Identification of Candidate Gene Regions in the Rat by Co-Localization of QTLs for Bone Density, Size, Structure and Strength

Abstract

Susceptibility to osteoporotic fracture is influenced by genetic factors that can be dissected by whole-genome linkage analysis in experimental animal crosses. The aim of this study was to characterize quantitative trait loci (QTLs) for biomechanical and two-dimensional dual-energy X-ray absorptiometry (DXA) phenotypes in reciprocal F2 crosses between diabetic GK and normo-glycemic F344 rat strains and to identify possible co-localization with previously reported QTLs for bone size and structure. The biomechanical measurements of rat tibia included ultimate force, stiffness and work to failure while DXA was used to characterize tibial area, bone mineral content (BMC) and areal bone mineral density (aBMD). F2 progeny (108 males, 98 females) were genotyped with 192 genome-wide markers followed by sex- and reciprocal cross-separated whole-genome QTL analyses. Significant QTLs were identified on chromosome 8 (tibial area; logarithm of odds (LOD) = 4.7 and BMC; LOD = 4.1) in males and on chromosome 1 (stiffness; LOD = 5.5) in females. No QTLs showed significant sex-specific interactions. In contrast, significant cross-specific interactions were identified on chromosome 2 (aBMD; LOD = 4.7) and chromosome 6 (BMC; LOD = 4.8) for males carrying F344mtDNA, and on chromosome 15 (ultimate force; LOD = 3.9) for males carrying GKmtDNA, confirming the effect of reciprocal cross on osteoporosis-related phenotypes. By combining identified QTLs for biomechanical-, size- and qualitative phenotypes (pQCT and 3D CT) from the same population, overlapping regions were detected on chromosomes 1, 3, 4, 6, 8 and 10. These are strong candidate regions in the search for genetic risk factors for osteoporosis.

Widespread Differential Maternal and Paternal Genome Effects on Fetal Bone Phenotype at Mid-Gestation

“…Fetal sex and nongenetic maternal effects Sex-specific quantitative trait loci (QTL) for BMD and long bone length were identified in previous studies. (21,73) Highly significant effects of fetal sex (p < 0.0001) on fetal bone wet weight ( Fig. 1A and Table 2) are consistent with previous reports of early sex differences in bone mass.…”

“…Sex‐specific quantitative trait loci (QTL) for BMD and long bone length were identified in previous studies . Highly significant effects of fetal sex ( p < 0.0001) on fetal bone wet weight (Fig.…”

“…Furthermore, we showed that tight correlations between muscle and bone parameters were accompanied by significant relationships with expression levels of the miRNA harboring imprinted lncRNA H19 in fetal muscle, suggesting that muscle and bone could interact via miRNA interference. Apart from genomic imprinting and/or interaction of miRNAs with target sites specific for parental alleles, other types of nonmendelian inheritance, such as maternally inherited mitochondrial DNA and X‐ and Y‐chromosome effects, are likely to contribute to widespread differential parental genome effects on fetal bone. The present data provide the starting point for molecular dissection of genetic and epigenetic mechanisms that operate across pre‐ and postnatal development to determine adult bone phenotype.…”

“…Genetic and epigenetic factors following nonmendelian modes of inheritance have emerged as an important source of variation in postnatal bone mass and bone geometry parameters in human and animal models . This includes effects of maternally inherited mitochondrial DNA, X‐ and Y‐chromosomes, and genomic imprinting . The important functions of genes with genomic imprinting (ie, parent‐of‐origin–dependent allele‐specific gene expression) for pre‐ and postnatal skeletal development have been demonstrated in mouse models.…”