IN THE BEGINNING Early embryos (a four-cell embryo shown) from mice and humans look the same on the outside, but gene activity studies show some big differences under the hood.
In the first days after an egg is fertilized, throwing a few key genetic switches revs up human embryo development, two new studies suggest.
That ignition pattern differs from the one that fires up early mouse embryos, the research finds.
One study, to be published online September 11 in Nature Communications, found that a much smaller number of genes than previously believed serve as the ignition switch for human embryo development.
A second study, by a different research group, tracked human and mouse embryo development from fertilized egg to about six days later, just before the embryo implants in the uterine wall. Timing and some genetic programming during development vary between the two species, researchers report online August 20 in Development.