[P1.53]: Characterization of the interaction between Mmp2 and Frac during axon guidance

Motor axon guidance is thought to be regulated by the balance of attractive and repulsive cues that serve to guide axons along their migratory path. In this way, defined axon pathways are created and connections within the adult nervous system are ultimately established. The two Drosophila MMPs, Mmp1 and Mmp2, have recently been reported to promote fasciculation during motor axon guidance in the Drosophila embryo, however, the mechanism by which these proteases function is unknown. In order to identify Mmp2 substrates and interacting proteins important for axon guidance, a yeast two-hybrid screenwasperformedusing full-length Mmp2. From the identified candidate proteins, we have focused on Fatal Attraction (Frac) as themost likelyMmp2 substrate to function in neuronal development. frac is a previously uncharacterized gene predicted to encode an adhesion molecule containing EGF-like calcium binding domains, matrilin repeats, and a Hyalin repeat domain. frac cDNA is expressed strongly throughout the muscle tissue consistent with a role in axon guidance and with modulation by Mmp2. Overexpression of frac in Drosophila embryos results in a phenotype in which branch ‘‘b’’ of the intersegmental nerve (ISNb) exhibits loosely bundledbranches, extra projections, and a fraying of nerve bundles. Interestingly, this phenotype is indistinguishable from that observed in Mmp2 loss-of-function (LOF) mutants and suggests that the balance of attractive and repulsive cues regulating pathfinding has been disrupted. Based on this similarity, we propose that Frac acts in muscle to promote defasciculation by attracting motor axons to their muscle targets. Mmp2 would then promote fasciculation by cleaving Frac and downregulating this adhesive interaction. Mmp2 may deactivate Frac by cleaving a particular domain or abrogating an adhesive interaction, a role consistent with the Mmp2 mutant phenotype. We will present our continued progress toward characterizing the interaction between Mmp2 and Frac including analysis of frac LOF embryos.