Visceral organs, such as the lungs, stomach and liver, are derived from the fetal foregut through a series of inductive interactions between the definitive endoderm (DE) and the surrounding splanchnic mesoderm (SM). While DE patterning is fairly well studied, the paracrine signaling controlling SM regionalization and how this is coordinated with epithelial identity is obscure. Here, we use single cell transcriptomics to generate a high-resolution cell state map of the embryonic mouse foregut. This identifies a diversity of SM cell types that develop in close register with the organ-specific epithelium. We infer a spatiotemporal signaling network of endoderm-mesoderm interactions that orchestrate foregut organogenesis. We validate key predictions with mouse genetics, showing the importance of endodermderived signals in mesoderm patterning. Finally, leveraging these signaling interactions, we generate different SM subtypes from human pluripotent stem cells (hPSCs), which previously have been elusive. The single cell data can be explored at: https://research.cchmc.org/ ZornLab-singlecell.

Organogenesis of the trachea and lungs requires a complex series of mesoderm-endoderm interactions mediated by WNT, BMP, retinoic acid (RA) and hedgehog (Hh), but how these pathways interact in a gene regulatory network is less clear. Using Xenopus embryology, mouse genetics, and human ES cell cultures we identified a conserved signaling cascade that initiates respiratory lineage specification. We show that RA has multiple roles; first RA pre-patterns the lateral plate mesoderm and then it promotes Hh ligand expression in the foregut endoderm. Hh subsequently signals back to the pre-patterned mesoderm to promote expression of the lung-inducing ligands Wnt2/2b and Bmp4. Finally, RA regulates the competence of the endoderm to activate the Nkx2-1+ respiratory program in response to these mesodermal WNT and BMP signals. These data provide insights into early lung development and a paradigm for how mesenchymal signals are coordinated with epithelial competence during organogenesis.

Elevated circulating concentrations of the gut bacteria choline metabolite trimethylamine N-oxide (TMAO) were found in patients with type 2 diabetes mellitus (T2DM). However, whether a high level of TMAO is related to the risk of diabetes has not been studied. We aimed to synthesize the evidence on the relation between TMAO levels and the risk of diabetes mellitus (DM) and to investigate the association further in a dose-response meta-analysis. PubMed, Web of Science, and Scopus databases were searched for studies from inception to June 2018. A total of 12 clinical studies were included in this study, and 15 314 enrolled subjects were included. A meta-analysis of two-class variables and continuous variables were used to obtain pooled effects. Dose-response meta-analysis was used to investigate the dose-response relationship between TMAO concentrations and the risk of DM.Meta-regression and subgroup analyses were applied to identify the source of heterogeneity in this study. High levels of circulating TMAO were associated with an increased risk of DM (odds ratio [OR] = 1.89) using the two-class meta-analysis.Plasma levels of TMAO in patients with diabetes were higher than in subjects without diabetes (standardized mean difference [SMD]: 0.36) using a meta-analysis of continuous variables. The OR for DM prevalence increased by 54% per 5 μmol L −1 increment of plasma TMAO (OR = 1.54) according to the dose-response metaanalysis. This is the first systematic review and meta-analysis to demonstrate a positive dose-dependent association between circulating TMAO levels and increased diabetes risk.