Mitochondrial DNA-like sequences in the nuclear genome of the opossum genus Didelphis (Marsupialia: Didelphidae)

This study reports the occurrence of mtDNA-like sequences in the nuclear genome of the opossum genus Didelphis (Didelphidae, Marsupialia). A specific primer pair designed to amplify a region encompassing a 3' terminal 118 bp region of the cytochrome b gene, the Thr and Pro tRNA genes, and a 489 bp region of the D-loop of the D. virginiana mtDNA, was used in highly stringent PCR reactions. These PCR reactions resulted in several fragments per individual varying in size from 259 bp to 1 kb. The sequencing of some of these fragments showed the occurrence of paralogous mtDNA-like sequences among the PCR amplified fragments. Analyses of qualitative aspects of these sequences, their transition/transversion ratios, and phylogenetic relationships were conclusive in showing the occurrence of mtDNA-like sequences in the nuclear genome of the genus Didelphis. Comparisons and phylogenetic analysis of orthologous mtDNA from the four Didelphis species and paralogous nuclear sequences suggested that mtDNA migration to the nuclear genome occurred more than once in Didelphis evolution.