Kinesin family member 7 : dependent hedgehog pathway in development of the enteric nervous system

Abstract

The enteric nervous system (ENS) encompasses interconnecting ganglion that is residing in the myenteric and submucosal layers of the gut and distributing along the entire length of the gut. ENS regulates not only the bowel movement but also gastrointestinal physiology to maintain the homeostasis of the bowel. ENS is primarily derived from the vagal neural crest cells, and these NCCs are called enteric neural crest cells (ENCCs) once they reach the foregut. ENCCs undergo extensive proliferation and differentiation to give rise to different subtypes of nerve cells, while they are migrating rostro-caudally to populate the entire gut gradually. Improper development of ENCCs leads to malformation of ENS, affecting the bowel function.

Hedgehog (Hh) signaling pathway is critical for both gut morphogenesis and the development of ENS. In vertebrates, the output of Hh pathway is determined by the activation of Gli proteins. Kinesin family member 7 (Kif7) is a cilia-associated motor protein, which maintains the architecture of primary cilium and mediates cilium trafficking of Gli protein to confer a full activation of Hh signal in mammalian cells. Mutations in KIF7 are frequently associated with various ciliopathies. Importantly, a significant portion of the ciliopathy patients also has gastrointestinal motility disorders, suggesting that their ENS may also be affected. However, the role of Kif7 in the development of ENS remains mostly unknown. Kif7 null mice die before birth, precluding the analysis of the function of Kif7 in ENS development at the later stage. Therefore, in this study, mice with NCC-specific deletion of Kif7 (Kif7 cKO) were used to address how cilia dysfunction may interfere with the development of ENS.

Kif7 mutant mice displayed growth retardation with a reduced survival rate, and that would be the result of the uncoordinated colonic motility. A significant reduction in the number of neuronal progenitors and erratic migratory behaviour of ENCCs were observed; these abnormalities resulted in a decrease in the number of inhibitory subtype neurons and disorganization of the enteric ganglion. Moreover, Hedgehog signaling was aberrantly activated in Kif7 -/- ENCCs via upregulation of Gli2, leading to the downregulation of genes involved in early ENCC development. RNA-sequencing data and machine-learning tools revealed that the proportion of neuronal precursors was dramatically diminished in Kif7 -/- ENCCs. Furthermore, a reduced Gli2 dosage rescued the neuronal lineage differentiation defects of Kif7 cKO. All these data indicate that Kif7 negatively regulates the Hedgehog pathway to prevent aberrant upregulation of Gli2 and thereby controls the neuronal lineage differentiation and migration pattern of ENCCs in the developing ENS.