xenopus laevis oocytes. This effect shows the specificity expected of a receptor-mediated mechanism. It is potentiated by ethynylestradiol, a steroid antagonist of pregesterone (the natural hormone that provokes meiosis). The Xenopus laevis oocytes may serve as a model for the study of the poorly understood effect of insulin on cell division.

[Effect of carbidine on the sex glands of rats chronically exposed to ethanol]

In experiments on rats it was shown that carbidine injected intramuscularly for two weeks does not effect gonadotropic action in a dose effective in experimental therapy of alcohol dependence (4 mg/kg). The drug neither potentiates adverse after-effects of chronic action of ethanol on ovo- and spermatogenesis nor slows down the course of the reparative processes in the gonads after ethanol is discontinued. However, further regressive changes in the gonadal generative elements were recorded in administering carbidine against the background of continued use of ethanol.

Action of porcine follicular fluid oocyte maturation inhibitor in vitro: possible role of the cumulus cells

To study the mode of action of porcine follicular fluid oocyte maturation inhibitor isolated cumulus-enclosed or mechanically denuded pig oocytes were used. Two types of culture media were employed, a complex containing 15% pig serum (TC199A) and a defined, minimal medium (BMOC). The maturation of cumulus-enclosed oocytes was comparable in the two types of culture media, but only in the complex medium did the cumulus cells remain functional in terms of morphology and progesterone secretion. The low molecular weight portion of follicular fluid partially inhibited oocyte meiosis and cumulus progesterone secretion in 199A. No inhibition of oocyte maturation was seen when follicular fluid was added to BMOC. Since denuded oocytes did not respond to follicular fluid in either culture medium, it is suggested that the cumulus cells may mediate the action of the follicular fluid oocyte maturation inhibitor.

Mammalian oocyte maturation: model systems and their physiological relevance

Maturation of mammalian oocytes is studied mainly in two dissimilar in vitro models: isolated oocytes maturing spontaneously in culture, and hormone-induced maturation of follicle-enclosed oocytes. In this discussion the following aspects of maturation in vitro in the two aforementioned models were compared: timing of germinal vesicle breakdown (GVB), involvement of cyclic nucleotides, protein synthesis and divalent cations. A third approach to the study of oocyte maturation in vitro, namely oocyte co-culture with follicular constituents was adopted in order to test the role of follicular components in the control of the resumption of meiosis. Such studies demonstrated an inhibitory action of granulosa cells, granulosa cell-conditioned medium and of follicular fluid upon the spontaneous maturation of the co-cultured oocytes. Furthermore, addition of LH to co-cultures of oocytes and granulosa cells induced resumption of meiosis. Although oocytes obtained by spontaneous or by hormone-induced maturation cannot be distinguished morphologically, the developmental potential of oocytes matured spontaneously has been questioned, at least in some species. Furthermore, analysis of the kinetics of spontaneous maturation suggests that oocytes dislodged from their follicles escape physiologic mechanisms ensuring meiotic arrest and skip some of the regulatory steps involved in the normal hormonal triggering of maturation. Oocyte co-culture with granulosa cells offers a close approximation to physiological conditions in that meiotic maturation depends on hormonal stimulation, while the system permits the application of separate treatments to the oocyte-cumulus complex and granulosa cells. As in any in vitro system, critical evaluation is required to discriminate between artifacts inherent in the model and physiological processes.

Correlations between chromosome segments and fitness in Drosophila melanogaster III. Differential genetic responses to zinc sulfate and selenocystine

Genetic X environmental interactions are examined at an intrachromosomal level in Drosophila melanogaster. With respect to two fitness components, egg production and egg-to-adult viability, evidence is provided that different segments of the X chromosome are affected differently by each of the chemical substances, zinc sulfate and selenocystine. The extent of a segment's effect on a trait is not always parallelled by the extent of its association with that trait's sensitivity to chemical treatment. Both attributes are functions of the genetical background. The degree of dominance of each segment is not always greater in the chemical environments, a finding inconsistent with Parson's concept of "extreme-environment heterosis".

