First Sequenced Mitochondrial Genome from the Phylum Acanthocephala(Leptorhynchoides thecatus) and Its Phylogenetic Position Within Metazoa

Abstract

The complete sequence of the mitochondrial genome of Leptorhynchoides thecatus (Acanthocephala) was determined, and a phylogenetic analysis was carried out to determine its placement within Metazoa. The genome is circular, 13,888 bp, and contains at least 36 of the 37 genes typically found in animal mitochondrial genomes. The genes for the large and small ribosomal RNA subunits are shorter than those of most metazoans, and the structures of most of the tRNA genes are atypical. There are two significant noncoding regions (377 and 294 bp), which are the best candidates for a control region; however, these regions do not appear similar to any of the control regions of other animals studied to date. The amino acid and nucleotide sequences of the protein coding genes of L. thecatus and 25 other metazoan taxa were used in both maximum likelihood and maximum parsimony phylogenetic analyses. Results indicate that among taxa with available mitochondrial genome sequences, Platyhelminthes is the closest relative to L. thecatus, which together are the sister taxon of Nematoda; however, long branches and/or base composition bias could be responsible for this result. The monophyly of Ecdysozoa, molting organisms, was not supported by any of the analyses. This study represents the first mitochondrial genome of an acanthocephalan to be sequenced and will allow further studies of systematics, population genetics, and genome evolution.

The complete mitochondrial genome of Cephalothrix simula (Iwata) (Nemertea: Palaeonemertea)

“…6, 7). Similar results were found in previous molecular studies (e.g., Winnepenninckx, et al, 1995;Carranza et al, 1997;Steinauer et al, 2005;Passamaneck and Halanych, 2006). Bourlat et al (2008) hypothesized as explanation for these results that the mitochondrial DNA of some mollusks had accelerated evolutionary rates or had an unusual doubly uniparental mode of mitochondrial inheritance, which might affect the accuracy of tree reconstruction.…”

Two Circular Chromosomes of Unequal Copy Number Make Up the Mitochondrial Genome of the Rotifer Brachionus plicatilis

“…The only other rotiferan mitochondrial genome in GenBank is the acanthocephalan L. thecatus, which has a single circular chromosome with noncanonical tRNA genes, no obvious D-loop region, and 2 possible but unorthodox copies of atp8 (Steinauer et al 2005). There is no conservation of gene order between L. thecatus and B. plicatilis or between either species and other sequenced mitochondrial genomes.…”

“…The tRNA genes range in size from 61 to 69 nt, with and average A þ T content of 71.2%, which is higher than the overall A þ T composition of the mtDNAs (table 1). In some metazoans, including the acanthocephalan rotifer L. thecatus, some mitochondrial tRNA genes have lost either T or D arms or have other unusual features (Steinauer et al 2005). However, the tRNAs of B. plicatilis have almost complete cloverleaf structures.…”

“…Analysis of the sequence and structure of these genomes has led to a greater understanding of mitochondrial function and origin and has proven useful in elucidating the phylogeny of their host organisms (Wolstenholme 1992;Boore and Brown 1998;Helfenbein and Boore 2004;Valles and Boore 2006). The complete mitochondrial genome of the acanthocephalan rotifer Leptorhynchoides thecatus was published in 2005 and found to contain several atypical features, including unusually short ribosomal RNA (rRNA) genes, transfer RNA (tRNA) genes missing the TWC arm, and no obvious control region (Steinauer et al 2005). With the hope that the first description of the mitochondrial genome of a monogonont rotifer would pave the way for the sequencing of other gnathiferan mitochondrial genomes and lead to a better understanding of the evolution of Gnathifera, Rotifera, and the B. plicatilis species complex, we sequenced the complete mitochondrial genome of B. plicatilis sensu strictu.…”

The Mitochondrial Genome of the Screamer Louse Bothriometopus (Phthiraptera: Ischnocera): Effects of Extensive Gene Rearrangements on the Evolution of the Genome

“…The only other arthropod known to have all genes on the same strand is the copepod Tigriopus (Machida et al 2002;Burton et al, unpublished data). More broadly, a mt genome with all genes on the same strand is found in many metazoan phyla including Acanthocephala (Steinauer et al 2005), Annelida (Boore and Brown 2000), Cnidaria (Medina et al 2006;Brugler and France 2007), Mollusca (Hoffmann et al 1992), Nematoda (He et al 2005; but this is not the ancestral condition for the phylum, see Lavrov and Brown 2001), Platyhelminthes , Terebrantia (Helfenbein et al 2001) and Urochordata (Yokobori et al 1999(Yokobori et al , 2005. Indeed, genes transcribed on both strands only appears to be the ancestral state within Ecdysozoa , Vertebrata (Boore 1999) and several basal metazoan groups such as Porifera (Lavrov and Lang 2005a) and Placozoa (Signorovitch et al 2007).…”