Distribution and polysome association of full-length and 3' truncated preproenkephalin mRNA in the guinea-pig brain.
The preproenkephalin gene is expressed in the mammalian central and peripheral nervous system as well as in other tissues, including the pituitary, adrenal medulla, lymphocytes, and reproductive and digestive systems. In the guinea-pig brain, preproenkephalin mRNA transcripts are cleaved at a specific site located in the 3' untranslated region. We used a solution hybridization RNAse protection assay to measure total levels of preproenkephalin mRNA and to determine the ratio of full-length to truncated forms in the pituitary and 12 brain regions of the guinea-pig. The overall distribution of preproenkephalin mRNA was found to be similar to that observed in other species in which it has been measured, with the highest levels of expression located in the caudate putamen and nucleus accumbens. The 3' truncated form was found throughout the brain in varying levels depending on the region. In nine regions examined, levels of the shorter form varied between 35 and 59% of total preproenkephalin mRNA content. The cerebellum and pons/medulla contained 17% each. In the pituitary, the only non-brain tissue studied, the truncated form constituted only 4% of total preproenkephalin mRNA. No correlation between absolute mRNA levels and the distribution between the two forms was observed. Both the full-length and 3' truncated mRNA forms were associated with polysomes isolated from the guinea-pig caudate putamen by sucrose density gradient centrifugation, suggesting that both mRNA forms may be actively translated. The distribution between the two forms, however, was different on the polysomal and dissociated monosomal gradients: the polysomal preproenkephalin mRNA contained a higher proportion of the full-length form whereas the monosomal fractions contained slightly more of the truncated form. This discontinuity in the amount of the two forms between polysomal and non-polysomal mRNA may suggest that the full-length form is more readily incorporated into polysomes.
LaForge
K S
KS
Rockefeller University, New York, NY 10021, USA. laforgk@rockvax.rockefeller.edu
Ho
A
A
Kreek
M J
MJ
D000818:Animals; D001921:Brain / Q000378:metabolism*; D004745:Enkephalins / Q000235:genetics / Q000378:metabolism*; D006168:Guinea Pigs; D008297:Male; D011132:Polyribosomes / Q000378:metabolism*; D014176:Protein Biosynthesis; D011498:Protein Precursors / Q000235:genetics / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism
D004745:Enkephalins; D011498:Protein Precursors; D012333:RNA, Messenger; C033660:preproenkephalin