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Two new learning mutants of Drosophila have emphasized the importance of cell-adhesion molecules in the processes underlying learning. The Volado gene encodes two isoforms of a novel alpha-integrin, a type of molecule that dynamically mediates cell adhesion and signal transduction. The gene is expressed preferentially in mushroom body cells, neurons known to mediate olfactory learning in insects, and the Volado proteins are concentrated in the mushroom body neuropil, brain areas that contain mushroom body processes in synaptic contact with other neurons. Volado mutants display an impairment of olfactory memories within 3 minutes after training but conditional expression of a Volado transgene during adulthood rescues the memory impairment. A modified behavioral paradigm has revealed that one of the integrin products serves memory formation, while the other is required for both memory formation and stability. The mutant, fasII, encodes a cell-adhesion molecule of the immunoglobulin superfamily. The gene is highly specific for mushroom bodies and when mutant, produces a learning deficit like Volado mutants. Conditional transgenes provide for rescue only during adulthood, confirming a physiological role for the gene product in learning processes. These observations demonstrate the critical importance of cell-adhesion molecules of the immunoglobulin superfamily and integrin family for mediating the formation of memory.
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