Colonial marine invertebrates—animals like corals, sponges, and ascidians—are capable of distinguishing their own tissues from those of other members of their species purely by cell-cell contact. This ability, called allorecognition, determines if interacting animals will fuse together and become physiologically integrated or remain separate and aggressively compete for space.
The Nicotra laboratory seeks to understand the molecular basis, evolutionary history, and biomedical relevance of invertebrate allorecognition systems through the study of the Hydractinia symbiolongicarpus. In this species, allorecognition is controlled by two linked genes, alr1 and alr2, which encode transmembrane proteins with highly polymorphic extracellular domains. The sequences of these proteins predict allorecognition responses such that animals with matching alleles fuse, while those with mismatched alleles do not. Nicotra’s current research focuses on determining how the alr1 and alr2 proteins confer allorecognition specificity and regulate allorecognition responses. He hopes to determine whether invertebrate allorecognition systems are homologous to elements of mammalian immune systems, particularly those involved in transplant rejection. This could lead to the identification of new or previously unappreciated signaling pathways involved in immune recognition that, in turn, could serve as novel targets for immunosuppressive therapies.