We propose to use the Drosophila medulla neurons as a model to study dendritic development in CNS. Like vertebrate cortex and retina, the medulla neuropil is organized in columns and layers, suggesting that the fly medulla neurons and vertebrate cortex neurons confront similar challenges in routing their dendrites to specific layers and columns. In addition, the fly visual system has several unique advantages: (i) the medulla neurons extend dendritic arbors in a three-dimensional lattice structure, facilitating morphometric analysis;(ii) the presynaptic targets for many medulla neuron types are known from our anatomical studies;(iii) genetic tools for labeling specific classes of medulla neurons and determining their connectivity have been developed. We have developed novel techniques to analyze dendritic structures in 3D and to exploit the unique advantages of this system. First, to image reliably the slender dendrites of medulla neurons, we developed a dual imaging technique that generates isotropic 3D-images of dendrites. Second, we developed an image registration technique that makes uses of the regular array structures of the optic lobe to standardize dendritic branching patterns. This, in combination with a series of statistical methods we established, allows us to analyze dendritic patterns in three-dimension space. Third, we have established an imaging technique (GRASP) to detect synaptic contacts at light-microscopic level. We used these techniques to generate a data set of three types of medulla neurons. Our preliminary analyses suggested (i) that the medulla neurons exhibit stereotypic dendritic arbors but the detailed branching pattern and topology are not conserved;(ii) that the synaptic partnership between axons and dendrites are robust and specific. Based on these results, we hypothesize that dendritic development in the optic lobe neurons proceed in two distinct processes: (i) routing dendrites in type-specific fashion, which, at least in part, serves to maximize the possibility of finding appropriate synaptic partners;(ii) matching different sections of dendrites with specific afferents, which likely requires specific interactions between axons and dendrites to ensure synaptic specificity. The mechanisms governing these processes are the focuses of the following two specific aims.
