The obligate intracellular bacterial pathogen Chlamydia trachomatis is reliant on a developmental cycle consisting of two cell forms, termed the elementary body (EB) and the reticulate body (RB). The EB is infectious and utilizes a type III secretion system and preformed effector proteins during invasion, but it does not replicate. The RB replicates in the host cell but is noninfectious. This developmental cycle is central to chlamydial pathogenesis. In this study, we developed mathematical models of the developmental cycle that account for potential factors influencing RB-to-EB cell type switching during infection. Our models predicted that two categories of regulatory signals for RB-to-EB development could be differentiated experimentally, an “intrinsic” cell-autonomous program inherent to each RB and an “extrinsic” environmental signal to which RBs respond. To experimentally differentiate between mechanisms, we tracked the expression of C. trachomatis development-specific promoters in individual inclusions using fluorescent reporters and live-cell imaging. These experiments indicated that EB production was not influenced by increased multiplicity of infection or by superinfection, suggesting the cycle follows an intrinsic program that is not directly controlled by environmental factors. Additionally, live-cell imaging revealed that EB development is a multistep process linked to RB growth rate and cell division. The formation of EBs followed a progression with expression from the euo and ihtA promoters evident in RBs, while expression from the promoter for hctA was apparent in early EBs/IBs. Finally, expression from the promoters for the true late genes, hctB, scc2, and tarp, was evident in the maturing EB.

中文翻译：

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沙眼衣原体发育的单一包涵体动力学

专性细胞内细菌病原体沙眼衣原体依赖于由两种细胞形式组成的发育周期，称为基本体 (EB) 和网状体 (RB)。EB 具有传染性，在入侵过程中利用 III 型分泌系统和预先形成的效应蛋白，但它不会复制。RB 在宿主细胞中复制但不具有感染性。这种发育周期是衣原体发病机制的核心。在这项研究中，我们开发了发育周期的数学模型，该模型解释了感染期间影响 RB 到 EB 细胞类型转换的潜在因素。我们的模型预测，RB 到 EB 发展的两类调节信号可以通过实验区分，每个 RB 固有的“内在”细胞自主程序和 RB 响应的“外在”环境信号。为了通过实验区分机制，使用荧光报告基因和活细胞成像检测单个包裹体中沙眼衣原体发育特异性启动子。这些实验表明 EB 的产生不受感染多样性增加或重复感染的影响，这表明该循环遵循不受环境因素直接控制的内在程序。此外，活细胞成像显示 EB 发育是一个与 RB 生长速率和细胞分裂相关的多步骤过程。EB的形成随后从表达的进展EUO和ihtA启动子以RB显而易见的，而从所述启动子用于表达hctA在早期的EB /的IB显而易见。最后，来自真正晚期基因hctB的启动子的表达，SCC2和篷布，是在成熟的EB明显。