Simultaneous quantitation of substance P-encoding preprotachykinin alternatively spliced mRNAs and substance P receptor NK-1 mRNA by an RNase protection assay

Tachykinins form a family of peptides with neurotransmitter/neuromodulator function. Four tachykinins, substance P, neurokinin A, neuropeptide 7 and neuropeptide K, are encoded by the same PreProTachykinin (PPT) gene. Alternatively spliced mRNAs encode different combinations of these peptides (Brown, E.R, Harlan, R.E., Krause, J.E., Gonadal steroid regulation of substance P (SP) and SP-encoding mRNA in the rat anterior pituitary and hypothalamus, Endocrinology, 126 (1990) 330-340 [1]; Krause, J.E., Chirgwin, J.M., Carter, M.S., Xu, Z.S., Hershey, A.D., Three rat preprotachykinin mRNAs encode the neuropeptides substance P and neurokinin A, Proc. Natl. Acad. Sci. USA, 84 (1987) 881-885 [10]). The proportion of PPT mRNAs varies from tissue to tissue (Carter, M.S., Krause, J.E., Structure, expression, and some regulatory mechanisms of the rat preprotachykinin gene encoding substance P, neurokinin A, neuropeptide K, and neuropeptide γ, J. Neurosci., 10 (1990) 2203-2214 [2]), and within the rat hypothalamus according to the estrous cycle-related hormonal status (Gautreau, A., Duval, P., Kerdelhue, B., Variations in substance P-encoding preprotachykinin and substance P receptor NK-1 mRNA transcripts in the rat hypothalamus throughout the estrous cycle: a correlation between amounts of β-preprotachykinin and NK-1 mRNA, Mol. Brain Res., (1997) in press [7]). Tachykinin receptors as well as tachykinins are regulated at the mRNA level. A fully quantitative method is needed to deal with the complex physiological regulation of the tachykinin system. Here, we describe an RNase protection assay that allows the simultaneous quantitation of alternatively spliced PPT mRNAs, Substance P receptor NK-1 mRNA, and glyceraldehyde-3- phosphodehydrogenase (GAPDH) mRNA as an internal control, in the rat hypothalamus. The advantages of this method are its high sensitivity (0.1 pg) and a wide range of linearity (more than 3 orders of magnitude). Moreover, this protocol provides guidelines to set up a quantitative multiprobe RNase protection assay for other genes.