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. Micromanipulation 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.