microRNA-mediated regulation of microRNA machinery controls cell fate decisions

microRNAs associate with Argonaute proteins, forming the microRNA-induced silencing complex (miRISC), to repress target gene expression post-transcriptionally. Although microRNAs are critical regulators in mammalian cell differentiation, our understanding of how microRNA machinery, such as the miRISC, are regulated during development is still limited. We previously showed that repressing the production of one Argonaute protein, Ago2, by Trim71 is important for mouse embryonic stem cells (mESC) self-renewal (Liu et al., 2021). Here we show that among the four Argonaute proteins in mammals, Ago2 is the major developmentally regulated Argonaute protein in mESCs. Moreover, in pluripotency, besides the Trim71-mediated regulation of Ago2 (Liu et al., 2021), Mir182/Mir183 also repress Ago2. Specific inhibition of this microRNA-mediated repression results in stemness defects and accelerated differentiation through the let-7 microRNA pathway. These results reveal a microRNA-mediated regulatory circuit on microRNA machinery that is critical to maintaining pluripotency.

Epicardial HDAC3 promotes myocardial growth through a novel microRNA pathway

RationalEstablishment of the myocardial wall requires proper growth cues from nonmyocardial tissues. During heart development, the epicardium and epicardium-derived cells (EPDCs) instruct myocardial growth by secreting essential factors including fibroblast growth factor 9 (FGF9) and insulin-like growth factor 2 (IGF2). However, it is poorly understood how the epicardial secreted factors are regulated, in particular by chromatin modifications for myocardial formation.ObjectiveTo understand whether and how histone deacetylase 3 (HDAC3) in the developing epicardium regulates myocardial growth.Methods and ResultsWe deleted Hdac3 in the developing murine epicardium and mutant hearts showed ventricular myocardial wall hypoplasia with reduction of EPDCs. The cultured embryonic cardiomyocytes with supernatants from Hdac3 knockout (KO) mouse epicardial cells (MECs) also showed decreased proliferation. Genome-wide transcriptomic analysis revealed that Fgf9 and Igf2 were significantly down-regulated in Hdac3 KO MECs. We further found that Fgf9 and Igf2 expression is dependent on HDAC3 deacetylase activity. The supplementation of FGF9 or IGF2 can rescue the myocardial proliferation defects treated by Hdac3 KO supernatant. Mechanistically, we identified that microRNA (miR)-322 and miR-503 were upregulated in Hdac3 KO MECs and Hdac3 epicardial KO hearts. Overexpression of miR-322 or miR-503 repressed FGF9 and IGF2 expression, while knockdown of miR-322 or miR-503 restored FGF9 and IGF2 expression in Hdac3 KO MECs.ConclusionsOur findings reveal a critical signaling pathway in which epicardial HDAC3 promotes compact myocardial growth by stimulating FGF9 and IGF2 through repressing miR-322/miR-503, providing novel insights in elucidating etiology of congenital heart defects, and conceptual strategies to promote myocardial regeneration.

Recovery from heat shock requires the microRNA pathway in Caenorhabditis elegans

The heat shock response (HSR) is a highly conserved cellular process that promotes survival during stress. A hallmark of the HSR is the rapid induction of heat shock proteins (HSPs), such as HSP-70, by transcriptional activation. Once the stress is alleviated, HSPs return to near basal levels through incompletely understood mechanisms. Here, we show that the microRNA pathway acts during heat shock recovery in Caenorhabditis elegans. Depletion of the miRNA Argonaute, Argonaute Like Gene 1 (ALG-1), after an episode of heat shock resulted in decreased survival and perdurance of high hsp-70 levels. We present evidence that regulation of hsp-70 is dependent on miR-85 and sequences in the hsp-70 3’UTR that contain target sites for this miRNA. Regulation of hsp-70 by the miRNA pathway was found to be particularly important during recovery from HS, as animals that lacked miR-85 or its target sites in the hsp-70 3’UTR overexpressed HSP-70 and exhibited reduced viability. In summary, our findings show that down-regulation of hsp-70 by miR-85 after HS promotes survival, highlighting a previously unappreciated role for the miRNA pathway during recovery from stress.

microRNA-mediated regulation of microRNA machinery controls cell fate decisions

microRNAs associate with Argonaute proteins, forming the microRNA-induced silencing complex (miRISC), to repress target gene expression post-transcriptionally. Although microRNAs are critical regulators in mammalian cell differentiation, our understanding of how microRNA machinery, such as the miRISC, are regulated during development is still limited. We previously showed that repressing the production of one Argonaute protein, Ago2, by Trim71 is important for mouse embryonic stem cells (mESC) self-renewal (Liu et al., 2021). Here we show that among the four Argonaute proteins in mammals, Ago2 is the major developmentally regulated Argonaute protein in mESCs. Moreover, in pluripotency, besides the Trim71-mediated regulation of Ago2 (Liu et al., 2021), microRNA-182/microRNA-183 also repress Ago2. Specific inhibition of this microRNA-mediated repression results in stemness defects and accelerated differentiation through the let-7 microRNA pathway. These results reveal a microRNA-mediated regulatory circuit on microRNA machinery that is critical to maintaining pluripotency.

The RabGAP TBC-11 controls Argonaute localization for proper microRNA function in C. elegans

Once loaded onto Argonaute proteins, microRNAs form a silencing complex called miRISC that targets mostly the 3’UTR of mRNAs to silence their translation. How microRNAs are transported to and from their target mRNA remains poorly characterized. While some reports linked intracellular trafficking to microRNA activity, it is still unclear how these pathways coordinate for proper microRNA-mediated gene silencing and turnover. Through a forward genetic screen using Caenorhabditis elegans, we identified the RabGAP tbc-11 as an important factor for the microRNA pathway. We show that TBC-11 acts mainly through the small GTPase RAB-6 and that its regulation is required for microRNA function. The absence of functional TBC-11 increases the pool of microRNA-unloaded Argonaute ALG-1 that is likely associated to endomembranes. Furthermore, in this condition, this pool of Argonaute accumulates in a perinuclear region and forms a high molecular weight complex. Altogether, our data suggest that the alteration of TBC-11 generates a fraction of ALG-1 that cannot bind to target mRNAs, leading to defective gene repression. Our results establish the importance of intracellular trafficking for microRNA function and demonstrate the involvement of a small GTPase and its GAP in proper Argonaute localization in vivo.

Evaluation of expression of messenger RNA (RNAm) of the key proteins of the route of the microRNA (miRNA) in RD cells infected with the Mayaro Virus

Introduction: The Mayaro virus (MAYV) is an arbovirus belonging to the Togaviridae family of the alphavirus genus, which is transmitted by hematophagous arthropods to vertebrate hosts, whereas non-human primates are considered primary reservoirs. Objective: To evaluate the expression of messenger RNAs (mRNA) of crucial proteins in the microRNA pathway and inflammatory cytokines in human cells during infection by the MAYV. Materials and Methods: Viral samples propagated in RD cell cultures. The RNAs were collected and extracted at predetermined times. The total RNA was then used to detect mRNA by PCR in real time (qRT-PCR). Results: the Mayaro virus RNA was verified in the cells during all the days of infection. The AgR2 mRNA protein dropped sharply by 2 dpi and 3 dpi. Conclusion: The present study demonstrated the reduction of proteins in infection with the Mayaro virus.