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J C Osborn

Publications and source records attributed to J C Osborn.

At least 37 records · Page 2Linked to original sources
PubMed1985

cAMP in ovine oocytes: localization of synthesis and its action on protein synthesis, phosphorylation, and meiosis.

In the first series of experiments, the source of cAMP in the sheep oocyte was studied. Cholera toxin was shown to be a potent stimulator of cAMP in isolated sheep oocytes, demonstrating the presence of adenyl cyclase. There was no evidence for transmission of cAMP from stimulated myocardial cell monolayers to cumulus-enclosed oocytes even though the existence of a concentration gradient of cAMP and of intercellular communication were demonstrated. However, gonadotrophin-stimulated follicle shells were able to induce a rise in the cAMP content of denuded or cumulus-enclosed oocytes in the same dish, independently of cell contact. Further experiments were designed to study the effects of a cholera toxin-stimulated rise in cAMP on the maturation of oocytes. When applied to cumulus-oocyte complexes, cholera toxin did not block germinal vesicle breakdown (GVBD), nor the accompanying changes in protein synthesis and phosphorylation, although there was evidence for a delaying effect. There were, however, indications that the toxin was inducing abnormalities that became gross when the concentration was raised to 1 microgram/ml. This high concentration of cholera toxin was able to block the maturation of oocytes in intact, gonadotrophin-treated follicles, although once again abnormalities were evident. We conclude that the role of cAMP in the maturation of the sheep oocyte is different from that proposed in the mouse.

Animals↗
PubMed1985

Dental cariogenic evaluation of foods using human plaque pH and an experimental rat-caries model.

Five well-characterized foods were used to compare two systems for estimating the cariogenic potential of food: human plaque-acidity using interdental metallic touch electrodes, and cariogenicity testing in rats. Both systems identified the same food as the least cariogenic or acidogenic food and identified the same three foods as being both cariogenic in rats and acidogenic in man, although the ranking of these foods differed. The systems differed in their assessment of potato chips, a food high in cooked starch and low in free sugars. The results confirmed that non-acidogenic foods are non-cariogenic, but that foods acidogenic in man may exhibit a greater range of cariogenicity in rats. Data from both human plaque pH studies and rat caries models may permit better assessment of cariogenic potential of foods containing fermentable carbohydrates.

Adult↗
PubMed1985

Gonadotrophin-induced abnormalities in sheep oocytes after superovulation.

The development of preovulatory follicles involves an initial phase of somatic cell differentiation and a final phase, initiated by the LH surge, when both the somatic and germinal compartments alter. Abnormalities in this pattern of compartmental development after superovulation have been identified by examining follicles from control, PMSG- and FSH-treated sheep. The pattern of proteins synthesized by oocytes from untreated sheep did not differ after culture of follicles in hormone-free medium from that of germinal vesicle oocytes in vivo. Similarly, 93.5% of oocytes from sheep injected with a pituitary gonadotrophin (FSH-P) synthesized the unchanged germinal vesicle pattern of proteins during culture in an hormonally neutral culture environment. By contrast, the administration of the placental gonadotrophin, PMSG, induced in 28% of oocytes changes in the pattern of synthesis which are normally associated with maturation. An examination of follicular steroidogenesis showed that both total output and particularly oestrogen secretion was over twice as high in follicles from PMSG-treated as compared with FSH-treated animals (P less than 0.01). We conclude that the compartmental pattern of development and steroidogenesis is grossly perturbed in many follicles from PMSG-treated animals. Premature activation of the germinal compartment results in aged or abnormal oocytes and a hostile reproductive tract.

Animals↗
PubMed1984

Changes in protein phosphorylation during the maturation of mammalian oocytes in vitro.

Cumulus-enclosed sheep oocytes were cultured in gonadotrophin-containing medium for up to 9 hr and were then incubated for 3 hr in the presence of [32P]phosphate. The incorporation of 32P into TCA-insoluble material was measured, and oocyte proteins were separated by one- and two-dimensional gel electrophoresis. Incorporation of [32P]phosphate into protein increased after 3 hr culture and again after 9 hr, the time of germinal vesicle breakdown (GVBD). Qualitative and quantitative changes in the phosphorylation of proteins occurred over the 12-hr period studied. One of the most prominent changes was the appearance of a band of Mr 33,000, which was absent at 0-3 hr but appeared with increasing intensity with longer periods of culture. Two-dimensional electrophoresis revealed that the bulk of material in this band was a neutral polypeptide. No significant incorporation of [32P]phosphate was found in ribosomal extracts of oocytes.

