Anat Embryol (2004) 208:33–41 DOI 10.1007/s00429-003-0371-0 ORIGINAL ARTICLE M. Fu · P. K. H. Tam · M. H. Sham · V. C. H. Lui Embryonic development of the ganglion plexuses and the concentric layer structure of human gut: a topographical study Accepted: 11 November 2003 / Published online: 27 February 2004 # Springer-Verlag 2004 Abstract In this study, we performed a detailed topo- graphical study on the development of ganglion plexuses and the smooth muscle layers of human embryonic and fetal gut. Neuron and glia differentiation was investigated with anti-PGP9.5 and anti-S100 antibodies respectively. The differentiation of smooth muscle and interstitial cells of Cajal (ICC) was studied with anti-smooth muscle a- actin and anti-C-Kit antibodies respectively. By week 7, rostro-caudal neural crest cell (NCC) colonization of the gut was complete, and NCCs have differentiated into neurons and glia. At the foregut, neurons and glia were aggregated into ganglion plexus in the myenteric region, and the longitudinal and circular muscle layers have started to differentiate; however, neurons and glia were not found in the submucosa. At the hindgut, neurons and glia were dispersed within the mesenchyme. Myenteric plexus, longitudinal and circular muscle layers formed along the entire gut by week 9. Scattered and individual neurons and glia, and small ganglion plexuses were detected in the foregut and midgut submucosa by week 12. Ganglion plexus was not seen in the hindgut submu- cosa until week 14. Muscularis mucosae was formed at the foregut and midgut by week 12 but was only discernible at the hindgut 2 weeks later. As the gut wall developed, ganglion plexus increased in size with more neurons and glia, and the formation of intra-plexus nerve fascicle. ICCs were localized in the ganglion plexus as early as week 7. ICCs were initially dispersed in the plexus and were preferentially localized at the periphery of the plexus by week 20. The specification of the annular layers of human embryonic and fetal gut follows a strict spatio-temporal pattern in a rostro-caudal and centripetal manner suggesting that interaction between (1) homotypic and/or heterotypic cells; and (2) cells and the extracellular matrix is critical for the embryonic development of the gut mesenchyme and the enteric nervous system. Keywords Enteric nervous system · Neural crest · Smooth muscle · Human embryos · Gastrointestinal tract Introduction Gut is formed as a closed primitive tube from the association of the endoderm with the splanchnic mesen- chyme at the early embryonic period. Interactions be- tween the endoderm and the mesenchyme further specify the primitive gut tube into concentric layers of morpho- logical and functionally distinct cell types (see Roberts 2000; Rawdon 2001). The endoderm gives rise to the mucosa lining the entire gut lumen. The mesenchyme differentiates into circular and longitudinal muscle layers, the submucosa, and the muscularis mucosae in concentric layers from the serosal to the luminal side of the gut wall. Concomitant with the specialization of different annular layers of the gut wall, neural crest cells (NCCs) that originate from the neuroepithelium of the neural tube differentiate into neurons and glia of the enteric nervous system (ENS). Neurons and glia coalesce into ganglion plexuses in the myenteric region between the longitudinal and circular muscle layers, and at the submucosa on the luminal side of the circular muscle. The development of the annular layers of the gut and the ENS is complex, and dependent on the interactions between (1) homotypic and/ or heterotypic cells; and (2) cells and the extracellular matrix (ECM). Abnormal interactions can lead to devel- opmental anomaly of the ENS in patients with Hirsch- sprung’s disease (HSCR) which is characterized by the deficiency of ganglion cells (aganglionosis) in the myen- teric region of the distal colon (Newgreen and Young 2002a, 2002b). Vagal NCCs that emigrate from the level of the neural tube adjacent to somites 1 to 5 enter the foregut, migrate, M. Fu · P. K. H. Tam · V. C. H. Lui ( ) ) Department of Surgery, University of Hong Kong Medical Center, Queen Mary Hospital, Hong Kong, SAR China e-mail: vchlui@hkucc.hku.hk Tel.: . +852-28199607 Fax: +852-28199621 M. H. Sham Department of Biochemistry, University of Hong Kong, Hong Kong, SAR China