Hirai Hirohisa, Hirai Yuriko, LoVerde Philip T
Primate Research Institute, Kyoto University, Inuyama, Aichi 484-8506, Japan.
Parasitol Int. 2012 Dec;61(4):684-9. doi: 10.1016/j.parint.2012.07.007. Epub 2012 Jul 22.
Chromosomes of schistosome parasites among digenetic flukes have a unique evolution because they exhibit the sex chromosomes ZW, which are not found in the other groups of flukes that are hermaphrodites. We conducted molecular cytogenetic analyses for investigating the sex chromosome evolution using chromosome paint analysis and BAC clones mapping. To carry this out, we developed a technique for making paint probes of genomic DNA from a single scraped chromosome segment using a chromosome microdissection system, and a FISH mapping technique for BAC clones. Paint probes clearly identified each of the 8 pairs of chromosomes by a different fluorochrome color. Combination analysis of chromosome paint analysis with Z/W probes and chromosome mapping with 93 BAC clones revealed that the W chromosome of Schistosoma mansoni has evolved by at least four inversion events and heterochromatinization. Nine of 93 BAC clones hybridized with both the Z and W chromosomes, but the locations were different between Z and W chromosomes. The homologous regions were estimated to have moved from the original Z chromosome to the differentiated W chromosome by three inversions events that occurred before W heterohcromatinization. An inversion that was observed in the heterochromatic region of the W chromosome likely occurred after W heterochromatinization. These inversions and heterochromatinization are hypothesized to be the key factors that promoted the evolution of the W chromosome of S. mansoni.
复殖吸虫中的血吸虫寄生虫染色体具有独特的进化过程，因为它们呈现出ZW性染色体，而在其他雌雄同体的吸虫类群中并未发现这种性染色体。我们进行了分子细胞遗传学分析，使用染色体涂染分析和BAC克隆定位来研究性染色体的进化。为了实现这一目标，我们开发了一种利用染色体显微切割系统从单个刮取的染色体片段制备基因组DNA涂染探针的技术，以及一种用于BAC克隆的荧光原位杂交定位技术。涂染探针通过不同的荧光染料颜色清晰地识别出8对染色体中的每一对。染色体涂染分析与Z/W探针的联合分析以及93个BAC克隆的染色体定位显示，曼氏血吸虫的W染色体至少通过四次倒位事件和异染色质化进化而来。93个BAC克隆中有9个与Z和W染色体都杂交，但在Z和W染色体上的位置不同。同源区域估计是通过在W异染色质化之前发生的三次倒位事件从原始的Z染色体转移到分化的W染色体上的。在W染色体异染色质区域观察到的一次倒位可能发生在W异染色质化之后。这些倒位和异染色质化被认为是促进曼氏血吸虫W染色体进化的关键因素。
