Science2014-06-10 5:55 PM

我的卵子决定了我的基因会更快地演化 Acquisition of Germ Plasm Accelerates Vertebrate Evolution

论文摘要 

生殖细胞(即雄性的精子及雌性的卵子)可世世代代地传输重要的遗传信息。在许多脊椎动物中,这些细胞受到了一个叫做后生过程的塑造,在该过程中有关的信号会作用于多能干细胞。然而,在其它脊椎动物中演化出了一种另类的方式;在该方式中,生殖细胞在一个叫做预成的过程中受到了种质的影响。随着脊椎动物的演化,预成也一再得到演化,但科学家们对其成因则不甚确定。

为了进行某种阐释,Teri Evans及其同事在此对应用预成过程的脊椎动物物种与其应用后生过程的姊妹类群进行了蛋白编码序列的比较。将蝾螈——其有着受到后生过程支配的生殖细胞——与蛙类——其生殖细胞是从种质形成的——进行比较研究,Evans及其同事发现,在蛙类中,基因演化要更为快速。

这项研究支持一个现有的假说,该假说认为,种质会在胚胎发育的早期(这是基因受到严重约束的一个时期)消除对基因的约束,而这可导致演化加快。因此,Evans等人的研究结果可能会影响科学家们比较系谱图中生物的方式。

Abstract 

Primordial germ cell (PGC) specification occurs either by induction from pluripotent cells (epigenesis) or by a cell-autonomous mechanism mediated by germ plasm (preformation). Among vertebrates, epigenesis is basal, whereas germ plasm has evolved convergently across lineages and is associated with greater speciation. We compared protein-coding sequences of vertebrate species that employ preformation with their sister taxa that use epigenesis and demonstrate that genes evolve more rapidly in species containing germ plasm. Furthermore, differences in rates of evolution appear to cause phylogenetic incongruence in protein-coding sequence comparisons between vertebrate taxa. Our results support the hypothesis that germ plasm liberates constraints on somatic development and that enhanced evolvability drives the evolution of germ plasm.

Editor's Summary

Tangling Evolutionary Trees

Evolutionary rates tend to vary among taxa and may result in phylogenetic trees that do not reflect the true relationships among taxa, depending on the sequences input into the analysis. Examining vertebrate trees, Evans et al. (p. 200) demonstrate that differences in evolutionary rates, leading to phylogenetic distortions, are correlated with the mechanisms underlying germ cell formation. Evolutionary rate is faster in cases where germ cells are established by maternal molecules (“preformed”) relative to those that are induced during embryogenesis (“epigenesis”) in slowly evolving and, presumably, ancestral lineages. For example, frogs evolve more rapidly than salamanders, and teleosts more rapidly than ascipenseriform fishes. Thus, epigenesis constrains the ability of gene regulatory networks to change, with the repeated and convergent evolution of preformation eliminating this constraint.

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