Phox2b expression is absent from gill and lung epithelia.
(a–f’) In wild-type zebrafish at 5- and 7-dpf, Phox2b is expressed by a subset of cells in the hindbrain (b,e), but not by gill NECs or putative NECs in the orobranchial epithelium (arrowheads; c–c',f–f'). (g–j’) At E16 (g–h') and E18 (i–j') in the sea lamprey, Phox2 expression is seen in the neural tube, the epibranchial (petrosal and nodose) ganglia (identified in section by the neuronal marker Elavl3/4), and in patches of ectoderm and subjacent mesenchyme ventral to the epibranchial ganglia (arrowheads). However, Phox2 expression is absent from the gill epithelium, where putative NECS would be located. Dotted lines in panels g and i indicate the section plane in h and j. (k–l') In a section of an E16.5 Sox172A-iCre/+;R26tdTomatomouse lung, Phox2b expression is seen in intrinsic pulmonary ganglia (arrows), but not in Ascl1/serotonin-positive PNECs located in the lung airway epithelium (dotted lines outline clusters of PNECs). (m,m’) In a section of an E13.5 chicken lung, Phox2b expression is seen in an intrinsic pulmonary ganglion (arrow), but not in serotonin-positive PNECs scattered in the lung airway epithelium (arrowheads). Insets show higher power views. a, airway; Ba, branchial arch; Bac, branchial arch cartilage; G, gill; Gf, gill filament; N, nodose ganglion; Nt, neural tube; Obc, orobranchial cavity; Oc, oral cavity; P, petrosal ganglion. Scale bars: 50 μm in a,d,h,j,m; 25 μm in b,c,e,f,k,l.