The absence of mitochondrial DNA diversity among common laboratory inbred mouse strains.

Mitochondrial DNA (mtDNA), which exhibits a maternal inheritance and a high rate of evolution, has been widely used as a genetic marker when analyzing maternal lineage and inferring phylogenetic relationships among species. In this study, mtDNA variations among four classical (BALB/c, C3H, C57BL/6J and DBA/2) and three Chinese (TA2, 615 and T739) inbred strains of laboratory mice were analyzed by PCR-RFLP (polymerase chain reaction coupled with restriction fragment length polymorphism) and PCR-SSCP (polymerase chain reaction coupled with single-stranded conformational polymorphism) techniques. PCR-RFLP analyses on 46 restriction sites revealed no variations in mtDNA D-loop (displacement loop), tRNA(Met+Glu+Ile) and ND3 (NADH dehydrogenase subunit 3) gene fragments in these strains. Furthermore, PCR-SSCP analyses demonstrated no variations in D-loop 5' and 3' end fragments in them. In view of enormous polymorphisms in mtDNA among mice and dramatic differences in nuclear genomes of these seven strains, our findings were surprising. However, in light of the maternal inheritance of mtDNA, the results indicate that the three Chinese strains, including TA2, T739 and 615, and the four classical strains, share a common maternal lineage.