title: Hardening of zona pellucida of mouse oocytes and embryos in vivo and in vitro.
abstract: OBJECTIVE
  To evaluate the effect of in vitro culture on zona pellucida resistance in mouse oocytes and embryos.
  
  
  METHODS
  Zona pellucida resistance was assessed by comparing duration of zona lysis in the presence of alpha-chymotrypsin. The effects of artificial or physiological conditions of development were evaluated by comparing embryos in vitro with those left to reach the same stage of development in vivo.
  
  
  RESULTS
  The time required for zona lysis of oocytes increased after 2, 24, and 48 hours in vitro (P < .001). The same observation holds true for oocytes left in vivo during 24 hours. Fertilization both in vivo and in vitro induced a major increase in zona resistance. At the two-cell stage, in vitro culture did not harden the zona pellucida. At the morula stage and beyond, enzymatic lysis was slightly longer in vitro as compared to that of similar stages recovered from the genital tract.
  
  
  CONCLUSIONS
  Our data indicate that in vitro culture conditions do not modify zona hardening in oocytes and only slightly increased zona resistance from the morula stage on.
authors.affiliation: Department of Gynecology, C.H.U. Saint Pierre, Free University of Brussels, Belgium.
authors.forename: I
authors.initials: I
authors.lastname: DeMeestere
authors.forename: P
authors.initials: P
authors.lastname: Barlow
authors.forename: F
authors.initials: F
authors.lastname: Leroy
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004622:Embryo, Mammalian / Q000502:physiology*; D005306:Fertilization / Q000502:physiology*; D066298:In Vitro Techniques; D051379:Mice; D009865:Oocytes / Q000502:physiology*; D013997:Time Factors; D015044:Zona Pellucida / Q000201:enzymology*