Loss of Kinesin family member 7 (Kif7) in enteric neural crest interrupts the gangliogenesis of enteric nervous system.

Abstract

Enteric nervous system (ENS) is composed of interconnected enteric ganglia, which are derived from a small population of progenitors, namely enteric neural crest cells (ENCCs). During development, ENCCs undergo extensive proliferation and differentiation, precisely coordinating with a long migration journey to fully colonize the entire gut and form a functional nervous system. Defects in any of these developmental processes may result in Hirschsprung (HSCR) disease or other gut motility disorders. Our group has previously demonstrated that Hedgehog (Hh) signaling is indispensable for ENS development. Here, we focused on another key Hh component, Kinesin family member 7 (Kif7), which is a motor protein regulating Hh signaling transduction in cilium. To delineate the roles of Kif7 in ENS development, we conditionally knocked out Kif7 in NCCs. We found that Kif7KO mice exhibit retarded growth with poor survival rate. In particular, the growth retardation was closely associated with the severity of the gut defects. Colonic migrating motor complexes (CMMCs) analysis further suggested that colonic motility of Kif7KO mice is interrupted, leading to extended intestinal transit time and growth retardation. We then investigated how Kif7 may affect ENS development. Deletion of Kif7 consistently disrupted both neuronal differentiation and proliferation of ENCCs at early developmental stages, accompanied by disorganization of nerve network in embryonic gut. Subsequent immunohistochemistry analyses with various glial and neuronal markers further revealed the presence of giant myenteric ganglion in mutant adult gut. In addition, a dramatic reduction in nNOS+ inhibitory neurons in the myenteric plexuses of distal small intestine and colon, deficiency of submucosal plexuses and reduced neuronal/glial projections in intestinal villi were observed in the mutant mice. All these data suggested that Kif7 regulates the formations of both myenteric and submucosal plexuses, probably also neuronal subtypes. Aberrant ganglion formation and loss of nNOS+ neurons may account for the gut motility defects in the mutants. To further delineate the underlying molecular mechanism, microarray analysis was performed with control and Kif7KO ENCCs, where genes regulating the proliferation and differentiation of progenitor population (Erbb3, Sox2 and Sox10) were found down-regulated in Kif7KO ENCCs, implying that loss of Kif7 interrupts the regulatory networks of these molecules and interferes the development of ENS.