Figure 7
From: Distal spinal nerve development and divergence of avian groups
Diapsid spinal nerve development. (A-C) Alligator (Alligator mississippiensis) embryo spinal nerve development. (A) Stage 13 alligator embryo, wholemount, co-stained for neural tissue (Tuj 1, red) and myotome (MF20, green) (tail curved to the right; tail tip at the bottom right). Neural development is observed at the left, proximal side of the curve, but lacking at the right, distal end of the tail; white arrowhead denotes posteriormost level of neural crest, out of view). (B) Stage 20 alligator embryo, wholemount, stained for neural tissue with Tuj 1 antibody. The spinal cord extends to the end of the tail, but spinal nerve branches terminate significantly before the tail terminus. (C) Stage 23 alligator embryo cryosection, co-stained for neural tissue (Tuj 1) and muscle tissue (MF20). The most distal DRG was observed between the 6th and 7th vertebrae from the end of the tail, consistent with earlier stages. (D,E) Stage 10 anole (Anolis sagrei) wholemount embryo. (D) Embryo tail co-stained for intervertebral discs (Col2, red; noted by asterisks) and neural tissue (Tuj 1, green). (E) Same embryo tail as in D, showing only Tuj 1-specific 488 nm fluorescence. The most distal DRG is observed between the 6th and 7th most distal prevertebrae, similar to alligator. (F) Cladogram of the diapsids examined in this study, showing emu as the only tested diapsid with DRG formation extending to the end of the tail. (G) Diagram comparing dorsal views of the diapsids examined in this study. Chicken, quail, and rock dove lack spinal nerve development in their distal tails, as do alligator and Anolis. Emu is unique, with DRGs and eventual spinal nerves forming to the tail terminus. Light blue elements: pygostyle-specific; dark blue: free vertebrae; yellow: DRGs; red: spinal nerves.
