Intracellular signalling, gene induction and histone modifications in Drosophila melanogaster

In eukaryotes, histone H3 residues at the promoter and transcriptional start site of immediate early genes are phosphorylated at serine 10, a process mediated by histone kinases downstream of the p38 and ERK cascades. However, this phosphorylation event has not yet been investigated in Drosophila melanogaster, and the existence of an inducible histone kinase is uncertain. To identify the kinases involved in the nucleosomal response in Drosophila, I first investigated the stimuli inducing MAPK signal transduction pathways. In mouse cells, anisomycin at sub-inhibitory concentration is a strong activator of JNK and p38, but no activation of MAPKs was observed in Drosophila. Peptidoglycan treatment induced JNK activation without altering histone H3 phosphorylation, demonstrating that this part of signal transduction is conserved between vertebrate and insect cells. However, in contrast to mammalian cells, inducing ERK activity by stimulation with hydrogen peroxide, insulin, serum or heat shock does not lead to histone H3 phosphorylation. Osmotic stress resulted in a strong increase in phosphoacetylated histone H3, suggesting that p38 is upstream of the histone H3 kinase in Drosophila, but the presence of p38 inhibitor SB203580 did not decrease histone H3 phosphoacetylation. Further evidence suggesting that the nucleosomal response in Drosophila is not conserved includes the absence of induction of classical immediate early gene jra after stimulation with either sorbitol or sodium arsenite. In summary, these results indicate that histone phosphorylation and IE gene induction differ in mammals and Drosophila and provide the basis for further experiments aiming to identify the relationship between histone phosphorylation and transcription.