Cover photograph (Copyright © 2001, American Society for Microbiology. All rights reserved.): The absence of RotundRacGAP in rotund null mutants induces male sterility in Drosophila melanogaster. Electron microscopic observation of the testicular cysts of rotund null mutant flies defines the cellular phenotype as the absence of interspermatid membrane, random spermatid orientation, and reduced cytoplasmic condensation. Decreasing Ras signaling in these null mutant flies reveals cross talk between RotundRacGAP-regulated signaling and the Ras pathway: the defects in membrane deposition and spermatid packing in rotund null mutants are suppressed by heterozygous hypomorphic mutation of either the Dras1 gene (top) or the drk gene (bottom), which encodes the Drk adaptor protein upstream of Ras. (See related article on page 6280.)