The sympathoadrenal lineage in avian embryos. I. Adrenal chromaffin cells lose neuronal traits during embryogenesis

Cells of the sympathoadrenal lineage, including sympathetic neurons, adrenal chromaffin cells (pheochromocytes), and small intensely fluorescent (SIF) cells, arise from the neural crest. We have used antisera against catecholamine biosynthesis enzymes in conjunction with the monoclonal antibody A2B5 and an antiserum against the 160-kDa neurofilament (NF) protein, as markers of neuronal differentiation, to characterize the ontogeny of the sympathoadrenal lineage in quail embryos. The precursors of sympathetic neurons and pheochromocytes, present in the primary sympathetic chains, express neuronal traits and tyrosine hydroxylase (TH) early in development. The precursors that enter the developing adrenal gland from the primary sympathetic chain lose neuronal traits and later express the enzyme phenylethanolamine N-methyltransferase (PNMT). To TH⁺ cells differentiate in cultures of early (E7) embryonic adrenal glands after all A2B5⁺ cells have been immunoablated. When transplanted onto the neural crest migratory pathway, cells present in older (E13) embryonic adrenal glands can give rise to NF⁺ cells in the sympathetic ganglia. We conclude that both sympathetic neurons and pheochromocytes in avian embryos arise from a common bipotential precursor that initially expresses neuronal traits.