ABSTRACT
Cell types associated with angiotensinogen mRNA in rat brain were identified in individual brain sections by in situ hybridization with tritiated RNA probes or with a sulfur-35--labeled oligonucleotide combined with immunocytochemical detection of either glial fibrillary acidic protein (GFAP) for astrocytes or microtubule-associated protein (MAP-2) for neurons. Autoradiography revealed silver grains clustered primarily over GFAP-reactive soma and processes; most grain clusters were not associated with MAP-2--reactive cells. These results demonstrate that, in contrast to other known neuropeptide precursors, angiotensinogen is synthesized by glia.
Subject(s)
Angiotensinogen/biosynthesis , Astrocytes/metabolism , Brain/metabolism , Angiotensinogen/genetics , Animals , Glial Fibrillary Acidic Protein/analysis , Histocytochemistry , Microtubule-Associated Proteins/analysis , Nucleic Acid Hybridization , RNA, Messenger/analysis , RNA, Messenger/genetics , RatsABSTRACT
Renin (EC 3.4.23.15) is an aspartyl protease that cleaves its only known substrate, angiotensinogen, to release the vasopressor hormone angiotensin. We have isolated full-length cDNAs for renin from a rat kidney cDNA library. The cDNAs are complementary to a 1434-nucleotide rat kidney mRNA that encodes preprorenin, the 402-amino acid precursor of renin. This rat cDNA was used to isolate the complete copy of a renin gene from a rat genomic library, and a comparison of this genomic clone with rat genomic DNA showed that renin is a single-copy gene in the rat. Rat renin is 85% identical to one mouse renin isozyme (renin-1) and 81% identical to the second mouse renin isozyme (renin-2), suggesting that the duplication of the mouse renin genes is a more recent event than the speciation of rats and mice. Analyses of rat, human, and mouse renin sequences revealed that the potential to form two-chain renin is apparently peculiar to mouse renin, and the expression of a tenth exon (which results in a three-amino acid insertion) is observed only in the human renin gene.
Subject(s)
Cloning, Molecular , DNA/metabolism , Amino Acid Sequence , Animals , Base Sequence , DNA Restriction Enzymes/metabolism , Deoxyribonuclease EcoRI , Kidney/enzymology , Mice , RNA, Messenger/metabolism , Rats , Renin/geneticsABSTRACT
The topographical distribution of rat brain angiotensinogen (Ao) mRNA was determined using hybridization histochemistry (in situ hybridization) with two different hybridization probes, a 32P-labelled 42 residue oligonucleotide and a full-length complementary (antisense) RNA labelled with either sulfur 35 or phosphorus 32. Low levels of Ao mRNA sequences were detected throughout the brain while high levels were restricted to specific areas often corresponding to classical nuclear boundaries. All areas in which angiotensin II-like immunoreactivity had been previously detected contained moderate to high levels of Ao mRNA and many previously undetected areas were also found to contain high levels of this mRNA. The results underline the ubiquitous presence of angiotensinogen-synthesizing cells in the brain and support previous evidence that the angiotensinogen gene could be expressed by several types of brain cells.
