In humans, the immune system has two subsystems: the innate and the adaptive immune systems. The innate system first recognizes the presence of a pathogen and alerts the adaptive system to make antibodies and directs other adaptive responses. However, only vertebrates have an adaptive system, while invertebrates such as the purple sea urchin survive with only the innate system. The sea urchin innate immune system responds to the presence of pathogens by marking them as foreign, which results in the uptake of the pathogens by cells capable of killing them. Recent study designed to identify genes that were turned on in response to the presence of bacteria showed that one particular gene, called 185/333, was activated significantly more than all the rest. Although the protein encoded by this gene has not been previously identified in other organisms and its function is unknown, analysis has shown a significant level of diversity in these proteins, reminiscent of the antibody diversity generated by the adaptive immune system in higher vertebrates. This variability includes the protein structure, which shows the presence and absence of 24 different regions and variability in the sequence of the amino acids. The protein appears to be secreted, has separate regions rich in glycine and histidine, repeated sequence regions that may be used to bind to cell surfaces, and short regions that are very acidic. Curiously, no clear mechanism to keep the protein stably folded was found. The diversity in the proteins was expected to be encoded by many genes in an animal like sea urchin, however, evidence suggests that there are only a few. In order to understand the diversity in the genes and how it may affect the functions of the encoded proteins, two major aims will be undertaken: Aim 1. Characterization of the gene(s). The number and structure of genes will be analyzed in order to reveal how different regions of the protein are linked together, uncover the source of the amino acid variability, and investigate the response to bacterial challenge by specific cell types. Aim 2. Characterization of protein(s). It will be determined when the proteins are produced with respect to bacterial challenge. The function(s) of the proteins will also be characterized and any functional diversity among the proteins will be identified. This project is an initial investigation of an unexpectedly diverse innate immune response mounted by the sea urchin towards bacterial pathogens and may lead to a significant change in the understanding of the immune responses in animals other than higher vertebrates. Broader impacts: A change in the understanding of invertebrate immune capabilities may eventually alter the approaches employed within the research community for investigating immune responses in animals other than vertebrates. Research training will be undertaken for graduate and post-doctoral students and will promote exchanges of both student and senior researchers between the US and the co-investigator's lab in Australia. Research opportunities for undergraduates will be available in our laboratories, and assistance will be offered to undergraduates searching for research opportunities for placement in other local laboratories. In the past, trainees were 69% women and 46% underrepresented minorities. This demographic is not expected to change in the future.
