Figure 5. NECs are endoderm-derived, like PNECs.

(a–d) In Sox17^2A-iCre/+;R26^R/+ mice, all endoderm-derived lineages, as well as vascular endothelial cells and the hematopoietic system, constitutively express β-galactosidase (Engert et al., 2009). Serial sections of an E19.5 Sox17^2A-iCre/+;R26^R/+ mouse lung show that X-gal labels PNECs (a,b; black arrowheads), whose identity is confirmed by serotonin expression (c,d; white arrowheads). The serotonin-positive cells are clearly all in the epithelium, which is entirely X-gal-positive, although there is some variation in staining level from cell to cell. (e–e’’’) A high-power view of a cluster of Ascl1-expressing PNECs in a section of an E16.5 Sox17^2A-iCre/+;R26R^tdTomato mouse lung, in which endoderm-derived lineages express tdTomato. Only the occasional PNEC is serotonin-positive at this stage. The Ascl1-expressing PNECs are tdTomato-positive, i.e., endoderm-derived. (f–i’’) An endodermal contribution to putative NECs in Xenopus was investigated by performing focal DiI injections into the anterior endoderm at stage 14 (f), as described in Chalmers and Slack (2000). At stage 45, DiI labels the endoderm lining the orobranchial cavity (g,h), and serotonergic cells (putative NECs, arrowheads) in the orobranchial epithelium (i–i’’). (j–l) In Tg(sox17:creER^T2;cmlc2:DsRed);Tg(-3.5ubi:loxP-GFP-loxP-mCherry) zebrafish, the endoderm is labeled with mCherry and (m–n’’) NECs in the gill filaments are mCherry-positive (arrowheads). 5-HT, serotonin; A, anterior; a, airway; Bac, branchial arch cartilage; Gf, gill filament; Obc, orobranchial cavity; P, posterior; tdTom, tdTomato. Scale-bars: 50 μm in a,c,g,k,m; 25 μm in b,d,h,i,l,n; 20 μm in e.

DOI: http://dx.doi.org/10.7554/eLife.21231.012

Figure 5—figure supplement 1. The neural crest does not contribute to amniote PNECs.

(a–b’) Transverse sections through the lungs of Wnt1-Cre;R26R-YFP mouse embryos, in which neural crest cells are permanently labeled with YFP (Danielian et al., 1998; Srinivas et al., 2001), at E14.5 (a,a’) and E18.5 (b,b’). PNECs (Ascl1 [Mash1]-positive cells in the airway epithelium; Ito et al., 2000) are unlabeled, whether solitary or clustered (white dotted line in b,b’), although nearby neural crest-derived cells in the subjacent mesenchyme (yellow arrowheads) are YFP-positive, including putative Schwann cells on a nerve innervating the PNECs (yellow arrowheads in b,b’) and an intrinsic pulmonary ganglion (white arrow in b,b’), as expected (Freem et al., 2010). (In a,a’, the two fainter, out-of-focus green spots within the epithelium are background artefacts from the anti-GFP immunostaining.) (c) The vagal neural crest was labeled in the chicken using GFP-transgenic to wild-type neural tube grafts at E1.5 (schematic modified from Le Douarin, 2004). (d–e’) Transverse sections through the lungs of grafted embryos at E14.5 (d,d’) and E16.5 (e,e’). PNECs (serotonergic cells in the lung airway epithelium) are unlabeled (white arrowheads), while putative Schwann cells (elongated cells, yellow arrowheads) and a nearby intrinsic pulmonary ganglion (white arrow) are GFP-positive, as expected (Burns and Delalande, 2005). 5-HT, serotonin; a, airway; Ot, otic vesicle; s, somite. Scale-bars: 10 μm in a; 50 μm in b,d,e.

DOI: http://dx.doi.org/10.7554/eLife.21231.013