Elucidation of the function of piRNAs ubiquitously expressed in mollusks

本研究旨在揭示合浦珠母贝嫁接移植过程中参与免疫应答的sncRNA。在移植物移植期间，成功地从P. fucata血淋巴中提取了外泌体。在移植和初始阶段的miRNA和piRNA的表达模式没有实质性差异，但是在初始和后期阶段之间显著变化。靶标预测和功能分析表明，这些miRNAs和piRNAs与嫁接移植后的免疫应答相关，而piRNAs也可能通过与基因组转座子元件靶向而与转座子沉默相关。piRNA在环节动物、刺胞动物、棘皮动物、甲壳动物、节肢动物和软体动物的索马体和生殖细胞中普遍表达，但在脊索动物中仅限于生殖细胞。皮尔纳的双重功能在P. fucata体细胞和性腺组织中进行了检测。结果表明，体细胞组织的piRNA可能与基因调控有关，而性腺组织的piRNA与转座子沉默更密切相关。这项研究将增强我们对piRNA在软体动物中的作用、转座子沉默以及PIWI/皮尔纳通路对无脊椎动物生殖系细胞外蛋白质编码基因的调节功能的理解。

We aimed to reveal the sncRNAs involved in the immune response during grafting transplantation by the pearl oyster Pinctada fucata. Exosomes were successfully extracted from the P. fucata haemolymph during graft transplantation. The expression patterns of the miRNAs and piRNAs at the grafting and initial stages were not substantially different, but varied significantly between the initial and later stages. Target prediction and functional analysis indicate that these miRNAs and piRNAs are related to immune response upon grafting transplantation, whereas piRNAs may also be associated with transposon silencing by targeting with genome transposon elements. This work provides the basis for a functional understanding of exosome-derived sncRNAs and helps to gain further insight into the PIWI/piRNA pathway function outside of germline cells in molluscs.Ubiquitously expressed piRNAs have been discovered in the soma and germ lines in Annelida, Cnidaria, Echinodermata, Crustacea, Arthropoda, and Mollusca, but they are limited to germ lines in Chordata. The dual functions of piRNA were examined in P. fucata somatic and gonadal tissues. The results indicated that piRNAs from somatic tissues may be related to gene regulation, whereas piRNAs from gonadal tissues are more closely associated to transposon silencing. This study will enhance our understanding of the role of piRNAs in mollusks, transposon silencing, and the regulatory function of the PIWI/piRNA pathway on protein-coding genes outside of germ line cells in invertebrates.