Robinson T, Katz L A
Department of Biological Sciences, Smith College, USA.
Mol Biol Evol. 2007 Nov;24(11):2495-503. doi: 10.1093/molbev/msm203. Epub 2007 Sep 22.
Recognition of the role of non-Mendelian inheritance is on the rise, particularly as epigenetic phenomena are shown to shape the transformation of genomes into phenotypes. Ciliates provide a model system in which to explore the role of epigenetics because ciliates have both a germ line (micronuclear) and somatic (macronuclear) genome within every cell. In the ciliate Chilodonella uncinata, the macronucleus is extensively fragmented such that many genes end up on their own chromosomes. Hence, it is possible to track the fate of unlinked genes within macronuclei of C. uncinata. Here we demonstrate that the pattern of inheritance in isolates of C. uncinata is complex and involves both Mendelian transmission between micronuclei and macronuclei and epigenetic phenomena. The macronuclei from 2 isolates of C. uncinata and their progeny share identical rDNA loci and 2 identical beta-tubulin paralogs, yet have different actin paralogs and some beta-tubulin paralogs that are not shared. We propose a model in which all the divergent paralogs are present in the ciliate micronuclei. Under this model, different paralogs are retained in developing macronuclei following conjugation. We further speculate that an epigenetic mechanism, such as RNA interference, is involved in selective retention of specific paralogs within lines. This system allows the exploration of epigenetic phenomena that shape somatic genomes and provides parallels to studies of the development of somatic nuclei within animals.
对非孟德尔遗传作用的认识正在不断提高，尤其是当表观遗传现象被证明会影响基因组向表型的转变时。纤毛虫提供了一个探索表观遗传学作用的模型系统，因为纤毛虫的每个细胞内都有生殖系（微核）和体细胞（大核）基因组。在纤毛虫斜管虫中，大核被广泛分割，以至于许多基因最终位于它们自己的染色体上。因此，有可能追踪斜管虫大核内不连锁基因的命运。在这里，我们证明了斜管虫分离株的遗传模式是复杂的，涉及微核和大核之间的孟德尔遗传传递以及表观遗传现象。来自2个斜管虫分离株及其后代的大核共享相同的rDNA位点和2个相同的β-微管蛋白旁系同源物，但具有不同的肌动蛋白旁系同源物和一些不共享的β-微管蛋白旁系同源物。我们提出了一个模型，其中所有不同的旁系同源物都存在于纤毛虫的微核中。在这个模型中，不同的旁系同源物在接合后发育中的大核中被保留。我们进一步推测，一种表观遗传机制，如RNA干扰，参与了特定旁系同源物在品系内的选择性保留。这个系统允许探索塑造体细胞基因组的表观遗传现象，并为动物体内体细胞核发育的研究提供了类似的情况。
