Colonial animals such as sponges, hydroids, corals, and ascidians can discriminate between their own tissues and those of other members of their species based on cellular contact, leading to a response in which they either fuse or reject. This phenomenon, called allorecognition, is controlled by genetic systems encoding highly variable allorecognition molecules. Despite their importance to the life histories of colonial organisms, the biochemical and biophysical basis of these invertebrate allorecognition systems remains poorly understood. The goal of this project is to elucidate these mechanisms in the cnidarian, Hydractinia symbiolongicarpus. In Hydractinia, allorecognition is controlled by two highly variable genes, alr1 and alr2. In this project the investigators will use a combination of in vitro biochemical assays and in vivo genetic approaches with transgenic animals to identify extracellular and intracellular ligands for the alr proteins and to characterize their role in cell signaling. These results will explain how the alr proteins, by themselves discriminate self from non-self, and how they signal allorecognition effector systems. Data generated will also enable comparisons to other self-recognition systems, including plant self-incompatibility loci and fungal mating type loci. Within animals, if homology is discovered between the Hydractinia allorecognition system and the ascidian allorecognition system or the vertebrate immune system, it would suggest that extant self-recognition systems evolved from a system present in the last common ancestor of all metazoans. This project will include training opportunities for undergraduate, graduate, and post-doctoral students, research opportunities for area high school students, and educational outreach to middle and elementary school students in southwestern Pennsylvania. Results of this work will be incorporated into undergraduate and graduate immunology courses at the University of Pittsburgh, as well as presentations and a newsletter for transplant patients at the University of Pittsburgh Medical Center.
