Lisachov Artem P, Trifonov Vladimir A, Giovannotti Massimo, Ferguson-Smith Malcolm A, Borodin Pavel M
Institute of Cytology and Genetics, Russian Academy of Sciences, Siberian Branch, Novosibirsk 630090, Russia.
Institute of Molecular and Cellular Biology, Russian Academy of Sciences, Siberian Branch, Novosibirsk 630090, Russia.
Comp Cytogenet. 2017 Mar 6;11(1):129-141. doi: 10.3897/CompCytogen.v11i1.10916. eCollection 2017.
Although the evolutionary importance of meiotic recombination is not disputed, the significance of interspecies differences in the recombination rates and recombination landscapes remains under-appreciated. Recombination rates and distribution of chiasmata have been examined cytologically in many mammalian species, whereas data on other vertebrates are scarce. Immunolocalization of the protein of the synaptonemal complex (SYCP3), centromere proteins and the mismatch-repair protein MLH1 was used, which is associated with the most common type of recombination nodules, to analyze the pattern of meiotic recombination in the male of two species of iguanian lizards, Voigt, 1832 and (Cope, 1862). These species are separated by a relatively long evolutionary history although they retain the ancestral iguanian karyotype. In both species similar and extremely uneven distributions of MLH1 foci along the macrochromosome bivalents were detected: approximately 90% of crossovers were located at the distal 20% of the chromosome arm length. Almost total suppression of recombination in the intermediate and proximal regions of the chromosome arms contradicts the hypothesis that "homogenous recombination" is responsible for the low variation in GC content across the anole genome. It also leads to strong linkage disequilibrium between the genes located in these regions, which may benefit conservation of co-adaptive gene arrays responsible for the ecological adaptations of the anoles.
尽管减数分裂重组在进化上的重要性并无争议，但物种间重组率和重组图谱差异的意义仍未得到充分重视。许多哺乳动物物种已通过细胞学方法研究了交叉频率和交叉分布情况，而关于其他脊椎动物的数据则很少。利用联会复合体（SYCP3）蛋白、着丝粒蛋白和错配修复蛋白MLH1的免疫定位分析了两种鬣蜥科蜥蜴（1832年命名的沃氏鬣蜥和1862年命名的某种鬣蜥）雄性减数分裂重组模式，MLH1与最常见的重组结节类型相关。尽管这两个物种保留了鬣蜥科的祖先核型，但它们有着相对较长的进化历史。在这两个物种中，均检测到沿常染色体二价体的MLH1位点分布相似且极不均匀：约90%的交叉位于染色体臂长度的远端20%处。染色体臂的中间和近端区域几乎完全抑制重组，这与“均匀重组”导致安乐蜥基因组中GC含量低变异的假设相矛盾。这也导致位于这些区域的基因之间存在强烈的连锁不平衡，这可能有利于负责安乐蜥生态适应的共适应基因阵列的保存。
