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Maternal contamination of some NZB sublines and genetic profiles of NZ-strains.

Six sublines of NZB mice bred in Japan were collected and their mitochondrial DNA (mtDNA) was examined by restriction analysis. The phenotypes of at least three of these sublines (NZB/Nrs, NZB/Nga and NZB/KlJms) differed from a standard one (NZB/BlWehi). Since mtDNA is inherited maternally, all sublines of a single inbred strain should share the same mtDNA phenotype. Therefore, b-type of mtDNA should be observed in all NZB sublines. Nevertheless, the above-mentioned sublines showed d-type mtDNA. These results suggested a genetic contamination of these sublines. This was confirmed by the finding that six aberrant alleles were detected also in their nuclear genomes using biochemical markers. For elucidation of the cause of contamination, we characterized the genetic profiles of four standard NZ-strains, NZB/BlWehi NZO/BlWehi, NZC/BlWehi and NZX/BlWehi, and of common inbred strains with black coat color, C57BL/6J, C57BL/10Sn, C57BL/Ks, C58/J and AU/SsJ. We found that five of the six aberrant alleles most strongly corresponded with those of C57BL/Ks. These results suggest that this contamination was ascribable to cross of NZB mice with a certain C56BL strain. We also deduced that NAB/BlPt and NZB/Füll also probably were contaminated strains, suggesting that this contamination was not restricted to Japan.