Hindgut epithelium regulates enteric ganglion size and patterning. Chick-quail chimeras were generated by recombining E5 quail hindgut mesenchyme (HGmes) and E6 chick hindgut epithelium (HGep) (A-D; n=11) or E9 chick bursa epithelium (BFep) (E-H; n=11). Recombinants were implanted into E3 chick coelom for 9 days. QCPN immunostaining confirms that the mesenchyme is quail derived (A,E), while 8F3 (B,F) immunostaining reveals the chick origin of the epithelium, enteric ganglia and blood vessels (B, arrowheads). When gut epithelium is replaced by bursa epithelium, enteric ganglia are larger and closer to the epithelium (F,G) than in control recombinations (B,C). This was confirmed quantitatively (I,J). The muscularis propria also appears thickened in bursa epithelium recombinations (H), confirmed by quantitative analysis showing increased thickness of the gut wall (K) and muscularis propria (L), the latter comprising a greater proportion of the wall than in controls (M). Muscularis mucosae appears closer to the epithelium in bursa recombinants (H) than in the control (D, the dotted line marks epithelial basement membrane). ep, epithelium; mp, myenteric plexus; smp, submucosal plexus; SMA, alpha-smooth muscle actin. *P<0.05, **P<0.01, ***P<0.001.