Progesterone-induced meiosis in Xenopus laevis oocytes: a role for cAMP at the "maturation-promoting factor" level

Cholera toxin inhibition of progesterone-induced meiosis of Xenopus laevis oocytes in vitro has been correlated with increased cAMP levels. Inhibition of germinal vesicle breakdown (Gvbd) and cAMP increase occurred after a lag period of 2 hr, when cholera toxin was injected, or 4--5 hr, when applied externally. The ability of the maturation-promoting factor (Mpf) to provoke Gvbd when injected into recipient oocytes was found to be dependent upon whether the oocytes had been exposed to cholera toxin alone or to toxin and progesterone. With the former, cAMP levels were elevated and Mpf activity was abolished, whereas with the latter, the increase in cAMP was less pronounced and Mpf activity was observed. Injection of cAMP or its 8-thio derivatives shortly before the appearance of progesterone-induced Mpf abolished Gvbd. If injected earlier or later, no inhibition was observed. In contrast, cholera toxin inhibited maturation even when added several hours before progesterone, suggesting a sustained accumulation of cAMP. No Gvbd occurred when 8-thio-methyl-cAMP was injected together with Mpf. These data suggest that cAMP is involved in the control of the formation/amplification and/or activity of Mpf-a result which may be of general significance in cell division mechanisms.

Studies on oocyte maturation of the medaka, Oryzias latipes. VI. Relationship between the circadian cycle of oocyte maturation and activity of the pituitary gland

The relationship between pituitary activity and oocyte maturation was examined in Oryzias latipes (medaka), which has a circadian cycle of oviposition. Throughout the circadian cycle of oviposition, females possessed a population of large oocytes more than 800 micronmeter in diameter that could mature in the presence of gonadotropin. Oocyte maturation was observed in vitro in females hypophysectomized between three and ten hours after the beginning of the light period with the number of maturing oocytes increasing as hypophysectomy was delayed. Although in vivo oocyte maturation was blocked by hypophysectomy within two hours after the beginning of the light period, it was restored by a single injection of synthetic or mammalian pituitary hormones (gonadotropic, corticotropic and thyrotropic hormones) within ten hours after hypophysectomy. Of these pituitary hormones, FSH, LH and TSH could induce in vitro maturation of isolated oocytes. Oocytes matured in vitro in the absence of exogeneous hormones if they were isolated nine or more hours after the onset of light. The present study indicates that the circadian cycle of maturation of Oryzias oocytes is controlled by the release of pituitary hormone between three and nine hours after the beginning of the light period.

Steroid-induced meiotic division in Xenopus laevis oocytes: surface and calcium

Progesterone reinitiates meiotic maturation in Xenopus oocytes. Evidence is reported which indicates that the steroid acts at the level of the cell surface and suggests that an induced change of Ca2+ distribution triggers in turn a cascade of cytoplasmic events including protein synthesis and germinal vesicle (nucleus) breakdown. These novel features of steroid hormone action in amphibian oocytes are discussed in relation to presently accepted views of the mechanism of action of steroid hormones in somatic cells.

Rat oocyte maturation in vitro: relief of cyclic AMP inhibition by gonadotropins

The hormone-independent, spontaneous maturation that rat oocytes undergo in vitro can be inhibited by derivatives of cyclic AMP and inhibitors of cyclic nucleotide phosphodiesterase. In this study, we have shown that this inhibition of maturation can be partially relieved by preparations of ovine and rat luteinizing hormone or follicle-stimulating hormone. The ability of gonadotropins to foster the resumption of maturation in cultures of cyclic AMP-inhibited oocytes suggests that this system is suitable for studies of the hormonal control of oocyte development. The dose and time dependency of the response to gonadotropins has been examined in order to study the role of these hormones in oocyte maturation and to compare this effect to other known responses of the cumulus-oocyte complex. These studies show that highly purified preparations of rat gonadotropins are less effective inducers of maturation than the more commonly used, but considerably less purified, preparations of ovine gonadotropins. Almost complete relief of inhibition is observed, however, when the oocytes are exposed to a combination of rat luteinizing hormone and follicle-stimulating hormone. Oocyte maturation was not influenced by the sex steroids progesterone or 17beta-estradiol. Our results suggest that: (i) cyclic AMP is involved in the intrafollicular inhibition of oocyte maturation; (ii) both gonadotropins are required for maximal stimulation of the resumption of oocyte meiosis; and (iii) steroids are not involved in this response to gonadotropins.

