Lüke Lena, Vicens Alberto, Tourmente Maximiliano, Roldan Eduardo R S
Reproductive Ecology and Biology Group, Museo Nacional de Ciencias Naturales (CSIC), Madrid, Spain.
Biol Reprod. 2014 Mar 27;90(3):67. doi: 10.1095/biolreprod.113.115956. Print 2014 Mar.
Little is known about the genetic basis of evolutionary changes in sperm phenotype. Postcopulatory sexual selection is associated with differences in protamine gene sequences and promoters and is a powerful force acting on sperm form and function, although links between protamine evolution and sperm phenotype are scarce. Protamines are involved in sperm chromatin condensation, and protamine deficiency negatively affects sperm morphology and male fertility, thus suggesting that they are important for sperm design and function. We examined changes in protamine genes and sperm phenotype in rodents to understand the role of sexual selection on protamine evolution and sperm design. We performed a genotype-phenotype association study using root-to-tip dN/dS (nonsynonymous/synonymous substitutions rate ratio) to account for evolutionary rates and phylogenetic generalized least squares analyses to compare genetic and morphometric data. Evolutionary rates of protamine 1 and the protamine 2 domain cleaved off during chromatin condensation correlated with head size and elongation. Protamine 1 exhibited restricted positive selection on some functional sites, which seemed sufficient to preserve its role in head design. The cleaved-protamine 2, whose relaxation is halted by sexual selection, seems to ensure small, elongated heads that would make sperm more competitive. No association existed between mature-protamine 2 and head phenotype, suggesting little involvement during chromatin condensation and a likely role maintaining the condensed state. Our results suggest that evolutionary changes in protamines could be related to complex developmental modifications in the sperm head. This represents an important step toward understanding the role of changes in gene coding sequences in the divergence of germ cell phenotype.
关于精子表型进化变化的遗传基础，我们所知甚少。交配后的性选择与鱼精蛋白基因序列和启动子的差异有关，并且是作用于精子形态和功能的一股强大力量，尽管鱼精蛋白进化与精子表型之间的联系很少见。鱼精蛋白参与精子染色质浓缩，鱼精蛋白缺乏会对精子形态和男性生育能力产生负面影响，因此表明它们对精子设计和功能很重要。我们研究了啮齿动物中鱼精蛋白基因和精子表型的变化，以了解性选择在鱼精蛋白进化和精子设计中的作用。我们使用根到末端的非同义/同义替换率比（dN/dS）进行基因型-表型关联研究，以考虑进化速率，并进行系统发育广义最小二乘法分析来比较遗传和形态测量数据。在染色质浓缩过程中被切割掉的鱼精蛋白1和鱼精蛋白2结构域的进化速率与头部大小和伸长相关。鱼精蛋白1在一些功能位点表现出受限的正选择，这似乎足以保留其在头部设计中的作用。被切割的鱼精蛋白2，其松弛受到性选择的抑制，似乎确保了小而细长的头部，这会使精子更具竞争力。成熟的鱼精蛋白2与头部表型之间不存在关联，这表明其在染色质浓缩过程中参与度较低，可能在维持浓缩状态方面发挥作用。我们的结果表明，鱼精蛋白的进化变化可能与精子头部复杂的发育修饰有关。这代表了朝着理解基因编码序列变化在生殖细胞表型差异中的作用迈出的重要一步。
