Genetic loci linked to intermale aggression were identified in an intercross between C57BL/6J and NZB/BlNJ. Male animals from inbred strain NZB/BlNJ display more intense and frequent aggression towards other male mice compared to inbred strain C57BL/6J. Sixty-five microsatellite markers at an average spacing of 22.5 cM were used for the genome scan.
Male animals were tested under two different conditions. Condition 1 ("non-isolated")- males were housed with a female littermate until testing at 66 days old. Condition 2 ("isolated intruder")- males were housed with a female littermate until 54 days of age and then removed to a separate cage for 13 days before testing. Upon testing, experimental males were challenged with a male from the A/J strain (considered to be non-aggressive). Aggressive behavior was measured starting when the experimental male sniffed the A/J male. Latency to rattling behavior and biting or attempt at biting, as well as the number of each event, were recorded.
Imab2 (intermale aggressive behavior 2) mapped to 44 cM - 47 cM on mouse Chromosome 8 near D8Mit8. This locus displays significant linkage to first rattling latency in Condition 2 (LOD=6.22; 59% of variance) and suggestive linkage to first rattling latency (LOD=3.51; 15% of variance) and number of attacks (LOD=3.85; 21% of variance) in Condition 1. Got2 at 46 cM is a potential candidate gene for Imab2.
Imab3 (intermale aggressive behavior 3) mapped to 39 cM - 47 cM on mouse Chromosome 9 near D9Mit12. This locus is linked tofirst rattling latency (LOD=3.69; 26% of variance) and first attack latency (LOD=2.7; 9% of variance) in Condition 1, as well as first rattling latency (LOD=2.99; 6% of variance) in Condition 2. Htr1b at 46 cM is a potential candidategene for Imab3.
Imab4 (intermale aggressive behavior 4) mapped to 75 cM on mouse Chromosome X near Sts (which is also a potential candidate gene). This locus displays significant linkage to first rattling latency (LOD=4.9; 27% of variance), first attacklatency (LOD=4.79; 43%of variance), and number of attacks (LOD=3.57; LOD=3.57; 37% of variance) in Condition 1. A second locus at 28 cM, named Imab7 (intermale aggressive behavior 7), mapped near DXMit25 and is significantly linked to first attack latency in Condition 2 (LOD=4.68; 37% of variance). Potential candidate genes for Imab7 include Ar (36 cM) and Gabra3 (28 cM).
Imab5 (intermale aggressive behavior 5) mapped to 24 cM - 44 cM on mouse Chromosome 11 near D11Mit39. Imab5 exhibits significant linkage to number of attacks (LOD=4.51; 17% of variance) in Condition 1 and suggestive linkage to number of rattling (LOD=4.02; 12% of variance) and number of attacks (LOD=3.05; 17% of variance) in Condition 2. Gabra1 (19 cM) and Gria1 (31 cM) are potential candidate genes for Imab5.
Imab6 (intermale aggressive behavior 6) mapped to 26 cM on mouse Chromosome 12 near D12Mit2. Imab6 exhibits linkage to first attack latency (LOD=LOD=3.9; 14% of variance), number of rattling (LOD=2.8; 9% of variance), and number of attack (LOD=3.1; 11% of variance) in Condition 2, and linkage to number of attacks (LOD=2.71; 12% of variance)in Condition 1.