“Spontaneous” hardening of the zona pellucida of mouse oocytes during in vitro culture

Abstract

Culture in vitro causes a slow, progressive hardening of the zona pellucida (ZP) of fully grown dictyate oocytes isolated from the mouse ovary. Hardening cannot be prevented by inhibitors of peroxidase or by a tyrosine analogue. Culture in anaerobic conditions is very effective in preventing ZP hardening. If the oocyte is cultured surrounded by its own follicle cells or in contact with cumuli oophori obtained from superovulated females, hardening is much reduced. The results suggest that the “spontaneous” hardening in cultured ovarian oocytes is not due to a cortical reaction, and that a diffusible factor is produced by follicle cells that protect the ZP from hardening.

Effect of the size of zona pellucida opening by laser assisted hatching on clinical outcome of frozen cleaved embryos that were cultured to blastocyst after thawing in women with multiple implantation failures of embryo transfer: a retrospective study

“…A failure in hatching does prevent implantation. Hatching deficiencies can result from zona hardening, which might occur after cryopreservation [16,17] or after in vitro culture of human embryos [18,19]. Balaban et al reported that implantation rate of cryopreserved day 3 embryos that were allowed to cleave one day in vitro after thawing and were transferred without AH was 9.9% (58 of 585) in a prospective randomized study [6].…”

Zona pellucida resistance to sperm penetration before the completion of human oocyte maturation

“…Under physiological conditions the zona is responsible for homologous gamete recognition and binding (Hartmann, 1983) and it also plays a major role in the mechanism that prevents polyspermy (Wolf, 1981;Sathananthan & Trounson, 1982). On the other hand, the development of increased zona resistance to sperm penetration, leading to decreased oocyte fertilizability, has been described in various experimental systems, such as during maturation of cumulus-free mouse oocytes in vitro (De Felici & Siracusa, 1982) or in mouse oocytes aged in vivo or in vitro (Austin, 1970;Szòllòsi, 1975;Longo, 1981;Gianfortoni & Gulyas, 1985). Impairment of sperm-zona interaction has also been suggested to be a contributing factor to idiopathic human infertility (Trounson et al, 1980;Mahadevan et al, 1983).…”

Analysis of the human zona pellucida during culture: Correlation with diagnosis and the preovulatory hormonal environment

“…The presence of specific free amino acids in the culture medium are necessary for proper hatching, attachment, and outgrowth of mouse embryos (12). Studies have reported that 70 to 75% of embryos fail to hatch in culture (13,14), and suboptimal culture conditions can be responsible for the spontaneous "hardening" of the zona (15,16). The absence of serum, follicular fluid, or fetuin in the medium will induce zona hardening (15,17,18), and this is more significant with aging (19).…”