Diffusible proteins regulate neural development at a variety ofstages. Using a novel neuronal culture assay, I have identified severalcytokines that regulate the expression of neurotransmitters andneuropeptides in sympathetic neurons. These cytokines fall into twofamilies. The first group is termed the neuropoietic cytokines, whileincluding CDF/LIF, CNTF, OSM and GPA, induces expression of the sameset of neuropeptide mRNAs in cultured sympathetic neurons. These fourfactors not only exhibit similar biological activities; they also share apredicted secondary structure and bind to a signal-transducing receptorsubunit in common with IL-6 and IL-11. The latter two cytokines display aweaker activity in this assay. In addition, I find that several members ofthe TGF-β superfamily, activin A, BMP-2, and BMP-6, have a selectiveoverlap with the neuropoietic family in the spectrum of neuropeptidesthat these cytokines induce in sympathetic neurons. Different patterns ofneuropeptides induced by the TGF-β family members, however,demonstrate that the activities of these cytokines are distinct from those ofthe neuropoietic family. Another 30 cytokines are without detectable effectin this neuronal assay.
Activin A induces a set of neurotransmitters and neuropeptides thatis somewhat similar to the phenotype of sympathetic neurons innervatingsweat glands in rat footpads. In situ hybridization and RNase protectionwere carried out to test whether activins were involved in the phenotypictransition when sympathetic neurons contact sweat glands. I find thatactivin mRNA is present in both cholinergic and noradrenergic targets.Moreover, homogenates of footpads do not contain activin-like activity inthe neuronal assay in vitro. Taken together, these data do not supportactivins as the best candidates for the sweat gland factor.
Several novel factors that regulate neuropeptide expression exist inheart cell conditioned medium. I attempted to purify these factors incollaboration with Dr. Jane Talvenheimo. Our results suggest that thesefactors are sensitive to the storage conditions used. Several modificationsof purification strategy are discussed.
