Oocyte maturation as regulated by follicular factors

Isolation and functional characterization for oocyte maturation and sperm motility of the oocyte maturation arresting factor from the Japanese scallop, Patinopecten yessoensis

In bivalves, serotonin (5-hydroxytriptamine, 5-HT) acts as a major promotional factor in oocyte maturation, sperm motility, and sequential spawning. The previously reported novel neuronal protein, oocyte maturation arresting factor (OMAF) that was found in the central nervous system and hemolymph of the Japanese scallop, Patinopecten yessoensis, has an inhibitory activity in the 5-HT-induced oocyte maturation via a receptor-mediated mechanism, resulting in an arrest of spawning [30]. In this study, OMAF protein was isolated from the supernatant of hemolymph of the scallop using gel and anion-exchange chromatography, and SDS-PAGE. Three digested partial peptides with 4, 11, and 16 amino acid residues were determined through reversed-phase HPLC and amino acid sequencing. The anti-OMAF antibodies generated against the obtained peptides with 11 and 16 amino acid residues were applied to immunohistochemistry and 5-HT-induced spawning and oocyte maturation assays. Fusiform OMAF neurons were localized in the external area of the anterior lobe of the cerebral ganglion, supporting our presumption that OMAF was secreted from the cerebral and pedal ganglia (CPG). Pretreatment with anti-OMAF antibody on three kinds of bivalve species showed a strong in vivo amplification of 5-HT-induced release of egg and sperm, and an in vitro restoration of 5-HT-induced germinal vesicle breakdown (GVBD) from inhibition by the CPG extract, suggesting the release from suppressive activity of OMAF due to the absorption with antibody. These results confirm that the isolated peptides are from OMAF and OMAF acts as an inhibitor of 5-HT-induced oocyte maturation and sperm motility as previously reported.

A novel oocyte maturation arresting factor in the central nervous system of scallops inhibits serotonin-induced oocyte maturation and spawning of bivalve mollusks

Serotonin (5-hydroxytriptamine; 5-HT) is a major neurotransmitter that triggers oocyte maturation and sequential spawning in bivalve mollusks. A proteinous and heat-labile substance that proved to be a novel inhibitor of 5-HT-induced egg release from ovarian tissue was found in the cerebral and pedal ganglia (CPG) of the scallop Patinopecten yessoensis. The same inhibitory activity was also observed in the proteinous fraction from the supernatant of hemolymph. Histological observation demonstrated that the novel inhibitor prevented 5-HT from inducing oocyte maturation in the scallop ovary and that no prostaglandin F2alpha (PGF2alpha) inhibited 5-HT-induced oocyte maturation, although PGF2alpha strongly prohibited 5-HT-induced egg release through the gonoduct from ovarian tissue. The novel inhibitor from the scallop CPG also prohibited 5-HT-induced oocyte maturation of other bivalve species as well as scallops. The novel inhibitor, mediated through a receptor mechanism on oocyte membranes, blocked extracellular Ca2+ uptake into oocytes, which was observed in 5-HT-induced oocyte maturation. It is suggested that the novel inhibitor with a molecular mass of 60 kDa, named oocyte maturation arresting factor, which appears to be a universal substance for bivalve species, may be transported from the CPG to the ovary via hemolymph and may prohibit 5-HT-induced oocyte maturation due to the interference of extracellular Ca2+ influx into oocytes, eventually resulting in the inhibition of spawning. On the other hand, it seems that PGF2alpha inhibits 5-HT-induced transport of mature eggs through the gonoduct.

Influence of human chorionic gonadotropin (hCG) and hCG internalization by granulosa cells on the rate of in vitro fertilization and embryonic development of human oocytes

Follicular fluids and granulosa cells were obtained from 28 aspirated follicles of nine women undergoing laparoscopy in an in vitro fertilization program. Follicular growth was stimulated by a human menopausal gonadotropin regimen and laparoscopy was performed 32 hours after human chorionic gonadotropin (hCG) administration. Follicular fluid 17 beta-estradiol (E2) levels were higher and hCG levels were lower in follicles with oocytes that fertilized and cleaved beyond two blastomeres (greater than two-cell group) than in those with nonfertilizable oocytes (NF group) (P less than 0.05). Compared to those from the NF group, granulosa cells from the greater than two-cell group secreted less progesterone (P) in vitro and had a fourfold increase in percentage of cells with internalized hCG. These results demonstrate that the steroidogenic capacity of granulosa cells from follicles whose oocytes fertilize and undergo accelerated embryonic development in vitro differs from the capacity of granulosa cells from NF follicles. This difference may be due to their enhanced ability to bind and subsequently internalize hCG.

Intraovarian markers of follicular and oocyte maturation

The use of ovulation induction for multiple follicular growth in in vitro fertilization (IVF) has introduced the problem of follicular asynchrony. As a consequence of the asynchrony, the parameters most commonly used by IVF groups to assess follicular and oocyte quality within those follicles are not sufficiently sensitive or specific. Thus, each follicle must be considered separately, and specific markers of follicular and/or oocyte maturation must be sought from within the follicle. In this review we analyze previous reports of potential markers of follicular and oocyte maturation. In regards to the follicular fluid constituents, the level of estradiol in follicular fluid correlates with fertilization and pregnancy in stimulated cycles. Other steroids are only helpful when specific stimulation protocols are used. The level of some follicular proteins such as alpha-1-antitrypsin and fibrinogen also correlates with fertilization and pregnancy outcome. Cyclic AMP levels in follicular fluid are significantly reduced in follicles leading to conception. Regulators of oocyte maturation, such as the Oocyte Maturation Inhibitor (OMI) or the Meiosis Inducing Substance (MIS) have also been correlated with IVF outcome, but their exact structure remains still unknown. In addition, other sophisticated parameters, such as chemotactic activity of human leukocytes, or simple methods, such as the presence of intrafollicular echoes, have also been used as successful markers in predicting IVF outcome.