Department of Biological Sciences, SLRC-Sea Lice Research Center, University of Bergen, Bergen, Norway.
PLoS One. 2021 May 20;16(5):e0251575. doi: 10.1371/journal.pone.0251575. eCollection 2021.
The salmon louse, Lepeophtheirus salmonis, is an ectoparasitic crustacean that annually inflicts substantial losses to the aquaculture industry in the northern hemisphere and poses a threat to the wild populations of salmonids. The salmon louse life cycle consists of eight developmental stages each separated by a molt. Fushi Tarazu Factor-1 (FTZ-F1) is an ecdysteroid-regulated gene that encodes a member of the NR5A family of nuclear receptors that is shown to play a crucial regulatory role in molting in insects and nematodes. Characterization of an FTZ-F1 orthologue in the salmon louse gave two isoforms named αFTZ-F1 and βFTZ-F1, which are identical except for the presence of a unique N-terminal domain (A/B domain). A comparison suggest conservation of the FTZ-F1 gene structure among ecdysozoans, with the exception of nematodes, to produce isoforms with unique N-terminal domains through alternative transcription start and splicing. The two isoforms of the salmon louse FTZ-F1 were expressed in different amounts in the same tissues and showed a distinct cyclical expression pattern through the molting cycle with βFTZ-F1 being the highest expressed isoform. While RNA interference knockdown of βFTZ-F1 in nauplius larvae and in pre-adult males lead to molting arrest, knockdown of βFTZ-F1 in pre-adult II female lice caused disruption of oocyte maturation at the vitellogenic stage. No apparent phenotype could be observed in αFTZ-F1 knockdown larvae, or in their development to adults, and no genes were found to be differentially expressed in the nauplii larvae following αFTZ-F1 knockdown. βFTZ-F1 knockdown in nauplii larvae caused both down and upregulation of genes associated with proteolysis and chitin binding and affected a large number of genes which are in normal salmon louse development expressed in a cyclical pattern. This is the first description of FTZ-F1 gene function in copepod crustaceans and provides a foundation to expand the understanding of the molecular mechanisms of molting in the salmon louse and other copepods.
鲑鱼虱，Lepeophtheirus salmonis，是一种寄生在甲壳类动物体表的寄生虫，每年都会给北半球的水产养殖业造成巨大损失，并对鲑鱼科鱼类的野生种群构成威胁。鲑鱼虱的生命周期由 8 个发育阶段组成，每个阶段都有一次蜕皮。蜕皮甾酮受体因子-1（FTZ-F1）是一种蜕皮甾酮调节基因，编码核受体 NR5A 家族的成员，在昆虫和线虫的蜕皮过程中发挥着关键的调节作用。鲑鱼虱 FTZ-F1 同源基因的特征分析产生了两种同工型，分别命名为αFTZ-F1 和βFTZ-F1，它们除了存在独特的 N 端结构域（A/B 结构域）外完全相同。比较表明，除了线虫外，所有节肢动物的 FTZ-F1 基因结构都具有保守性，通过不同的转录起始和剪接产生具有独特 N 端结构域的同工型。鲑鱼虱 FTZ-F1 的两种同工型在相同组织中的表达量不同，并在蜕皮周期中表现出明显的周期性表达模式，其中βFTZ-F1 的表达量最高。虽然在桡足类幼虫和未成熟雄性中 RNA 干扰敲低βFTZ-F1 会导致蜕皮停止，但在未成熟 II 期雌性虱子中敲低βFTZ-F1 会导致卵母细胞在卵黄生成阶段成熟中断。在αFTZ-F1 敲低幼虫或其发育为成虫的过程中，没有观察到明显的表型，在αFTZ-F1 敲低桡足类幼虫后也没有发现差异表达的基因。在桡足类幼虫中敲低βFTZ-F1 会导致与蛋白水解和几丁质结合相关的基因下调和上调，并影响大量在正常鲑鱼虱发育中呈周期性表达的基因。这是首次描述 FTZ-F1 基因在桡足类甲壳动物中的功能，为扩展对鲑鱼虱和其他桡足类动物蜕皮分子机制的理解提供了基础。
