Sand flies are the vectors of Leishmania parasites. To develop in the sand fly midgut, Leishmania multiplies and undergoes various stage differentiations giving rise to the infective form, the metacyclic promastigotes. To determine the changes in sand fly midgut gene expression caused by the presence of Leishmania, we performed RNA-Seq of uninfected and Leishmania infantum-infected Lutzomyia longipalpis midguts from seven different libraries corresponding to time points which cover the various Leishmania developmental stages. The combined transcriptomes resulted in the de novo assembly of 13,841 sand fly midgut transcripts. Importantly, only 113 sand fly transcripts, about 1%, were differentially expressed in the presence of Leishmania parasites. Further, we observed distinct differentially expressed sand fly midgut transcripts corresponding to the presence of each of the various Leishmania stages suggesting that each parasite stage influences midgut gene expression in a specific manner. Two main patterns of sand fly gene expression modulation were noted. At early time points (days 1–4), more transcripts were down-regulated by Leishmania infection at large fold changes (> 32 fold). Among the down-regulated genes, the transcription factor Forkhead/HNF-3 and hormone degradation enzymes were differentially regulated on day 2 and appear to be the upstream regulators of nutrient transport, digestive enzymes, and peritrophic matrix proteins. Conversely, at later time points (days 6 onwards), most of the differentially expressed transcripts were up-regulated by Leishmania infection with small fold changes (< 32 fold). The molecular functions of these genes have been associated with the metabolism of lipids and detoxification of xenobiotics. Overall, our data suggest that the presence of Leishmania produces a limited change in the midgut transcript expression profile in sand flies. Further, Leishmania modulates sand fly gene expression early on in the developmental cycle in order to overcome the barriers imposed by the midgut, yet it behaves like a commensal at later time points where a massive number of parasites in the anterior midgut results only in modest changes in midgut gene expression.

中文翻译：

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利什曼原虫感染在沙蝇中肠诱导了有限的差异基因表达。

沙蝇是利什曼原虫寄生虫的媒介。为了在沙蝇中肠发育，利什曼原虫繁殖并经历各种阶段分化，从而产生了传染性形式，即元环前鞭毛体。为了确定由利什曼原虫的存在引起的沙蝇中肠基因表达的变化，我们对来自七个不同文库的未感染和婴儿利什曼原虫感染的Lutzomyia longipalpis中肠进行了RNA-Seq测序，对应的时间点涵盖了利什曼原虫的各个发育阶段。组合的转录组导致了从头开始的13,841沙蝇中肠转录本的组装。重要的是，在利什曼原虫寄生虫的存在下，仅有113个沙蝇转录本（约1％）被差异表达。进一步，我们观察到与各个利什曼原虫阶段的存在相对应的不同差异表达的沙蝇中肠转录本，表明每个寄生虫阶段均以特定方式影响中肠基因表达。注意到了沙蝇基因表达调控的两个主要模式。在早期时间点（第1-4天），利什曼原虫感染以较大的倍数变化（> 32倍）下调了更多的转录本。在下调的基因中，转录因子Forkhead / HNF-3和激素降解酶在第2天受到差异调节，并且似乎是营养运输，消化酶和营养缺陷型基质蛋白的上游调节剂。相反，在稍后的时间点（从第6天开始），利什曼原虫感染使大多数差异表达的转录本上调，但折叠变化很小（<32倍）。这些基因的分子功能已经与脂质的代谢和异生物的解毒有关。总的来说，我们的数据表明利什曼原虫的存在在沙蝇中肠转录本表达谱中产生了有限的变化。此外，利什曼原虫在发育周期的早期就调节了沙蝇基因的表达，以克服中肠造成的障碍，但在以后的时间点表现得像共鸣，因为中肠前部的大量寄生虫只会导致适度的变化在中肠基因表达中。这些基因的分子功能已经与脂质的代谢和异生物的解毒有关。总的来说，我们的数据表明利什曼原虫的存在在沙蝇中肠转录本表达谱中产生了有限的变化。此外，利什曼原虫在发育周期的早期就调节了沙蝇基因的表达，以克服中肠造成的障碍，但在以后的时间点表现得像共鸣，因为中肠前部的大量寄生虫只会导致适度的变化在中肠基因表达中。这些基因的分子功能与脂质的代谢和异生物的解毒有关。总的来说，我们的数据表明利什曼原虫的存在在沙蝇中肠转录本表达谱中产生了有限的变化。此外，利什曼原虫在发育周期的早期就调节了沙蝇基因的表达，以克服中肠造成的障碍，但在以后的时间点表现得像共鸣，因为中肠前部的大量寄生虫只会导致适度的变化在中肠基因表达中。