The female Drosophila melanogaster fly undergoes behavioral changes after mating, including an increase in egg laying and an avoidance of remating. Accessory-gland products elicit these changes transiently when introduced into unmated female flies. We report here the generation and phenotype of flies that lack functional accessory-gland main cells as a consequence of genetically directed delivery of diphtheria toxin subunit A to those ceUls. Only main-cell secretions are essential for the short-term inhibition to remating; no other products of the genital tract can replace their function. Long-term inhibition to remating depends only on the storage of sperm in the female. Both sperm and main-cell secretions have roles in the increase of egg laying by the mated female. In addition to full-strength diphtheria toxin, we used low-activity toxins to kill only those ceUls that express toxin at high levels. These transgenic strains that express diphtheria toxins of different strengths in accessory-gland main cels wiUl be useful in further defining the role of these cells.In insects, mating causes females to undergo physiological and behavioral changes that persist for several days (1, 2). After mating, females lay eggs at a high rate and they reject further male courtship and remating. They store and utilize sperm they receive. In Drosophila melanogaster, these behavioral changes are due in part to sperm and in part to seminal fluid (3-5). Seminal-fluid components have been shown to cause the initial decrease in receptivity, called the "copulation effect" (3), but the long-term decrease in receptivity, called the "sperm effect" (4, 5), is correlated with the presence of sperm in the female's sperm-storage organs.To determine which molecules are responsible for these behavioral changes, we need to know their source. Seminalfluid effects on oviposition (egg laying) rate and receptivity were demonstrated in Hihara's study (3) of mates of males that had depleted their seminal secretions due to multiple prior matings. Hihara (3) postulated that products of the accessory gland, a secretory tissue in the male reproductive tract, caused these behavioral changes. He reasoned this because the accessory glands of multiply mated males were shrunken, apparently due to depletion of their contents, and because transplantation ofaccessory glands (6, 7) or injection of their extracts (for review, see ref.2) was known to cause increases in oviposition and decreases in receptivity. Chen et al. (8) and Aigaki et al. (9) later showed that a single accessory-gland peptide, the sex peptide, is able to induce oviposition and rejection when introduced into female flies.

A model system has been established in which PC12 cells are converted to neuronal-like cells that undergo transcription-dependent cell death following removal of NGF. Nineteen sublines of PC12 cells were tested to establish parameters for making cells dependent on NGF for survival. In most sublines, a relatively small percentage of cells become dependent on NGF for survival, and following removal of NGF, most of the cells begin proliferating in serum-containing medium. In several sublines, however, a significant percentage of cells die following removal of NGF. One of these sublines, PC6-3, can be grown under conditions in which 90% of the cells undergo transcription-dependent cell death following removal of NGF in either serum-free or serum-containing medium. Fourteen hours after removing NGF, 50% of the cells are committed to die, while initial morphological signs of cell death as determined by time-lapse videomicroscopy occur 2-6 hr later and include loss of neurites followed by a 1-3 hr period of active membrane "blebbing" and protrusions. Cell death can be blocked by the RNA synthesis inhibitor actinomycin D, the protein synthesis inhibitor cycloheximide, KCl, basic fibroblast growth factor, or dibutryl-cAMP, but not by epidermal growth factor, leupeptin, or the endonuclease inhibitor aurintricarboxylic acid (ATA). Removal of NGF activates an endonuclease that causes nucleosomal laddering of the DNA; however, endonuclease activity does not appear to be required for cell death. In agreement with previous studies (Batistatou and Greene, 1991; Rukenstein et al., 1991) demonstrating that naive PC12 cells undergo transcription-independent cell death when shifted into serum-free medium in the absence of growth factors, all cell lines tested except for one die when cultured in RPMI medium lacking growth factors. DNA fragmentation is a prominent feature of transcription-independent cell death, and death can be blocked with NGF, ATA, and dibutryl-cAMP but not with actinomycin D or KCl. The PC12 model system described here should be useful for identifying cell death genes and for characterizing cellular and molecular events in programmed neuronal cell death.

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