Biodiversity Research Center, Academia Sinica, Taipei, 11529, Taiwan.
Department of Molecular Genetics and Gene Technology, College of Forestry Biotechnology, Vietnam National University of Forestry, Hanoi, Vietnam.
Sci Rep. 2017 Oct 9;7(1):12819. doi: 10.1038/s41598-017-13215-4.
Organismal genome sizes vary by six orders of magnitude and appear positively correlated with organismal size and complexity. Neutral models have been proposed to explain the broad patterns of genome size variation based on organism population sizes. In the Caenorhabditis genus, hermaphrodite genomes are smaller than those of gonochoristic species. One possible driving force for this genome size difference could be non-random chromosome segregation. In Caenorhabditis elegans, chromosome assortment is non-independent and violates Mendel's second law. In males, the shorter homologue of a heterozygous autosome pair preferentially co-segregates with the X chromosome while the longer one preferentially co-segregates with the nullo-X (O) chromosome in a process we call "skew". Since hermaphrodites preferentially receive the shorter chromosomes and can start populations independently, their genome size would be predicted to decrease over evolutionary time. If skew is an important driver for genome size reduction in hermaphroditic Caenorhabditis species, then it should be present in all congeneric species. In this study, we tested this hypothesis and found that skew is present in all eight examined species. Our results suggest that skew is likely the ancestral state in this genus. More speculatively, skew may drive genome size patterns in hermaphroditic species in other nematodes.
生物体的基因组大小差异可达六个数量级，并且似乎与生物体的大小和复杂性呈正相关。基于生物体种群大小，已经提出了中性模型来解释基因组大小变化的广泛模式。在秀丽隐杆线虫属中，雌雄同体的基因组比雌雄异体的物种小。这种基因组大小差异的一个可能驱动力可能是非随机的染色体分离。在秀丽隐杆线虫中，染色体组合是非独立的，违反了孟德尔第二定律。在雄性中，杂合子常染色体对的较短同源物优先与 X 染色体共分离，而较长的同源物优先与 nullo-X（O）染色体共分离，这个过程我们称之为“偏斜”。由于雌雄同体优先接收较短的染色体，并且可以独立启动种群，因此它们的基因组大小预计会随着进化时间的推移而减小。如果偏斜是雌雄同体秀丽隐杆线虫物种基因组减小的重要驱动力，那么它应该存在于所有同属物种中。在这项研究中，我们检验了这一假设，发现偏斜存在于所有 8 种被检查的物种中。我们的研究结果表明，偏斜可能是该属的原始状态。更具推测性的是，偏斜可能会驱动其他线虫雌雄同体物种的基因组大小模式。
