Arai K, Fujimoto T
Hokkaido University, Hakodate, Japan. araikt @ fish.hokudai.ac.jp
Cytogenet Genome Res. 2013;140(2-4):226-40. doi: 10.1159/000353301. Epub 2013 Jul 9.
The loach (Misgurnus anguillicaudatus) is an excellent animal model to elucidate biological origin and evolutionary significance of genome duplication and unisexual reproduction because artificially induced and naturally occurring polyploids and parthenogenetic (gynogenetic, androgenetic) animals can be compared. First, we summarize the chromosome manipulation techniques to induce triploids and tetraploids by inhibiting meiotic or mitotic divisions of inseminated eggs, respectively, as well as parthenogenetic animals, obtained after fertilization with genetically inactivated gametes. Then, we review the knowledge on natural polyploid and unisexual lineages found in Misgurnus loaches. A natural diploid-tetraploid complex occurs in wild populations in central China, and these diploid and tetraploid loaches reproduce bisexually. Chinese tetraploids are considered autotetraploid, which may have arisen by doubling of the entire genome of an ancestral diploid, based on cytogenetic results from FISH (fluorescence in situ hybridization) karyotypes and meiotic configurations. In contrast, gynogenetically reproducing clonal diploid lineages have been discovered in a few wild populations in Japan, although most wild-type individuals are bisexually reproducing diploids. Such clonal diploid loaches sometimes produce triploid progeny by accidental incorporation of a sperm nucleus into an unreduced diploid egg, and the resulting triploid generates haploid eggs by meiotic hybridogenesis. Unreduced diploid gametes of clonal loaches are generated by a cytological mechanism, premeiotic endomitosis, which likely occurs in the early (gonium stage) germ cells. Initiation of gynogenetic development is related to a failure of decondensation of the male (sperm) pronucleus in unreduced diploid eggs of a clonal loach. Clonal lineages may have arisen from a past hybrid event between genetically divergent groups, but their exact origins are unknown at present. See also the sister article focusing on plants by Hegarty et al. in this themed issue.
泥鳅（Misgurnus anguillicaudatus）是阐明基因组复制和孤雌生殖的生物学起源及进化意义的优良动物模型，因为可以对人工诱导产生的和自然出现的多倍体以及孤雌生殖（雌核发育、雄核发育）动物进行比较。首先，我们总结了分别通过抑制受精卵的减数分裂或有丝分裂来诱导三倍体和四倍体的染色体操作技术，以及用遗传灭活配子受精后获得的孤雌生殖动物。然后，我们回顾了在泥鳅中发现的天然多倍体和孤雌生殖谱系的相关知识。在中国中部的野生种群中存在天然的二倍体 - 四倍体复合体，这些二倍体和四倍体泥鳅进行两性生殖。基于荧光原位杂交（FISH）核型分析和减数分裂构型的细胞遗传学结果，中国的四倍体被认为是同源四倍体，可能是由一个祖先二倍体的整个基因组加倍产生的。相比之下，在日本的一些野生种群中发现了进行雌核生殖的克隆二倍体谱系，尽管大多数野生型个体是进行两性生殖的二倍体。这种克隆二倍体泥鳅有时会通过精子核偶然进入未减数的二倍体卵子而产生三倍体后代，并且产生的三倍体通过减数分裂杂种发生产生单倍体卵子。克隆泥鳅的未减数二倍体配子是通过一种细胞学机制——减数分裂前核内有丝分裂产生的，这种机制可能发生在早期（生殖原细胞阶段）生殖细胞中。雌核生殖发育的起始与克隆泥鳅未减数二倍体卵子中雄性（精子）原核去浓缩失败有关。克隆谱系可能起源于过去遗传上不同群体之间的杂交事件，但它们的确切起源目前尚不清楚。另见本期主题中Hegarty等人聚焦植物的姊妹文章。
