Case Report: Esophageal Bronchus in a Neonate, With Image, Histological, and Molecular Analysis.

In this case report, we describe the clinical course of a neonate who presented initially with respiratory distress and later with choking during feeding. He was subsequently found to have an esophageal bronchus to the right upper lung lobe, a rare communicating bronchopulmonary foregut malformation. Histological and molecular analysis of the fistula and distal tissues revealed that the proximal epithelium from the esophageal bronchus has characteristics of both esophageal and respiratory epithelia. Using whole exome sequencing of the patient's and parent's DNA, we identified gene variants that are predicted to impact protein function and thus could potentially contribute to the phenotype. These will be the subject of future functional analysis.

Disruption of a hedgehog-foxf1-rspo2 signaling axis leads to tracheomalacia and a loss of sox9+ tracheal chondrocytes.

Congenital tracheomalacia, resulting from incomplete tracheal cartilage development, is a relatively common birth defect that severely impairs breathing in neonates. Mutations in the Hedgehog (HH) pathway and downstream Gli transcription factors are associated with tracheomalacia in patients and mouse models; however, the underlying molecular mechanisms are unclear. Using multiple HH/Gli mouse mutants including one that mimics Pallister-Hall Syndrome, we show that excessive Gli repressor activity prevents specification of tracheal chondrocytes. Lineage tracing experiments show that Sox9+ chondrocytes arise from HH-responsive splanchnic mesoderm in the fetal foregut that expresses the transcription factor Foxf1. Disrupted HH/Gli signaling results in 1) loss of Foxf1 which in turn is required to support Sox9+ chondrocyte progenitors and 2) a dramatic reduction in Rspo2, a secreted ligand that potentiates Wnt signaling known to be required for chondrogenesis. These results reveal a HH-Foxf1-Rspo2 signaling axis that governs tracheal cartilage development and informs the etiology of tracheomalacia.

Endosome-Mediated Epithelial Remodeling Downstream of Hedgehog-Gli Is Required for Tracheoesophageal Separation.

The trachea and esophagus arise from the separation of a common foregut tube during early fetal development. Mutations in key signaling pathways such as Hedgehog (HH)/Gli can disrupt tracheoesophageal (TE) morphogenesis and cause life-threatening birth defects (TEDs); however, the underlying cellular mechanisms are unknown. Here, we use mouse and Xenopus to define the HH/Gli-dependent processes orchestrating TE morphogenesis. We show that downstream of Gli the Foxf1+ splanchnic mesenchyme promotes medial constriction of the foregut at the boundary between the presumptive Sox2+ esophageal and Nkx2-1+ tracheal epithelium. We identify a unique boundary epithelium co-expressing Sox2 and Nkx2-1 that fuses to form a transient septum. Septum formation and resolution into distinct trachea and esophagus requires endosome-mediated epithelial remodeling involving the small GTPase Rab11 and localized extracellular matrix degradation. These are disrupted in Gli-deficient embryos. This work provides a new mechanistic framework for TE morphogenesis and informs the cellular basis of human TEDs.

Esophageal Organoids from Human Pluripotent Stem Cells Delineate Sox2 Functions during Esophageal Specification.

Tracheal and esophageal disorders are prevalent in humans and difficult to accurately model in mice. We therefore established a three-dimensional organoid model of esophageal development through directed differentiation of human pluripotent stem cells. Sequential manipulation of bone morphogenic protein (BMP), Wnt, and RA signaling pathways was required to pattern definitive endoderm into foregut, anterior foregut (AFG), and dorsal AFG spheroids. Dorsal AFG spheroids grown in a 3D matrix formed human esophageal organoids (HEOs), and HEO cells could be transitioned into two-dimensional cultures and grown as esophageal organotypic rafts. In both configurations, esophageal tissues had proliferative basal progenitors and a differentiated stratified squamous epithelium. Using HEO cultures to model human esophageal birth defects, we identified that Sox2 promotes esophageal specification in part through repressing Wnt signaling in dorsal AFG and promoting survival. Consistently, Sox2 ablation in mice causes esophageal agenesis. Thus, HEOs present a powerful platform for modeling human pathologies and tissue engineering.