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The regulatory protein calmodulin is a major mediator of calcium-induced changes in cellular activity. To analyze the roles of calmodulin in an intact animal, we have generated a calmodulin null mutation in Drosophila melanogaster. Maternal calmodulin supports calmodulin null individuals throughout embryogenesis, but they die within 2 days of hatching as first instar larvae. We have detected two pronounced behavioral abnormalities specific to the loss of calmodulin in these larvae. Swinging of the head and anterior body, which occurs in the presence of food, is three times more frequent in the null animals. More strikingly, most locomotion in calmodulin null larvae is spontaneous backward movement. This is in marked contrast to the wild-type situation where backward locomotion is seen only as a stimuluselicited avoidance response. Our finding of spontaneous avoidance behavior has striking similarities to the enhanced avoidance responses produced by some calmodulin mutations in Paramecium. Thus our results suggest evolutionary conservation of a role for calmodulin in membrane excitability and linked behavioral responses.The small calcium binding protein calmodulin has evolved to play a role in transducing changes in intracellular calcium levels into changes in cellular metabolism and behavior. Calmodulin has been found in essentially all eukaryotes examined and is believed to be present in all tissue types in vertebrates (for reviews, see refs. 1 and 2). Particularly high levels are found in neural tissues, indicating a dominant role for calmodulin in mediation of calcium signaling in the nervous system. Biochemical studies have uncovered a large number of enzymes and other proteins whose function is modified by binding of the calcium-saturated form of calmodulin, and many of these targets, including calmodulin-dependent protein kinase 11 (3) and calcineurin, a calmodulin-dependent protein phosphatase (4), are concentrated in the nervous system. In vitro studies aimed at unraveling the mechanism by which calmodulin regulates its various targets are relatively well advanced (5,6).Genetic studies, focused on dissecting calmodulin's functions in the context of the whole cell, were initiated more recently and are being actively pursued in several simple eukaryotes (7-10). Evidence that calmodulin regulates the cell cycle and related cytoskeletal functions (10-14) and ion channel activity (8,15) Fig. 1), at -34 bp relative to the calmodulin transcription start site, was mobilized, and individual chromosomes showing a loss of the w+ phenotype and conversion to homozygous adult lethality were selected. Genomic Southern blots were probed with fragments of the calmodulin gene to identify deletions flanking the insertion site.In Situ Hybridization. Late stage (12-16 h at 22°C) embryos from a balanced stock of the Camn339 mutation were hybridized with a calmodulin probe as described (23).Immunoblot Analysis. Larvae were prepared for SDS/ PAGE electrophoresis as described (24). Immunoblots were prepared by using a ca...

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