Basheva Ekaterina A, Torgasheva Anna A, Gomez Fernandez Maria Jimena, Boston Emma, Mirol Patricia, Borodin Pavel M
Russian Academy of Sciences, Siberian Department, Institute of Cytology and Genetics, Novosibirsk, 630090, Russia.
Chromosome Res. 2014 Sep;22(3):351-63. doi: 10.1007/s10577-014-9429-5. Epub 2014 Jun 13.
The chromosomal speciation hypothesis suggests that irregularities in synapsis, recombination, and segregation in heterozygotes for chromosome rearrangements may restrict gene flow between karyotypically distinct populations and promote speciation. Ctenomys talarum is a South American subterranean rodent inhabiting the coastal regions of Argentina, whose populations polymorphic for Robertsonian and tandem translocations seem to have a very restricted gene flow. To test if chromosomal differences are involved in isolation among its populations, we examined chromosome pairing, recombination, and meiotic silencing of unsynapsed chromatin in male meiosis of simple and complex translocation heterozygotes using immunolocalization of the MLH1 marking mature recombination nodules and phosphorylated histone γH2A.X marking unrepaired double-strand breaks. We observed small asynaptic areas labeled by γH2A.X in pericentromeric regions of the chromosomes involved in the trivalents and quadrivalents. We also observed a decrease of recombination frequency and a distalization of the crossover distribution in the heterozygotes and metacentric homozygotes compared to acrocentric homozygotes. We suggest that the asynapsis of the pericentromeric regions are unlikely to induce germ cell death and decrease fertility of the heterozygotes; however, suppressed recombination in pericentromeric areas of the multivalents may reduce gene flow between chromosomally different populations of the Talas tuco-tuco.
染色体物种形成假说认为，染色体重排杂合子在联会、重组和分离过程中的异常可能会限制核型不同的种群之间的基因流动，并促进物种形成。塔拉鼠是一种生活在阿根廷沿海地区的南美地下啮齿动物，其种群在罗伯逊易位和串联易位方面具有多态性，似乎基因流动非常有限。为了检验染色体差异是否参与其种群间的隔离，我们使用标记成熟重组结节的MLH1和标记未修复双链断裂的磷酸化组蛋白γH2A.X的免疫定位，研究了简单和复杂易位杂合子雄性减数分裂中染色体配对、重组和未联会染色质的减数分裂沉默。我们在涉及三价体和四价体的染色体着丝粒区域观察到由γH2A.X标记的小的未联会区域。我们还观察到，与近端着丝粒纯合子相比，杂合子和中着丝粒纯合子的重组频率降低，交叉分布向远端移动。我们认为，着丝粒区域的未联会不太可能诱导生殖细胞死亡并降低杂合子的生育力；然而，多价体着丝粒区域重组的抑制可能会减少塔拉土豚染色体不同种群之间的基因流动。
