[Abstract unavailable

Extracellular growth factors are required for the survival of most animal cells. They often signal through the activation of the Ras pathway. However, the molecular mechanisms by which Ras signaling inhibits the intrinsic cell death machinery are not well understood. Here, we present evidence that in Drosophila, activation of the Ras pathway specifically inhibits the proapoptotic activity of the gene head involution defective (hid). By using transgenic animals and cultured cells, we show that MAPK phosphorylation sites in Hid are critical for this response. These findings define a novel mechanism by which growth factor signaling directly inactivates a critical component of the intrinsic cell death machinery. These studies provide further insights into the function of ras as an oncogene.

Induction of apoptosis in Drosophila requires the activity of three closely linked genes, reaper, hid and grim. Here we show that the proteins encoded by reaper, hid and grim activate cell death by inhibiting the anti-apoptotic activity of the Drosophila IAP1 (diap1) protein. In a genetic modifier screen, both loss-of-function and gain-of-function alleles in the endogenous diap1 gene were obtained, and the mutant proteins were functionally and biochemically characterized. Gain-of-function mutations in diap1 strongly suppressed reaper-, hid- and grim-induced apoptosis. Sequence analysis of these alleles revealed that they were caused by single amino acid changes in the baculovirus IAP repeat domains of diap1, a domain implicated in binding REAPER, HID and GRIM. Significantly, the corresponding mutant DIAP1 proteins displayed greatly reduced binding of REAPER, HID and GRIM, indicating that REAPER, HID and GRIM kill by forming a complex with DIAP1. These data provide strong in vivo evidence for a previously published model of cell death regulation in Drosophila.

A P-element vector has been constructed and used to generate lines of flies with single autosomal P-element insertions. The lines were analyzed in two ways: (1) the identification of cis-acting patterning information within the Drosophila genome, as revealed by a lacZ reporter gene within the P element, and (2) the isolation of lethal mutations. We examined 3768 independent lines for the expression of lacZ in embryos and looked among these lines for lethal mutations affecting embryonic neurogenesis. This type of screen appears to be an effective way to find new loci that may play a role in the development of the Drosophila nervous system.[Key Words: P element; lacZ; mutagenesis; cell market; Drosophila; pattern]Received May 30, 1989; revised version accepted July 11, 1989. One approach to studying development is to obtain genetic variants that are defective in some crucial step. This type of genetic analysis has been very successful in identifying virtually all of the zygotic loci required for the early stages of segmentation during embryogenesis in Drosophila melanogaster Niisslein-Volhard et al. 1984;Wieschaus et al. 1984). Besides chemical mutagenesis, transposon tagging has been used as a mutagen and allows rapid cloning of genes of interest (Bingham et al. 1981;Kidwell 1986).Recently, a scheme wherein single P elements are mobilized to new chromosomal locations has been implemented successfully (Cooley et al. 1988). The essential nature of this approach is to use two separate P elements to provide the two functions necessary for transposition. The first is a genetically marked P element that is defective in production of transposase but contains the ends required for its own transposition. The second is a P element with functional transposase activity but a much reduced likelihood for its own transposition (Robertson et al. 1988). Transposition of the marked P element then is initiated by crossing flies that carry only the marked P element to those that harbor only transposase. Insertions generated by this scheme are recovered in flies lacking tranposase activity and are therefore genetically stable.P-element vectors also have been used recently to search for cis-acting sequences which confer tissue-specific expression of a p-galactosidase [lacZ] fusion gene driven by the weak promoter of the P-element transpoPresent addresses: