TEG-1 CD2BP2 controls miRNA levels by regulating miRISC stability in C. elegans and human cells

Redundant mechanisms regulating the proliferation vs. differentiation balance in the C. elegans germline

The proper production of gametes over an extended portion of the life of an organism is essential for a high level of fitness. The balance between germline stem cell (GSC) proliferation (self-renewal) and differentiation (production of gametes) must be tightly regulated to ensure proper gamete production and overall fitness. Therefore, organisms have evolved robust regulatory systems to control this balance. Here we discuss the redundancy in the regulatory system that controls the proliferation vs. differentiation balance in the C. elegans hermaphrodite germline, and how this redundancy may contribute to robustness. We focus on the various types of redundancy utilized to regulate this balance, as well as the approaches that have enabled these redundant mechanisms to be uncovered.

Drosophila as a Model for Human Viral Neuroinfections

The study of human neurological infection faces many technical and ethical challenges. While not as common as mammalian models, the use of Drosophila (fruit fly) in the investigation of virus–host dynamics is a powerful research tool. In this review, we focus on the benefits and caveats of using Drosophila as a model for neurological infections and neuroimmunity. Through the examination of in vitro, in vivo and transgenic systems, we highlight select examples to illustrate the use of flies for the study of exogenous and endogenous viruses associated with neurological disease. In each case, phenotypes in Drosophila are compared to those in human conditions. In addition, we discuss antiviral drug screening in flies and how investigating virus–host interactions may lead to novel antiviral drug targets. Together, we highlight standardized and reproducible readouts of fly behaviour, motor function and neurodegeneration that permit an accurate assessment of neurological outcomes for the study of viral infection in fly models. Adoption of Drosophila as a valuable model system for neurological infections has and will continue to guide the discovery of many novel virus–host interactions.

An ortholog of the Vasa intronic gene is required for small RNA-mediated translation repression in Chlamydomonas reinhardtii

Small RNAs (sRNAs) are a class of noncoding RNAs that regulate complementary mRNAs, by triggering translation repression and/or transcript decay, and influence multiple biological processes. In animals, land plants, and some protists like the alga Chlamydomonas, sRNAs can repress translation of polyribosome-associated mRNAs, without or with only minimal transcript destabilization. However, the precise silencing mechanism is poorly understood. We found that Chlamydomonas VIG1, a homolog of the Drosophila melanogaster Vasa intronic gene and a member of a widely conserved protein family in eukaryotes, is involved in this process. VIG1 appears to be an ancillary ribosomal constituent. Additionally, VIG1 copurifies with core components of sRNA effector complexes and plays a key role in the sRNA-mediated translation repression of polyribosomal transcripts.

Small RNAs (sRNAs) associate with Argonaute (AGO) proteins in effector complexes, termed RNA-induced silencing complexes (RISCs), which regulate complementary transcripts by translation inhibition and/or RNA degradation. In the unicellular alga Chlamydomonas, several metazoans, and land plants, emerging evidence indicates that polyribosome-associated transcripts can be translationally repressed by RISCs without substantial messenger RNA (mRNA) destabilization. However, the mechanism of translation inhibition in a polyribosomal context is not understood. Here we show that Chlamydomonas VIG1, an ortholog of the Drosophila melanogaster Vasa intronic gene (VIG), is required for this process. VIG1 localizes predominantly in the cytosol and comigrates with monoribosomes and polyribosomes by sucrose density gradient sedimentation. A VIG1-deleted mutant shows hypersensitivity to the translation elongation inhibitor cycloheximide, suggesting that VIG1 may have a nonessential role in ribosome function/structure. Additionally, FLAG-tagged VIG1 copurifies with AGO3 and Dicer-like 3 (DCL3), consistent with it also being a component of the RISC. Indeed, VIG1 is necessary for the repression of sRNA-targeted transcripts at the translational level but is dispensable for cleavage-mediated RNA interference and for the association of the AGO3 effector with polyribosomes or target transcripts. Our results suggest that VIG1 is an ancillary ribosomal component and plays a role in sRNA-mediated translation repression of polyribosomal transcripts.

Recent Molecular Genetic Explorations of Caenorhabditis elegans MicroRNAs

MicroRNAs are small, noncoding RNAs that regulate gene expression at the post-transcriptional level in essentially all aspects of Caenorhabditis elegans biology. More than 140 genes that encode microRNAs in C. elegans regulate development, behavior, metabolism, and responses to physiological and environmental changes. Genetic analysis of C. elegans microRNA genes continues to enhance our fundamental understanding of how microRNAs are integrated into broader gene regulatory networks to control diverse biological processes, including growth, cell division, cell fate determination, behavior, longevity, and stress responses. As many of these microRNA sequences and the related processing machinery are conserved over nearly a billion years of animal phylogeny, the assignment of their functions via worm genetics may inform the functions of their orthologs in other animals, including humans. In vivo investigations are especially important for microRNAs because in silico extrapolation of their functions using mRNA target prediction programs can easily assign microRNAs to incorrect genetic pathways. At this mezzanine level of microRNA bioinformatic sophistication, genetic analysis continues to be the gold standard for pathway assignments.

VIG-1 is required for maintenance of genome stability in Caenorhabditis elegans

To explore the function of VIG-1 in Caenorhabditis elegans, we analyzed the phenotypes of two vig-1 deletion mutants: vig-1(tm3383) and vig-1(ok2536). Both vig-1 mutants exhibited phenotypes associated with genome instability, such as a high incidence of males (Him) and increased embryonic lethality. These phenotypes became more evident in succeeding generations, implying that the germline of vig-1 accumulates DNA damage over generations. To examine whether vig-1 causes a defect in the DNA damage response, we treated worms with UV or camptothecin, a specific topoisomerase I inhibitor. We observed that the embryonic survival of the vig-1 mutants was reduced compared with that of the wild-type worms. Our results thus suggest that VIG-1 is required for maintaining genome stability in response to endogenous and exogenous genotoxic stresses.