The role of microRNAs inAnophelesbiology-an emerging research field

Filtering the Junk: Assigning Function to the Mosquito Non-Coding Genome

The portion of the mosquito genome that does not code for proteins contains regulatory elements that likely underlie variation for important phenotypes including resistance and susceptibility to infection with arboviruses and Apicomplexan parasites. Filtering the non-coding genome to uncover these functional elements is an expanding area of research, though identification of non-coding regulatory elements is challenging due to the lack of an amino acid-like code for the non-coding genome and a lack of sequence conservation across species. This review focuses on three types of non-coding regulatory elements: (1) microRNAs (miRNAs), (2) long non-coding RNAs (lncRNAs), and (3) enhancers, and summarizes current advances in technical and analytical approaches for measurement of each of these elements on a genome-wide scale. The review also summarizes and highlights novel findings following application of these techniques in mosquito-borne disease research. Looking beyond the protein-coding genome is essential for understanding the complexities that underlie differential gene expression in response to arboviral or parasite infection in mosquito disease vectors. A comprehensive understanding of the regulation of gene and protein expression will inform transgenic and other vector control methods rooted in naturally segregating genetic variation.

Global Analysis of Small Non-Coding RNA Populations across Tissues in the Malaria Vector, Anopheles gambiae

Malaria is a major global health problem, where the anautogenous female mosquito Anopheles gambiae serves as a major vector. In order to combat this devastating disease, understanding mosquito physiology is paramount. Numerous studies in the vector field demonstrate that small non-coding RNAs (ncRNAs) play essential roles in numerous aspects of mosquito physiology. While our previous miRNA annotation work demonstrated expression dynamics across differing tissues, miRNAs represented less than 20% of all small ncRNAs in our small RNA-Seq libraries. To this end, we systematically classified multiple small ncRNA groups across mosquito tissues. Here we (i) determined a new enriched-midgut miRNA, (ii) updated the piRNA annotation in ovaries with a genomic map of unique-mapping piRNAs, (iii) identified pan-tissue and tissue-enriched mRNA-derived small ncRNAs, and (iv) assessed AGO1- and AGO2- loading of candidate small ncRNAs. Continued research will broaden our view of small ncRNAs and greatly aide in our understanding on how these molecules contribute to mosquito physiology.

Broad spectrum immunomodulatory effects of Anopheles gambiae microRNAs and their use for transgenic suppression of Plasmodium

Malaria, caused by the protozoan parasite Plasmodium and transmitted by Anopheles mosquitoes, represents a major threat to human health. Plasmodium’s infection cycle in the Anopheles vector is critical for transmission of the parasite between humans. The midgut-stage bottleneck of infection is largely imposed by the mosquito’s innate immune system. microRNAs (miRNAs, small noncoding RNAs that bind to target RNAs to regulate gene expression) are also involved in regulating immunity and the anti-Plasmodium defense in mosquitoes. Here, we characterized the mosquito’s miRNA responses to Plasmodium infection using an improved crosslinking and immunoprecipitation (CLIP) method, termed covalent ligation of endogenous Argonaute-bound RNAs (CLEAR)-CLIP. Three candidate miRNAs’ influence on P. falciparum infection and midgut microbiota was studied through transgenically expressed miRNA sponges (miR-SPs) in midgut and fat body tissues. MiR-SPs mediated conditional depletion of aga-miR-14 or aga-miR-305, but not aga-miR-8, increased mosquito resistance to both P. falciparum and P. berghei infection, and enhanced the mosquitoes’ antibacterial defenses. Transcriptome analysis revealed that depletion of aga-miR-14 or aga-miR-305 resulted in an increased expression of multiple immunity-related and anti-Plasmodium genes in mosquito midguts. The overall fitness cost of conditionally expressed miR-SPs was low, with only one of eight fitness parameters being adversely affected. Taken together, our results demonstrate that targeting mosquito miRNA by conditional expression of miR-SPs may have potential for the development of malaria control through genetically engineered mosquitoes.

Malaria is caused by the Plasmodium parasite that is transmitted by Anopheles mosquitoes. The mosquito’s innate immune system plays an important role in controlling parasite infection. We have identified mosquito microRNAs (miRNAs) that are involved in regulating mosquito immunity to parasite infection. Transgenic mosquitoes that deplete the immunity-related miRNAs aga-miR-14 or aga-miR-305 through miRNA sponges, show increased resistance to both human and rodent parasite infection, and enhanced antibacterial defenses. Depletion of aga-miR-14 or aga-miR-305 resulted in an increased expression of multiple immunity-related and anti-Plasmodium genes, and the overall fitness cost of transgenic mosquitoes upon depletion of aga-miR-14 or aga-miR-305 was negligible. We show that targeting mosquito miRNA by transgenic expression of miRNA sponges may have potential for the development of malaria control through genetically engineered mosquitoes.

