Preprotachykinin gene expression in the human basal ganglia: characterization of mRNAs and pre-mRNAs produced by alternate RNA splicing.

The nature and distribution of preprotachykinin (PPT, i.e. substance P/neurokinin A-encoding) gene expression in human basal ganglia was determined. Northern blot analysis visualized a single band of approximately 1300 bases, confirming the postmortem stability of PPT mRNA. Gross anatomical analysis indicated that PPT gene expression was relatively evenly distributed throughout the human caudate and putamen, but absent in the globus pallidus and substantia nigra. Nuclease protection analysis of these tissues established that human PPT mRNA consisted of approximately 80-85% beta-PPT (exon 1-7 derived) mRNA and 15-20% gamma-PPT (minus exon 4), with no alpha-PPT (minus exon 6) mRNA detected; these data contrast with the proportions of PPT mRNAs seen in non-human species. The incompletely spliced PPT RNA species detected in basal ganglia accounted for approximately 8% of total human PPT RNA and suggested a fixed order of exon splicing. Since various PPT mRNAs encode different combinations of tachykinin peptides with distinct biological activities, the markedly different proportions of PPT mRNAs seen in human basal ganglia compared to non-human tissues may be of physiological significance.