Journal Article Unusually large number of mutations in asexually reproducing clonal planarian Dugesia japonica

Nishimura, Osamu  ,  Hosoda, Kazutaka  ,  Kawaguchi, Eri  ,  Yazawa, Shigenobu  ,  Hayashi, Tetsutaro  ,  Inoue, Takeshi  ,  Umesono, Yoshihiko  ,  Agata, Kiyokazu

10 ( 11 ) 2015-11-20 , Public Library of Science
We established a laboratory clonal strain of freshwater planarian (Dugesia japonica) that was derived from a single individual and that continued to undergo autotomous asexual reproduction for more than 20 years, and we performed large-scale genome sequencing and transcriptome analysis on it. Despite the fact that a completely clonal strain of the planarian was used, an unusually large number of mutations were detected. To enable quantitative genetic analysis of such a unique organism, we developed a new model called the Reference Gene Model, and used it to conduct large-scale transcriptome analysis. The results revealed large numbers of mutations not only outside but also inside gene-coding regions. Non-synonymous SNPs were detected in 74% of the genes for which valid ORFs were predicted. Interestingly, the high-mutation genes, such as metabolism- and defenserelated genes, were correlated with genes that were previously identified as diverse genes among different planarian species. Although a large number of amino acid substitutions were apparently accumulated during asexual reproduction over this long period of time, the planarian maintained normal body-shape, behaviors, and physiological functions. The results of the present study reveal a unique aspect of asexual reproduction.

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