Limitations of pulse oximetry: respiratory insufficiency--a failure of detection.

<h3>Abstract</h3> During gastrulation pluripotent epiblast cells specify and spatially arrange the three germ layers. Human pluripotent stem cells (PSCs) have been shown to undergo spatially-organized fate specification on micropatterned surfaces. Since <i>in vivo</i> validation is not possible for the human, we developed a mouse PSC micropattern system and, by making direct comparisons to mouse embryos, reveal the robust specification of distinct regional identities. BMP, WNT, ACTIVIN and FGF directed mouse epiblast-like cells to undergo an epithelial-to-mesenchymal transition and radially pattern posterior mesoderm fates. Conversely, WNT, ACTIVIN and FGF patterned anterior mesoderm and endoderm identities. By contrast, epiblast stem cells, a more developmentally advanced state, only specified anterior identities but without patterning. The mouse micropattern system offers a robust scalable method to generate regionalized cell types present <i>in vivo</i>, resolve how signals promote distinct cellular identities and generate patterns, and compare mechanisms operating <i>in vivo</i> and <i>in vitro</i> and across species.