Fig. 2.

Tubb3⁺cells at the periphery of the chicken carotid body at E7.5–8.5 express the neuron-specific RNA-binding proteins Elavl3/Elavl4 (HuC/D) and multiple ‘sympathoadrenal’ genes. All panels show transverse sections of chicken embryos at E7.5–E8.5 at the level of the carotid body and nodose ganglion. Dotted lines indicate the estimated periphery of the carotid body. Insets are magnified from the regions indicated by boxes. Panels A and C-H¹ show sections from the same E7.5 embryo; panel B shows a section from a different E7.5 embryo. At least 3 embryos were analysed per gene at E7.5–E9.5 (some of the embryos analysed for expression of the positive control Phox2b had received unilateral grafts of hindbrain neural folds to label neural crest-derived cells; the data shown are from an unmanipulated embryo). (A) At E7.5, the developing carotid body can be identified as a bulge from the wall of the third pharyngeal arch artery (future carotid artery), between the nodose ganglion and the parathyroid gland, surrounded by Tubb3⁺ neurites (green). Tubb3⁺ cells (green) at the carotid body periphery (shown at higher-power in the inset) are immunoreactive for the neuron-specific RNA-binding proteins Elavl3/Elavl4⁺ (Elavl3/4; magenta). (B) At E7.5, a few of the Elavl3/4⁺ neurons at the carotid body periphery express serotonin (5-HT; green, arrowheads). (C-J¹) Neurons at the carotid body periphery express Phox2b (C), Ret (D), Hif2a (E,E¹; expression only seen in a subset of neurons, e.g. compare Hif2a and Elavl3/4 distribution in main panels E,E¹; intense signal marks endothelial cells), Hand2 (F,F¹), Gata2 (G,G¹; also expressed by non-neuronal cells in the carotid body core - arrows in second [bottom] inset highlight examples), Hif1a (H,H¹; expression only seen in a subset of neurons, e.g. compare Hif1a and Elavl3/4 distribution in first [top] inset in panels H,H¹) and Sox11 (I,I¹). The neural crest-derived peripheral neuronal precursor/glial marker Sox10 was also expressed in non-neuronal cells associated with the neurons at the periphery of the carotid body (Fig. 2J,J¹). [If shown in serial section order, this section would be located between panels F (Hand2) and G (Gata2).] 5-HT, serotonin; cb, carotid body; ng, nodose ganglion; paa3, third pharyngeal arch artery; pth, parathyroid gland; v, vein. Scale-bar: 50 µm.