The peculiarities of piRNA expression upon heat shock exposure in Drosophila melanogaster.

Different types of stress including heat shock may induce genomic instability, due to the derepression and amplification of mobile elements (MEs). It remains unclear, however, whether piRNA-machinery regulating ME expression functions normally under stressful conditions. The aim of this study was to explore the features of piRNA expression after heat shock (HS) exposure in Drosophila melanogaster. We also evaluated functioning of piRNA-machinery in the absence of major stress protein Hsp70 in this species. We analyzed the deep sequence data of piRNA expression after HS treatment and demonstrated that it modulates the expression of certain double-stranded germinal piRNA-clusters. Notable, we demonstrated significant changes in piRNA levels targeting a group of MEs after HS only in the strain containing normal set of hsp70 genes. Surprisingly, we failed to detect any correlation between the levels of piRNAs and the transcription of complementary MEs in the studied strains. We propose that modulation of certain piRNA-clusters expression upon HS exposure in D. melanogaster occurs due to HS-induced altering of chromatin state at certain chromosome regions.