Cover photograph (Copyright © 2002, American Society for Microbiology. All Rights Reserved.): Losses or gains of ACK tyrosine kinase function cause developmental defects in Drosophila melanogaster. (Left) Wild-type Drosophilia eye (top); effect of kinase-dead Drosophila ACK (DACK) expression on eye development (bottom). (Right) Wild-type wing (top); formation of ectopic wing vein tissue (arrows) following expression of kinase-dead DACK (middle); effect of overexpression of DACK (bottom). (See related article on p. 3685.)