Laboratory of Fish Genetics, Institute of Animal Physiology and Genetics, Czech Academy of Sciences, Rumburská 89, 277 21 Liběchov, Czech Republic.
Laboratory of Arachnid Cytogenetics, Department of Genetics and Microbiology, Faculty of Science, Charles University, Viničná 5, 128 44 Prague, Czech Republic.
Genes (Basel). 2020 Jul 24;11(8):849. doi: 10.3390/genes11080849.
Spiders are an intriguing model to analyse sex chromosome evolution because of their peculiar multiple X chromosome systems. Y chromosomes were considered rare in this group, arising after neo-sex chromosome formation by X chromosome-autosome rearrangements. However, recent findings suggest that Y chromosomes are more common in spiders than previously thought. Besides neo-sex chromosomes, they are also involved in the ancient XXY system of haplogyne spiders, whose origin is unknown. Furthermore, spiders seem to exhibit obligatorily one or two pairs of cryptic homomorphic XY chromosomes (further cryptic sex chromosome pairs, CSCPs), which could represent the ancestral spider sex chromosomes. Here, we analyse the molecular differentiation of particular types of spider Y chromosomes in a representative set of ten species by comparative genomic hybridisation (CGH). We found a high Y chromosome differentiation in haplogyne species with XXY system except for spp. CSCP chromosomes exhibited generally low differentiation. Possible mechanisms and factors behind the observed patterns are discussed. The presence of autosomal regions marked predominantly or exclusively with the male or female probe was also recorded. We attribute this pattern to intraspecific variability in the copy number and distribution of certain repetitive DNAs in spider genomes, pointing thus to the limits of CGH in this arachnid group. In addition, we confirmed nonrandom association of chromosomes belonging to particular CSCPs at spermatogonial mitosis and spermatocyte meiosis and their association with multiple Xs throughout meiosis. Taken together, our data suggest diverse evolutionary pathways of molecular differentiation in different types of spider Y chromosomes.
蜘蛛是分析性染色体进化的有趣模型，因为它们具有特殊的多 X 染色体系统。Y 染色体被认为在这个群体中很少见，是通过 X 染色体-常染色体重排形成新性染色体后产生的。然而，最近的发现表明，Y 染色体在蜘蛛中的出现频率比以前认为的要高。除了新性染色体外，它们还参与了haplogyne 蜘蛛的古老 XXY 系统，其起源尚不清楚。此外，蜘蛛似乎表现出强制性的一对或两对隐性同形 XY 染色体（更多隐性性染色体对，CSCPs），这可能代表了祖先蜘蛛的性染色体。在这里，我们通过比较基因组杂交（CGH）分析了十个代表性物种中特定类型的蜘蛛 Y 染色体的分子分化。我们发现，除了 spp. 之外，具有 XXY 系统的 haplogyne 物种中的 Y 染色体分化很高。CSCP 染色体通常分化较低。讨论了观察到的模式背后的可能机制和因素。还记录了带有雄性或雌性探针的常染色体区域的存在。我们将这种模式归因于蜘蛛基因组中某些重复 DNA 的数量和分布在种内的变异，从而指出 CGH 在这个蛛形纲动物群体中的局限性。此外，我们证实了属于特定 CSCP 的染色体在精原细胞有丝分裂和精母细胞减数分裂中的非随机关联，以及它们在整个减数分裂过程中与多个 X 染色体的关联。总之，我们的数据表明，不同类型的蜘蛛 Y 染色体的分子分化存在多种进化途径。
