Abstract
Epigenetic gene regulation is essential for developmental processes. Eggless (Egg), the Drosophila orthologue of the mammalian histone methyltransferase, SETDB1, is known to be involved in the survival and differentiation of germline stem cells and piRNA cluster transcription during Drosophila oogenesis; however the detailed mechanisms remain to be determined. Here, using high-throughput RNA sequencing, we investigated target genes regulated by Egg in an unbiased manner. We show that Egg plays diverse roles in particular piRNA pathway gene expression, some long non-coding RNA expression, apoptosis-related gene regulation, and Decapentaplegic (Dpp) signaling during Drosophila oogenesis. Furthermore, using genetic and cell biological approaches, we demonstrate that ectopic upregulation of dpp caused by loss of Egg in the germarium can trigger apoptotic cell death through activation of two pro-apoptotic genes, reaper and head involution defective. We propose a model in which Egg regulates germ cell differentiation and apoptosis through canonical and noncanonical Dpp pathways in Drosophila oogenesis.
Highlights
Epigenetic regulation is a fundamental mechanism required for proper gene expression, cell proliferation, and survival during development[1]
The expression of egg gene was strongly reduced in egg mutant ovaries compared with wild-type ovaries, which was further confirmed by quantitative Real Time-PCRs (Fig. 1a) as well as Western blots (Supplementary Fig. S2)
To confirm the RNA sequencing (RNA-seq) data, we performed validation tests by quantitative Real Time-PCRs (qRT-PCR) using separate RNA obtained from wild-type and egg mutant ovaries
Summary
Epigenetic regulation is a fundamental mechanism required for proper gene expression, cell proliferation, and survival during development[1]. Histone modifications, such as methylation and acetylation, play important roles in epigenetic regulation through global transcriptional changes[2]. Egg mutant ovaries show defects in the survival of germline cells and surrounding somatic cells at very early stages of Drosophila oogenesis, resulting in rudimentary ovaries associated with apoptosis[7,10]. Given the increased occurrence of apoptosis at early stages of oogenesis in egg mutant germline and somatic cells[7,10,11], activation of TEs by a reduction of piRNAs in egg mutants may result in an increase in DNA damage, which in turn may trigger cell death. We used RNA-seq to investigate egg mutation-induced transcriptional changes that may well be missed by conventional methods, thereby uncovering unprecedented insights into the role of Egg in oogenesis
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