Bikchurina Tatiana I, Golenishchev Fedor N, Kizilova Elena A, Mahmoudi Ahmad, Borodin Pavel M
Laboratory of Recombination and Segregation Analysis, Institute of Cytology and Genetics, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia.
Laboratory of Structural and Functional Genome Organization, Novosibirsk State University, Novosibirsk, Russia.
Front Genet. 2021 May 10;12:653837. doi: 10.3389/fgene.2021.653837. eCollection 2021.
The formation of hybrid sterility is an important stage of speciation. The voles of the genus , which is the most speciose genus of rodents, provide a good model for studying the cytological mechanisms of hybrid sterility. The voles of the "" group of the subgenus (2 = 54) comprising several recently diverged forms with unclear taxonomic status are especially interesting. To resolve the taxonomic status of and , we crossed both with , and alone with "obscurus" and and examined the reproductive performance of their F1 hybrids. All interspecies male hybrids were sterile. Female × and × hybrids were sterile as well. Therefore, , , and could be considered valid species. To gain an insight into the cytological mechanisms of male hybrid sterility, we carried out a histological analysis of spermatogenesis and a cytological analysis of chromosome synapsis, recombination, and epigenetic chromatin modifications in the germ cells of the hybrids using immunolocalization of key meiotic proteins. The hybrids showed wide variation in the onset of spermatogenesis arrest stage, from mature (although abnormal) spermatozoa to spermatogonia only. Chromosome asynapsis was apparently the main cause of meiotic arrest. The degree of asynapsis varied widely across cells, individuals, and the crosses-from partial asynapsis of several small bivalents to complete asynapsis of all chromosomes. The asynapsis was accompanied by a delayed repair of DNA double-strand breaks marked by RAD51 antibodies and silencing of unpaired chromatin marked by γH2A.X antibodies. Overall, the severity of disturbances in spermatogenesis in general and in chromosome synapsis in particular increased in the hybrids with an increase in the phylogenetic distance between their parental species.
杂种不育的形成是物种形成的一个重要阶段。田鼠属是啮齿动物中物种最丰富的属，为研究杂种不育的细胞学机制提供了一个很好的模型。亚属“”组的田鼠（2n = 54）包括几种最近分化的形态，其分类地位尚不清楚，特别引人关注。为了确定和的分类地位，我们将它们分别与杂交，并将单独与“obscurus”杂交，然后检查其F1杂种的繁殖性能。所有种间雄性杂种均不育。雌性×和×杂种也不育。因此，、和可被视为有效物种。为了深入了解雄性杂种不育的细胞学机制，我们对杂种生殖细胞的精子发生进行了组织学分析，并对染色体联会、重组和表观遗传染色质修饰进行了细胞学分析，采用关键减数分裂蛋白的免疫定位技术。杂种在精子发生停滞阶段的起始表现出广泛的差异，从成熟（尽管异常）精子到仅精原细胞。染色体联会异常显然是减数分裂停滞的主要原因。联会异常的程度在细胞、个体和杂交组合之间差异很大——从几个小二价体的部分联会异常到所有染色体的完全联会异常。联会异常伴随着由RAD51抗体标记的DNA双链断裂的延迟修复以及由γH2A.X抗体标记的未配对染色质的沉默。总体而言，随着亲本物种之间系统发育距离的增加，杂种中精子发生紊乱的严重程度，特别是染色体联会紊乱的严重程度也增加。
