DIFFERENTIAL EXPRESSION OF ANGIOTENSIN RECEPTOR 1A AND 1B IN MOUSE

At least two distinct genes (AT(1A) and AT(1B)) encode type 1 angioten sin II (AT(1)) receptors in rodents. Receptor binding and Northern blo t analysis have clearly demonstrated the presence of AT(1) receptors a nd AT(1)-receptor mRNA in many tissues but fail to differentiate which type 1 receptor subtype is expressed. A reverse-transcriptase polymer ase chain reaction restriction fragment length polymorphism (RT-PCR-RF LP) assay was developed to differentiate the expressed mRNA by subtype . Expression of AT(1A) was clearly evident in kidney, liver, adrenal g land, ovary, brain, testes, adipose tissue, lung, and heart of adult m ice. AT(1B) was absent from most of these tissues but was detectable i n brain, testes, and adrenal gland. No significant differences in expr ession were evident in kidney, liver, brain, lung, or heart from 16.5- or 18.5-gestation-day fetuses, and only AT(1A) was evident in placent a. Expression of AT(1B) was confirmed in adrenal gland, brain, and tes tes, using a primer set that specifically amplifies only AT(1B) mRNA. Expression of AT(1A) and AT(1B) was also examined in As4.1 cells, a re nin-expressing mouse kidney tumoral cell line. Receptor binding and co mpetition assays using AT(1)- and AT(2)-receptor antagonists revealed that only AT(1) receptors are present on the cell surface. Extremely l ow levels of AT(1)-receptor mRNA was detected by Northern blot, and RT -PCR-RFLP analysis revealed that only the AT(1A) subtype is expressed in this cell line. Despite the high homology between the coding sequen ce of the AT(1A) and AT(1B) genes, they exhibit disparate tissue-speci fic expression profiles.