iv12 Gut 2000;(Suppl IV)47:iv12–iv14 Embryology and development of the enteric Gut: first published as 10.1136/gut.47.suppl_4.iv12 on 1 December 2000. Downloaded from nervous system H M Young, C J Hearn, D F Newgreen Origin and migration of neural crest derived cells in the gut The neurones and glial cells of the enteric nervous system (ENS) are derived from the Neural crest Ectoderm neural crest (fig 1). While they are migrating, neural crest cells are morphologically indistin- guishable from mesenchymal cells through which they migrate, and thus a variety of experimental approaches have been used to examine colonisation of the gut by neural crest derived cells. Yntema and Hammond (1954)1 ablated defined rostrocaudal regions of the Notochord neural crest of chicken embryos and examined the eVects of the ablations on the ENS. They found that ablation of vagal level (somites 1–7) neural crest resulted in absence of enteric neu- Ectoderm rones throughout the gut, and therefore concluded that vagal level neural crest is the sole source of the ENS. Following transplanta- tion of vagal level neural tubes from quail embryos into chicken embryos, in which the Somite equivalent region of neural tube had been removed, quail cells were found throughout the gut of the chimera. This also supported the Neural tube idea that vagal level neural crest cells give rise to enteric neurones throughout the gut.2 How- ever, when the quail neural tube was trans- planted into the sacral level (caudal to somite 28) of chicken embryos, quail cells were found Figure 1 Development of the enteric nervous system from http://gut.bmj.com/ within the myenteric plexus of the hindgut of the neural crest. the chimeras, indicating that sacral level neural GFRá1,11 12 and endothelin receptor B,13 and the crest cells also contribute to the ENS in the transcription factors MASH1,14 Phox2a,15 hindgut.2 Since then, the contribution of sacral Phox2b,16 and SOX10.17 18 We have examined level neural crest to the ENS in the hindgut has colonisation of the embryonic mouse gut using been controversial. Studies in which explants antibodies to Phox2b, p75, and RET. Most of of chicken gut were removed and grown on the the above markers of neural crest derived cells on September 30, 2021 by guest. Protected copyright. chorioallantoic membrane of host embryos,3 or within the gut are downregulated during devel- in which the midgut of chicken embryos was opment. However, expression of Phox2b is transected prior to the arrival of vagal neural maintained in adult mice and all diVerentiated crest cells,4 suggested that either the vagal neu- enteric neurones show Phox2b immunoreactiv- ral crest cells are the sole source of enteric neu- ity. Thus it would seem likely that Phox2b is rones throughout the gut or that sacral level expressed by all enteric neurone precursors. Department of neural crest cells do not give rise to enteric Double label studies revealed that Phox2b, p75, Anatomy and Cell neurones in the hindgut unless the vagal level and RET are expressed by identical populations Biology, University of neural crest cells are present. In contrast, stud- of neural crest derived cells in embryonic day Melbourne, Parkville, ies in which pre-migratory cells had been 12–14 (E12–E14) mice, and it appears likely 3052, Victoria, labelled with a lipophilic dye or retroviruses Australia that these three molecules are expressed by all H Young have shown that some cells that populate the migratory, or immediate post-migratory, neural hindgut arise from sacral level neural crest, and crest cells in the gut. We mapped the appearance The Murdoch these cells colonise the hindgut well before the of Phox2b, p75, and RET immunoreactive cells Institute, Royal arrival of vagal level neural crest cells.56 in the embryonic mouse gut.19 At E9.5-E10, Children’s Hospital, While they are migrating through the gut, labelled cells were present only in the stomach, Parkville, neural crest derived cells do not express a 3052,Victoria, and during subsequent development Phox2b, Australia neuronal or glial cell phenotype. Recently, a p75, and RET positive cells appeared as a unidi- C J Hearn number of markers of neural crest derived cells rectional, rostral to caudal wave along the D F Newgreen within the mouse gut have been identified, and gastrointestinal tract; the entire gut was colo- thus colonisation of the mouse gut by neural Correspondence to: crest cells can be observed directly. These mark- Abbreviations used in this paper: ENS, enteric Dr H Young. 