Trypanosome Cell Biology Unit, Institut Pasteur & INSERM U1201, 25, rue du Docteur Roux, 75015, Paris, France.
UtechS Ultrastructural Bioimaging (Ultrapole), C2RT, Institut Pasteur, 75015, Paris, France.
Parasit Vectors. 2020 Apr 5;13(1):169. doi: 10.1186/s13071-020-04026-0.
Trypanosoma brucei exhibits a complex life-cycle alternating between tsetse flies and mammalian hosts. When parasites infect the fly, cells differentiate to adapt to life in various tissues, which is accompanied by drastic morphological and biochemical modifications especially in the proventriculus. This key step represents a bottleneck for salivary gland infection.
Here, we monitored flagellum assembly in trypanosomes during differentiation from the trypomastigote to the epimastigote stage, i.e. when the nucleus migrates to the posterior end of the cell, by using three-dimensional electron microscopy (focused ion beam scanning electron microscopy, FIB-SEM) and immunofluorescence assays.
The combination of light and electron microscopy approaches provided structural and molecular evidence that the new flagellum is assembled while the nucleus migrates towards the posterior region of the body. Two major differences with well-known procyclic cells are reported. First, growth of the new flagellum begins when the associated basal body is found in a posterior position relative to the mature flagellum. Secondly, the new flagellum acquires its own flagellar pocket before rotating on the left side of the anterior-posterior axis. FIB-SEM revealed the presence of a structure connecting the new and mature flagellum and serial sectioning confirmed morphological similarities with the flagella connector of procyclic cells. We discuss the potential function of the flagella connector in trypanosomes from the proventriculus.
These findings show that T. brucei finely modulates its cytoskeletal components to generate highly variable morphologies.
布氏锥虫表现出复杂的生命周期，在采采蝇和哺乳动物宿主之间交替。当寄生虫感染苍蝇时，细胞会分化以适应各种组织中的生活，这伴随着剧烈的形态和生化修饰，特别是在前胃中。这个关键步骤代表了唾液腺感染的瓶颈。
在这里，我们通过三维电子显微镜（聚焦离子束扫描电子显微镜，FIB-SEM）和免疫荧光分析监测了从锥虫体到锥鞭毛体阶段的寄生虫分化过程中的鞭毛组装，即核迁移到细胞后端时。
光镜和电镜方法的结合提供了结构和分子证据，表明新的鞭毛是在核向身体后端迁移的同时组装的。与著名的前鞭毛体细胞有两个主要区别。首先，当相关的基体在后鞭毛体的位置时，新鞭毛的生长开始。其次，新鞭毛在其自身的鞭毛囊中旋转之前，先在前后轴的左侧获得。FIB-SEM 显示存在一种结构将新鞭毛和成熟鞭毛连接起来，连续切片证实了与前鞭毛体细胞鞭毛连接器的形态相似性。我们讨论了前胃中锥虫鞭毛连接器的潜在功能。
这些发现表明，布氏锥虫精细地调节其细胞骨架成分以产生高度可变的形态。
