Resolving the heterogeneity of diaphragmatic mesenchyme: a novel mouse model of congenital diaphragmatic hernia.

Louise Cleal,Martin Lee,Nick Hastie,You-Ying Chau,Sophie L Mchaffie,Ofelia M Martínez-Estrada

doi:10.1242/dmm.046797

Abstract

ABSTRACTCongenital diaphragmatic hernia (CDH) is a relatively common developmental defect with considerable mortality and morbidity. Formation of the diaphragm is a complex process that involves several cell types, each with different developmental origins. Owing to this complexity, the aetiology of CDH is not well understood. The pleuroperitoneal folds (PPFs) and the posthepatic mesenchymal plate (PHMP) are transient structures that are essential during diaphragm development. Using several mouse models, including lineage tracing, we demonstrate the heterogeneous nature of the cells that make up the PPFs. The conditional deletion of Wilms tumor 1 homolog (Wt1) in the non-muscle mesenchyme of the PPFs results in CDH. We show that the fusion of the PPFs and the PHMP to form a continuous band of tissue involves movements of cells from both sources. The PPFs of mutant mice fail to fuse with the PHMP and exhibit increased RALDH2 (also known as ALDH1A2) expression. However, no changes in the expression of genes (including Snai1, Snai2, Cdh1 and Vim) implicated in epithelial-to-mesenchymal transition are observed. Additionally, the mutant PPFs lack migrating myoblasts and muscle connective tissue fibroblasts (TCF4+/GATA4+), suggesting possible interactions between these cell types. Our study demonstrates the importance of the non-muscle mesenchyme in development of the diaphragm.

Highlights

Congenital diaphragmatic hernia (CDH) is a severe developmental defect that affects approximately one in 3000 live births (Greer, 2013) and can have devastating clinical outcomes
Diaphragm development is disrupted in Prx1Cre/+;Wt1loxp/loxp embryos In our model, male Prx1Cre/+;Wt1loxp/+ mice were crossed with female Wt1loxp/loxp mice to inactivate Wilms tumor 1 homolog (Wt1) conditionally using Prx1Cre
This suggests that in addition to the muscle connective tissue fibroblasts (Merrell et al, 2015), Prx1-Cre-expressing cells give rise to another cell type in the developing diaphragm, with mesenchymal properties. We show that these Wilms tumor 1 homolog (WT1)-expressing pleuroperitoneal folds (PPFs) cells have the ability to expand and form a continuous band of cells with posthepatic mesenchymal plate (PHMP), sealing off the thoracic and peritoneal cavities

Summary

Introduction

Congenital diaphragmatic hernia (CDH) is a severe developmental defect that affects approximately one in 3000 live births (Greer, 2013) and can have devastating clinical outcomes. Several embryonic structures are implicated in diaphragm development: the pleuroperitoneal folds (PPFs), the septum transversum (ST), the posthepatic mesenchymal plate (PHMP) and the somites (Carmona et al, 2016; Merrell and Kardon, 2013; Sefton et al, 2018). The ST is a thin layer of mesodermal cells overlying the liver and is formed at approximately embryonic day (E) 8.5 in the mouse. This is followed by the formation of the PPFs, which develop at E10.5-E12.5. Myoblasts migrate from the somites, leading to the muscularisation of this membrane to form the mature diaphragm

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Conclusion