Chinone Ayako, Matsumoto Midori
Department of Biosciences and Informatics, Keio University, Yokohama, Japan.
Mol Reprod Dev. 2014 May;81(5):409-21. doi: 10.1002/mrd.22308. Epub 2014 Apr 22.
Rad51, a conserved eukaryotic protein, mediates the homologous-recombination repair of DNA double-strand breaks that occur during both mitosis and meiosis. During prophase I of meiosis, homologous recombination enhances the linkage between homologous chromosomes to increase the accuracy of segregation at anaphase I. In polyploidy situations, however, difficulties with homologous chromosome segregation often disrupt meiosis. Yet, triploid individuals of the planarian Dugesia ryukyuensis are able to produce functional gametes through a specialized form of meiosis. To shed light on the molecular mechanisms that promote successful meiosis in triploid D. ryukyuensis, we investigated rad51 gene function. We isolated three genes of the Rad51 family, the Rad51 homolog Dr-rad51 and the Rad51 paralogs Dr-rad51B and Dr-rad51C. Dr-rad51 was expressed in germ-line and presumably in somatic stem cells, but was not necessary for the regeneration of somatic tissue. RNA-interference (RNAi) depletion of Dr-rad51 during sexualization did not affect chromosome behavior in zygotene oocytes, but did result in the loss of chiasmata at the diplotene stage. Thus, homologous recombination does not appear to be necessary for synapsis, but is needed for crossover and proper segregation in D. ryukyuensis.
Rad51是一种保守的真核生物蛋白质，介导有丝分裂和减数分裂过程中发生的DNA双链断裂的同源重组修复。在减数分裂前期I，同源重组增强了同源染色体之间的联系，以提高后期I分离的准确性。然而，在多倍体情况下，同源染色体分离的困难常常会破坏减数分裂。不过，琉球涡虫的三倍体个体能够通过一种特殊形式的减数分裂产生功能性配子。为了阐明促进三倍体琉球涡虫减数分裂成功的分子机制，我们研究了rad51基因的功能。我们分离出了Rad51家族的三个基因，即Rad51同源物Dr-rad51以及Rad51旁系同源物Dr-rad51B和Dr-rad51C。Dr-rad51在生殖系中表达，可能也在体干细胞中表达，但对于体组织的再生并非必需。在性成熟过程中，通过RNA干扰（RNAi）耗尽Dr-rad51不会影响偶线期卵母细胞中的染色体行为，但会导致双线期交叉的缺失。因此，同源重组似乎对偶线期配对不是必需的，但对琉球涡虫的交叉和正确分离是必需的。
