Complete Sequence of the Mitochondrial DNA of the Primitive Opisthobranch Gastropod Pupa strigosa: Systematic Implication of the Genome Organization

Abstract

The complete sequence (14,189 bp) of the mitochondrial DNA of the opisthobranch gastropod Pupa strigosa was determined. The genome contains 13 protein, 2 rRNA, and 22 tRNA genes typical of metazoan mtDNA. The Pupa mitochondrial genome is highly compact and shows the following unusual features, like pulmonate land snails: (1) extremely small genome size, (2) absence of lengthy noncoding regions (with the largest intergenic spacer being only 46 nt), (3) size reduction of encoded genes, and (4) many overlapping genes. Several tRNA genes exhibit bizarre secondary structures with reduced T or D stems, and many tRNA genes have unstable acceptor stems that might be corrected by posttranscriptional RNA editing. The Pupa mitochondrial gene arrangement is almost identical to those of pulmonate land snails but is radically divergent from those of the prosobranch gastropod Littorina saxatilis and other molluscs. Our finding that the unique gene arrangement and highly compact genome organization are shared between opisthobranch and pulmonate gastropods strongly suggests their close phylogenetic affinity.

Rolling circle amplification of metazoan mitochondrial genomes

“…Because of this limited sampling, what is now considered to be "typical" mt genomes may someday be considered unique to their respective lineages. This is especially apparent when we consider the complexity of gene rearrangements so far documented by the limited number of complete mt genomes in mollusks and other spiralians (e.g., Boore and Brown, 1995;HoVmann et al, 1992;Kurabayashi and Ueshima, 2000). Additional data will undoubtedly provide a better understanding of the variation present in metazoan mt genomes, especially as continued development of RCA accelerates our progress in sequencing complete organellar genomes.…”

The mitochondrial genome of Ifremeria nautilei and the phylogenetic position of the enigmatic deep-sea Abyssochrysoidea (Mollusca: Gastropoda)

“…The gene order of the mt genome of I. nautilei was compared to the gene arrangement of other reported mollusk mitochondrial genomes (Table 1): one cephalopod, Octopus vulgaris (Yokobori et al, 2004), and 14 gastropods: one Vetigastropoda: Haliotis rubra (Maynard et al, 2005), one Neritimorpha: Nerita melanotragus (Castro and Colgan, 2010), one Patellogastropoda: Lottia digitalis (Simison et al, 2006), six Heterobranchia: Roboastra europea (Grande et al, 2002), Pyramidella dolabrata and Onchidella celtica (Grande et al, 2008), Albinaria caerulea (Hatzoglou et al, 1995), Aplysia californica (Knudsen et al, 2006), Pupa strigosa (Kurabayashi and Ueshima, 2000) and five Caenogastropoda: Oncomelania hupensis (Zhao et al, 2010), Dendropoma maximum (Rawlings et al, 2010) and Cymatium parthenopeum, Bolinus brandaris and Conus borgesi (Cunha et al, 2009). …”

“…1). The largest one was found adjacent to cox3 gene, in a position that has been postulated as candidate to contain the control region in other gastropod mt genomes (Kurabayashi and Ueshima, 2000).…”

Molecular phylogenetics of the Metazoan clade Lophotrochozoa

“…Most of the major clades in the Mollusca first appear in the fossil record during the Cambrian (Runegar and Pojeta, 1985), which has been viewed as a period of diversification and cladogenesis thoughout the Metazoa (Valentine, 1994 (Kurabayashi and Ueshima, 2000), greater variation in mitochondrial gene rearrangements has been observed than between the polyplacophoran Katharina tunicata and the brachiopod Terebratulina retusa (Stechmann and Schlegel, 1999). In some cases these rearangements appear to have occurred between closely related species over relatively short time scales (Rawlings et aI., 2001).…”