Integrated morphological and transcriptome profiles reveal a highly-developed extrusome system associated to virulence in the notorious fish parasite, <i>Ichthyophthirius multifiliis</i>

<i>Ichthyophthirius multifiliis</i> is an obligate parasitic ciliate that causes severe economic damage in aquaculture. The parasite contains numerous extrusive organelles (extrusomes) that assist in its pathogenesis and reproduction. However, the structure of these extrusomes and the molecular profiles involved in exocytosis remain unclear. In the present study, through comparative ultrastructural observations across the life cycle of <i>I. multifiliis</i>, we demonstrated that all three of its life stages (theront, trophont, and tomont) exhibited an abundance of extrusomes. In addition, two different types of extrusomes were identified according to their unique structures. Type I extrusomes (mucocysts) are crystalline, oval-shaped, 0.7–1.4 × 0.6–1.1 μm, and distributed as “rosettes” below the trophont membrane. Type II extrusomes, 2.0–3.0 × 0.2–0.3 μm, are rod-shaped with tubular cores and identified as toxicysts, the aggregation of which in the anterior part of the theront and cortex of the trophont revealed their potential roles in <i>I. multifiliis</i> invasion. This was confirmed by our transcriptome investigations of the three stages of <i>I. multifiliis</i>, which revealed that a set of genes involved in proteolysis and DNA/protein biogenesis was highly expressed in the theront and trophont. Furthermore, to map the molecular mechanisms of extrusome release, we characterized 25 Rab family genes in <i>I. multifiliis</i> and determined their expression profiles across the life cycle, reflecting the distribution patterns of the two extrusomes. Collectively, our data revealed that a highly developed extrusome system could play a potential role in the virulence of <i>I. multifiliis</i>, which facilitates a better understanding of the parasite’s development.

多子小瓜虫（Ichthyophthirius multifiliis）是一种专性寄生纤毛虫，可对水产养殖业造成严重经济损失。该寄生虫拥有大量辅助其致病与繁殖的外排细胞器（extrusomes）。然而，这类外排细胞器的结构以及参与外排作用的分子特征仍不明确。本研究通过对多子小瓜虫全生活周期的比较超微结构观察，证实其三个生活史阶段——动体（theront）、滋养体（trophont）与包囊体（tomont）——均含有丰富的外排细胞器。此外，根据结构特征可将其分为两种不同类型的外排细胞器：I型外排细胞器（粘液泡，mucocysts）呈结晶状椭圆形，大小为0.7–1.4 × 0.6–1.1 μm，以“玫瑰花簇”形式分布于滋养体膜下方。II型外排细胞器大小为2.0–3.0 × 0.2–0.3 μm，为具管状核心的杆状结构，经鉴定为毒丝泡（toxicysts）；该类细胞器在动体前端与滋养体皮层的聚集模式，提示其在多子小瓜虫入侵过程中发挥潜在作用。上述结论通过转录组分析得到了进一步验证：对多子小瓜虫三个生活史阶段的转录组研究显示，一系列参与蛋白水解及DNA与蛋白质生物合成的基因在动体与滋养体中呈高表达。此外，为解析外排细胞器释放的分子机制，本研究对多子小瓜虫的25个Rab家族基因进行了特征分析，并明确了其在全生活周期中的表达谱，该表达谱与两种外排细胞器的分布模式相契合。综上，本研究数据表明，高度发达的外排细胞器系统可能在多子小瓜虫的致病力中发挥关键作用，这一发现有助于我们更深入地理解该寄生虫的发育机制。

搜集汇总

背景与挑战

背景概述

该数据集聚焦于鱼类寄生虫Ichthyophthirius multifiliis的外排体系统及其与毒力的关联，通过形态学和转录组分析揭示了两种外排体的结构特征及其在寄生虫生命周期中的潜在作用。研究还鉴定了与寄生虫侵袭相关的基因表达模式和外排体释放的分子机制，为理解该寄生虫的发育和毒力提供了新的见解。