Role of follicular cells in the inertia period of oocyte maturation in the common frog

Out of the breeding season the in vitro maturation of Rana temporaria oocytes in the state of maturation inertia or close to it depends on the follicular cells. In 28 females the presence of follicular cells stimulated oocyte maturation, in 12 females inhibited it. Dibutyrylcyclic AMP (5 X 10(-5) M) increased the percentage of maturation of follicle--enclosed oocytes close to the state of maturation inertia; estrone (4 X 10(-5)-10(-7) M and more) decreased the percentage of maturation of oocytes in the state of inertia, both with and without follicular envelopes.     

Difference in activation capacity between oocytes of Pleurodeles waltl matured in vivo and in vitro.

Oocytes of Pleurodeles waltl were activated after in vivo maturation by needle pricking or electric shock. After in vitro maturation, the oocytes were not activated by these stimuli. Coelomic oocytes and the oocytes which began their maturation in vivo could be activated by electric shock. During in vivo oocyte maturation, the activity of glucose-6-phosphate dehydrogenase (G6PDH), the key enzyme of the pentose phosphate cycle, increased while that of phosphofructokinase, the key enzyme of glycolysis, remained unchanged. During progesterone-induced in vitro oocyte maturation, the activity of both enzymes remained unchanged. Oocytes of Misgurnus fossilis matured in vivo and in vitro were activated spontaneously. No changes in the activity of G6PDH were observed during their maturation. These results suggest a relationship between G6PDH activity in the oocyte and oocyte capacity for activation by needle pricking or electric shock.     

The effect of the composition of the medium on the concentration of free calcium ions in the cells of the follicular wall in the common frog and in the clawed toad]

The concentration of intracellular free calcium ions in the follicle wall cells and in the follicle cells of Rana temporaria in Ringer solution is 150 +/- 10 and in the follicle wall cells of Xenopus laevis, 220 +/- 10 nM. In a chloride-free saline, its concentration in the same cells is 2.5-3 times that in Ringer solution. Voltage-dependent Ca(2+)-channel blockers diltiazem and verapamil (100 microM) reduce the level of intracellular free calcium ions in R. temporaria follicle wall cells cultivated in a chloride-free saline to 170 +/- 20 nM, which practically does not differ from the level in Ringer solution. Inhibitors (100 microM) decrease the rate of "spontaneous" maturation of R. temporaria follicle-enclosed oocytes both in chloride-free and Ringer solutions. It was concluded that an increased level of intracellular free calcium ions in the follicle cells, among other factors, may determine the stimulating effect of the medium (Ringer or chloride-free solution) on "spontaneous" maturation of follicle-enclosed amphibian oocytes. Voltage-dependent calcium channels appear to be involved in Ca2+ influx into the cells.     

The role of germinal vesicle in maturation of Pleurodeles waltlii oocytes induced by steroids

The maturation of oocytes from unstimulated Pleurodeles waltlii females can be induced in vitro. All full-grown oocytes covered by follicular envelopes mature under the influence of progesterone, testosterone, and a synthetic steroid (CDMT). Enucleation of oocytes prior to maturation induction resulted in a significantly lower percentage of maturation. Irradiation, or the treatment of oocytes with actinomycin D, did not affect their maturation. Therefore the lower percentage of maturation after enucleation must be due to the lack of karyoplasm. Karyoplasm appears to be necessary for the production of the maturation-promoting factor in P. waltlii oocytes.     

The fusion of oocytes of the starfish Aphelasterias japonica. III. Reconstruction of oocytes from cells and cell fragments (cytoplasts)

The oocytes of the starfish Aphelasterias japonica were divided into anuclear (cytoplasts) and nuclear (germinal vesicles) fragments by centrifugation in a Ficoll gradient with cytochalasin B. Cell hybrids between the oocytes and the cytoplasts were then prepared with the aid of polyethylene glycol treatment. These cell hybrids were capable of responding to 1-methyladenine by maturation.     

Hormone-induced in vitro maturation and ovulation of <Emphasis Type="Italic">Danio rerio</Emphasis> oocytes and production of eggs capable of fertilization and futher development

It is common knowledge that zebrafish, Danio rerio, oocytes in their follicular envelope that have reached definitive size undergo in vitro maturation in 90% Leibovitz’s medium, pH 9.0, when treated with 17α, 20β-dihydroxyprogesterone and acquire developmental competence but do not ovulate (Seki et al., 2008). We have demonstrated that zebrafish oocytes that have undergone maturation under the indicated conditions ovulate when treated with prostaglandin F_2α (5 μg/mL) and/or 20% carp ovarial fluid and are capable of development towards the actively feeding larvae upon fertilization (the maximum follow-up period).     

In vitro stimulation of oocyte ovulation in teleosts by gonadotropic and steroid hormones

Published data on in vitro stimulation of oocyte maturation and ovulation by gonadotropic and steroid hormones in different teleost species are reviewed. The involvement of meiosis-inducing steroids, eicosanoids, and nuclear progestogen receptor in the mechanism of ovulation induction is considered.     

The nuclei of follicular cells do not control oocyte maturation in amphibians induced by gonadotropic hormones in vitro]

The inhibitory effect of actinomycin D (5 micrograms/ml) on maturation of the follicle-enclosed oocytes of Rana temporaria and Xenopus laevis induced in vitro by pituitary suspension and human chorionic gonadotropin, respectively, is not observed at low concentrations of the hormones. These data suggest that nuclei of the follicle cells are not involved in the control of the pituitary-dependent oocyte maturation in amphibians.