Only skin deep: shared genetic response to the deadly chytrid fungus in susceptible frog species

Amphibian populations around the world are threatened by an emerging infectious pathogen, the chytrid fungus Batrachochytrium dendrobatidis (Bd). How can a fungal skin infection kill such a broad range of amphibian hosts? And why are certain species particularly susceptible to the impacts of Bd? Here we use a genomics approach to understand the genetic response of multiple susceptible frog species to Bd infection. We characterize the transcriptomes of two closely-related endangered frog species (Rana muscosa and Rana sierrae) and analyze whole genome expression profiles from frogs in controlled Bd-infection experiments. We integrate the Rana results with a comparable dataset from a more distantly-related susceptible species (Silurana tropicalis). We demonstrate that Bd-infected frogs show massive disruption of skin function and show no evidence of a robust immune response. The genetic response to infection is shared across the focal susceptible species, suggesting a common effect of Bd on susceptible frogs. A total of five (12-plex) chips were analyzed from 60 samples comprising 2 conditions (control and infected), 3 tissues (skin, liver and spleen) and 2 timepoints (early and late). Three biological replicates were used for each condition and tissue at each time point. Twentyfour arrays were analyzed for skin samples, 24 for liver, and 12 for spleen. The same dye, Cy5, was used for all samples.

全球范围内的两栖动物种群正受到一种新兴传染病原体——蛙壶菌（Batrachochytrium dendrobatidis, Bd）的威胁。这种真菌性皮肤感染为何能致死如此广泛的两栖动物宿主？又为何部分物种对Bd的致病效应尤为易感？本研究采用基因组学方法，探究多种易感蛙类对Bd感染的遗传应答。我们对两种亲缘关系紧密的濒危蛙类（Rana muscosa与Rana sierrae）的转录组进行解析，并分析了受控Bd感染实验中蛙类的全基因组表达谱；同时将上述Rana属物种的研究结果，与另一种亲缘关系更远的易感物种——热带爪蟾（Silurana tropicalis）的对应数据集进行整合分析。研究证实，感染Bd的蛙类会出现皮肤功能的大规模紊乱，且未表现出强烈免疫应答的迹象。各目标易感物种对感染的遗传应答具有共通性，这表明Bd对易感蛙类的致病效应存在共性。本研究共分析了5张（12重标记）基因芯片，样本总量为60份，涵盖2种处理条件（对照组与感染组）、3种组织（皮肤、肝脏与脾脏）以及2个时间节点（早期与晚期）；每个时间节点下，每种处理条件与组织均设置3个生物学重复。其中皮肤样本共分析24张芯片，肝脏样本24张，脾脏样本12张；所有样本均使用同一种荧光染料Cy5进行标记。