Immunogene~cs39:286-288,1994 llnlHullo- genetics © Springer-Verlag 1994 C57BL/6 and C57BL/10 inbred mouse strains differ at multiple loci on chromosome 4 Peter J. McClive, Dexing Huang, Grant Morahan The Walter and Eliza Hall Institute of Medical Research, Post Office, Royal Melbourne Hospital, Parkville, Victoria 3050, Australia Received November 3, 1993 Inbred mouse strains are valuable tools in biological research. As members of a given strain are all identical, independent studies on such mice can be readily re- produced and compared. C57BL is one of the most commonly used of these strains, and two of its major substrains are C57BL/6 (B6) and C57BL/10 (B10). The separation of B6 and B10 as lines occurred prior to 1937, and they have since provided the genetic back- grounds for the derivation of many congenic strains (for example, those congenic for the H-2; Boyse 1977). Since their separation, they have been characterized as differing at only 3 loci of 161 tested (Festing 1992): the minor histocompatability locus H-9, the im- munoglobulin heavy chain locus Igh-2 (chromosome 12), and the locus for delta-aminolevulinate dehydratase Lv (chromosome 4). The two substrains thus have a close genetic relationship and experimental results using either strain have been considered equivalent. However, in genetic studies of diabetes using a backcross of non- obese diabetic (NOD) mice to the B6 strain, we ob- served that on distal chromosome 4, B 10 alleles differed from those of B6 and were instead the same as the NOD type. These surprising results led us to examine other chromosome 4 loci. DNA from B6, B10, and NOD mice was analyzed by conventional Southern blotting techniques (Sambrook et al. 1989) or by analysis of microsatellite markers (Dietrich et al. 1992). Probe and enzyme combinations were used that had previously identified polymorphisms between NOD and B6 mice (Morahan and co-workers, submitted; McClive et al. 1993). Probes were used to detect restriction fragment length polymorphisms (RFLP) at the following loci: ClqC (Petry et al. 1992), Correspondence to: G. Morahan. Fig. 1A-D. Southern blots using probe/enzyme combinations which have previously detected polymorphisms between NOD and B6 mice. Lane 1 B6, lane 2 B10. Ticks to the left of each blot represent ~/BstEII molecular weight markers of 4.3 kb, 3.7 kb, 2.3 kb, 1.9 kb, and 1.4 kb. A Nhe-1/Taq I B Lap 18/Taq I C ClqC/ Bst EII D Tnfr-2/Bam HI. Ifa (Kerry 1990), Lck (Marth et al. 1985), Lapl8 (Ferrari et al. 1990), Nhe-1 (Sardet et al. 1989), and Tnfr-2 (Barrett et al. 1991). Polymerase chain reaction (PCR) analysis was performed with primer pairs specific for microsatellite markers on chromosome 4 (Research Genetics Huntsville, AL). Five of the nine chromosome 4 loci tested differed between B6 and B10 mice. Figure 1 a shows RFLP for Nhe-1 (coding for a sodium/hydrogen exchanger (Sardet et al. 1989). B6-specific bands of 1.9 kilobase (kb) and 1.6 kb and a 2.5 kb B10-specific band were obtained