Lüke Lena, Tourmente Maximiliano, Dopazo Hernan, Serra François, Roldan Eduardo R S
Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), c/Jose Gutierrez Abascal 2, 28006, Madrid, Spain.
Department of Ecology, Genetics and Evolution, Universidad de Buenos Aires, Buenos Aires, Argentina.
BMC Evol Biol. 2016 Jan 22;16:21. doi: 10.1186/s12862-016-0588-1.
Protamines are sperm nuclear proteins with a crucial role in chromatin condensation. Their function is strongly linked to sperm head morphology and male fertility. Protamines appear to be affected by a complex pattern of selective constraints. Previous studies showed that sexual selection affects protamine coding sequence and expression in rodents. Here we analyze selective constraints and post-copulatory sexual selection acting on protamine 2 (Prm2) gene sequences of 53 species of primates and rodents. We focused on possible differences in selective constraints between these two clades and on the two functional domains of PRM2 (cleaved- and mature-PRM2). We also assessed if and how changes in Prm2 coding sequence may affect sperm head dimensions.
The domain of Prm2 that is cleaved off during binding to DNA (cleaved-Prm2) was found to be under purifying selection in both clades, whereas the domain that remains bound to DNA (mature-Prm2) was found to be positively selected in primates and under relaxed constraint in rodents. Changes in cleaved-Prm2 coding sequence are significantly correlated to sperm head width and elongation in rodents. Contrary to expectations, a significant effect of sexual selection was not found on either domain or clade.
Mature-PRM2 may be free to evolve under less constraint due to the existence of PRM1 as a more conserved and functionally redundant copy. The cleaved-PRM2 domain seems to play an important role in sperm head shaping. However, sexual selection on its sequence may be difficult to detect until it is identified which sperm head phenotype (shape and size) confers advantages for sperm performance in different mammalian clades.
鱼精蛋白是精子核蛋白，在染色质凝聚中起关键作用。它们的功能与精子头部形态和男性生育能力密切相关。鱼精蛋白似乎受到复杂的选择限制模式的影响。先前的研究表明，性选择会影响啮齿动物中鱼精蛋白的编码序列和表达。在此，我们分析了作用于53种灵长类和啮齿类动物鱼精蛋白2（Prm2）基因序列的选择限制和交配后的性选择。我们关注这两个进化枝之间选择限制的可能差异以及PRM2的两个功能域（切割型和成熟型PRM2）。我们还评估了Prm2编码序列的变化是否以及如何影响精子头部尺寸。
发现在两个进化枝中，在与DNA结合过程中被切割掉的Prm2结构域（切割型Prm2）都受到纯化选择，而与DNA保持结合的结构域（成熟型Prm）则在灵长类动物中受到正选择，在啮齿动物中受到的限制较宽松。在啮齿动物中，切割型Prm2编码序列的变化与精子头部宽度和伸长显著相关。与预期相反，未发现性选择对任何一个结构域或进化枝有显著影响。
由于存在更保守且功能冗余的拷贝PRM1，成熟型PRM2可能在较少的限制下自由进化。切割型PRM2结构域似乎在精子头部塑形中起重要作用。然而，在确定哪种精子头部表型（形状和大小）在不同哺乳动物进化枝中赋予精子性能优势之前，可能难以检测到对其序列的性选择。
