Links between genes involved in development, proliferation and apoptosis have been difficult to establish. In the Drosophila wing disc, the vestigial (vg) and the scalloped (sd) gene products dimerize to form a functional transcription factor. Ectopic expression of vg in other imaginal discs induces outgrowth and wing tissue specification. We investigated the role of the VG-SD dimer in proliferation and showed that vg antagonizes the effect of dacapo, the cyclin-cdk inhibitor. Moreover, ectopic vg drives cell cycle progression and in HeLa cultured cells, the VG-SD dimer induces cell proliferation per se. In Drosophila, ectopic vg induces expression of dE2F1 and its targets dRNR2 and string. In addition vg, but not dE2F1, interacts with and induces expression of dihydrofolate reductase (DHFR). Moreover, a decrease in VG or addition of aminopterin, a specific DHFR inhibitor, shift the dorso-ventral boundary cells of the disc to a cell death sensitive state that is correlated with reaper induction and DIAP1 downregulation. This indicates that vg in interaction with dE2F1 and DHFR is a critical player for both cell proliferation and cell survival in the presumptive wing margin area.

We have determined the nucleotide sequence of the Drosophila retrotransposon 1731. 1731 is 4648 bp long and is flanked by 336 bp terminal repeats (LTRs) previously described as being reminiscent of provirus LTRs. The 1731 genome consists of two long open reading frames (ORFs 1 and 2) which slightly overlap each other. The ORF 1 and 2 present similarities with retroviral gag and pol genes respectively as shown by computer analysis. The pol gene exhibits several enzymatic activities in the following order: protease, endonuclease and reverse transcriptase. It is possible that 1731 also encompasses a ribonuclease H activity located between the endonuclease and reverse transcriptase domains. Moreover, comparison of the 1731 pol gene with the pol region of copia shows similarities extending over the protease, endonuclease and reverse transcriptase domains. We show that codon usage in the two retrotransposons is different. Finally, no ORF able to encode an env gene is detected in 1731.

We report here the characterisation of 1731, a new copia-like element of Drosophila melanogaster. 1731 was first isolated in a screening for ecdysterone modulated genes. This element is about 4.6 Kb long and is flanked by two long terminal repeats (LTRs) 336 base pairs in length. The whole 1731 element is transcribed into polyA+ RNAs, and these transcripts decrease rapidly upon hormonal treatment. 1731 is moderately repeated in the fly genome and slightly amplified in Kc/cells where extrachromosomal circular forms are found. The LTRs were sequenced in one cloned copy of 1731 and show a structural organisation similar to that of several other copia-like elements and retroviral proviruses. Small nucleotide stretches, similar to those found in Mouse Mammary Tumor Virus LTRs and known to be important in its regulation by a steroid hormone, occur in 1731 LTRs.

Drosophila cells of a clone derived from line Kc were treated with various concentrations of hydrogen peroxide (H202). The concentration of 10 mM was lethal, whereas concentrations of 1 -100 pM did not affect cell viability, rate of multiplication or protein synthesis. The intermediate concentration of 1 mM H z 0 2 was used to study the response of the cells to an oxidative stress.We observed a transitory decrease of the global protein synthesis, which was accompanied by changes in the polypeptide pattern. There was a 2.5-fold increase of the synthesis of the heat-shock proteins 70-68 and 23. The most prominent response was a 6.5-fold increase of actin synthesis 3 h after a 1 mM H 2 0 2 treatment. When aminotriazole (an inhibitor of catalase) was added in association with H202, the increase of actin synthesis became 8.5-fold. Experiments in which catalase was added at various times after H 2 0 2 showed that a 10-min treatment with H 2 0 2 was sufficient to induce actin and heat-shock protein synthesis 3 h later. HzOz was shown to induce the transcriptional activation of an actin gene and of the heat-shock protein genes 70 and 23 within minutes.These results are coherent with the hypothesis that the byproducts of O2 reduction (the superoxide ion and hydrogen peroxide) could be inducers of the heat-shock response. Whether the increase of actin synthesis is a stress-related response, and the mode of action of H 2 0 2 are discussed The heat-shock proteins (hsps), which are synthesised when all living organisms or in vitro cells are exposed to temperatures approximately 5 -20 "C above their optimal growth temperature, can also be induced by a wide range of various agents (for reviews see [l, 21). For example, in Drosophila Kc cells, hsps were shown to be induced without elevation of temperature, by ethanol, arsenite [3], recovery from anoxia [4] and cadmium [5]. The mechanism of induction of hsps is not entirely understood. A heat-shock transcription factor, which binds a consensus sequence in all the heatshock genes has recently been isolated and characterised (for a review see [6]). The heat-shock transcription factor is activated in heat-shocked cells, but what triggers this activation is not known. An interesting question, considering the different agents capable of inducing the synthesis of hsps, is to what extent they might act through a common pathway.We showed previously that in Kc Drosophifa cells the hsps were induced when the cells were reoxygenated after a period of anoxia. At the same time the rate of oxygen consumption was twice the normal rate [4]. This rapid increase of O2 uptake could lead to an overproduction of the products of O2 reduction such as the superoxide ion (0;) and hydrogen peroxide (H20z) [7]. These highly reactive and toxic O2 species were shown to be implicated in many disease states and particularly in tumor promotion [7 -101. We suggested that they might play a role in the chain of events leading to hsp synthesis [4]. In order to test this hypothesis we studied the effect of hydrogen...