A morphological study of blastocyst hatching in the mouse and rat.

摘要

In cultured mouse and rat blastocysts, hatching was found to begin with protrusion of trophectoderm cells from the zona pellucida at the expanded stage. Protrusion of the cells occurred at the mural trophectoderm and at the polar trophectoderm. After protrusion, a slit was formed in the zona pellucida in all mouse and rat blastocysts. It was also confirmed that hatching was completed in the form of either expansion or contraction in both mouse and rat blastocysts. Based on these results, the process of blastocyst hatching was classified into 6 types in the mouse. Five of the 6 types of hatching process in mouse blastocysts were observed in rat blastocysts. The mean duration of hatching was 22.4 and 40.9 h in and rat blastocysts respectively. Trypsin-like proteinase activity was histochemically detected in blastocysts from the compacted 16-cell stage to the expanded blastocyst stage. This enzyme activity was present in both mural and polar trophectoderm cells.