Garnier Olivier, Serrano Vincent, Duharcourt Sandra, Meyer Eric
Laboratoire de Génétique Moléculaire, CNRS UMR 8541, Ecole Normale Supérieure, 46, rue d'Ulm, 75005 Paris, France.
Mol Cell Biol. 2004 Sep;24(17):7370-9. doi: 10.1128/MCB.24.17.7370-7379.2004.
The germ line genome of ciliates is extensively rearranged during development of the somatic macronucleus. Numerous sequences are eliminated, while others are amplified to a high ploidy level. In the Paramecium aurelia group of species, transformation of the maternal macronucleus with transgenes at high copy numbers can induce the deletion of homologous genes in sexual progeny, when a new macronucleus develops from the wild-type germ line. We show that this trans-nuclear effect correlates with homology-dependent silencing of maternal genes before autogamy and with the accumulation of approximately 22- to 23-nucleotide (nt) RNA molecules. The same effects are induced by feeding cells before meiosis with bacteria containing double-stranded RNA, suggesting that small interfering RNA-like molecules can target deletions. Furthermore, experimentally induced macronuclear deletions are spontaneously reproduced in subsequent sexual generations, and reintroduction of the missing gene into the variant macronucleus restores developmental amplification in sexual progeny. We discuss the possible roles of the approximately 22- to 23-nt RNAs in the targeting of deletions and the implications for the RNA-mediated genome-scanning process that is thought to determine developmentally regulated rearrangements in ciliates.
在体细胞大核的发育过程中，纤毛虫的种系基因组会发生广泛重排。大量序列被消除，而其他序列则被扩增至高倍性水平。在双小核草履虫物种组中，当新的大核从野生型种系发育而来时，用高拷贝数的转基因转化母本大核可诱导有性后代中同源基因的缺失。我们发现这种跨核效应与自配前母本基因的同源依赖性沉默以及约22至23个核苷酸（nt）的RNA分子的积累相关。在减数分裂前用含有双链RNA的细菌喂养细胞也会诱导相同的效应，这表明类似小干扰RNA的分子可以靶向缺失。此外，实验诱导的大核缺失在随后的有性世代中会自发重现，并且将缺失的基因重新引入变异大核中可恢复有性后代中的发育扩增。我们讨论了约22至23 nt的RNA在靶向缺失中的可能作用以及对RNA介导的基因组扫描过程的影响，该过程被认为决定了纤毛虫中发育调控的重排。
