Computational Biology Unit, Scientific Institute IRCCS E. MEDEA, 23842 Bosisio Parini, Italy.
Genes (Basel). 2024 Sep 3;15(9):1159. doi: 10.3390/genes15091159.
Structural Maintenance of Chromosomes (SMC) complexes are an evolutionary conserved protein family. In most eukaryotes, three SMC complexes have been characterized, as follows: cohesin, condensin, and SMC5/6 complexes. These complexes are involved in a plethora of functions, and defects in SMC genes can lead to an increased risk of chromosomal abnormalities, infertility, and cancer. To investigate the evolution of SMC complex genes in mammals, we analyzed their selective patterns in an extended phylogeny. Signals of positive selection were identified for condensin NCAPG, for two SMC5/6 complex genes ( and ), and for all cohesin genes with almost exclusive meiotic expression (, , , and ). For the latter, evolutionary rates correlate with expression during female meiosis, and most positively selected sites fall in intrinsically disordered regions (IDRs). Our results support growing evidence that IDRs are fast evolving, and that they most likely contribute to adaptation through modulation of phase separation. We suggest that the natural selection signals identified in SMC complexes may be the result of different selective pressures: a host-pathogen arms race in the condensin and SMC5/6 complexes, and an intragenomic conflict for meiotic cohesin genes that is similar to that described for centromeres and telomeres.
结构维持染色体（SMC）复合物是一个进化保守的蛋白质家族。在大多数真核生物中，已经鉴定出三种 SMC 复合物，如下所示：黏连蛋白、凝聚素和 SMC5/6 复合物。这些复合物参与了大量的功能，SMC 基因的缺陷会导致染色体异常、不育和癌症的风险增加。为了研究 SMC 复合物基因在哺乳动物中的进化，我们在扩展的系统发育中分析了它们的选择模式。发现凝聚素 NCAPG、两个 SMC5/6 复合物基因（和）以及所有具有几乎排他性减数分裂表达的黏连蛋白基因（、、和）存在正选择信号。对于后者，进化速率与雌性减数分裂期间的表达相关，并且大多数正选择位点位于固有无序区域（IDR）中。我们的结果支持越来越多的证据表明 IDR 是快速进化的，并且它们很可能通过调节相分离来促进适应。我们认为，在 SMC 复合物中鉴定出的自然选择信号可能是不同选择压力的结果：在凝聚素和 SMC5/6 复合物中是宿主-病原体的军备竞赛，而在减数分裂黏连蛋白基因中则是类似于描述的着丝粒和端粒的基因组内冲突。
