Koga Akihiko, Iida Atsuo, Hori Hiroshi, Shimada Atsuko, Shima Akihiro
Division of Biological Science, Graduate School of Science, Nagoya University, Nagoya, Japan.
Mol Biol Evol. 2006 Jul;23(7):1414-9. doi: 10.1093/molbev/msl003. Epub 2006 May 3.
DNA-based transposable elements, or DNA transposons, transpose in a cut-and-paste fashion, involving excision from the chromosome. If this process affects the function of a host gene and the excision rate is high, any gene associated with such an element would clearly be in a genetically "unstable" state, and there are many examples of unstable genes in various organisms. However, none have hitherto been reported in vertebrates. We here document the finding of an unstable mutant gene in the medaka fish, Oryzias latipes, a useful model animal for vertebrate genetics and evolutionary studies. In an inbred strain, excision of the Tol2 element inserted in a pigmentation gene occurs spontaneously, giving rise to different heritable phenotypes and new mutant genes that carry different excision footprint sequences. The phenotypic mutation rate is as high as 2% per gamete, representing a 1000-fold increase from spontaneous mutation rates so far determined with the same organism. With mutations caused by insertion, and then excision, of transposons, one can no longer recognize participation of transposons in their generation. Thus, the impact of DNA transposons on vertebrate genomes may be, and may have been, larger than commonly supposed.
基于DNA的转座元件，即DNA转座子，以“剪切和粘贴”的方式进行转座，包括从染色体上切除。如果这个过程影响宿主基因的功能且切除率很高，那么与这种元件相关的任何基因显然都处于遗传“不稳定”状态，而且在各种生物体中有许多不稳定基因的例子。然而，迄今为止在脊椎动物中尚未有相关报道。我们在此记录了在青鳉（Oryzias latipes）中发现的一个不稳定突变基因，青鳉是用于脊椎动物遗传学和进化研究的一种有用的模式动物。在一个近交系中，插入色素沉着基因中的Tol2元件会自发切除，产生不同的可遗传表型以及携带不同切除足迹序列的新突变基因。表型突变率高达每配子2%，比目前用同一生物体测定的自发突变率高出1000倍。由于转座子插入然后切除导致突变，人们无法再识别转座子在其产生过程中的参与情况。因此，DNA转座子对脊椎动物基因组的影响可能一直比通常认为的要大。
