Human nonovulatory oocyte‐cumulus complexes: Ultrastructure, macromolecular synthesis, and developmental potential

Abstract

Human nonovulatory oocyte-cumulus complexes were obtained from large antral follicles 34 h after the injection of hCG. Their ultrastructure, RNA and protein synthesis, and the ability of oocyte maturation and subsequent fertilization in vitro werc the subject of this study. The oocyte nucleus was situated in the cell periphery, possessing one or two dense nucleoli. Intranucleolar vacuoles were sometimes present. Mitochondria and smooth endoplasmic reticulum were the most abundant cytoplasmic structures. The number of cortical granules was rather low. Cumulus cells showed responsiveness to exogeneous hCGiendogeneous LH stimulation as morphologic signs of the oocyte-cumulus uncoupling and o f the early luteinization. Furthermore, the oocytes were capable of meiotic maturation in vitro, and following subsequent in vitro insemination the majority of them were penetrated by spermatozoa. However, polyspermy was detected in most cases, and clcavage was not achieved. A developmental defect of nonovulatory oocytes was suggested by an extremely low level of RNA synthesis while continuing active protein synthesis by nonovulatory oocytes was demonstrated. In contrast, the associated cumulus cells synthesized both RNA and protein, suggesting that the majority of granulosa cells of the nonovulatory follicles was probably unaltered. It is hypothesized that the development of nonovulatory follicles after induction of ovulation might reveal the developmental pattern which would lead, in some cases, to ovulation of nonviable human oocytes both in stimulated and natural cycles.

Chromatin configuration and transcriptional control in human and mouse oocytes

“…2A, insert). This unknown structure was already observed by other authors (Tesarik et al, 1984). Few patches of partly condensed chromatin could be seen, as well as clusters of granules, which seemed to represent interchromatin granules clusters (IGCs) (Parfenov et al, 2000).…”

Competent mouse oocytes isolated from antral follicles exhibit different chromatin organization and follow different maturation dynamics

“…The ultrastructural differences observed at GV between SN-and NSN-type oocytes, namely, the extent of nucleolar compaction and chromatin condensation, the number of twisted fibrils, and the presence of perinuclear MTOCs and microtubules, probably reflect metabolic differences between these two classes of oocytes. Compaction of the nucleolus correlates in mammals with a sharp decrease in rRNA synthesis (Tesafik et al, 1983(Tesafik et al, , 1984Crozet et al, 1981Crozet et al, , 1986). In addition, Parfenov et al (1989) find a complete cessation of RNA synthesis in nuclei with condensed perinucleolar chromatin.…”

Mammalian oocyte maturation

“…RNAs labelled during growth are present in the cytoplasm of ovulated oocytes (Fourcroy, 1982 ;Piko, 1982). At (Bleil and Wassarman, 1980) Albertini, 1976 ;Anderson, 1977 ;Gilula et al, 1978 ;Szbll6si, 1978 ;Szollosi et al, 1978) (Daguet, 1980 ;Gdrard et al, 1979) and in human oocytes (Tesarik et al, 1984) Calarco, 1972) and in the cow (Kruip et al, 1983 ;Hyttel et al, 1986) oocytes and in lesser detail in the rabbit (Szollosi, 1975) Sz6ll6si et al, 1972a). No (Calarco, 1972 ;Calarco et al, 1972 ;Sz6ll6si et al, 1972a).…”