Mesenteric Neural Crest Cells Are The Embryological Basis Of Skip Segment Hirschsprung’s Disease

The enteric nervous system（ENS）,the intrinsic nervous system of the gut that regulates the functions of the gastrointestinal（GI）tract.ENS is mostly derived from vagal neural crest cells（v NCCs）,which arise at the level of somites 1–7,invade the foregut,and rostrocaudally colonize the gut to give rise to neurons and glia.HSCR occurs in 1/5000 live births,which is characterized by aganglionosis in variable lengths of the distal intestine and is caused by the incomplete colonization of the gut by v NCCs.However,the occurrence of skip segment Hirschsprung’s disease（SSHD）,a rare variant of HSCR involving a“skip area”of ganglion cell containing intestine within an otherwise aganglionic intestine,contradicts the current consensus about the pathogenesis of HSCR,and lacks a clear embryological basis.Therefore,the characterization of the embryonic origin of the segmental ENS in SSHD will not only further our understanding of ENS development,but will also support the development of potential HSCR treatments.The mesentery,according to its structure,function,and role in disease,which surrounds the entire GI tract to provide a conduit for extrinsic innervation and blood vessels to the intestine,has recently been classified as a new organ.Previous studies have identified NCCs within the mesentery of HSCR murine models.What’s the function of NCCs in the mesentery?The objectives of this project are:（1）Searching for SSHD cases by preparing biopsies from HSCR patients;（2）Identifying the origin of the ganglionic segments in SSHD during embryonic stage;（3）Providing novel insights into the development of the ENS.We identified two new cases of SSHD from 183 HSCR patients.The development of the ENS was traced using different transgenic mouse lines.v NCCs separated into two populations:enteric NCCs（e NCCs）invaded the foregut to migrate along the gut,whereas mesenteric NCCs（m NCCs）proceeded to migrate along the mesentery.m NCCs not only give rise to neurons and glia within the mesentery,but also continuously contributed to the ENS.Finally we want to know whether m NCCs could migrate into the e NCC-absent gut via tracing m NCCs in HSCR mouse embryos.In contrast to the high incidence of SSHD in Wnt1^Cre;R26^{td Tom};Ednrb^-/-mice,no enteric neurons were detected within the aganglionic Ret^-/-intestines.EDN3/EDNRB,but not GDNF/RET,signaling pathway plays roles in the migration and differentiation of m NCCs.In summary,m NCCs,a subset of v NCCs that migrate into the gut via the mesentery to give rise to enteric neurons and glia,could provide an embryologic explanation for SSHD.These findings lead to novel insights into the development of the enteric nervous system.