Effects of isoniazid (INH) on the oogenesis of mice

Mutagenic damages in female germ cells of mice have been tested with the dominant lethal assay and the cytogenetic analysis of unfertilized M II-oocytes. Concluding one can say that from the experimental data presented here do not show any mutagenic effect of INH on oogenesis of different strains of mice can be stated.

Induction of maturation in Xenopus laevis oocytes by a steroid linked to a polymer

A progesterone analog has been covalently linked via an amide bond to polyethylene oxide (molecular weight, 20,000). This macromolecular steroid molecule displays the biological activity of progesterone in inducing meiotic maturation when incubated with Xenopus laevis oocytes (stage VI) in vitro. Its efficiency (half-maximum effective concentration, 30 muM) is approximately 10 times lower than that of its low molecular weight homolog (3 muM). Control experiments with polyethylene oxide and an estradiol derivative (up to 1 mM) assessed the specificity of the progesterone macromolecular analog. Uptake experiments using radioactive derivatives revealed a small (if not negligible) intake of the macromolecular progesterone analog by the oocytes compared to that of free steroids, and no parallelism was found between radioactivity incorporation and effect. The possibility of cleavage of the macromolecular derivative during the incubation was ruled out. Furthermore, injection of the polymer-linked progesterone into the oocytes did not induce maturation. These observations suggest that the macromolecular progesterone analog itself is responsible for the biological effect and that the presence of this compound inside the cell is neither necessary nor sufficient for triggering reinitiation of meiosis. These conclusions are in agreement with the proposal that interaction with the plasma membrane of the oocyte is necessary for progesterone action in this particular system, in contrast to the case of somatic cells which have intracellular steroid receptors.

Amphibian oocyte maturation and protein synthesis: related inhibition by cyclic AMP, theophylline, and papaverine

Two inhibitors of cyclic AMP phosphodiesterase (3':5'-cyclic-AMP 5'-nucleotidohydrolase, EC 3.1.4.17), theophylline and papaverine, inhibit the maturation of Xenopus laevis oocytes induced by four different stimuli: human chorionic gonadotropin, progesterone, testosterone, and lanthanum ions. Addition of 1 mM cyclic AMP to the medium delays maturation by approximately 2 hr. Papaverine, theophylline, and cyclic AMP inhibit amino acid incorporation into oocyte proteins by 50% or more but do not inhibit amino acid uptake. The capacity of theophylline to block maturation and protein synthesis is reversed in a parallel fashion by addition of 1-5 mM calcium ion to the medium. Addition of papaverine, theophylline, and cycloheximide to oocytes at different times after hormonal treatment shows that the step sensitive to blockage by the three drugs is coincident and precedes germinal vesicle breakdown by about 1.5 hr. Theophylline and papaverine do not increase endogenous cyclic AMP levels in oocytes but do block the decrease of cyclic AMP levels observed 3 hr after progesterone treatment. Both drugs inhibit oocyte cyclic AMP phosphodiesterase measured in vivo and severely inhibit the stimulus of calcium uptake caused by progesterone and human chorionic gonadotropin. These results suggest that cyclic AMP, theophylline, and papaverine may block oocyte maturation by inhibiting protein synthesis, possibly via a cyclic AMP-dependent protein kinase as shown in reticulocytes [Datta, A., De Haro, C., Sierra, J. & Ochoa, S. (1977) Proc. Natl. Acad. Sci., USA 74, 1463-1467].

Free calcium in full grown Xenopus laevis oocyte following treatment with ionophore A 23187 or progesterone

Free intracellular Ca2+ was monitored in isolated Xenopus laevis oocyte during induced maturation using the Ca2+ -sensitive luminescent protein, aequorin. Internal free Ca2+ was not precisely measured but data suggest it was quite low (in the micromolar range). No change in internal free Ca2+ was detected during maturation induced either by progesterone or by p-chloromercuribenzoate. By contrast, the ionophore A 23187 gave an increase in the free Ca2+ level when there was a raised external Ca2+ (10 mM), conditions which also induce oocyte maturation. About 3 h after progesterone or p-chloromercuribenzoate stimulation, the oocyte membrane potential decreased by about 50 mV while the membrane resistance increased transitorily.

