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Brief Summary of DSCAM/Dscam Functions

Cell adhesion molecules are important during the neuro-developmental processes with events such as cell migration, axon growth, and dendrite arborization. In flies, DSCAM encodes a cell adhesion protein that is important in neuronal wiring and immune responses. Drosophila generates 38,016 Dscam isoforms from a mutually exclusive splicing events of 4 cassette exon clusters - 4, 6, 9, and 17. This degree of transcript diversity however, has not been found in mammalian homologs of Dscam. Physiologenic analysis of the Dscam across arthropods reveal that homologous recombination is the major mechanism by which Dscam exons evolve. The photoreceptor terminals in Drosophila is thought to form tetrad synapses that connect an invariable pair of postsynaptic elements. Dscam is thought to aid this process by regulating the synaptic specificity through exclusion of inappropriate synaptic combination at the contact site. Studies confirm that Dscam play a role in neural circuit assembly. Mutants of Dscam ectodomains produce severly disorganized neural circuits. However, it is still unclear how the diversity of the isoform contribute to the neural circuit assembly process. Dscam1 in drosophila is thought to mediate self-avoidance while Dscam2 mediates tiling. In mice, DSCAM functions in both self-avoidance and tiling. The isoforms of Dscam have isoform-specific binding properties that mediate homophilic repulsion. This becomes the basis of self-avoidance, which is a crucial developmental mechanism for uniform distribution of axonal and dendritic processes in the formation of synaptic fields. Tiling occurs when homophilic repulsion mediated by Dscam2 prevents the processes of the same class of cells from overlapping. Dscam (Down syndrome cell adhesion molecule) appears to be involved in phagocytosis of pathogens, and shows pathogen-specific splice-form expression between divergent pathogen (or parasite) types.