MICROSURGICAL CORRECTION OF PARTIALLY DEGENERATE MOUSE EMBRYOS PROMOTES HATCHING AND RESTORES THEIR VIABILITY

We have evaluated the effects of degeneration of blastomeres on the developmental fate of mouse embryos. Micro-manipulation techniques were used first to destroy one or two blastomeres of a 4-cell embryo (thereby creating three-quarter and half embryos), and later to repair the anomaly by removing the degenerate material. The embryos were either cultured in protein-free or protein-supplemented medium. When cultured in protein-supplemented medium, three-quarter embryos hatched at the same rate as intact embryos (84 and 91%, respectively), but this rate was reduced (54%; 67/125) when the embryos were cultured in a protein-free environment. Destruction of two blastomeres of a 4-cell embryo and culture in protein-free medium was detrimental, as only 3.2% (4/124) hatched. By supplementing the culture medium with protein, some of these half embryos were rescued, as shown by a 34% (32/95) hatching rate. A more dramatic increase in hatching was achieved, however, after repair of the half embryos by microsurgical removal of the degenerate material. In this case, 72% (78/109) of the repaired embryos were able to hatch. These findings may have implications for human in-vitro fertilization where partial embryonic degeneration or fragmentation often leads to embryonic demise and reduced implantation. Moreover, these observations may provide important clues to mechanisms of mammalian embryonic hatching.