Nuclear maturation inducers in Bufo arenarum oocytes.

The present study analyses the effect of dihydrotestosterone (DHT) and mammalian insulin on the nuclear maturation of Bufo arenarum oocytes under in vitro conditions. The response of fully grown follicle oocytes to DHT, shown by germinal vesicle breakdown (GVBD), occurred in a manner dependent on dose, time and sexual cycle period. The highest oocyte sensitivity to the hormone appeared during the breeding period, a fact evinced by high GVBD percentages after short incubation periods and at a low hormone concentrations. Insulin also proved effective in inducing nuclear maturation, although its action was only visible at high concentrations and after a long incubation period. The combination of insulin and steroid hormones (DHT or progesterone), both at subliminal doses, caused a noticeable potentiating synergism, resulting in a rapid and important increase in GVBD. Another effect of insulin was the acquisition by oocytes of steroid sensitivity during folliculogenesis.

Ultrastructural changes during nuclear maturation in Bufo arenarum oocytes.

During progesterone-induced nuclear maturation the oocytes of Bufo arenarum undergo a series of nuclear and cytoplasmic changes. The breakdown of heterocellular communications between the follicular cell projections and the oocyte microvilli, and the consequent enlargement of the perivitelline space, were observed at the animal pole. The more evident cytoplasmic feature during nuclear maturation comprised the gathering of glycogen granules in clusters, some phagocytosed by empty vesicles. With respect to the location of these vesicles, some were observed in close proximity to the oolemma and others were freely suspended in the perivitelline space, extruded from the oocyte. Other visible events were the disruption of the annulate lamellae, the formation of an elaborate cortical endoplasmic reticulum and the rearrangement of the cortical granules in a monolayer immediately beneath the oolemma together with aggregates of endoplasmic reticulum cisternae. Our results show that during nuclear maturation the nuclear oocyte changes include a flattening of the spherical oocyte nucleus, its migration towards the surface of the animal pole, the disappearance of the nucleoli and the dissolution of the nuclear envelope.

Morphological and cytochemical changes during nuclear maturation in Bufo arenarum oocytes

The morphological and cytochemical changes undergone by the oocyte during progesterone-induced nuclear maturation were analyzed in fully grown follicle oocytes of Bufo arenarum during the breeding period. The distribution and the staining properties of the nuclear material and of the perinuclear cytoplasm were studied. Our observations indicate that, during this complex process, the germinal vesicle (GV) undergoes migration and dissolution. The nuclear sap, which in the control has an homogeneous aspect, during maturation adopts a fibrillar appearance in the basal zone, showing basophilia and positive reaction to PAS, Feulgen and Methyl green-Pyronin staining. When the GV breakdown occurs, the nuclear contents become mixed with the cortical cytoplasm, developing a different cytoplasmic mass that disappears about 12 h after the beginning of incubation. The perinuclear cytoplasm exhibits metachromasia and orthochromasia with Toluidine Blue at pH 5.6 and a strong basophilia with PAS, suggesting the existence of acid compounds. The presence of nucleic acids such as RNA and DNA is a strong possibility because of the positive reaction to Methyl green-Pyronin, Feulgen and DAPI. This cytoplasmic mass remains until the end of the meiotic resumption process

Morphological and cytochemical changes during nuclear maturation in Bufo arenarum oocytes

The morphological and cytochemical changes undergone by the oocyte during progesterone-induced nuclear maturation were analyzed in fully grown follicle oocytes of Bufo arenarum during the breeding period. The distribution and the staining properties of the nuclear material and of the perinuclear cytoplasm were studied. Our observations indicate that, during this complex process, the germinal vesicle (GV) undergoes migration and dissolution. The nuclear sap, which in the control has an homogeneous aspect, during maturation adopts a fibrillar appearance in the basal zone, showing basophilia and positive reaction to PAS, Feulgen and Methyl green-Pyronin staining. When the GV breakdown occurs, the nuclear contents become mixed with the cortical cytoplasm, developing a different cytoplasmic mass that disappears about 12 h after the beginning of incubation. The perinuclear cytoplasm exhibits metachromasia and orthochromasia with Toluidine Blue at pH 5.6 and a strong basophilia with PAS, suggesting the existence of acid compounds. The presence of nucleic acids such as RNA and DNA is a strong possibility because of the positive reaction to Methyl green-Pyronin, Feulgen and DAPI. This cytoplasmic mass remains until the end of the meiotic resumption process

Morphological and cytochemical changes during nuclear maturation in Bufo arenarum oocytes.

The morphological and cytochemical changes undergone by the oocyte during progesterone-induced nuclear maturation were analyzed in fully grown follicle oocytes of Bufo arenarum during the breeding period. The distribution and the staining properties of the nuclear material and of the perinuclear cytoplasm were studied. Our observations indicate that, during this complex process, the germinal vesicle (GV) undergoes migration and dissolution. The nuclear sap, which in the control has an homogeneous aspect, during maturation adopts a fibrillar appearance in the basal zone, showing basophilia and positive reaction to PAS, Feulgen and Methyl green-Pyronin staining. When the GV breakdown occurs, the nuclear contents become mixed with the cortical cytoplasm, developing a different cytoplasmic mass that disappears about 12 h after the beginning of incubation. The perinuclear cytoplasm exhibits metachromasia and orthochromasia with Toluidine Blue at pH 5.6 and a strong basophilia with PAS, suggesting the existence of acid compounds. The presence of nucleic acids such as RNA and DNA is a strong possibility because of the positive reaction to Methyl green-Pyronin, Feulgen and DAPI. This cytoplasmic mass remains until the end of the meiotic resumption process.