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Sci Adv. 2015 Oct 16;1(9):e1500228. doi: 10.1126/sciadv.1500228. eCollection 2015 Oct.

Drosophila Dicer-2 has an RNA interference-independent function that modulates Toll immune signaling.

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State Key Laboratory of Virology, College of Life Sciences, Wuhan University, Wuhan, Hubei 430072, China.
Hubei Key Laboratory of Genetic Regulation and Integrative Biology, College of Life Science, Central China Normal University, Wuhan, Hubei 430079, China.
School of Medicine, Tsinghua University, Beijing 100084, China.


Dicer-2 is the central player for small interfering RNA biogenesis in the Drosophila RNA interference (RNAi) pathway. Intriguingly, we found that Dicer-2 has an unconventional RNAi-independent function that positively modulates Toll immune signaling, which defends against Gram-positive bacteria, fungi, and some viruses, in both cells and adult flies. The loss of Dicer-2 expression makes fruit flies more susceptible to fungal infection. We further revealed that Dicer-2 posttranscriptionally modulates Toll signaling because Dicer-2 is required for the proper expression of Toll protein but not for Toll protein stability or Toll mRNA transcription. Moreover, Dicer-2 directly binds to the 3' untranslated region (3'UTR) of Toll mRNA via its PAZ (Piwi/Argonaute/Zwille) domain and is required for protein translation mediated by Toll 3'UTR. The loss of Toll 3'UTR binding activity makes Dicer-2 incapable of promoting Toll signaling. These data indicate that the interaction between Dicer-2 and Toll mRNA plays a pivotal role in Toll immune signaling. In addition, we found that Dicer-2 is also required for the Toll signaling induced by two different RNA viruses in Drosophila cells. Consequently, our findings uncover a novel RNAi-independent function of Dicer-2 in the posttranscriptional regulation of Toll protein expression and signaling, indicate an unexpected intersection of the RNAi pathway and the Toll pathway, and provide new insights into Toll immune signaling, Drosophila Dicer-2, and probably Dicer and Dicer-related proteins in other organisms.


Dicer-2; RNA silencing; Toll signaling; invertebrate immunity; posttranscriptional gene regulation

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