Laboratory of Emerging Infectious Diseases, Department of Frontier Veterinary Medicine, Kagoshima University, Kagoshima, Japan.
Autophagy. 2010 May;6(4):473-81. doi: 10.4161/auto.6.4.11668. Epub 2010 May 16.
Ticks are long-lived hematophagous arthropods and have tolerance to starvation. They can survive without food during the host-seeking period for several months to years. To understand how ticks obtain energy over a long period of non-feeding (starvation), we focused on autophagy, a crucial proteolysis system via the lysosomes for various cellular processes that is induced during starvation in eukaryotes. In the present study, EST databases for several organs of the tick Haemaphysalis longicornis led to the identification of HlATG3, HlATG4 and HlATG8, homologues of 3 autophagy-related (ATG) genes, ATG3, ATG4 and ATG8/LC3/GABARAP, respectively, which are essential for the Atg8 conjugation system in model animals. Real-time PCR results revealed that the expression of HlATG3, HlATG4 and HlATG8 in the tick showed higher levels during the non-feeding period than the feeding period, suggesting that the Atg8 conjugation system is at work in unfed ticks. Notably, their expression levels were higher in the midgut, a digestive organ, of unfed than fed adults. Histological analysis demonstrated that lipids and glycogen accumulated within the epithelial cells of the midgut in unfed ticks, implying that the midgut of unfed ticks serves as storage of those components as nutrients during non-feeding. Furthermore, autophagic organelles were found in the midgut undifferentiated cells of unfed ticks. The starved condition appears to be associated with the increased expression of HlATG genes in the midgut of unfed ticks. Tick autophagy might help compensate for the loss of nutrients derived from host blood components during the non-feeding period.
蜱是一种长寿命的吸血节肢动物，对饥饿有耐受性。它们可以在寻找宿主的时期内不进食，存活数月至数年。为了了解蜱在长时间不进食（饥饿）期间如何获得能量，我们专注于自噬作用，这是一种通过溶酶体进行的关键蛋白水解系统，对于真核生物在饥饿期间诱导的各种细胞过程至关重要。在本研究中，对几种蜱 Haemaphysalis longicornis 器官的 EST 数据库进行了分析，导致鉴定了 HlATG3、HlATG4 和 HlATG8，它们分别是自噬相关 (ATG) 基因 ATG3、ATG4 和 ATG8/LC3/GABARAP 的同源物，这些基因对于模型动物中的 Atg8 缀合系统是必不可少的。实时 PCR 结果显示，蜱中 HlATG3、HlATG4 和 HlATG8 的表达在非进食期比进食期更高，表明 Atg8 缀合系统在未进食的蜱中起作用。值得注意的是，它们在未进食的成虫的中肠（消化器官）中的表达水平高于进食的成虫。组织学分析表明，未进食的蜱的中肠上皮细胞内积累了脂质和糖原，这意味着未进食的蜱的中肠作为非进食期间这些成分的储存作为营养物质。此外，在未进食的蜱的中肠未分化细胞中发现了自噬细胞器。饥饿状态似乎与未进食的蜱的中肠中 HlATG 基因的表达增加有关。蜱的自噬可能有助于补偿非进食期间宿主血液成分丧失的营养物质。