7 [email protected]. ers include the transgene DBH-nlacZ, receptors nervous system; GDNF, glial derived neurotrophic edu.au for neurotrophic factors including p75,89RET,10 factor. www.gutjnl.com Embryology and development of the enteric nervous system iv13 Recently, an important study was reported Gut: first published as 10.1136/gut.47.suppl_4.iv12 on 1 December 2000. Downloaded from Midgut Neural crest 23 E10.5 derived cells by Burns and Le Douarin (1998) in which present they repeated some of the experiments per- Anal 2 end formed by Le Douarin and Teillet in the 1970s Foregut Hindgut where sacral level neural tubes of quail E11.5 embryos were transplanted into chicken em- Caecal bryos in which the equivalent region of neural swelling Midgut tube had been removed. They extended the Hindgut original studies in two crucial ways. Firstly, they examined whether the sacral level neural Anal crest cells (that is, quail cells) that entered the end hindgut diVerentiated into neurones (rather Caecal than glia or some other cell type), and secondly, swelling E12.5 they examined when the sacral neural crest cells enter the hindgut. The sacral level neural Anal crest cells that entered the hindgut were indeed end found to diVerentiate into neurones. Thus Hindgut there now appears to be no doubt that sacral level neural crest cells give rise to some enteric neurones in the hindgut of birds. The second E14.5 To caecum important observation made in the study by Anal 23 end Burns and Le Douarin was that the sacral level neural crest cells did not appear to enter Hindgut the hindgut until around the time that the vagal Figure 2 Colonisation of the gut by vagal level neural level neural crest cells arrived. If sacral level crest cells. neural crest cells do not enter the hindgut of embryonic mice until the vagal neural crest cells have colonised the hindgut, then we would nised by E14 (fig 2). This wave of migrating cells not have been able to detect them with the represents colonisation of the gut by vagal level techniques that we used.19 To examine whether neural crest cells and is very similar to that cells within the pelvic plexus can give rise to described using the transgene DBH-nlacZ as a 7 enteric neurones in the hindgut of embryonic marker of neural crest derived cells. To confirm mice, we have recently removed segments of the location of enteric neurone precursors hindgut prior to the arrival of vagal neural crest deduced from the use of Phox2b, RET, and p75 cells and grown them in organ culture either antisera, explants from spatiotemporally defined alone or with attached dorsal tissue containing regions of embryonic mouse gut were removed the pelvic plexus primordium. No neurones and grown either under the kidney capsule of were observed in the explants of hindgut alone. 20 adult host mice or in organ culture under con- However, the appearance of neurones in the http://gut.bmj.com/ ditions in which the gut retains its tubular three explants of hindgut with attached pelvic plexus 21 dimensional structure. The explants were was variable. Some of the explants contained grown for 1–3 weeks and examined for the pres- no neurones whereas other explants contained ence of enteric neurones. The location and a small number of ganglia. Thus it appears that sequence of appearance of enteric neurone pre- sacral level neural crest cells normally give rise cursors deduced from the explants were very to only a small number of enteric neurones in similar to those seen with Phox2b, RET, and the hindgut of embryonic mice or they require on September 30, 2021 by guest. Protected copyright. p75 antisera. These results are diYcult to recon- the presence of vagal neural crest cells before 6 cile with those of Serbedzija et al (1991) who significant migration into the hindgut or diVer- used DiI to label pre-migratory neural crest cells entiation of sacral neural crest cells into in embryonic mice, and reported that sacral neurones occurs. neural crest cells leave the neural tube between E9 and E9.5 and arrive in the hindgut approxi- Development of diVerent classes of mately 12 hours later. However, as the fate of enteric neurones DiI labelled cells could not be determined, it is During and following colonisation of the gut by possible that DiI labelled cells that migrated into neural crest cells, massive proliferation of neu- the hindgut were not precursors of the ENS. ral crest cells occurs, followed by diVerentia- In our study, no Phox2b, p75, or RET posi- tion into glial cells or into one of the many dif- tive cells were observed in the hindgut of ferent types of enteric neurones. Little is known embryonic mice prior to the arrival of the vagal of the factors that direct an individual neural neural crest cells.19 However, from as early as crest cell along a glial or neuronal lineage, or E10, groups of labelled cells were observed along the lineages leading to diVerent neuronal outside of the hindgut in the primordium of the classes.