The enteric nervous system arises mainly from vagal and sacral neural crest cells that colonise the gut between 9.5 and 14 days of development in mice. Using the Cre-LoxP system, we removed ␤1 integrins in the neural crest cells when they emerge from the neural tube. ␤1-null enteric neural crest cells fail to colonise the gut completely, leading to an aganglionosis of the descending colon, which resembles the human Hirschsprung's disease. Moreover, ␤1-null enteric neural crest cells form abnormal aggregates in the gut wall, leading to a severe alteration of the ganglia network organisation. Organotypic cultures of gut explants reveal that ␤1-null enteric neural crest cells show impaired adhesion on extracellular matrix and enhanced intercellular adhesion properties. They display migration defects in collagen gels and gut tissue environments. We also provide evidence that ␤1 integrins are required for the villi innervation in the small intestine. Our findings highlight the crucial roles played by ␤1 integrins at various steps of enteric nervous system development.

Integrins are the major adhesive receptors for extracellular matrix and have various roles in development. To determine their role in cell migration, the gene encoding the β1 integrin subunit (Itgb1) was conditionally deleted in mouse neural crest cells just after their emigration from the neural tube. We previously identified a major defect in gut colonisation by conditional Itgb1-null enteric neural crest cells (ENCCs) resulting from their impaired migratory abilities and enhanced aggregation properties. Here, we show that the migration defect occurs primarily during the invasion of the caecum, when Itgb1-null ENCCs stop their normal progression before invading the caecum and proximal hindgut by becoming abnormally aggregated. We found that the caecum and proximal hindgut express high levels of fibronectin and tenascin-C, two well-known ligands of integrins. In vitro, tenascin-C and fibronectin have opposite effects on ENCCs, with tenascin-C decreasing migration and adhesion and fibronectin strongly promoting them. Itgb1-null ENCCs exhibited an enhanced response to the inhibitory effect of tenascin-C, whereas they were insensitive to the stimulatory effect of fibronectin. These findings suggest that β1 integrins are required to overcome the tenascin-C-mediated inhibition of migration within the caecum and proximal hindgut and to enhance fibronectin-dependent migration in these regions.

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