Meeting Abstract
Wide-ranging aspects of organismal biology are influenced by the microbial world. By orchestrating these relationships – through protecting against pathogens and promoting a beneficial microbiota – the immune system operates at the forefront of evolutionary biology. Immune response is a system-wide phenomenon that integrates mechanisms for microbial detection and clearance with physiological pathways that maintain host homeostasis. The larval stage of the purple sea urchin (Strongylocentrotus purpuratus) provides an experimentally tractable, morphologically simple system in which to study immunity from a system-wide perspective. In response to marine bacterium Vibrio diazotrophicus in the seawater, larvae elicit a synchronous, non-lethal inflammatory response. The cellular response consists of changes in gut morphology, immune cell recruitment, and changes in cell motility. Analysis of gene activity reveals that the most acutely upregulated gene in the early phase of response are two groups of IL17 paralogs, which are expressed exclusively in gut epithelial cells. Perturbation of IL17 receptor signaling results in reduced levels of tnfaip3 (an IL17 feedback inhibitor), nfkbiz (an IL17 target gene in vertebrates), transcription factors cebpα and cebpγ and soul1 (SOUL domains are evolutionarily widespread and involved in immune responses). These results indicate that the highly regulated IL17 expression in the gut epithelium and signaling through IL17R1 form a central axis of larval gut-associated immunity. Transcriptional regulation is also apparent within a battery of genes with homologs throughout non-vertebrate bilaterian organisms. As invertebrate deuterostomes, sea urchin larvae share an important genetic heritage with the vertebrates but provide an experimentally tractable system. These findings define fundamental aspects of immune control and are relevant for understanding gut immunity in a wide range of animals.
