Structural changes in bovine oocytes during final maturation in vivo

Abstract

On the basis of structural observations bovine oocytes were grouped into four successive classed: 0, those before the luteinizing hormone (LH) surge; 1, those up to 8 h following the LH peak level; 2, those between 8 and 19 h after the LH peak level; and 3, those between 19 h after the LH peak level and ovulation. Oocytes in class 0 had mitochondria located in a generally peripheral position. Interior to the mitochondria were elements of rough endoplasmic reticulum (RER) and numerous membrane‐bound vesicles which bore ribosome‐like particles on their outer surface. The first visible changesater the LH peak level as seen in class 1 were the formation of the periviteline space with loss of contact between the cumulus cells and the oocyte, and ruffing of the nuclear envelope. These changes were followed b the resumption of meiosis as defined by germinal‐vesicle breakdown (GVBD), the disappearance of RER, and the formation fo clusters of mitochondria in association with lipid droplets and elementrs of smooth endolasmic reticulum (SER). The period between 8 and 19 h following LH peak level (class 2) was characterized by intensive clustering of mitochoncria in association with lipid droplets and elements of SER, conversion of lipid, fusion of vesicles, and the appearance of ribosomes in the cytoplasm. During the final stage (class 3), the polar body was extruded, the mitochondria dispersed, and the majority of the organelles became located toward the center of the cell. The relatively organelle‐free cortical region contained cortical granules immediately adjacent to the plasma membrane together with aggregates of tubular SER. The structural changes are discussed in the context of follicular steroidogenesis and oocyte developmental competence.

Morphological and ultrastructural changes occurring during degeneration of goat preantral follicles preserved in vitro

“…In addition, bovine oocytes showed large aggregates of SER surrounded by mitochondria after 48 h of culture (Hyttel et al, 1986). Kruip et al (1983) suggesting the existence of metabolic units in which vesicles and mitochondria are combined via the SER. Thus, the clustering of organelles appears to indicate a decrease in oocyte metabolism during culture (Hyttel et al, 1986).…”

In Vitro Fertilization and Cortical Granule Distribution of Bovine Oocytes Having Heterogeneous Ooplasm with Dark Clusters.

“…Cortical granules are distributed throughout the entire inner surface of the sphere of the oocyte during final maturation [10,17]. Exocytosis of cortical granules is the most common mechanism for the prevention of polyspermy.…”

Effects of monoclonal antibody against PMSG administered shortly after the preovulatory LH surge on time and number of ovulations in PMSG/PG-treated cows

“…This may also be inferred from the marked reduction of the number of embryos and corpora lutea when anti-PMSG serum is administered before oestrus (Bouters et al, 1983). PMSG may therefore cause disorders during final follicular and oocyte maturation which is known to proceed according to a chronologically fixed hormonal sequence in normally cyclic cows (Dieleman et al, 1983a, b;Kruip et al, 1983;Dieleman & Blankenstein, 1984.…”