In its first day of development, a human embryo follows instructions produced by its mother’s nearby cells. Afterward, the embryo begins following its own genetic instructions. Scientists haven’t yet uncovered the instructions that cause this transition, but new Yale research offers clues.In shifting from dependent to self-directing, an embryo must turn on three specific genes, the team reported online September 22 in Nature.Sequencing the genomes of zebrafish embryos, the team found that among genes that are turned on first, Nanog, SoxB1, and Pou5f1 had the highest expression levels. When the scientists blocked these genes, the embryos failed to continue developing. Interestingly, these same three genes have been found to reprogram adult human cells into stem cells resembling those found in an embryo.These genetic factors “provide an entry point to understanding the first domino to fall in the creation of life,” says Antonio J. Giraldez, Ph.D., associate professor of genetics and senior author of the study.