Tissue-specific overexpression of systemic RNA interference components limits lifespan in C. elegans.

Intertissue RNA transport recently emerged as a novel signaling mechanism. In mammals, mounting evidence suggests that small RNA transfer between cells is widespread and used in various physiological contexts. In the nematode C. elegans, a similar mechanism is conferred by the systemic RNAi pathway. Members of the Systemic RNA Interference Defective (SID) family act at different steps of cellular RNA uptake and export. The limiting step in systemic RNA interference (RNAi) is the import of extracellular RNAs via the conserved double-stranded (dsRNA)-gated dsRNA channel SID-1. To better understand the role of RNAs as intertissue signaling molecules, we modified the function of SID-1 in specific tissues of C. elegans. We observed that sid-1 loss-of-function mutants are as healthy as wild-type worms. Conversely, overexpression of sid-1 in C. elegans intestine, muscle, or neurons rendered worms short-lived. The effects of intestinal sid-1 overexpression were attenuated by silencing the components of systemic RNAi sid-1, sid-2 and sid-5, implicating systemic RNA signaling in the lifespan reduction. Accordingly, tissue-specific overexpression of sid-2 and sid-5 also reduced worm lifespan. Additionally, an RNAi screen for components of several non-coding RNA pathways revealed that silencing the miRNA biogenesis proteins PASH-1 and DCR-1 rendered the lifespan of worms with intestinal sid-1 overexpression similar to controls. Collectively, our data support the notion that systemic RNA signaling must be tightly regulated, and unbalancing that process provokes a reduction in lifespan. We termed this phenomenon Intercellular/Extracellular Systemic RNA imbalance (InExS).

DICER: structure, function, and regulation.

Regulation of gene expression by small non-coding RNAs, such as miRNAs and siRNAs, is an inherent part of complex biological processes that allow function and survival of eukaryotic cells. The type III ribonuclease DICER is widely recognized as a key step in the production of miRNAs and siRNAs, although it also has non-canonical functions such as DNA repair and induction of apoptosis. DICER is at the cornerstone of most biological processes; hence, its mRNA and protein levels are subject to multiple layers of regulation. Accordingly, DICER derangement is related to disease and leads to accelerated aging. Interventions that boost DICER function hold great potential as strategies to promote health and longevity. In this review, we will summarize the structural features of DICER, describe its canonical and non-canonical roles, and discuss the most common regulatory mechanisms having an impact on DICER abundance and function. We will also touch upon the current literature demonstrating that DICER deregulation can lead to diseases, thus highlighting the importance of DICER in warranting the beneficial effects of health-promoting interventions.