Creation of trophectoderm, the first epithelium, in mouse preimplantation development

Abstract

Trophectoderm (TE) is the first cell type that emerges during development and plays pivotal roles in the viviparous mode of reproduction in placental mammals. TE adopts typical epithelium morphology to surround a fluid-filled cavity, whose expansion is critical for hatching and efficient interaction with the uterine endometrium for implantation. TE also differentiates into trophoblast cells to construct the placenta. This chapter is an overview of the cellular and molecular mechanisms that control the critical aspects of TE formation, namely, the formation of the blastocyst cavity, the expression of key transcription factors, and the roles of cell polarity in the specification of the TE lineage. Current gaps in our knowledge and challenging issues are also discussed that should be addressed in future investigations in order to further advance our understanding of the mechanisms of TE formation.

Fig. 9.1

Morphological transformation of the mouse embryo from the 1-cell stage to the blastocyst stage, which takes place during the first 3 days after fertilization

Fig. 9.2

(a) Snapshot images taken by time-lapse cinematography of a developing mouse embryo, showing the initial formation of microlumens and their expansion to generate the blastocyst cavity. (b) Schematic diagrams, depicting the microlumen formation by exocytosis of vacuoles at the basal membrane in the outer cells. (c) Schematic diagrams, portraying three critical steps to expand and maintain the blastocyst cavity, namely, directional sodium ion transport, water influx, and paracellular sealing. See text for details

Fig. 9.3

(a)Schematic drawing, showing the formation of the apical–basal cell polarity in the outer cells. (b) Confocal optical sections of morula-stage embryos that are immunofluorescently stained for polarity proteins, Pard6b (apical component) or Scribble (basal component). (c) A schematic diagram of a model for the regulation of tight junction formation and TE-specific gene activation by the apical polarity regulators. See text for details. (d) Schematic diagrams, showing the control of cell division patterns by the polarity regulators to influence the positions of daughter cells