Fertilization and early embryology: Microsurgical correction of partially degenerate mouse embryos promotes hatching and restores their viability

We have evaluated the effects of degeneration of blastomereson the developmental fate of mouse embryos. Micro-manipulationtechniques were used first to destroy one or two blastomeresof a 4-cell embryo (thereby creating three-quarter and halfembryos), and later to repair the anomaly by removing the degeneratematerial. The embryos were either cultured in protein-free orprotein-supplemented medium. When cultured in protein-supplementedmedium, three-quarter embryos hatched at the same rate as intactembryos (84 and 91%, respectively), but this rate was reduced(54%; 67/125) when the embryos were cultured in a protein-freeenvironment. Destruction of two blastomeres of a 4-cell embryoand culture in protein-free medium was detrimental, as only3.2% (4/124) hatched. By supplementing the culture medium withprotein, some of these half embryos were rescued, as shown bya 34% (32/95) hatching rate. A more dramatic increase in hatchingwas achieved, however, after repair of the half embryos by microsurgicalremoval of the degenerate material. In this case, 72% (78/109)of the repaired embryos were able to hatch. These findings mayhave implications for human in-vitro fertilization where partialembryonic degeneration or fragmentation often leads to embryonicdemise and reduced implantation. Moreover, these observationsmay provide important clues to mechanisms of mammalian embryonichatching.