Mercedes Ducayen

Alterations of mammalian oocyte meiosis I with divalent cations and calmodulin

Experiments using a Ca2+/Mg2+, serum free media were carried out aimed at clarifying proposed effects of these divalent cations on in vitro meiotic maturation of mouse and cow oocytes. Agents known to perturb intracellular Ca2+ or calmodulin were also studied. Total absence of both cations restricts both oocyte species from completing meiosis I. Media containing Mg2+ and no Ca2+ permitted some maturation in both species. Absence or small amounts of Mg2+ in the media containing control amounts of Ca2+ was much more inhibitory for the cow than the mouse oocyte. Studies of mouse oocyte maturation with Verapamil, Epinephrine and A23187 demonstrated an inhibition of maturation perhaps by the intracellular Ca2+ changes these agents are alleged to induce. A dependency of mouse oocyte maturation on active Ca-Calmodulin complexes was suggested by the calmodulin inhibitor studies.

Further Studies Of Inhibitors Of In Vitro Mammalian Oocyte Maturation

Studies of luteinizing hormone (LH)-mediated serum inhibition and of follicular fluid and granulosa cell inhibition of in vitro porcine, ewe, and cow oocyte meiotic maturation have been carried out. A porcine serum inhibitor or inhibitors with a molecular weight above 15,000, similar to the ewe and cow serum inhibitor(s), have been demonstrated. An LH-inactivated inhibitor or inhibitors in fluid from medium-sized ewe and cow follicles have been shown and a minimally effective porcine follicular fluid inhibitor has been confirmed. The estimated molecular weight of these inhibitors is below 1,000. Granulosa cells from the three species were not found to be dramatically inhibitory. It is postulated that the follicular fluid inhibitor(s) may be derived from the larger serum molecule(s) by an action of LH within an intermediate cell type.

SO2 and its metabolite: effects on mammalian egg chromosomes.

Abstract The ubiquity of sulfur dioxide as an air pollutant combined with reports of effects of the gas and its blood metabolite on DNA and chromosomes, prompted a study of possible mutagen action on mammalian oocytes. Utilizing in vitro and in vivo systems, mouse, ewe, and cow oocytes were examined for cytologic evidence of structural or numerical damage in meiosis. Fragmentation with rearrangement seen at M 1 and M 2 and anaphase lagging seen in vitro in each species are classically known to be etiologic in chromosome abnormalities and must be considered, especially in contaminated areas with foci of fetal loss involving ewe and cow.

Meiosis suppression by caffeine in female mice.

SummaryThe effects of caffeine on meiosis of mouse ova in vitro and in vivo have been studied. Concentrations of 200 μg/cc or more suppressed entry of ova into in vitro meiosis without production of any numerical or structural abnormalities at dose levels above or below that. Acute superovulation by the standard technique was prevented at a dose of 0.25 mg/g/body weight and examination of the intrafollicular ova revealed presistence of the germinal vesicle stage. Chronic administration of the same dose (0.25 mg/g/bw) throughout the period from weaning to puberty did not induce any cytologically detectable meiotic abnormalities in ova studied in vitro at the end of that period. It is suggested that the reduced fertility seen by some previous authors may have been due to the suppression of entry into meiosis of the ova with diminished numbers of ova being ovulated.

Colcemid effects on homologue pairing and crossing over during fetal mouse oogenesis.

Colcemid was administered to gestational day 13 female mice to test effects on homologue pairing, synapsis and recombination of fetal oogenesis. Pairing abnormalities were detected in pachytene oocytes by light and electron microscopy examination of bivalents and synaptonemal complexes. Reduction of total chiasmata per treated diplotene oocyte (22.74) compared to controls (31.07) was found.

Inhibition of Bovidae oocyte meiosis by serine protease inhibitors.

Summary Specific inhibitors of serine proteases have been shown for the first time to inhibit meiotic progression in mammalian oocytes, suggesting involvement of these enzymes in the process of maturation.

A cytogenetic analysis of oocytes from Macaca mulatta and nemestrina matured in vitro.

SummaryCytogenetic analysis of first and second metaphase configurations of oocytes from M. mulatta and M. nemestrina matured in vitro were carried out. 76 diakinesis/metaphase I cells from M. mulatta obtained after 19–30 hrs of culture revealed an average chiasmata frequency per bivalent of 1.58 and 119 second metaphase cells all contained 21 pairs save for one cell with 22.51 oocytes from M. nemestrina cultured for 24–31 hrs revealed diakinesis/first metaphase configurations with an average chiasmata frequency of 1.52. 54 second metaphase cells were normal. Two peaks of timing for second metaphase were observed in both species.ZusammenfassungEine cytogenetische Analyse der ersten und zweiten meiotischen Teilungen von Oocyten von M. mulatta und M. nemestrina wurde nach Reifung in vitro durchgeführt. 76 Diakinese/Metaphase I-Zellen von M. mulatta, die nach einer Kulturzeit von 19–30 Std gewonnen wurden, ergaben eine durchschnittliche Chiasmahäufigkeit von 1,58/Bivalent; von 119 Zellen der Metaphase II zeigten 21 Chromosomenpaare, während eine Zelle 22 Chromosomenpaare aufwies. 51 Oocyten von M. nemestrina zeigten nach einer Kulturzeit von 24 bis 31 Std Diakinese/Metaphase I-Konfigurationen mit einer durchschnittlichen Chiasmafrequenz von 1,52. 54 Metaphase II-Zellen waren normal. In beiden Species war die Zeitkurve der Metaphase II zweigipfelig.

Genetic characteristics of spermatogenesis in the turkish hamster (mesocricetus brandti) subjected to reduced temperature or light

Abstract 1. 1.|A genetic study of Turkish hamster (Mesocricetus brandti) spermatogenesis exposed to reduced temperature and/or light was made of pachytene pairing, crossing-over and disjunction during testicular regression and recrudescence. 2. 2.|Abnormalities were found in all three mechanisms in all experimental groups particularly in cold exposed testes during recrudescence.

Unique Effects of Spindle Inhibitors on Mammalian Oocyte Meiosis

Abstract The effects of Nocodazole, reported to be a rapidly reversible inhibitor of microtubules in somatic cells (1), and Colcemid, a classic microtubule inhibitor, were studied for their effects on mouse and cow oocyte in vitro meiotic resumption. When present throughout the maturation period to Metaphase II/Polar Body I, both compounds predictably inhibited progression at Metaphase I (MI). An unexpected effect was seen on mouse germinal vesicle breakdown (GVB) with both inhibitors, but not in cow oocytes tested with Nocodazole. Recovery from Nocodazole was notably retarded in mouse oocytes even with brief exposure times. Addition of 1 μg/ml of Nocodazole 10 min after commencement of mouse and cow oocyte incubation was sufficient time to allow normal GVB, while inhibition at MI still took place suggesting that the critical events of GVB occur very quickly in vitro.

X-chromosome heteromorphism and appearance of meiosis in the rat fetal ovary

Abstract Fetal rat oogenesis was examined attempting to test the hypothesis that two functional X chromosomes are required for the onset of meiosis. The presence of a Barr body in germ cells was considered to be evidence for one inactive X chromosome and the detection of leptotene oocytes as the criterion for the establishment of meiotic prophase. It was found that on Day 16 of gestation, 3.9% of the germ cells were leptotene oocytes, but the incidence of Barr body-positive oogonia persisted at 9.9%. On Day 17, the leptotene oocytes had increased to 26.6% and the Barr body-positive oogonia had decreased to 3.5%. It was concluded that X-chromosome reactivation, though occurring at some time during the onset of meiosis, was not the initiating event.