UC San Diego

The Intracellular Pathogen Response (IPR) is an innate immunity pathway in Caenorhabditis elegans that is used to defend against natural intracellular pathogens of the intestine. Activation of the IPR increases host resistance to pathogens such as the microsporidia Nematocida parisii, which is the most commonly described pathogen of C. elegans in the wild. The IPR comprises of hundreds of genes including members of the “protein containing ALS2cr12 signature” (pals) gene family with unknown biochemical function and which is highly expanded in C. elegans. While some regulators of the IPR have been discovered amongst the pals genes, it remains unclear whether there are specific IPR induced genes that are responsible for the pathogen resistance phenotype conferred by the IPR.

To address this question, I previously used different mutants that have subsets of IPR genes constitutively induced and are more resistant to N. parisii, in combination with a reverse genetics approach to narrow down genes likely involved in pathogen resistance. My preliminary data showed that knock-down of pals-14 causes a modest increase in pathogen susceptibility. I hypothesized that pals-14 is an important gene in IPR-driven immunity and a potential regulator of the resistance phenotype.

In my master’s thesis, I conducted microsporidia pathogen load assays after RNAi-mediated knock-down of pals-14 in several genetic backgrounds and observed an increase in the susceptibility to N. parisii in wild-type worms, as well as three different strains with constitutive IPR expression. I generated pals-14 knock-out mutants in these genetic backgrounds to further confirm the susceptibility phenotype. Analysis of PALS-14::GFP localization using the pals-14 transgeneOme construct indicated expression in the intestine and localization to unique spherical structures upon N. parisii infection. Distinct localization patterns were observed in different genetic backgrounds with constitutively induced IPR.

Based on the infection phenotype and protein localization findings, pals-14 appears to be involved in regulating resistance against N. parisii in C. elegans. The understanding of pals-14 in the larger scope of the IPR has shed light onto the innate immune response of C. elegans and identifies the first induced pals gene to control pathogen resistance.