Prows, D. R. | Search bioRxiv

bioRxiv2019

Heart Disease in a Mutant Mouse Model of Spontaneous Eosinophilic Myocarditis Maps to Three Highly Significant Loci

BackgroundHeart disease (HD) is the major cause of morbidity and mortality in patients with hypereosinophilic diseases. Due to a lack of adequate animal models, our understanding of the pathophysiology of eosinophil-mediated diseases with heart complications is limited. We have discovered a mouse mutant, now maintained on an A/J inbred background, that spontaneously develops hypereosinophilia in multiple organs. Cellular infiltration into the heart causes an eosinophilic myocarditis, with affected mice of the mutant line (i.e., A/JHD) demonstrating extensive myocardial damage and remodeling that leads to HD and premature death, usually by 15-weeks old. Maintaining the A/JHD line for many generations established that the HD trait was heritable and implied the mode of inheritance was not too complex. Backcross and intercross populations generated from mating A/JHD males with females from four different inbred strains produced recombinant populations with highly variable rates of affected offspring, ranging from none in C57BL/6J intercrosses, to a few mice with HD using 129S1/SvImJ intercrosses and C57BL/6J backcrosses, but nearly 8% of intercrosses and >17% of backcrosses from SJL/J related populations developed HD. Linkage analyses of these SJL/J derived recombinants identified three highly significant loci: a recessive locus mapping to distal chromosome 5 (LOD=4.88; named Emhd1 for eosinophilic myocarditis to heart disease-1); and two dominant variants mapping to chromosome 17, one (Emhd2; LOD=7.51) proximal to the major histocompatibility complex, and a second (Emhd3; LOD=6.89) that includes the major histocompatibility region. Haplotype analysis identified the specific crossovers that defined the Emhd1 (2.65Mb), Emhd2 (8.46Mb) and Emhd3 (14.59Mb) intervals. These results indicate the HD trait in this mutant mouse model of eosinophilic myocarditis is oligogenic with reduced penetrance, due to multiple segregating variants and possibly additional genetic or nongenetic factors. The A/JHD mouse model represents a unique and valuable tool to understand the interplay of causal factors that underlie the pathology of this newly discovered eosinophil-associated disease with cardiac complications.

genetics↗

bioRxiv2018

Gpr63 is a novel modifier of microcephaly in Ttc21b mouse mutants.

The primary cilium is a critical signaling center for proper embryonic development. Previous studies have demonstrated that mice lacking Ttc21b have impaired retrograde trafficking within the cilium and multiple organogenesis phenotypes, including microcephaly. Interestingly, the severity of the microcephaly in Ttc21baln/aln homozygous null mutants is considerably affected by the genetic background. Ttc21baln/aln mutants on an FVB/NJ background develop a forebrain significantly smaller than mutants on a C57BL/6J background. We performed a Quantitative Trait Locus (QTL) analysis to identify potential genetic modifiers and identified two regions linked to differential forebrain size: modifier of alien QTL1 (Moaq1) on chromosome 4 at 27.8 Mb and Moaq2 on chromosome 6 at 93.6 Mb. These QTLs were validated by constructing congenic strains. Further analysis of Moaq1 identified a brain specific orphan G-protein coupled receptor (GPCR), Gpr63, as a candidate gene. We identified a SNP between the FVB and B6 strains in Gpr63, which creates a missense mutation predicted to be deleterious in the FVB protein. We first demonstrated that Gpr63 can localize to the cilium and then used CRISPR-Cas9 genome editing to create FVB congenic mice with the B6 sequence of Gpr63 and a deletion allele leading to a truncation of the GPR63 C-terminal tail. These alleles genetically interact with Ttc21baln/aln, validating Gpr63 as a forebrain modifier of Ttc21b and strongly supporting Gpr63 as the variant causal gene (i.e., the quantitative trait gene, QTG) for Moaq1.

developmental biology↗