Cover image

Cover Like the opposite but interconvertible halves of Yin and Yang, the first two cells of a mouse embryo may have a tendency to choose different cell fates. In this issue, it is determined via single-cell RNA sequencing that cells in the same embryo express different genes. This suggests that mammalian embryonic cells exhibit reproducible molecular differences at much earlier developmental stages than previously thought. In the illustration, pink-colored cells represent the lineage primarily contributing to the inner cell mass and eventual offspring (the “Yang” half of the central embryo), whereas teal-colored cells (the “Yin” half) are inclined to become trophoblasts, the progenitor to the majority of extraembryonic tissues. Artwork © Victor O. Leshyk, 2014, www.victorleshyk.com.