Eimei Sato

Biochemical transmitters regulating the arrest and resumption of meiosis in oocytes

Publisher Summary This chapter discusses biochemical transmitters regulating the arrest and resumption of meiosis in oocytes. Germ cells migrate to the genital ridge from the yolk sac region during early embryonic development. In the genital ridge, the female germ cells start to divide and differentiate into oogonia. They enter meiosis and become primary oocytes. Nuclear division progresses to the diplotene stage of the first meiotic prophase and is arrested. The chromosomes decondense and are distributed diffusely throughout the oocyte nucleus. Progression of meiosis to the diplotene stage occurs before or shortly after birth. The oocytes may remain arrested at the dictyate stage for a prolonged period. Subsequently, a follicle develops enclosing the oocyte that contains a large clear nucleus designated as the germinal vesicle. The resumption of meiosis follows a sequence of programmed events while the oocytes are situated within the preovulatory follicles. The process is designated as oocyte maturation and is characterized by a series of biochemical, morphological, and functional changes that take place within the nucleus, highlighted by various events: (1) dissolution of the nuclear membranes manifested as germinal vesicle breakdown (GVBD), (2) chromatin condensation and the formation of distinct chromosomes, (3) formation of the first meiotic spindle, (4) translocation of the spindle to the peripheral region, (5) formation and extrusion of the first polar body, (6) formation and positioning of the second meiotic division, (7) rearrest at the second metaphase.

Inducement of blood vessel formation by ovarian extracts from mice injected with gonadotropins

Ovarian extracts prepared from immature mice injected with human chorionic gonadotropin (hCG) and pregnant mare serum gonadotropin (PMSG) were assayed for angiogenic activity. The assay method consisted of implanting a film coated with ovarian extracts to the lateral wall of the m.rectus abdominus of a mouse for 20 days and examining the site for vascularization. The higher angiogenic activity obtained with PMSG-treated extract may be related to its follicle stimulating activity.

Meiotic Arresting Substance Separated from Porcine Ovarian Granulosa Cells and Hypothetical Arresting Mechanism of Meiosis

In mammals, oogonia enter prophase of the first meiotic division in prenatal life, and shortly after birth, all oocytes are arrested in a late prophase known as the dictyate stage, and when an oocyte in an ovary reaches the end of its growth period, it contains a single large nucleus called the germinal vesicle (Franchi et al., 1962). It is now generally accepted that the resumption of the arrested first meiotic division occurs as a result of the surge of luteinizing hormone (LH) at each ovarian cycle (Shuetz, 1969; Tsafriri, 1978a), although the ability to complete the first meiotic division is related as well to the stage of follicular development (Tsafriri and Channing, 1975a; Sorensen and Wassarman, 1976).

Differential screening of ovarian cDNA libraries detected the expression of the porcine collagenase inhibitor gene in functional corpora lutea.

cDNA libraries were constructed from porcine granulosa cells of antral follicles as well as functional corpus luteum, and clones encoding stage-specific genes have been isolated by differential screening. A clone specific to the functional stage of corpus luteum was found to encode the porcine collagenase inhibitor gene and the stage-specific expression in luteinizing tissue was confirmed by Northern blot analysis. The complete open reading frame of the porcine collagenase inhibitor was deduced from the nucleotide sequence, and the localization of the product was examined by immunohistochemical staining as well in pig ovary; the inhibitor was detected in the intercellular space of luteal cells and in the connective tissue around blood vessels in the functional corpus luteum.

Effect of Inhibin-Like Substance Isolated from Porcine Follicular Fluid on the Follicle-Stimulating Hormone (FSH) Level in Mouse Serum and on FSH Binding to Porcine Granulosa Cells *

An inhibin-like substance, a follicle-stimulating hormone (FSH) inhibitor, was isolated from porcine follicular fluid and purified. Serum FSH levels of unilaterally ovariectomized mice which received injections of the inhibitor were lower than those of unilaterally ovariectomized mice which received injections of saline. The inhibitor also suppressed FSH binding to granulosa cells in vitro. These results suggest that this protein is an FSH inhibitor and that it has two modes of action: suppression of FSH levels in serum and suppression of FSH binding to granulosa cells.