Alcantara Carolina de Lima, de Souza Wanderley, da Cunha E Silva Narcisa L
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-902, RJ, Brazil; Núcleo de Biologia Estrutural e Bioimagens (CENABIO) - Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Biomagens (INBEB), Rio de Janeiro 21941-902, RJ, Brazil.
Instituto de Biofísica Carlos Chagas Filho, Universidade Federal do Rio de Janeiro, Rio de Janeiro 21941-902, RJ, Brazil; Núcleo de Biologia Estrutural e Bioimagens (CENABIO) - Instituto Nacional de Ciência e Tecnologia em Biologia Estrutural e Biomagens (INBEB), Rio de Janeiro 21941-902, RJ, Brazil.
Protist. 2018 Dec;169(6):887-910. doi: 10.1016/j.protis.2018.09.004. Epub 2018 Sep 29.
Trypanosoma cruzi epimastigotes internalize macromolecules avidly by endocytosis. Previously, we identified a tubule-vesicular network likely to correspond to the early-endosomes. However, a detailed ultrastructural characterization of these endosomes was missing. Here, we combined endocytosis assays with ultrastructural data from high-resolution electron microscopy to produce a 3D analysis of epimastigote endosomes and their interactions with endocytic organelles. We showed that endocytic cargo was found in carrier vesicles budding from the cytopharynx. These vesicles appeared to fuse with a tubule-vesicular network of early endosomes identified by ultrastructural features including the presence of intermembrane invaginations and coated membrane sections. Within the posterior region of the cell, endosomes localized preferentially on the side nearest to the cytopharynx microtubules. At 4°C, cargo accumulated at a shortened cytopharynx, and subsequent temperature shift to 12°C led to slow cargo delivery to endosomes and, later, to reservosomes. Bridges between reservosomes and endosomes resemble heterotypic fusion. Reservosomes are excluded from the posterior end of the cell, with no preferential cargo delivery to reservosomes closer to the nucleus. Our 3D analysis indicates that epimastigotes accomplish high-speed endocytic traffic by cargo transfer to a bona fide early-endosome and then directly from endosomes to reservosomes, via multiple and simultaneous heterotypic fusion events.
克氏锥虫前鞭毛体通过内吞作用大量内化大分子。此前，我们鉴定出一个可能对应于早期内体的小管-囊泡网络。然而，这些内体的详细超微结构特征尚不清楚。在这里，我们将内吞作用分析与高分辨率电子显微镜的超微结构数据相结合，对前鞭毛体内体及其与内吞细胞器的相互作用进行了三维分析。我们发现内吞货物存在于从胞咽芽生出的载体囊泡中。这些囊泡似乎与通过超微结构特征鉴定的早期内体的小管-囊泡网络融合，这些特征包括膜内陷和被膜部分的存在。在细胞的后部区域，内体优先定位在最靠近胞咽微管的一侧。在4°C时，货物聚集在缩短的胞咽处，随后温度升至12°C导致货物缓慢输送到内体，随后输送到储存体。储存体和内体之间的桥类似于异型融合。储存体被排除在细胞后端之外，没有优先将货物输送到更靠近细胞核的储存体。我们的三维分析表明，前鞭毛体通过货物转移到真正的早期内体，然后通过多次同时发生的异型融合事件直接从内体转移到储存体，从而完成高速内吞运输。
