Morphogen signals are essential for cell fate specification during embryogenesis. Some receptors that sense these morphogens are known to localize to only the apical or basolateral membrane of polarized cell lines in vitro. How such localization affects morphogen sensing and patterning in the developing embryo remains unknown. Here, we show that the formation of a robust BMP signaling gradient in the early mouse embryo depends on the restricted, basolateral localization of BMP receptors. The mis-localization of receptors to the apical membrane results in ectopic BMP signaling in the mouse epiblast in vivo. With evidence from mathematical modeling, human embryonic stem cells in vitro, and mouse embryos in vivo, we find that the geometric compartmentalization of BMP receptors and ligands creates a signaling gradient that is buffered against fluctuations. Our results demonstrate the importance of receptor localization and embryo geometry in shaping morphogen signaling during embryogenesis.

The complexity of gene regulatory networks that lead multipotent cells to acquire different cell fates makes a quantitative understanding of differentiation challenging. Using a statistical framework to analyze single-cell transcriptomics data, we infer the gene expression dynamics of early mouse embryonic stem (mES) cell differentiation, uncovering discrete transitions across nine cell states. We validate the predicted transitions across discrete states using flow cytometry. Moreover, using live-cell microscopy, we show that individual cells undergo abrupt transitions from a naïve to primed pluripotent state. Using the inferred discrete cell states to build a probabilistic model for the underlying gene regulatory network, we further predict and experimentally verify that these states have unique response to perturbations, thus defining them functionally. Our study provides a framework to infer the dynamics of differentiation from single cell transcriptomics data and to build predictive models of the gene regulatory networks that drive the sequence of cell fate decisions during development.DOI: http://dx.doi.org/10.7554/eLife.20487.001

Morphogen signals are essential for cell fate specification during embryogenesis. Some receptors that sense these morphogen signals are known to localize to only the apical or basal membrane of polarized cell lines in vitro. How such localization affects morphogen sensing and patterning in the developing embryo remains unknown. Here, we show in the early mouse embryo that the formation of a robust BMP signaling gradient depends on restricted, basolateral localization of the BMP receptors. Mis-localizing these receptors to apical membrane leads to ectopic BMP signaling in vivo in the mouse embryo. To reach the basolaterally localized receptors in epiblast, BMP4 ligand, secreted by the extra-embryonic ectoderm, has to diffuses through the narrow interstitial space between the epiblast and the underlying endoderm. This restricted, basolateral diffusion creates a signaling gradient. The embryo geometry further buffers the gradient from fluctuations in the levels of BMP4. Our results demonstrate the importance of receptor localization and embryo geometry in shaping morphogen signaling during embryogenesis. 2 The early mouse embryo (E6.0-E6.5) adopts an egg-cylinder geometry ( Fig. 1a) 5,6,16 . It contains a lumen (the pre-amniotic cavity) encased by two epithelial tissues: the epiblast and extraembryonic ectoderm (ExE). The ExE secretes the morphogen BMP4, which is sensed by receptors in epiblast 5,6 . The resulting BMP signaling is required for the differentiation of the epiblast into mesoderm 3,4 . Both the epiblast and ExE have stereotyped epithelial tissue geometries 17 , with their apical membranes surrounding the lumen and their basolateral membranes facing a narrow interstitial space (between these tissues and the underlying visceral endoderm (VE)). This lumen and interstitial space are separated by impermeable tight junctions present throughout the epithelia except at the border between the ExE and epiblast (Fig. 1a). Indeed, when small-molecule dye fluorescein was injected into the pre-amniotic cavity of an E6.5 mouse embryo, it did not penetrate the epiblast or ExE but diffused through a channel at the edge of the epiblast ( Supplementary Fig. 1). Thus, the extracellular space in the embryo through which BMP4 ligands diffuse is compartmentalized into a lumen and an interstitial space. Here, by combining mathematical modeling, quantitative imaging, embryological perturbation, and microfluidics, we demonstrate that restricted receptor localization in conjunction with the embryo geometry, constrains the diffusion of and therefore response to BMP4 ligands. We show that the BMP4 signaling gradient arises from the edge of epiblast even under conditions of uniform BMP4 stimulation. Further, the interplay between restricted receptor localization and the embryo geometry buffers BMP4 ligands in pre-amniotic cavity through an entropic effect. This entropic buffering renders the BMP4 signaling gradient robust to fluctuations in BMP4 level. Consistently, mis-localizing BMP receptors in the mouse embryo leads to ectopic B...

Preventing aberrant inflammation is essential to maintaining homeostasis in the mammalian intestine. Although P-glycoprotein (P-gp) expression in the intestine is critical for protecting the intestinal epithelium from toxins and damage due to neutrophil infiltration, its regulation in the intestine is poorly understood.