MicroRNA-449b-5p Suppresses Proliferation, Migration, and Invasion of Osteosarcoma by Targeting c-Met

Background

The aim of this study was to clarify the biological function of microRNA-449b-5p in the progression of osteosarcoma (OS) and to define the underlying mechanism.

Material/Methods

Relative levels of microRNA-449b-5p in OS tissues and cell lines was determined by quantitative real-time polymerase chain reaction (qRT-PCR). The correlation between microRNA-449b-5p level and pathological characteristics of OS patients was analyzed by chi-square test. Kaplan-Meier analysis was used for survival analysis of OS patients based on their expression level of microRNA-449b-5p. Regulatory effects of microRNA-449b-5p on cellular behaviors of OS cells were evaluated by cell counting kit-8 (CCK-8) and Transwell assay. The binding relationship between microRNA-449b-5p and c-Met was verified through dual-luciferase reporter gene assay, and their interaction in OS progression was further examined through a series of rescue experiments.

Results

MicroRNA-449b-5p was expressed at low levels in OS. Lower levels of microRNA-449b-5p were seen in OS tissues with worse tumor grade or histological differentiation. OS patients with low levels of microRNA-449b-5p had worse overall survival relative to those with high level of microRNA-449b-5p. Overexpression of microRNA-449b-5p markedly attenuated proliferative, migratory, and invasive abilities of OS cells. C-Met is the downstream target of microRNA-449b-5p, and its level was inhibited in OS cells overexpressing microRNA-449b-5p. Importantly, c-Met partially rescued the inhibitory effects of microRNA-449b-5p on behavior of OS cells.

Conclusions

MicroRNA-449b-5p is downregulated in OS, which alleviates the malignant progression of OS by targeting c-Met.

Over expression of bmo-miR-2819 suppresses BmNPV replication by regulating the BmNPV ie-1 gene in Bombyx mori

Bombyx mori nucleopolyhedrovirus (BmNPV) is a major pathogen that threatens the growth and sustainability of the sericulture industry. Accumulating studies in recent years suggest that insect viruses infection can change the host microRNAs (miRNAs) expression profile and both cellular and viral miRNAs play roles in host-pathogen interactions. Until now, the functional analysis of miRNA encoded by silkworm for host-virus interaction is limited. In this study, we validate the down-regulation of bmo-miR-2819 upon BmNPV infection by qRT-PCR and confirm the BmNPV immediately early 1 gene, ie-1 is one of the targets for bmo-miR-2819 based on the results of dual luciferase report assay. Overexpression of bmo-miR-2819 can significantly decline the abundance of IE-1 protein level in BmNPV-infected silkworm larvae. Further, the expression level of polyhedrin gene and VP39 protein of BmNPV in the infected larvae after applying bmo-miR-2819 mimics was significantly decreased comparing with that of larvae with mimic control. Our results suggest that overexpression of bmo-miR-2819 could suppress BmNPV replication by down-regulating the expression of BmNPV ie-1 gene, which demonstrate that cellular miRNAs could affect virus infection by regulating the expression of virus genes.

microRNA profiles and functions in mosquitoes

Mosquitoes are incriminated as vectors for many crippling diseases, including malaria, West Nile fever, Dengue fever, and other neglected tropical diseases (NTDs). microRNAs (miRNAs) can interact with multiple target genes to elicit biological functions in the mosquitoes. However, characterization and function of individual miRNAs and their potential targets have not been fully determined to date. We conducted a systematic review of published literature following PRISMA guidelines. We summarize the information about miRNAs in mosquitoes to better understand their metabolism, development, and responses to microorganisms. Depending on the study, we found that miRNAs were dysregulated in a species-, sex-, stage-, and tissue/organ-specific manner. Aberrant miRNA expressions were observed in development, metabolism, host-pathogen interactions, and insecticide resistance. Of note, many miRNAs were down-regulated upon pathogen infection. The experimental studies have expanded the identification of miRNA target from the 3' untranslated regions (UTRs) of mRNAs of mosquitoes to the 5' UTRs of mRNAs of the virus. In addition, we discuss current trends in mosquito miRNA research and offer suggestions for future studies.