The alg-1 Gene Is Necessary for Orsay Virus Replication in Caenorhabditis elegans

Natural variation in infection specificity of Caenorhabditis briggsae isolates by two RNA viruses

Antagonistic relationships such as host-virus interactions potentially lead to rapid evolution and specificity in interactions. The Orsay virus is so far the only horizontal virus naturally infecting the nematode C. elegans. In contrast, several related RNA viruses infect its congener C. briggsae, including Santeuil (SANTV) and Le Blanc (LEBV) viruses. Here we focus on the host's intraspecific variation in sensitivity to these two intestinal viruses. Many temperate-origin C. briggsae strains, including JU1264 and JU1498, are sensitive to both, while many tropical strains, such as AF16, are resistant to both. Interestingly, some C. briggsae strains exhibit a specific resistance, such as the HK104 strain, specifically resistant to LEBV. The viral sensitivity pattern matches the strains' geographic and genomic relationships. The heavily infected strains mount a seemingly normal small RNA response that is insufficient to suppress viral infection, while the resistant strains show no small RNA response, suggesting an early block in viral entry or replication. We use a genetic approach from the host side to map genomic regions participating in viral resistance polymorphisms. Using Advanced Intercrossed Recombinant Inbred Lines (RILs) between virus-resistant AF16 and SANTV-sensitive HK104, we detect Quantitative Trait Loci (QTLs) on chromosomes IV and III. Building RILs between virus-sensitive JU1498 and LEBV-resistant HK104 followed by bulk segregant analysis, we identify a chromosome II QTL. In both cases, further introgressions of the regions confirmed the QTLs. This diversity provides an avenue for studying virus entry, replication, and exit mechanisms, as well as host-virus specificity and the host response to a specific virus infection.

Caenorhabditis elegans immune responses to microsporidia and viruses

The model organism Caenorhabditis elegans is susceptible to infection by obligate intracellular pathogens, specifically microsporidia and viruses. These intracellular pathogens infect intestinal cells, or, for some microsporidia, epidermal cells. Strikingly, intestinal cell infections by viruses or microsporidia trigger a common transcriptional response, activated in part by the ZIP-1 transcription factor. Among the strongest activated genes in this response are ubiquitin-pathway members and members of the pals family, an intriguing gene family with cross-regulations of different members of genomic clusters. Some of the induced genes participate in host defense against the pathogens, for example through ubiquitin-mediated inhibition. Other mechanisms defend the host specifically against viral infections, including antiviral RNA interference and uridylation. These various immune responses are altered by environmental factors and by intraspecific genetic variation of the host. These pathogens were first isolated 15 years ago and much remains to be discovered using C. elegans genetics; also, other intracellular pathogens of C. elegans may yet to be discovered.