Dowell Noah L, Giorgianni Matt W, Kassner Victoria A, Selegue Jane E, Sanchez Elda E, Carroll Sean B
Howard Hughes Medical Institute and Laboratory of Molecular Biology, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53706, USA.
Howard Hughes Medical Institute and Laboratory of Molecular Biology, University of Wisconsin-Madison, 1525 Linden Drive, Madison, WI 53706, USA.
Curr Biol. 2016 Sep 26;26(18):2434-2445. doi: 10.1016/j.cub.2016.07.038. Epub 2016 Sep 15.
The genetic origin of novel traits is a central but challenging puzzle in evolutionary biology. Among snakes, phospholipase A2 (PLA2)-related toxins have evolved in different lineages to function as potent neurotoxins, myotoxins, or hemotoxins. Here, we traced the genomic origin and evolution of PLA2 toxins by examining PLA2 gene number, organization, and expression in both neurotoxic and non-neurotoxic rattlesnakes. We found that even though most North American rattlesnakes do not produce neurotoxins, the genes of a specialized heterodimeric neurotoxin predate the origin of rattlesnakes and were present in their last common ancestor (∼22 mya). The neurotoxin genes were then deleted independently in the lineages leading to the Western Diamondback (Crotalus atrox) and Eastern Diamondback (C. adamanteus) rattlesnakes (∼6 mya), while a PLA2 myotoxin gene retained in C. atrox was deleted from the neurotoxic Mojave rattlesnake (C. scutulatus; ∼4 mya). The rapid evolution of PLA2 gene number appears to be due to transposon invasion that provided a template for non-allelic homologous recombination.
新性状的遗传起源是进化生物学中的一个核心但具有挑战性的谜题。在蛇类中，磷脂酶A2（PLA2）相关毒素在不同谱系中进化，可作为强效神经毒素、肌毒素或血液毒素发挥作用。在此，我们通过研究神经毒性和非神经毒性响尾蛇中PLA2基因的数量、组织和表达，追踪了PLA2毒素的基因组起源和进化。我们发现，尽管大多数北美响尾蛇不产生神经毒素，但一种特殊的异二聚体神经毒素的基因早于响尾蛇的起源，并存在于它们的最后一个共同祖先中（约2200万年前）。然后，在导致西部菱斑响尾蛇（Crotalus atrox）和东部菱斑响尾蛇（C. adamanteus）的谱系中（约600万年前），神经毒素基因被独立删除，而保留在C. atrox中的一个PLA2肌毒素基因在神经毒性的莫哈韦响尾蛇（C. scutulatus；约400万年前）中被删除。PLA2基因数量的快速进化似乎是由于转座子入侵，它为非等位基因同源重组提供了模板。
