Multiple Genetic Loci From CAST/EiJ Chromosome 1 Affect vBMD Either Positively or Negatively in a C57BL/6J Background

Abstract

Skeletal phenotype analyses of 10 B6.CAST-1 congenic sublines of mice have revealed evidence for the presence of three closely linked QTLs in Chr 1 that influence femoral vBMD both positively and negatively.Introduction: BMD is an important component of bone strength and a recognized predictor of risk for osteoporotic fracture. Our goal in this study was to fine map the chromosomal location of volumetric BMD (vBMD) quantitative trait loci (QTLs) in mouse distal chromosome 1 (Chr 1). Materials and Methods: After several backcrosses of the B6.CAST-1T congenic strain, which carried the initial BMD QTL in Chr 1 with B6 mice, the N10F1 generation mice were intercrossed to obtain recombinations that yielded different regions of the QTL. Thirty-eight polymorphic markers were used to fine map the initial 1T QTL region . Different skeletal parameters were compared between the 10 sublines and B6 female mice at 16 weeks of age. A t-test was used to determine the significant difference between sublines and B6 control mice, whereas one-way ANOVA and posthoc (Newman-Keuls) tests were performed to compare the phenotype between the sublines. Results: Significantly higher femur vBMD was found in sublines that carried cast alleles from 100 to 169 and 172 to 185 Mb of the centromere compared with the B6 control mice (10-12%, p < 0.001). However, sublines that carried cast alleles from 185 to 192 Mb showed significantly lower femur vBMD compared with the control mice (−6%, p < 0.05). Furthermore, femur vBMD phenotype showed a negative correlation with endosteal circumference (r ‫ס‬ −0.8, p ‫ס‬ 0.003), and a strong correlation with cortical thickness for combined data from the 10 sublines (r ‫ס‬ 0.97, p < 0.001). Moreover, a high correlation was found between body weight and both periosteal and endosteal circumferences for sublines carrying cast alleles from 167 to 175, 168 to 185, and 169 to 185 Mb, whereas no significant correlation was found between these parameters for sublines carrying cast alleles from 172 to 185 Mb. Conclusions: Genetic analysis using congenic sublines revealed that the initial BMD QTL on Chr 1 is a complex site with multiple loci affecting bone phenotypes, showing the value of the congenic approach in clearly identifying loci that control specific traits.

Identification of mouse Duffy Antigen Receptor for Chemokines (Darc) as a BMD QTL gene

“…Together, the association and linkage studies point to the fact that osteoporosis susceptibility is determined by a large number of genes with a modest or small effect size and not by few genes of major effect as originally thought. Accordingly, our data with a large number of congenic strains carrying overlapping CAST chromosomal segments from Chr 1 BMD QTL have revealed that there are at least four BMD loci in Chr 1, each contributing to 4%-12% of the variation in peak bone mass (this work and Edderkaoui et al 2006).…”

“…The rationale for selecting these two inbred mouse strains was based on the fact that these strains are highly polymorphic for genetic differences at >95% of their genomes (Dietrich et al 1996). The B6.CAST F 2 mice were produced and maintained at the animal research facility of The Jackson Laboratory (TJL; Bar Harbor, ME), as previously described (Beamer et al 1999), while the congenic sublines of mice were generated and maintained at the Jerry L. Pettis VA Medical Center (LL; Loma Linda, CA) under the standard conditions previously described by Edderkaoui et al (2006). The animal work performed in this study was approved by the institutional animal care and use committees at both TJL and LL.…”

“…The animal work performed in this study was approved by the institutional animal care and use committees at both TJL and LL. Darc-knockout (Darc-KO) mice as well as the control mice were generated as previously described by Luo et al (2000), and were bred and maintained in LL under the same conditions previously described by Edderkaoui et al (2006).…”

“…In a recently published study (Edderkaoui et al 2006), we reported the identification of three BMD loci at Chr 1 by superimposing the CAST chromosomal regions carried by each congenic subline. The Bmd1a locus was located between D1mit133 and D1mit453 (133.2-165.2 Mb), the Bmd1b locus was located between , and a Bmd1c, which regulates BMD negatively, was located between D1mit221 and D1mit511 .…”

“…Therefore, to narrow down the size of the Bmd1b QTL region to permit our candidate gene search, we generated additional congenic sublines from the C168-185 subline, as described in Edderkaoui et al (2006). In the present study, we compared the skeletal phenotype of the congenic subline that carries the CAST chromosomal segment from D1mit370 to D1mit403 (168-176 Mb) and the congenic subline that carried the CAST chromosomal region located between the first and the second peaks/QTL with the B6 control mice (Fig.…”