Multiple nuclear pseudogenes of mitochondrial cytochrome b in Ctenomys (Caviomorpha, Rodentia) with either great similarity to or high divergence from the true mitochondrial sequence

A fragment of the mitochondrial cytochrome b gene was studied in 13 species of the South American fossorial rodent Ctenomys using PCR with 'universal' primers and DNA sequencing after cloning: Five different groups of sequences were found, one of which corresponds to the functional mitochondrial gene (mt). The other four groups (A, B, C and D) were believed to be nuclear pseudogenes. Sequences A-C were highly divergent from the mt sequences and included substitutions, deletions and insertions such that they could not possibly have coded a functional protein. They all shared a common insertion between positions 15055 and 15056 suggestive of a common origin, although the A, B and C sequences otherwise differed greatly from each other. The D sequences also could not have been functional on the basis of nucleotide sequence, but the differences with the mt sequences were far more subtle and in a more limited study the D sequences could easily have been classified as a true mtDNA sequence. It is suggested that there were two transfers of the cytochrome b gene from the mitochondrion to the nucleus; the first leading to sequences A-C and the second to the D sequence. Subsequent to transfer, a sequence of duplications within the nucleus appears to have generated the full range of pseudogenes that are observed. This study adds to other recent observations suggesting the frequent transfer of mtDNA sequences to the nucleus and reinforces the necessity of great care in interpreting PCR-generated sequences, particularly those produced with universal primers. There are now data from several species of mammals and birds relating to PCR-generated nuclear copies of cytochrome b, which we review.Facultad de Ciencias Veterinaria

Multiple nuclear pseudogenes of mitochondrial cytochrome b in Ctenomys (Caviomorpha, Rodentia) with either great similarity to or high divergence from the true mitochondrial sequence

A fragment of the mitochondrial cytochrome b gene was studied in 13 species of the South American fossorial rodent Ctenomys using PCR with 'universal' primers and DNA sequencing after cloning: Five different groups of sequences were found, one of which corresponds to the functional mitochondrial gene (mt). The other four groups (A, B, C and D) were believed to be nuclear pseudogenes. Sequences A-C were highly divergent from the mt sequences and included substitutions, deletions and insertions such that they could not possibly have coded a functional protein. They all shared a common insertion between positions 15055 and 15056 suggestive of a common origin, although the A, B and C sequences otherwise differed greatly from each other. The D sequences also could not have been functional on the basis of nucleotide sequence, but the differences with the mt sequences were far more subtle and in a more limited study the D sequences could easily have been classified as a true mtDNA sequence. It is suggested that there were two transfers of the cytochrome b gene from the mitochondrion to the nucleus; the first leading to sequences A-C and the second to the D sequence. Subsequent to transfer, a sequence of duplications within the nucleus appears to have generated the full range of pseudogenes that are observed. This study adds to other recent observations suggesting the frequent transfer of mtDNA sequences to the nucleus and reinforces the necessity of great care in interpreting PCR-generated sequences, particularly those produced with universal primers. There are now data from several species of mammals and birds relating to PCR-generated nuclear copies of cytochrome b, which we review.Facultad de Ciencias Veterinaria

Mitochondrial variability in the D-loop of four equine breeds shown by PCR-SSCP analysis

A fragment of 466 base pairs from a highly variable peripheral region of the mitochondrial D-loop of horses was amplified and analyzed by single stranded conformational polymorphism (SSCP). Fourteen distinct SSCP variants were detected in 100 horses belonging to four breeds (Arabian, ARB; Thoroughbred, TB; Argentinian Creole, ARC; and Peruvian Paso from Argentina, PPA). Each breed showed four to eight SSCP variants, many of which were shared between two or three of the studied breeds. Arabian horses were the most variable (eight variants), with three variants unique to the breed. PPA and ARC showed two and one characteristic SSCP variants, respectively, while TB shared all its variants with at least one of the other breeds. An analysis based on the presence/absence of the variants revealed a closer relationship between PPA and TB, which was not completely unexpected considering the mixed ancestry of the PPA mares. The results also confirm the efficiency of SSCP to detect variability in horse mitochondrial DNA.Instituto de Genética Veterinari

Multiple nuclear pseudogenes of mitochondrial cytochrome b in Ctenomys (Caviomorpha, Rodentia) with either great similarity to or high divergence from the true mitochondrial sequence

A fragment of the mitochondrial cytochrome b gene was studied in 13 species of the South American fossorial rodent Ctenomys using PCR with 'universal' primers and DNA sequencing after cloning: Five different groups of sequences were found, one of which corresponds to the functional mitochondrial gene (mt). The other four groups (A, B, C and D) were believed to be nuclear pseudogenes. Sequences A-C were highly divergent from the mt sequences and included substitutions, deletions and insertions such that they could not possibly have coded a functional protein. They all shared a common insertion between positions 15055 and 15056 suggestive of a common origin, although the A, B and C sequences otherwise differed greatly from each other. The D sequences also could not have been functional on the basis of nucleotide sequence, but the differences with the mt sequences were far more subtle and in a more limited study the D sequences could easily have been classified as a true mtDNA sequence. It is suggested that there were two transfers of the cytochrome b gene from the mitochondrion to the nucleus; the first leading to sequences A-C and the second to the D sequence. Subsequent to transfer, a sequence of duplications within the nucleus appears to have generated the full range of pseudogenes that are observed. This study adds to other recent observations suggesting the frequent transfer of mtDNA sequences to the nucleus and reinforces the necessity of great care in interpreting PCR-generated sequences, particularly those produced with universal primers. There are now data from several species of mammals and birds relating to PCR-generated nuclear copies of cytochrome b, which we review.Facultad de Ciencias Veterinaria

Mitochondrial variability in the D-loop of four equine breeds shown by PCR-SSCP analysis

A fragment of 466 base pairs from a highly variable peripheral region of the mitochondrial D-loop of horses was amplified and analyzed by single stranded conformational polymorphism (SSCP). Fourteen distinct SSCP variants were detected in 100 horses belonging to four breeds (Arabian, ARB; Thoroughbred, TB; Argentinian Creole, ARC; and Peruvian Paso from Argentina, PPA). Each breed showed four to eight SSCP variants, many of which were shared between two or three of the studied breeds. Arabian horses were the most variable (eight variants), with three variants unique to the breed. PPA and ARC showed two and one characteristic SSCP variants, respectively, while TB shared all its variants with at least one of the other breeds. An analysis based on the presence/absence of the variants revealed a closer relationship between PPA and TB, which was not completely unexpected considering the mixed ancestry of the PPA mares. The results also confirm the efficiency of SSCP to detect variability in horse mitochondrial DNA.Instituto de Genética Veterinari

African and European mitochondrial haplotypes in South American Creole cattle

South American Creole cattle are direct descendants of the animals brought to the New World by the Spanish and Portuguese during the 16th century. A portion of the mitochondrial D-loop was sequenced in 36 animals from five Creole cattle populations in Argentina and four in Bolivia. Individuals belonging to the potentially ancestral Spanish breed Retinta were also analysed. Sequence comparisons revealed three main groups: two with the characteristics of European breeds and a third showing the transitions representative of the African taurine breeds. The African sequences were found in two populations from Argentina and three populations from Bolivia, whose only connections go back to colonial times. The most probable explanation for the finding is that animals could have been moved from Africa to Spain during the long-lasting Arabian occupation that started in the seventh century, and from the Iberian Peninsula to America eight centuries later. However, since African haplotypes were not found in the Spanish sample, the possibility of cattle transported directly from Africa cannot be disregarded.Facultad de Ciencias VeterinariasInstituto de Genética Veterinari