LAUSR

The first stages of mammalian development, before implantation of the embryo in the maternal uterus, result in the establishment of three cell populations in the blastocyst: trophectoderm, epiblast, and primitive endoderm. These events involve only a small number of cells, and are initiated by morphological differences among them related to cell adhesion and polarity. Much attention has been paid to the master transcription factors that are critical for establishing and maintaining early lineage choices. Nevertheless, a large body of work also reveals that additional molecular mechanisms are involved. Here, we provide an updated view of the role of different signaling pathways in the first stages of mouse development, and how their cross‐talk and interplay determine the initial lineage decisions occurring in the blastocyst. We will also discuss how these pathways are critical for translating cellular phenotypes, the product of the morphogenetic events occurring at these stages, into transcriptional responses and expression of lineage‐specifying transcription factors. Developmental Dynamics 246:245–261, 2017. © 2016 Wiley Periodicals, Inc.