Itono Masaki, Okabayashi Naoki, Morishima Kagayaki, Fujimoto Takafumi, Yoshikawa Hiroyuki, Yamaha Etsuro, Arai Katsutoshi
Graduate School of Fisheries Sciences, Hokkaido University, Hakodate 041-8611, Japan.
J Exp Zool A Ecol Genet Physiol. 2007 Jan 1;307(1):35-50. doi: 10.1002/jez.a.344.
The loach Misgurnus anguillicaudatus comprises diploid clonal, triploid and diploid-triploid mosaic individuals in a wild population on Hokkaido island, Japan. When diploid eggs of clonal loaches are fertilized by haploid sperm of normal bisexual loaches, both diploid clonal and non-diploid aclonal individuals occur in the progeny. Flow cytometry and microsatellite analyses revealed that the occurrence of triploid, diploid-triploid and other progeny was essentially due to the genetic incorporation of sperm to diploid clonal genomes of unreduced eggs. In this study, we examined the influence of water temperature from fertilization to early embryogenesis on frequencies of diploid clonal and other progeny and observed that progeny of three out of four clonal females examined exhibited approximately constant rates of diploid clonal individuals (54.2-68.9%) at hatching stage. Thus, no drastic increase of non-diploid progeny was detected. However, the 28 degrees C group of the fourth clonal female gave significantly lower rate (28.1%) of diploid clonal progeny, suggesting that this temperature might be a critical or a borderline temperature inducing sperm incorporation. We also examined the cytological process by which diploid clonal and other aclonal progeny develop after fertilization. In some fertilized eggs, the sperm nucleus remained condensed throughout fertilization and early embryogenesis and never fused with the female pronucleus. This cytological observation concludes that clonal eggs develop by the mechanism of gynogenesis. However, some other eggs showed the cytological process of syngamy between the female pronucleus and an accidentally formed male nucleus, suggesting the formation of triploid progeny. The syngamy between an accidentally activated sperm nucleus with a male pronucleus-like structure and nucleus of a blastomere of gynogenetically developing clonal diploid embryo might produce a diploid-triploid mosaic individual.
在日本北海道岛的一个野生种群中，泥鳅（Misgurnus anguillicaudatus）包含二倍体克隆个体、三倍体个体以及二倍体 - 三倍体嵌合体个体。当克隆泥鳅的二倍体卵子被正常两性泥鳅的单倍体精子受精时，后代中会出现二倍体克隆个体和非二倍体非克隆个体。流式细胞术和微卫星分析表明，三倍体、二倍体 - 三倍体及其他后代的出现主要是由于精子基因整合到未减数卵子的二倍体克隆基因组中。在本研究中，我们检测了从受精到早期胚胎发育阶段的水温对二倍体克隆个体及其他后代频率的影响，观察到在孵化阶段，所检测的四只克隆雌鳅中有三只的后代中二倍体克隆个体的比例大致恒定（54.2 - 68.9%）。因此，未检测到非二倍体后代的大幅增加。然而，第四只克隆雌鳅在28摄氏度组中二倍体克隆后代的比例显著较低（28.1%），这表明该温度可能是诱导精子整合的临界温度或临界边缘温度。我们还研究了二倍体克隆个体和其他非克隆后代受精后发育的细胞学过程。在一些受精卵中，精子核在整个受精和早期胚胎发育过程中保持浓缩状态，从未与雌原核融合。这一细胞学观察结果表明，克隆卵子通过雌核发育机制发育。然而，其他一些卵子显示出雌原核与偶然形成的雄核之间发生了受精融合过程，这表明三倍体后代的形成。偶然激活的具有雄原核样结构的精子核与雌核发育的克隆二倍体胚胎的卵裂球核之间的受精融合可能产生二倍体 - 三倍体嵌合体个体。
