Unusual Origin of a Nuclear Pseudogene in the Italian Wall Lizard: Intergenomic and Interspecific Transfer of a Large Section of the Mitochondrial Genome in the Genus Podarcis (Lacertidae)
Two distinct cytochrome b-like sequences were discovered in the genome of Podarcis sicula. One of them represents a nuclear copy of a mitochondrial sequence (numt-sic) differing by 14.3% from the authentic mitochondrial (mt) sequence obtained from the same individual. This numt, however, differs by only 2.7% from the mt sequence found in one population of Podarcis muralis, a related species in which no corresponding numt was detected. The numt-sic sequence extends over at least 7637 bp and is homologous to a section of the mt genome spanning from the tRNA-Lys to the tRNA-Pro gene. Premature mt stop codons were detected in two of the nine protein coding genes of numt-sic. The distribution of substitutions among the three codon positions and the transition/transversion ratio of the numt-sic sequence resemble, with few exceptions, those of functional mt genes, indicating a rather recent transfer to the nucleus. Phylogenetic analyses performed on the data set including P. sicula numt-cytb sequences as well as mt-cytb sequences from the same individuals and mt sequences of various P. muralis populations suggest that numt-sic originated in P. muralis. In a geographic survey, P. sicula populations belonging to different mt lineages, covering most of the distribution area, were screened for the presence of numt-sic and for a 15-bp duplication polymorphism in the numt-nd5 sequence. Our results suggest that numt-sic has spread rapidly through the species range via sexual transmission, thereby being transferred to populations belonging to well-separated mt lineages that diverged 1–3 Mya.
Keywordsnumt Mitochondrial DNA Lacertidae Podarcis sicula P. muralis Interspecific transfer
The authors want to express their thanks to R. Godinho (Porto), Đ. Ugarković (Zagreb), and P. Wihlidal (Vienna) for valuable technical advice. We are also obliged to L. Kruckenhauser, F. Nittinger, and M. Pavlicev for valuable comments on the manuscript. The study was partially supported by the Research Fund of the Republic of Croatia, project no. 183007.
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