Experiment
Peak bone density QTL Pbd1 (51.8 cM) on mouse Chromosome 11 was refined using congenic line analysis. A 39 cM interval of SAMP2-derived DNA from D11Mit242 (31 cM) to D11Mit167 (71 cM) encompassing the Pbd1 locus was introgressed onto a SAMP6 genetic background. This congenic line is named P6.P2-Pbd1. Males age 16 weeks from donor strain SAMP2 display significantly increased cortical thickness index (CTI) compared to males from background strain SAMP6, and P6.P2-Pbd1 congenic males display higher CTI thanSAMP6 males thus confirming the effect of Pbd1. The QTL has a similar effect in 16 week old females.
A series of subcongenic lines derived from P6.P2-Pbd1 narrowed the Pbd1 interval to a 10.1 Mb region between D11Mit52 (62 cM) and D11Mit184 (78 cM). Subsequent SNP analysis refined the interval to 10 Mb between Itga2b (68 cM) and D11Mit184 (78 cM). The refined Pbd1 locus also shows significant linkage to midshaft bone area fraction, short axis length, and oblateness, with SAMP2-derived alleles increasingthese values compared to SAMP6.
Gene expression analysis was performed on 114 genes found between Itga2b and D11Mit184 using bone and kidney mRNA from SAMP6 and subcongenic line SS7. In bone mRNA, Plcd3 (63 cM) displayed 2-fold increased expression in SS7 relative to SAMP6, while Arsg displayed 2-fold reduced expression. In kidney mRNA, Axin2 (70 cM), Rgs9 (70 cM), and sequence Q8CE14_MOUSE displays ~2-fold reduced expression in SS7 relative to SAMP6. Of particular interest, Cacng4 displays 9-fold decreased expression in SS7 kidney mRNA relative to SAMP6.
The Pbd1 locus is syntenic to human chromosome 17q21.31 and 17q23.2-q24.3. These regions have also been associated with bone characteristics in humans.
Analysis Tools