A programmed oxyradical burst causes hatching of mouse blastocysts.

The emergence of the mammalian blastocysts from their thick glycoprotein investment known as the zona pellucida is an important, but poorly understood, event in embryogenesis. In this paper, we demonstrate that peri-hatching blastocysts generate a considerably high quantum of an active oxyradical species for an extremely short period of time when compared to the pre-hatching (unhatched) and post-hatching (hatched) blastocysts. Hatching could be induced in pre-hatching blastocysts by exposing them to superoxide artificially generated to match the observed peri-implantation stage specific levels of superoxide, without impairing their viability. These observations suggest the operation of a superoxide-dependent hatching initiation in developing mammalian embryos.