Animals↗
PubMed1983

Somatic control of protein synthesis in mammalian oocytes during maturation.

The extent to which signals from the follicular compartment regulate protein synthesis in sheep oocytes is considered. Evidence is derived from experiments on the control of actin synthesis and also from a quantitative analysis of protein synthesis in oocytes matured in follicles in which specific somatic signals have been altered. Actin represents about 10% of the total protein synthesized by oocytes enclosed by follicle cells but under 2% in denuded oocytes. Although follicle cells synthesize and release actin, no evidence of its uptake into oocytes has been obtained. Instead, the results suggest that regulatory signals of somatic origin are transmitted directly into the oocyte by intercellular transport. A variety of cell types in addition to those of follicular origin support actin synthesis in oocytes, provided only that functional communication between the somatic and germinal compartment is maintained. Finally, the results on precursor uptake, actin turnover and RNA inhibition, and those of Dawn Giebelhaus on actin mRNA measurements, indicate that the somatic signals act on post-transcriptional events, possibly by influencing the mobilization of stored actin message. The selective inhibition of 17 alpha-hydroxylase in follicles depresses oestrogen and androgen and enhances progesterone biosynthesis. These steroid alterations, if induced during the first 8 h of maturation, lead to developmental abnormalities at fertilization. In addition, these steroidogenic changes alter the synthesis of a small number of acidic proteins in the maturing oocyte. It is postulated that steroid signals regulate the synthesis of certain proteins associated specifically with maturation.

Actins↗
PubMed1983

Thecal vasculature and oocyte maturation during follicular atresia in the sheep and pig.

During follicular atresia in the sheep and pig there is a marked reduction in the vasculature of the theca interna underlying the membrana granulosa. In the sheep there is no reduction of thecal blood vessels adjacent to the cumulus which remains viable. By contrast, in the pig the cumulus degenerates during atresia and the underlying thecal vasculature is greatly diminished. However, despite loss of contact between the follicle cells and the oocyte, the germinal vesicle remains intact.

Animals↗
PubMed1983

Time-dependent effects of alpha-amanitin on nuclear maturation and protein synthesis in mammalian oocytes.

The addition of alpha-amanitin to extrafollicular, cumulus-enclosed ovine oocytes at explantation inhibits meiotic maturation and prevents many of the changes in protein synthesis that normally accompany maturation. By contrast, these inhibitory effects are considerably reduced by either delaying the addition of the drug for 1-4 h or by denuding the oocytes of all associated cumulus cells at the onset of culture. The observations that the inhibitory effect of cordycepin on nuclear maturation is also time-dependent and cumulus-cell-dependent and that the oocyte is susceptible to cordycepin for longer than its sensitivity to alpha-amanitin are consistent with the differential effects of these drugs on RNA synthesis. It is concluded that a transcriptional event at the onset of maturation is essential for the initiation of those changes in protein synthesis required for the regulation of nuclear and cytoplasmic maturation. It is uncertain, however, whether this transcriptional event occurs within the cumulus cells or within the oocyte.

Amanitins↗
PubMed1983

Mevalonate reverses the developmental arrest of preimplantation mouse embryos by Compactin, an inhibitor of HMG Co A reductase.

