Repetitive sequences in the lamprey mitochondrial DNA control region and speciation of Lethenteron

The sequence of the mitochondrial DNA control region was examined in four species of lamprey in the genus Lethenteron. The 3' half of the control region contains highly variable repeat sequences, showing variation in both copy number and nucleotide sequence, even within local populations. Detailed analyses of the sequences of the repeats allowed us to deduce that slipped-strand mispairing during DNA replication, accompanied by a high rate of substitutions and indels, was primarily responsible for the variation in the repeats. We also found that some cases might be better explained by gene conversion, due to intermolecular recombination. Based on the observed variable nature of the mitochondrial control region, we searched for molecular markers in mitochondrial DNA, because there are few fixed genetic markers for distinguishing between Lethenteron japonicum and Lethenteron kessleri. However, we found no reliable markers in the control region. No fixed substitution was observed in intron sequences of the nuclear gene SoxD. Thus, these two species likely diverged quite recently and may possess only a limited number of fixed genetic loci.