Polymorphism and reproductive mode in the rotifer, Asplanchna sieboldi: relationship between meiotic oogenesis and shape of body-wall outgrowths

Sexuality and polymorphism are closely coupled in the rotifer Asplanchna sieboldi. In a graded response to dietary tocopherol, embryos develop body-wall outgrowths of various sizes and shapes. Also in a graded response to this compound, some of the affected females produce eggs undergoing meiotic instead of mitotic oogenesis. The haploid eggs of such mictic females develop parthenogenetically into males instead of females. The incidence of mictic females among animals with different shapes was studied among cohorts from mothers subjected to different inducing conditions. The hypothesis that external tocopherol concentrations absolutely fix the probability of meiotic oogenesis was rejected. The other extreme hypothesis, that the probability of meiotic oogenesis is fixed by morphotype, was rejected for animals at the low end of the morphotypic scale but accepted for the more strongly-affected individuals. The probability of meiotic oogenesis is thus constant for the higher morphotypes. The ascertainment of morphotype frequencies in natural or laboratory populations may suffice for estimating the incidence of sexual forms; furthermore studies of factors affecting the body-wall-outgrowth response may also bear directly upon regulation of sexual reproduction in this species.

Stimulation of poly(adenosine diphosphate ribose) synthase activity of Xenopus germinal vesicle by progesterone

A practical procedure for the isolation of massive numbers of GV from oocytes of Xenopus laevis at various stages of oogenesis was developed. The method is simple, rapid, and easy to perform. The isolated GV possess high activity of poly(ADP-ribose) synthase. Incubation of class-A oocytes (stages V and VI) with progesterone resulted in a stimulation of the poly(ADP-ribose) synthase activity in the GV. The stimulation of enzymatic activity occurred prior to GVBD. This stimulatory effect of progesterone on enzymatic activity was blocked by cycloheximide and actinomycin D, suggesting that induction is dependent on protein and RNA synthesis. Progesterone, however, was unable to cause disintegration of GV or to stimulate poly(ADP-ribose) synthase activity of class-B oocytes (stages III and IV). This finding suggests that the oocytes must progress to a certain stage of differentiation before progesterone can induce GVBD or stimulate poly(ADP-ribose) synthase activity.

Discussion paper: induction by progesterone and a "maturation-promoting factor" of soluble proteins in Xenopus laevis oocytes in vitro

In vitro incubation of isolated X. laevis oocytes with progesterone induces the specific labeling of proteins during maturation. They are detected as several discrete peaks with a double-labeling technique that involves the injection of [3H] leucine into hormone-treated and [14C] leucine into control cells. The peaks are separated by sodium dodecyl sulfate polyacrylamide gel electrophoresis. Identical proteins are obtained with two other steroids that provoke maturation and with p-chloromercuribenzoate. The same progesterone-induced proteins are observed even if oocytes have been treated with actinomycin D or ethidium bromide or have been enucleated. Cycloheximide suppresses the labeling of proteins that are induced by progesterone, if administered either at the time of radioactive amino acid exposure or after prelabeling the oocytes to determine whether the hormone-induced peaks are due to compartmental changes of the proteins. A cytoplasmic fraction, obtained from maturing oocytes before GVBD, promotes maturation when injected into resting oocytes and therefore contains an MPF. After this injection, GVBD occurs earlier than during incubation with progesterone and is accompanied by the formation of the same proteins and of MPF, both suppressed by cycloheximide. The possibility that MPF is an induced protein is then discussed. It has been also found that there is a decrease in membrane permeability, as evidenced by decreased leucine uptake into proteins of oocytes incubated in radioactive amino acids and exposed to progesterone. The same decrease occurs after injection of MPF-containing cytoplasm into oocytes.