Hydroxymethyl glutaryl Co A reductase (HMG Co A reductase) is the key regulatory enzyme in the conversion of acetate to mevalonate. Mevalonate is the precursor for sterol and non-sterol isoprenes involved in membrane biogenesis, DNA replication and protein glycosylation. The influence of two inhibitors of HMG Co A reductase, Compactin (or ML236B) and an oxygenated sterol, Diosgenin, were tested on preimplantation development of mouse embryos. Compactin arrested development at about the 32-cell stage, leaving the blastomeres decompacted. Ultrastructural examination of the embryos revealed reduced membrane apposition but no major effects on cell organelles. There was however a predominance of nuclei with highly condensed chromatin. Glycosylation of proteins also appeared to be inhibited as shown by reduced incorporation of sugar precursors but not that of amino acids. The influence of Compactin was judged to be highly specific since only 10 micrograms/ml (0.08 mM) mevalonic acid abolished the effects of Compactin. Mevalonate in embryos may not be primarily utilized in the synthesis of sterols since a specific inhibitor of cholesterol synthesis, DL-4,4,10-beta-trimethyl-trans-decal-3-beta-ol had no detectable effect on development. The non-sterol isoprenes of mevalonate such as dolichol and isopentenyl adenine may play a more significant role during early development since the influence of Compactin resembled that previously described using tunicamycin, a specific inhibitor of dolichol mediated synthesis of N-glycosidically linked glycoproteins. Hence, lack of dolichol may partly be the cause of arrest of embryonic development by Compactin. Diosgenin caused embryonic arrest at about the 16-cell stage and the influence was not reversible by mevalonic acid. Cholesterol was able to rescue 50% of the embryos but the effect of Diosgenin could be non-specific and probably caused by its entry into the plasma membrane.

Animals↗
PubMed1983

The role of steroid signals in the maturation of mammalian oocytes.

The resumption of meiosis in mammalian oocytes is associated with sequential changes in follicular steroidogenesis, the principal features of which are an initial stimulation and then suppression of the secretion of oestrogens and androgens, followed by a steady increase in the secretion of progesterone. The addition of steroid enzyme inhibitors to isolated follicles in vitro alters the normal profile of steroids secreted during maturation and induces intracellular changes in the oocytes which are expressed as nuclear abnormalities at fertilization. Different abnormalities are induced by selectively modifying steroid biosynthesis during maturation, the maturing oocyte being more sensitive to an imbalance in the steroid profile rather than the total inhibition of steroid secretion. The cause of the developmental aberrations may either result from or be associated with the abnormal patterns of proteins synthesized by oocytes denied the support of the correct balance or sequence of steroids during maturation.

Androgens↗
PubMed1982

Cell interactions and actin synthesis in mammalian oocytes.

In this study, we have examined the profiles of proteins synthesized by mammalian oocytes in the presence and absence of cumulus cells. The results show that the patterns of protein synthesis are broadly similar in cumulus-enclosed and denuded oocytes, but that as a consequence of removing the cumulus cells, the presence of a 45,000-dalton band is greatly reduced. This band, identified by comigration studies on two-dimensional polyacrylamide gels as actin, is strongly synthesized in both isolated cumulus cells and in oocytes labeled in the presence of cumulus cells, but is only weakly synthesized by oocytes incubated in the absence of cumulus cells. We suggest that the presence of newly synthesized actin in the oocyte is dependent upon cellular cooperation between the cumulus cells and oocytes.

Actins↗
PubMed1982

Drug-nitrite interactions in human saliva: effects of food constituents on carcinogenic N-nitrosamine formation.

A simple and rapid high-pressure liquid chromatographic assay for monitoring N-nitrosodimethylamine (NDMA) in human saliva was developed. The method was used to study in vitro the effects of common food constituents on NDMA formation in saliva from the interaction of salivary nitrite with aminopyrine and oxytetracycline. Natural phenolic compounds, caffeic acid, and tannic acid, and synthetic additives, erythorbic acid, sorbic acid, propyl gallate, and butylated hydroxytoluene--all inhibited NDMA formation (20-80%). With ascorbic acid, up to 90% inhibition of NDMA synthesis in saliva was observed. In contrast, chlorogenic acid (a phenolic component of coffee) acted as a catalyst (up to 48% increase) of the nitrosamine formation under identical experimental conditions.

Adult↗
PubMed1981

Follicle cell regulation of protein synthesis and developmental competence in sheep oocytes.

