Ultrastructure of a 4-cell human embryo developed in vivo

Abstract

The ultrastructure of a 4-cell human embryo undergoing development in vivo is described. The embryo recovered from the Fallopian tube 130 h after a single episode of intercourse and 70 h after the luteinizing hormone peak in plasma, was partially surrounded by cumulus cells. The blastomeres, of even size, were nucleated and had a similar distribution of cytoplasmic organelles. No signs of abnormality or cellular degeneration were observed. Transmission electron microscopy of serial sections revealed the presence of primitive desmosomes between cells, abundant vesicles within the blebs of the outer sheet of the nuclear membrane, blebbing of the inner sheet of the nuclear membrane and close association between the inner sheet of the nuclear membrane and the intranuclear annulate lamellae. Nucleolar precursors lacking the structural organization of mature nucleoli were also found. Similarities and differences between this and other preimplantation human embryos reported earlier are analysed.

Pertinence of Apoptosis Markers for the Improvement of In Vitro Fertilization (IVF)

“…The degree of apoptosis, that is particularly elevated at the blastocyst stage, however, cannot exceed a certain threshold without leading to the collapse of embryonic homeostasis and developmental arrest. Despite this "natural selection" during the pre-implantation stages, there is still a substantial loss (estimated at 20 to 25 % in vivo) on account of defective implantation [63].…”

“…This fragmentation is observed in both in vivo and in vitro fertilized embryos [63,2]. The origin, the role and the mechanism of this fragmentation remain to be clarified.…”

Effect of cell-plating density on the steroidogenic activity of human cumulus cells

“…Ultimately, the ovulated egg is accompanied by the mucified cumulus mass, which remains with it in the oviduct for several days (Pereda et al, 1989).…”

Qualité ovocytaire et embryonnaire : les marqueurs apoptotiques ont-ils leur place dans le potentiel préimplantatoire ?

“…Le taux d'apoptose, particulièrement élevé au stade blastocyste, ne peut pas dépasser un certain niveau, sans mener à la rupture de l'homéostasie embryonnaire avec pour conséquence l'arrêt du développement. Malgré cette sélection naturelle durant les stades préimplantatoires, il existe un taux de perte important du fait de l'échec fréquent de l'implantation, estimée entre 20 à 25 % in vivo [63].…”

“…Cette fragmentation est observée aussi bien dans les embryons fécondés in vivo, que in vitro [63,2]. Le rôle, l'origine et les mécanismes de la fragmentation restent encore mal connus.…”