Research Interests

My lab studies immune mechanisms of aquatic animals, invertebrates and vertebrates. Of particular interest are the rearranging antigen receptors recently discovered in the oldest vertebrate taxon, jawless fish (Agnatha) such as lamprey and hagfish. Antigen recognition in lamprey and hagfish is mediated by variable lymphocyte receptors (VLR) consisting of diverse leucine-rich repeat (LRR) motifs. In jawless fish genomes there are only incomplete VLR genes, which lack any of the diversity LRR motifs, one VLR gene in lamprey and two in hagfish. Mature functional VLR genes are assembled in lymphocytes by recombinatorial insertion of LRR domains from flanking genomic cassettes into the incomplete germline gene via a unique DNA rearrangement mechanism. In sharp contrast, all studied jawed vertebrates (Gnathostomes) beginning with shark, skate and ray, assemble their B and T cell antigen receptors via RAG-mediated V(D)J rearrangement of Immunoglobulin (Ig) gene fragments. Thus, two strikingly different modes of lymphocyte-based adaptive immune systems appeared in the Cambrian period ~500-450 million years ago.

Figure 1. Rearranging antigen receptors of jawless and jawed vertebrates. The lamprey mature VLR gene consists of the signal peptide (SP), N-terminal LRR (LRRNT), first 18-residue LRR (LRR1), variable number of 24-residue LRR (LRRV), a connecting peptide (CP), C-terminal LRR (LRRCT) and threonine/proline-rich stalk. Portions of LRRNT and LRRCT that are not encoded in the germline VLR are hatched. Gnathostome antibody genes are assembled via random joining of Ig gene fragments consisting of variable (V), diversity (D) and joining (J) elements, and Ig constant (C) domains.

We are studying the process of immune activation in the sea lamprey to characterize similarities and differences between the immune systems of jawless and jawed vertebrates. Live larvae are immunostimulated with various antigens and lymphocyte activation is then analyzed in terms of size of the cells and antigen recognition via cell surface VLR and by soluble plasma VLR. Receptor-ligand pairs are selected from recombinant VLR libraries to define the binding properties. Our second research goal is to decipher the mechanism of lamprey VLR gene rearrangement. We are analyzing rearrangement intermediates, genomic sequences of the lamprey VLR locus and sequences generated by the ongoing sea lamprey genome sequencing project (Washington University, St Louis, MO). Computational approaches are employed to predict models of the VLR gene rearrangement and to estimate the potential diversity of VLR proteins and of their ligand-binding sites. Apart form basic science we are exploring the biotech potential of VLR as novel detection reagents and application of the DNA rearrangement machinery of VLR as genetic engineering tools.