Trypsin-like Hatching Enzyme of Mouse Blastocysts: Evidence for Its Participation in Hatching Process before Zona Shedding of Embryos6

Effects of twelve protease inhibitors on hatching of mouse embryos were investigated. Mouse hatching was strongly or moderately inhibited by trypsin inhibitors including p-toluenesulfonyl-Lys-CH₂Cl (TLCK) and chicken ovomucoid, while inhibitors for chymotrypsin and elastase showed weak or no inhibition. These results indicate the participation of a trypsin-like protease in the hatching of mouse embryos as a hatching enzyme., Since TLCK is the strongest and an irreversible inhibitor for the enzyme, timing of the participation of the hatching enzyme in the hatching process was examined by pulse treatment of embryos with TLCK before and during the zona shedding. The results indicated that a trypsin-like hatching enzyme functions before, but not during, the zona shedding of embryos, especially during a 15 h period immediately before the beginning of the shedding.