CG3533 plays an important role in axonal targeting and circuit formation in the olfactory system of Drosophila. Arzu Çelik¹, Thomas Hummel², Mustafa Talay¹, Kaan Apaydin¹, Selen Zülbahar¹. 1) Dept Mol Bio and Genetics, Bogazici Univ, Istanbul, Turkey; 2) Dept Neurobiology, Univ Vienna, Vienna, Austria.

   The olfactory system of Drosophila represents an interesting example of how a large repertoire of neuronal cell types are specified and assembled into functional circuits. Olfactory sensory neurons express one olfactory receptor from a large number of receptors in the genome to ensure proper sensory perception. Olfactory sensory neurons expressing specific types of receptors connect to second order neurons in the antennal lobe in discrete regions called glomeruli. The specification and patterning of projection neurons appears to be independent of sensory input. In contrast to the mammalian system an involvement of Drosophila ORs in orchestrating the establishment of class-specific connections in the brain have been excluded. The question of how a precise olfactory map can be established is thus of major interest. Neurons and glia largely depend on each other for their role in the nervous system, and their interaction has a distinct role in the functioning of the nervous system. Glial cells act as guiding cells and are usually located at choice points where they send out signals to which growth cones and axons respond. In an enhancer-trap screen for genes that are expressed in subsets of olfactory neurons we identified CG3533, a novel cell-adhesion molecule. This gene is primarily expressed in glia in olfactory organs as well as in the antennal lobe, mainly in glial cells. Cell adhesion molecules are known to have important roles in axonal targeting. Thus, the involvement of this cell adhesion molecule in wiring of the olfactory circuit was investigated using genetic tools. Analysis of mutants revealed severe targeting defects in all ORN classes that were analyzed and defects in the formation of the commissure, pointing to a critical role of this cell adhesion molecule in OR targeting and circuit formation. We are currently performing rescue experiments and are trying to identify interacting partners of CG3533 using genetic and biochemical experiments.