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      The complete mitochondrial genomes for three Toxocara species of human and animal health significance

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          Abstract

          Background

          Studying mitochondrial (mt) genomics has important implications for various fundamental areas, including mt biochemistry, physiology and molecular biology. In addition, mt genome sequences have provided useful markers for investigating population genetic structures, systematics and phylogenetics of organisms. Toxocara canis, Toxocara cati and Toxocara malaysiensis cause significant health problems in animals and humans. Although they are of importance in human and animal health, no information on the mt genomes for any of Toxocara species is available.

          Results

          The sizes of the entire mt genome are 14,322 bp for T. canis, 14029 bp for T. cati and 14266 bp for T. malaysiensis, respectively. These circular genomes are amongst the largest reported to date for all secernentean nematodes. Their relatively large sizes relate mainly to an increased length in the AT-rich region. The mt genomes of the three Toxocara species all encode 12 proteins, two ribosomal RNAs and 22 transfer RNA genes, but lack the ATP synthetase subunit 8 gene, which is consistent with all other species of Nematode studied to date, with the exception of Trichinella spiralis. All genes are transcribed in the same direction and have a nucleotide composition high in A and T, but low in G and C. The contents of A+T of the complete genomes are 68.57% for T. canis, 69.95% for T. cati and 68.86% for T. malaysiensis, among which the A+T for T. canis is the lowest among all nematodes studied to date. The AT bias had a significant effect on both the codon usage pattern and amino acid composition of proteins. The mt genome structures for three Toxocara species, including genes and non-coding regions, are in the same order as for Ascaris suum and Anisakis simplex, but differ from Ancylostoma duodenale, Necator americanus and Caenorhabditis elegans only in the location of the AT-rich region, whereas there are substantial differences when compared with Onchocerca volvulus, Dirofiliria immitis and Strongyloides stercoralis. Phylogenetic analyses based on concatenated amino acid sequences of 12 protein-coding genes revealed that the newly described species T. malaysiensis was more closely related to T. cati than to T. canis, consistent with results of a previous study using sequences of nuclear internal transcribed spacers as genetic markers.

          Conclusion

          The present study determined the complete mt genome sequences for three roundworms of human and animal health significance, which provides mtDNA evidence for the validity of T. malaysiensis and also provides a foundation for studying the systematics, population genetics and ecology of these and other nematodes of socio-economic importance.

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          Most cited references32

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          With its theoretical basis firmly established in molecular evolutionary and population genetics, the comparative DNA and protein sequence analysis plays a central role in reconstructing the evolutionary histories of species and multigene families, estimating rates of molecular evolution, and inferring the nature and extent of selective forces shaping the evolution of genes and genomes. The scope of these investigations has now expanded greatly owing to the development of high-throughput sequencing techniques and novel statistical and computational methods. These methods require easy-to-use computer programs. One such effort has been to produce Molecular Evolutionary Genetics Analysis (MEGA) software, with its focus on facilitating the exploration and analysis of the DNA and protein sequence variation from an evolutionary perspective. Currently in its third major release, MEGA3 contains facilities for automatic and manual sequence alignment, web-based mining of databases, inference of the phylogenetic trees, estimation of evolutionary distances and testing evolutionary hypotheses. This paper provides an overview of the statistical methods, computational tools, and visual exploration modules for data input and the results obtainable in MEGA.
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            We prospectively evaluated quality of life and visual analogue scale pain scores after bilateral thoracoscopic splanchnicectomy in 55 patients with small-duct chronic pancreatitis and abdominal pain. The perioperative morbidity rate was 11% and there were no perioperative deaths. Four late deaths occurred (7%), and three patients were lost to follow-up. Patients were divided into those who had prior operative or endoscopic interventions (N = 38) and those who did not (N = 17). Preoperatively there were no significant differences between the two groups with regard to age, sex, etiology, pain score, or narcotic use. Pain score, narcotic use, and symptoms scales improved significantly in both groups at 3 and 6 months postoperatively (P < 0.0001). The group with no prior surgical or endoscopic intervention did significantly better initially (P < 0.007), and the improvements in their quality-of-life and pain scores continued for the remainder of the study. In contrast, quality-of-life and pain scores in patients who had undergone prior surgical or endoscopic intervention returned to baseline by 12 months postoperatively and remained poor throughout the remainder of the study. Bilateral thoracoscopic splanchnicectomy appears to work best in patients who have had no prior operative or endoscopic interventions.
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                Author and article information

                Journal
                BMC Genomics
                BMC Genomics
                BioMed Central
                1471-2164
                2008
                16 May 2008
                : 9
                : 224
                Affiliations
                [1 ]Laboratory of Parasitology, College of Veterinary Medicine, South China Agricultural University, Guangzhou, Guangdong Province 510642, ProC
                [2 ]Department of Veterinary Medicine, Agricultural College, Guangdong Ocean University, Zhanjiang, Guangdong Province 524088, ProC
                [3 ]Key Laboratory of Marine Bio-resources Sustainable Utilization, South China Sea Institute of Oceanology, Chinese Academy of Sciences, Guangzhou, Guangdong Province 510301, ProC
                Article
                1471-2164-9-224
                10.1186/1471-2164-9-224
                2396643
                18482460
                3ec1fb8b-f6be-47ee-a277-2e9c5af17c01
                Copyright © 2008 Li et al; licensee BioMed Central Ltd.

                This is an Open Access article distributed under the terms of the Creative Commons Attribution License ( http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

                History
                : 24 September 2007
                : 16 May 2008
                Categories
                Research Article

                Genetics
                Genetics

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