Induction of oocytic maturation and differentiation: mode of progesterone action

Full-grown amphibian oocytes, arrested in prophase I or meiosis, respond in vitro to progesterone and certain other steroids. They undergo an apparently normal sequence of nuclear maturation and cytoplasmic differentiation, which are necessary precedents for fertilization and embryogenesis. Individual oocytes or populations of these cells thus provide a model system for investigations concerning the nature and mechanism of hormone-cellular interactions. In this system, previous studies have shown that certain aspects of hormonal (progesterone, DOCA) induction of morphologic and biochemical differentiation in the nucleus can be induced in part, as a result of the formation of secondary cytoplasmic factors, some of which do not require the presence of the nucleus for their formation. In addition to initiating nuclear events, progesterone or DOCA alters the functional activity of the plasma membrane and establishes the conditions necessary for fertilization and activation. Uptake of radioactive vitellogenin, a yolk protein precursor, was inhibited by progesterone and DOCA. Maximum inhibition was dependent on induction of nuclear breakdown, the dose of steroid used, and was correlated with morphologic alterations at the oocytic surface. Estrone neither stimulated nor inhibited vitellogenin incorporation and had no effect on nuclear breakdown. Oocytic capacity to exhibit activation responses (vitelline membrane elevation) was dependent on oocytic exposure to progesterone or DOCA and development subsequent to the initiation of nuclear breakdown. Onset of the activation response after steroid treatment varied with the type of activation stimulus utilized (pricking or divalent ionophore A-23187). The results suggest that hormones cause ionic alterations in oocytes and that ions are directly involved in the activation response. To study steroid interaction with the cell surface, a method was developed for culturing oocytes that permits localized application of steroids to portions of the oocytic or follicular surface. The results obtained suggest that oocytes exposed to steroid over part of their surface do not respond, with regard to nuclear breakdown, in the same manner as do oocytes exposed over their entire surface to similar concentrations of steroid. Studies of isotopic distribution within the oocyte after local application of steroid indicate that hormone does not readily diffuse through the oocyte. Evidence for the role of cytoplasmic factors in the mediation of nuclear and cytoplasmic events is discussed.

Altered yolk structure and reduced hatchability of eggs from birds fed single doses of petroleum oils

Yolk deposited by Japanese quail was abnormal for 24 hours after the oral administration of a single capsule containing 200 milligrams of bunker C oil. Both the structure and the staining properties of the yolk were affected. Fewer eggs were laid during the 4 days after dosing, compared to controls, and hatchability was drastically reduced. Hatchability returned to normal in 4 days. Three other reference oils also affected yolk structure. Canada geese given 2 grams and chickens given 500 milligrams of bunker C oil produced eggs with abnormal yolk rings.

Meiotic maturation of mouse oocytes in vitro: inhibition of maturation at specific stages of nuclear progression

In vitro studies of meiotic maturation of mouse oocytes have been carried out in the presence of several drugs. The individual steps of nuclear progression, including dissolution of the nuclear (germinal vesicle) membrane, condensation of dictyate chromatin into compact bivalents, formation of the first metaphase spindle, and extrusion of the first polar body, are each susceptible to one or more of these drugs. Germinal vesicle breakdown, the initial morphological feature characteristic of meiotic maturation, is inhibited by dibutyryl cyclic AMP. However, even in the presence of dibutyryl cyclic AMP, the nuclear membrane becomes extremely convoluted and condensation of chromatin is initiated but aborts at a stage short of compact bivalents. Germinal vesicle breakdown and chromatin condensation take place in an apparently normal manner in the presence of puromycin, Colcemid, or cytochalasin B. Nuclear progression is blocked at the circular bivalent stage when oocytes are cultured continuously in the presence of puromycin or Colcemid, whereas oocytes cultured in the presence of cytochalasin B proceed to the first meiotic metaphase, form an apparently normal spindle, and arrest. Emission of a polar body is inhibited by all of these drugs. The inhibitory effects of these drugs on meiotic maturation are reversible to varying degrees dependent upon the duration of exposure to the drug and upon the nature of the drug. These studies suggest that dissolution of the mouse oocyte's germinal vesicle and condensation of chromatin are not dependent upon concomitant protein synthesis or upon microtubules. On the other hand, the complete condensation of chromatin into compact bivalents apparently requires breakdown of the germinal vesicle. Failure of homologous chromosomes to separate after normal alignment on the meiotic spindle in the presence of cytochalasin B suggest that microfilaments may be involved in nuclear progression at this stage of maturation. Cytokinesis, in the form of polar body formation, is blocked when any one of the earlier events of maturation fails to take place.

[Oocyte maturation in Xenopus laevis. The entry of progesterone is necessary for maturation]

In vitro progesterone-induced maturation of Xenope ovocyte was studied as a function of progesterone uptake and extracellular progesterone concentration. Maturation depends on the initial total amount of progesterone in incubation medium and does not depend on the extracellular hormonal concentration. This result strongly argues for an intracellular receptor site for progesterone.