A new asymmetric division contributes to the continuous production of infective trypanosomes in the tsetse fly
A new asymmetric division contributes to the continuous production of infective trypanosomes in the tsetse fly
复制标题
一种新的不对称分裂有助于采采蝇中感染性锥虫的持续产生
作者：
B. Rotureau;I. Subota;Johanna Buisson;P. Bastin
非洲锥虫是有鞭毛的原生动物寄生虫，可引起昏睡病，并通过采采蝇的叮咬传播。为了完成它们在昆虫体内的生命周期，锥虫到达唾液腺并转化为亚循环感染形式。在昆虫的整个生命周期中，它们会在每次吸血时随唾液排出。在这里，我们揭示了一种方法，通过这种方法可以确保感染性寄生虫的连续生产。通过实时视频显微镜和定量免疫荧光分析，利用细胞骨架和表面抗原的分子标记，监测受感染采采蝇唾液腺中存在的分裂锥虫。这表明存在两种不同模式的锥虫增殖同时发生在唾液腺。第一个周期产生两个等效的细胞，它们不具有感染能力，并附着在上皮上。这种增殖模式在感染的早期阶段占主导地位，确保了腺体的快速定植。第二种模式在感染后期更为常见，涉及不对称分裂。它产生一个子细胞，成熟为具有传染性的元环细胞，释放到唾液中，具体的分子标记物calflins的表达证明了这一点。在不对称分裂期间，这些钙结合蛋白的水平仅在新鞭毛中增加，表明未来子细胞的分化承诺。这两种交替的细胞周期的协调有助于传染性寄生虫的持续产生，使采采蝇成为非洲锥虫的有效和持久的媒介。
African trypanosomes are flagellated protozoan parasites that cause sleeping sickness and are transmitted by the bite of the tsetse fly. To complete their life cycle in the insect, trypanosomes reach the salivary glands and transform into the metacyclic infective form. The latter are expelled with the saliva at each blood meal during the whole life of the insect. Here, we reveal a means by which the continuous production of infective parasites could be ensured. Dividing trypanosomes present in the salivary glands of infected tsetse flies were monitored by live video-microscopy and by quantitative immunofluorescence analysis using molecular markers for the cytoskeleton and for surface antigens. This revealed the existence of two distinct modes of trypanosome proliferation occurring simultaneously in the salivary glands. The first cycle produces two equivalent cells that are not competent for infection and are attached to the epithelium. This mode of proliferation is predominant at the early steps of infection, ensuring a rapid colonization of the glands. The second mode is more frequent at later stages of infection and involves an asymmetric division. It produces a daughter cell that matures into the infective metacyclic form that is released in the saliva, as demonstrated by the expression of specific molecular markers – the calflagins. The levels of these calcium-binding proteins increase exclusively in the new flagellum during the asymmetric division, showing the commitment of the future daughter cell to differentiation. The coordination of these two alternative cell cycles contributes to the continuous production of infective parasites, turning the tsetse fly into an efficient and long-lasting vector for African trypanosomes.