Characterization of a male-killing virus and its mode of action in Homona magnanima

在许多无脊椎动物物种中，母系遗传的雌性偏向性别比例已有文献记载。造成这种性别比例偏差的一个原因是男性被杀，也就是说，只有男性才会死亡。在大多数物种中，雄性杀死发生在胚胎阶段(早期雄性杀死)，并与细胞质细菌有关。然而，东方茶蛾是为数不多的在幼虫或蛹阶段发生雄性死亡的物种之一，因此是晚期雄性死亡的例子。在本研究中，我们观察了一株晚期杀雄虫幼虫(LMK)的大体形态和组织病理学，并对其在自然种群中的时空动态进行了研究，并对其进行了部分提纯。大多数LMK雄虫在最后一龄或蛹阶段死亡，死亡的雄虫表现出男性死亡的特征体征和症状。雄性Lmk幼虫在蜕皮进入f…后4天体色开始发生变化更多的是幼虫，变得越来越不透明的白色。雄性LMK幼虫的体重显著低于正常品系(NSR)的雄性。在最后一次蜕皮后7天，雄性LMK幼虫的中肠细胞以颗粒形式排入管腔，并在死亡前落入管腔。LMK雄虫脂肪体胞质内含有较大的脂肪颗粒，形成瘤样细胞团，最终与表皮细胞融合，通过蔗糖梯度超速离心法从雄LMK幼虫中提纯出一种致病物质。注射实验表明，纯化组分含有晚期杀雄剂，电子显微镜显示纯化组分具有直径10-15 nm的等轴测颗粒。纯化组分中的核酸被RNase A降解，但不被DNase I降解，这表明纯化组分中的核酸是RNA而不是DNA。从纯化的组份中鉴定出两个LMK特异的RNA序列：MK1068和MK1241。BLAST研究表明，它们的核苷酸和推导出的氨基酸序列与任何其他已知序列都不匹配。这些结果表明，雄鱼的死亡可能是由一种新的RNA病毒引起的。这种RNA病毒是从宫崎县、岐阜县、静冈县、崎玉县和茨城县采集的马齿象幼虫中检测到的。较少

Maternally inherited female-biased sex ratios have been documented in many invertebrate species. One cause of such biased sex ratios is male-killing ; that is, only males die. In most species, male-killing occurs during embryonic stages (early male-killing) and is associated with cytoplasmic bacteria. However, the oriental tea tortrix, Homona magnanima, is one of the few species in which male death occurs in the larval or pupal stage, and is thus an example of late male-killing. In this study, we examined the gross morphology and histopathology of a late male-killing strain (LMK) of H. magnanima larvae, and spatial and temporal dynamics of the agent in natural populations of H. magnanima, and partially purified the agent causing late male-killing in H. magnanima.Most male LMK larvae died during the last instar or pupal stage, and dead male larvae showed characteristic signs and symptoms of male-killing. The body color of male LMK larvae started to change 4 days after molting into the f … More ifth instar and became increasingly opaque white. Male LMK larvae weighed significantly less than normal strain (NSR) males. Midgut cells of male LMK larvae were discharged into the lumen as granules at 7 days after the final molt, and dropped into the lumen just before death. The fat body of male LMK larvae contained large fat granules in the cytoplasm but became a tumorlike cell mass that finally fused with the epidermal cells.To identify the late male-killing agent, we purified a causal agent from male LMK larvae by sucrose gradient ultracentrifugation. Injection experiment revealed that the purified fraction contained the late male-killing agent, and electron microscopy showed that the purified fraction has isometric particles of 10-15 nm in diameter. Nucleic acids in the purified fraction were degraded by RNase A but not by DNase I, which suggests that nucleic acids in the purified fraction were RNAs but not DNAs. LMK specific two RNA sequences, MK1068 and MK1241, were identified from the purified fraction. A BLAST research revealed that their nucleotide and deduced amino acid sequences did not match any other known sequences. These results suggested that male-killing in H. magnanima may be caused by a new RNA virus. This RNA virus was detected from H. magnanima larvae collected in Miyazaki, Gifu, Shizuoka, Saitama and Ibaragi Prefectures. Less