Figure 5
From: Distal spinal nerve development and divergence of avian groups
Tail peripheral nervous system in the emu embryo and hatchling. (A) HH36 equivalent stage cryosection, sagittal view (distal to the left), co-stained for nervous tissue (Tuj1, red) and myotome/musculature (MF20, green). Unlike chicken, dove, and quail, DRGs (arrowheads) and sympathetic ganglia (arrows) form in the pygostyle, to the very distal end of the tail. (B) Neural crest derivatives in the emu tail at HH36. Top, diagram of sagittal view indicating the axial level of DRGs, shown below. DRGs shown in yellow, pygostyle-specific prevertebrae in light blue, and free prevertebrae in dark blue. Below, DRGs (sagittal views) stained with HNK (red), indicating neural crest derivative, and Islet 1/2 (green), indicating neural crest-derived sensory neuron differentiation. Islet-positive cells are only observed outside the pygostyle (light blue in diagram), suggesting that despite development of neural-crest-derived DRGs, there is a lack of sensory neuron differentiation within the pygostyle. (C) Emu hatchling. Top panel, diagram, coronal/dorsal view; the distalmost intervertebral discs are labeled 1–3, posterior to anterior; IVDs in green, DRGs in yellow, nerve roots and spinal nerves as indicated; the central red bar denotes the spina cord. At this stage, the transverse processes of the vertebrae have not yet mineralized, and their cartilages are contiguous with the IVDs. Bottom panel, nervous system structures for each IVD as noted (IVD 1 and 2 are within the pygostyle; IVD 3 is outside the pygostyle); coronal cryosections stained with Tuj + RT97 (red) and overlayed on 488 nm background. The emu pygostyle ___domain is estimated from1 and from the MOR 186 specimen. Abbreviations: DRG: dorsal root ganglia, IVD: intervertebral disc, sp: spinal.
