Alterations in Fibronectin Type III Domain Containing 1 Protein Gene Are Associated with Hypertension

<div><p>Multiple quantitative trait loci (QTLs) for blood pressure (BP) have been detected in rat models of human polygenic hypertension. Great challenges confronting us include molecular identifications of individual QTLs. We first defined the chromosome region harboring <i>C1QTL1</i> to a segment of 1.9 megabases that carries 9 genes. Among them, we identified the gene encoding the fibronectin type III domain containing 1 protein (<i>Fndc1</i>)/activator of G protein signaling 8 (<i>Ags8</i>) to be the strongest candidate for <i>C1QTL1</i>, since numerous non-synonymous mutations are found. Moreover, the 5’ <i>Fndc1</i>/<i>Ags8</i> putative promoter contains numerous mutations that can account for its differential expression in kidneys and the heart, prominent organs in modulating BP, although the Fndc1/Ags8 protein was not detectable in these organs under our experimental conditions. This work has provided the premier evidence that <i>Fndc1</i>/<i>Ags8</i> is a novel and strongest candidate gene for <i>C1QTL1</i> without completely excluding other 8 genes in the <i>C1QTL1</i>-residing interval. If proven true by future <i>in vivo</i> function studies such as single-gene <i>Fndc1</i>/<i>Ags8</i> congenics, transgenesis or targeted-gene modifications, it might represent a part of the BP genetic architecture that operates in the upstream position distant from the end-phase physiology of BP control, since it activates a Gbetagamma component in a signaling pathway. Its functional role could validate the concept that a QTL in itself can influence BP ‘indirectly’ by regulating other genes downstream in a pathway. The elucidation of the mechanisms initiated by <i>Fndc</i>/<i>Ags8</i> variations will reveal novel insights into the BP modulation via a regulatory hierarchy.</p></div

Comparison of <i>fibronectin type III domain containing 1</i>/ <i>activator of G protein signaling 8</i> (<i>Fndc1</i>/<i>Ags8</i>) expressions by quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR) in the kidneys and heart.

<p>Comparison of <i>fibronectin type III domain containing 1</i>/ <i>activator of G protein signaling 8</i> (<i>Fndc1</i>/<i>Ags8</i>) expressions by quantitative real time reverse transcriptase polymerase chain reaction (qRT-PCR) in the kidneys and heart.</p

Mutation screening of genes in the <i>C1QTL1</i> -containing interval.

<p>The position of a mutation enumerates from the ATG start codon of that gene. The amino acid position begins from the first methionine. <b><i>Dynlt1</i></b>, <i>dynein light chain Tctex-type 1</i>; <b><i>Ezr</i></b>, <i>ezrin</i>; <b><i>Fndc1/Ags8</i></b>, <i>fibronectin type III domain containing 1</i>/ <i>activator of G protein signaling 8</i> (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151399#pone.0151399.s003" target="_blank">S3 Table</a>); <b><i>LOC100912128</i></b>, <i>parkin coregulated gene protein-like</i>; <b><i>RGD1560015</i></b>, <i>similar to glycoprotein</i>, <i>synaptic 2</i>; <b><i>Rsph3</i></b>, <i>radial spoke 3 homolog (Chlamydomonas)</i>; <b><i>Sytl3</i></b>, <i>synaptotagmin-like 3</i>; <b><i>Tagap</i></b>, <i>T-cell activation RhoGTPase activating protein</i> (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151399#pone.0151399.s004" target="_blank">S4 Table</a>); <b><i>Tmem181</i></b>, <i>transmembrane protein 181</i>. Pseudogenes are not included. In: intron, Ex: exon, (+) and (-): nucleotide after before a given exon respectively. Raw genome sequence data have been deposited at the European Nucleotide Archive with accesion #s: Accession#s: LT158646, LT158647, LT158648, and LT158649.</p

Genome (probable promoter) sequence comparisons up to 2 kilobases from the ATG start codon for the genes in the <i>C1QTL1</i>-lodging interval.

<p>Gene names are given in the legend for <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151399#pone.0151399.g002" target="_blank">Fig 2</a>. Nucleotides were trolled from our sequence data base of DSS and Lewis genomes (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0151399#pone.0151399.s002" target="_blank">S2 Table</a>). RGD1560015 curated in this region shares a high conserved homology with <i>Tecr trans-2</i>,<i>3-enoyl-CoA reductase</i> (<i>Tecr</i>) on Chr 19, thus cannot be differentiated from it. UTR, untranslated region.</p

Functional predictions of amino acid substitutions caused by missense mutations in genes in the <i>C1QTL1</i>-residing interval.

<p>Functional predictions of amino acid substitutions caused by missense mutations in genes in the <i>C1QTL1</i>-residing interval.</p

A proposed pathway in which Fndc1/Ags8 participates in potentially contributing to BP modulations.

<p>Arrows only indicate a general direction of a pathway and do not enumerate exact steps involved.</p

Defining BP QTLs on DSS Chr 1 by congenic strains.

<p>A solid bar under congenic strains represents the DSS fragment (a white bar) that has been replaced by that of Lewis (S.L). Striped bars on ends of the solid bars denote the ambiguity of crossover breakpoints between markers. The map is not drawn to scale. Mean arterial pressures (MAPs) for all the strains are averages for the duration of the measurement. Systolic and diastolic arterial pressures are consistent with their MAPs of all the strains (data not shown). <i>Fibronectin type III domain containing 1</i> (<b><i>Fndc1</i></b>)/ <i>activator of G protein signaling 8</i> (<b><i>Ags8</i></b>).</p