The developmental capacity of sheep oocytes cultured outside the follicle was greatly increased by the presence of high concentrations of gonadotrophins (10 micrograms/ml) in the medium. However, even under these conditions, the developmental capacity of the oocytes was only half that of oocytes cultured within the intact follicle. The presence of the cumulus was essential for development; nearly all denuded oocytes failed to undergo cleavage. Maturational changes in the oocyte involving increased amino acid uptake increased incorporation and specific changes in protein synthesis were inhibited by the follicle cells; this suppression was alleviated by gonadotrophic hormones. The cumulus cells suppressed amino acid incorporation and, to some extent, the changes in protein synthesis. However, the suppression of amino acid uptake required the presence of the whole follicle. Patterns of protein synthesis by oocytes cultured outside the follicle differed from those in oocytes cultured within the follicle, irrespective of the presence of the cumulus or gonadotrophins. Analysis of single oocytes cultured outside the follicle showed that the protein profiles varied markedly even under identical culture conditions.

Amino Acids↗
PubMed1981

Selective effect of gonadotrophins on cell coupling, nuclear maturation and protein synthesis in mammalian oocytes.

Individual gonadotrophic hormones were used to examine the degree to which changes in intercellular coupling between somatic and germ cells initiate meiotic maturation, regulate protein synthesis or alter the ultrastructure of the ovine oocyte. Follicle Stimulating Hormone (FSH; 50 ng ml-1) suppressed intercellular coupling to the same extent as that observed during oocyte maturation in vivo. At low concentrations FSH did not, however, initiate resumption of meiosis. By contrast, luteinising hormone (LH; 100-500 ng ml-1) invariably initiated meiosis in oocytes cultured within the follicle but did not disrupt intercellular coupling. We conclude that nuclear maturation is not dependent upon the disruption of cell contact between the oocyte and the surrounding follicle cells. The profile of proteins synthesized by untreated oocytes differed greatly from that of oocytes matured for 18 h in follicles treated with a combination of FSH and LH. Pretreatment of follicles with either FSH or LH at low concentrations resulted in the synthesis of an intermediate and more variable pattern of proteins. No correlation was found between changes in protein synthesis and the extent of junctional communication between the cumulus cells and oocyte. Membrane vesiculation and lysosomal change in the transzonal processes are early structural changes associated with the suppression of intercellular coupling in oocytes. These changes in coupling probably result in the relocation of intracellular organelles in the final stages of oocyte maturation.

Animals↗
PubMed1979

Role of calcium ions in the control of embryogenesis of Xenopus. Changes in the subcellular distribution of calcium in early cleavage embryos after treatment with the ionophore A23187.

Treatment of stage 5 Xenopus embryos with the ionophore A23187 for only 10 min, in the absence of extracellular Mg2+ and Ca2+, causes cortical contractions and a high incidence of abnormal embryos during subsequent development. Cation analysis shows that divalent ions are not lost from the embryos, but that Ca2+ is redistributed within the subcellular fractions. Ca2+ is probably released from yolk platelets and/or pigment granules by the action of A23187, [Ca2+] rises in the cytosol, and the mitochondria attempt to take up this free Ca2+. The mitochondria concomitantly undergo characteristic ultrastructural transformations, changing towards energized-twisted and energized-zigzag conformations. A23187 allows these changes to be demonstrated in situ. Extracellular divalent cations (10(-4) M) interfere with this intracellular action of A23187. Intracellular accumulation of Na+ (by treatment with ouabain) or Li+ also causes abnormal development, probably by promoting a release of Ca2+ from the mitochondria. It is suggested (a) that all these treatments cause a rise in [Ca2+]i which interferes with normal, integrated cell division, so causing, in turn, abnormal embryogenesis, (b) that levels of [Ca2+]i are of importance in regulating cleavage, (c) that the mitochondria could well have a function in regulating [Ca2+]i during embryogenesis in Xenopus, and (d) that vegetalizing agents may well act by promoting a rise in [Ca2+]i in specific cells in the amphibian embryo.

Animals↗
PubMed1976

Scanning electron microscopy of lithium-induced exogastrulae of Xenopus laevis.

Lithium-induced exogastrulae are abnormal embryos which fail to complete gastrulation and do not form normal neural structures. Scanning electron microscopy has been used to compare the surface structure of the ectoderm cells of exogastrulae with that of the ectoderm cells of normal embryos and has shown that the appearance of ciliated cells is delayed in exogastrulae. In addition, the structure of endoderm cells, which remain exposed in these embryos, has been studied.

Abnormalities, Drug-Induced↗