title: The angiotensin II receptor (Agtr1a): functional regulatory polymorphisms in a locus genetically linked to blood pressure variation in the mouse.
abstract: Hypertension is a complex trait with multiple genetic determinants. A previous genome-wide linkage study of systolic blood pressure in a mouse genetic backcross implicated a region of chromosome 13 (LOD = 3.3 at 16.0 cM) as a determinant of blood pressure differences between a hereditary low blood pressure strain of Mus musculus (BPL/1) and Mus spretus (SPRET); at this locus, the unexpected effect of the BPL/1 allele was to increase blood pressure. A plausible candidate locus encoding angiotensin II receptor isoform 1a (Agtr1a) is also located at 16.0 cM on chromosome 13. We therefore investigated structural and functional differences at Agtr1a between BPL/1 and SPRET, as well as the BPH/2 strain. Resequencing Agtr1a in the three strains established the exon/intron and proximal promoter structure of the mouse gene. Coding exon 3 spanned 1,960 bp (with 26 SNPs), including the 1,077-bp/359-amino acid ORF (with 5 cSNPs, all of which were synonymous). Promoter sequences revealed a consensus TATA box, conserved G/C-rich regions, and a striking, lengthy simple sequence repeat region, composed of di-, tri-, tetra-, and penta-nucleotide repeats, whose overall length varied markedly among the strains. Twenty-five other SNPs and three single nucleotide deletions differentiated the strains' promoters, six of which were in likely functional promoter motifs. Agtr1a mRNA abundance in the adrenal gland in vivo was greater (P < 0.05) in BPL/1 than SPRET, consistent with the predicted effect of the BPL/1 allele to confer higher blood pressure. When Agtr1a promoters were subcloned into luciferase reporter plasmids and transfected into PC12 chromaffin cells, basal promoter expression was higher (P < 0.001) in BPL/1 than in SPRET, consistent with the endogenous mRNA results. In summary, Agtr1a on chromosome 13 is highly polymorphic between mouse strains, although the amino acid sequence specified by the ORF is invariant, even across mouse species. We conclude that polymorphisms in the Agtr1a promoter account for differences in gene expression in vivo between BPL/1 and SPRET, in a way consistent with the effects of alleles at this locus on chromosome 13 to affect blood pressure in the mouse genome-wide linkage study.
authors.affiliation: Department of Medicine and Center for Molecular Genetics, University of California, and Veterans Affairs San Diego Healthcare System, San Diego, California 92161, USA.
authors.forename: Clifford
authors.initials: C
authors.lastname: Wong
authors.forename: Nitish R
authors.initials: NR
authors.lastname: Mahapatra
authors.forename: Surin
authors.initials: S
authors.lastname: Chitbangonsyn
authors.forename: Payam
authors.initials: P
authors.lastname: Mahboubi
authors.forename: Manjula
authors.initials: M
authors.lastname: Mahata
authors.forename: Sushil K
authors.initials: SK
authors.lastname: Mahata
authors.forename: Daniel T
authors.initials: DT
authors.lastname: O'Connor
mesh_terms: D000804:Angiotensin II / Q000378:metabolism* / Q000502:physiology; D000818:Animals; D001794:Blood Pressure / Q000235:genetics*; D002460:Cell Line; D019439:Chromaffin Cells / Q000737:chemistry / Q000378:metabolism; D017124:Conserved Sequence / Q000235:genetics / Q000502:physiology; D005091:Exons / Q000235:genetics; D008040:Genetic Linkage / Q000502:physiology*; D005819:Genetic Markers; D014644:Genetic Variation / Q000502:physiology*; D007438:Introns / Q000235:genetics; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008811:Mice, Inbred DBA; D008815:Mice, Inbred Strains; D009115:Muridae; D016716:PC12 Cells; D011110:Polymorphism, Genetic / Q000502:physiology*; D011401:Promoter Regions, Genetic / Q000235:genetics / Q000502:physiology; D012333:RNA, Messenger / Q000235:genetics; D051381:Rats; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin / Q000235:genetics / Q000502:physiology*; D020133:Reverse Transcriptase Polymerase Chain Reaction / Q000379:methods; D017422:Sequence Analysis, DNA
chemical_list: D005819:Genetic Markers; D012333:RNA, Messenger; D044140:Receptor, Angiotensin, Type 1; D011945:Receptors, Angiotensin; D000804:Angiotensin II