The Federal Research Center Institute of Cytology and Genetics SB RAS, Lavrentiev ave., 10, Novosibirsk, 630090, Russian Federation.
Evolutionary Biology, Zoological Institute, University of Basel, Basel, CH-4051, Switzerland.
Sci Rep. 2017 Jul 20;7(1):6066. doi: 10.1038/s41598-017-06498-0.
The free-living flatworm Macrostomum lignano is a model organism for evolutionary and developmental biology studies. Recently, an unusual karyotypic diversity was revealed in this species. Specifically, worms are either 'normal' 2n = 8, or they are aneuploid with one or two additional large chromosome(s) (i.e. 2n = 9 or 2n = 10, respectively). Aneuploid worms did not show visible behavioral or morphological abnormalities and were successful in reproduction. In this study, we generated microdissected DNA probes from chromosome 1 (further called MLI1), chromosome 2 (MLI2), and a pair of similar-sized smaller chromosomes (MLI3, MLI4). FISH using these probes revealed that MLI1 consists of contiguous regions homologous to MLI2-MLI4, suggesting that MLI1 arose due to the whole genome duplication and subsequent fusion of one full chromosome set into one large metacentric chromosome. Therefore, one presumably full haploid genome was packed into MLI1, leading to hidden tetraploidy in the M. lignano genome. The study of Macrostomum sp. 8 - a sibling species of M. lignano - revealed that it usually has one additional pair of large chromosomes (2n = 10) showing a high homology to MLI1, thus suggesting hidden hexaploidy in its genome. Possible evolutionary scenarios for the emergence of the M. lignano and Macrostomum sp. 8 genomes are discussed.
自由生活的扁形动物 Macrostomum lignano 是进化和发育生物学研究的模式生物。最近，在该物种中发现了一种不寻常的染色体组多样性。具体来说，这些蠕虫要么是“正常”的 2n = 8，要么是具有一个或两个额外大染色体的非整倍体（即 2n = 9 或 2n = 10，分别）。非整倍体蠕虫没有表现出明显的行为或形态异常，并且能够成功繁殖。在这项研究中，我们从染色体 1（进一步称为 MLI1）、染色体 2（MLI2）和一对类似大小的较小染色体（MLI3、MLI4）生成了显微解剖 DNA 探针。使用这些探针的 FISH 显示，MLI1 由与 MLI2-MLI4 连续同源的区域组成，表明 MLI1 是由于全基因组复制和随后将一整套完整染色体融合成一个大型着丝粒染色体而产生的。因此，一个假定的完整单倍体基因组被包装到 MLI1 中，导致 M. lignano 基因组中的隐藏四倍体。对 Macrostomum sp. 8 的研究——M. lignano 的一个姊妹种——表明它通常具有一对额外的大染色体（2n = 10），与 MLI1 具有高度同源性，因此表明其基因组中存在隐藏的六倍体。讨论了 M. lignano 和 Macrostomum sp. 8 基因组出现的可能进化情景。
