Environmentally regulated expression of soluble extracellular proteins of sympathetic neurons.

Sympathetic neurons in dissociated cell culture release 16-18 soluble proteins into the medium, which appear to be distinct from the cell membrane glycoproteins. The released proteins are major cellular products, comprising 2-3% of the newly synthesized protein. They turn over with a half-life of approximately 9 h. Their release is spontaneous and does not correlate with the release of neurotransmitter. Release occurs from distal axon regions and possibly from cell bodies and dendrites as well. Sympathetic neurons are adrenergic in culture, but become cholinergic if grown in medium conditioned by certain types of non-neuronal cells but not others (Patterson, P. H. (1978) Annu. Rev. Neurosci. 1, 1-17). Those conditioned media which induce cholinergic development also dramatically alter the expression of 4 of the 18 released proteins, suggesting a correlation between the expression of these secreted proteins and neurotransmitter choice. Such extracellular proteins may play a part in intercellular communication during the development of the nervous system.