Understanding Anti-Viral Immunity Mechanisms in C. elegans
C. elegans, a free-living nematode, forms an excellent model system to study several
aspects of biology including host-pathogen interactions. In this study, we looked at
factors involved in anti-viral immunity mechanisms in C. elegans with a prospect of being able to extrapolate into other systems. A reporter worm strain was used
(MS1395), in which GFP expression directly indicates the extent of viral replication in the system. A feeding RNAi screen was performed to identify genes in anti-viral immunity and a total of 11,700 C. elegans genes were knocked down and screened for the presence/ absence of GFP. Of these genes, 2180 genes were screened by me. A total of 691 genes (6% of total number of genes) were found to be positive. The screen was repeated to eliminate false positives and 260 genes (2.2% of the total number of genes) were found to be positive. Meanwhile, discovery of a naturally infecting C. elegans virus, Orsay, by Felix et al., helped us further our research. A subset of genes positive from the secondary screen was tested for susceptibility to Orsay infection. Chromosomal mutations for two of the genes identified by RNAi, him-14(it44) and nhr-68(gk708) showed increased susceptibility to Orsay infection. qRT-PCR, in situ hybridization and Northern blots showed higher levels of Orsay RNA1 molecules in these two mutants compared to the wild-type strain. We are currently in the process of understanding the roles played by these two genes in anti-viral immunity. him-14 gene encodes a protein that is required for promoting crossing over between homologous chromosomes and therefore is expressed in the germ-line. Evidence suggests that the increased susceptibility to Orsay infection in him-14(it44) mutants is germ-line dependent. Prior reports have linked the germline to longevity, suggesting that him-14 indirectly affects virus susceptibility by modifying some aspect of body physiology. nhr-68 belongs to nuclear hormone receptor family and are transcription factors typically regulated by lipophilic molecules like steroids, retinoids, bile and fatty acids. nhr-68 mutants also have increased fat content compared to wild-type animals. We hypothesize that the increase to Orsay susceptibility in these worms is due to increased lipid molecules in the body.
Currently, the lab is trying to understand the mechanism of action of these two genes in anti-viral immunity. We believe this study will provide a better understanding of the nature of host- pathogen interaction and will open a wide area of interesting biology for further investigation.