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Piwi regulates the usage of alternative transcription start sites in the Drosophila ovary via interaction with the FACT complex component Ssrp

ABSTRACT: Transcription from alternative transcription start sites (TSSs) is prevalent among mammalian genes and has important biological functions. However, how TSSs are selected remains elusive. We identified 87 genes with altered TSS usage (ATU) in Piwi-deficient Drosophila ovaries using the cap-analysis gene expression sequencing (CAGE-seq) method. Piwi regulates TSS usage of ATU genes in germ cells and somatic cells in ovaries as well as in cultured ovarian somatic cells (OSCs). Correspondingly, RNA Pol II initiation and elongation at TSSs of ATU genes were affected in germline-piwi-knockdown ovaries and piwi-knockdown OSCs. We identified a FACT complex component, Ssrp, as a novel interactor of Piwi in the nucleus. Temporally controlled knockdown of ssrp affected TSS usage of ATU genes whereas overexpression of ssrp partially rescued the TSS usage of ATU genes in piwi mutant ovaries. Thus, Piwi may interact with Ssrp to regulate TSS usage in Drosophila ovaries by affecting Pol II initiation and elongation.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE277263 | GEO | 2024/11/29

REPOSITORIES: GEO

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Project description:PIWI-clade Argonaute proteins silence transposon expression in animal gonads. Their target specificity is defined by bound ~23-30nt piRNAs that are processed from single-stranded precursor transcripts via two distinct pathways. Primary piRNAs are defined by the endo-nuclease Zucchini, while biogenesis of secondary piRNAs depends on piRNA-guided transcript cleavage and results in piRNA amplification. Here, we analyze the inter-dependencies between these piRNA biogenesis pathways in the developing Drosophila ovary. We show that secondary piRNA-guided target slicing is the predominant mechanism that specifies transcripts—including those from piRNA clusters—as primary piRNA precursors and that defines the spectrum of Piwi-bound piRNAs in germline cells. Post-transcriptional silencing in the cytoplasm therefore enforces nuclear, transcriptional target silencing, which ensures the tight suppression of transposons during oogenesis. As target slicing also defines the nuclear piRNA pool during mouse spermatogenesis, our findings uncover an unexpected conceptual similarity between the mouse and fly piRNA pathways. To understand the hierarchical order of primary versus secondary piRNA biogenesis in Drosophila ovaries, we sequenced piRNAs bound to total-Piwi, germline-Piwi, Aubergine and Argonaute3 from ovaries of germline specific knockdowns of control, piwi, aub, ago3 single knockdowns and aub/ago3 double knockdowns. To determine changes in Transposable Element (TE) transcription or TE RNA steady state in perturbed piRNA pathway conditions, we performed Pol2-ChIP-sequencing and polyA bound RNA-sequencing from ovaries of multiple germline knockdown genotypes. We also sequenced genomic DNA from ovaries of control knockdowns to experimentally estimate the TE copy number in our genetic background. Finally, we used CAP-seq from germline specific Piwi depletions to identify the Transcriptional Start Sites (TSS) in TEs in a deregulated background. Replicates are labeled with R1, R2, R3, R4 where indicated.

Project description:More than half of human protein-coding genes have an alternative transcription start site (TSS). We aimed to investigate the contribution of alternative TSSs to the acute-stress–induced transcriptome response in human tissue (skeletal muscle) using the cap analysis of gene expression approach. TSSs were examined at baseline and during recovery after acute stress (a cycling exercise). We identified 44,680 CAGE TSS clusters (including 3,764 first defined) belonging to 12,268 genes and annotated for the first time 290 TSSs belonging to 163 genes. The transcriptome dynamically changes during the first hours after acute stress; the change in the expression of 10% of genes was associated with the activation of alternative TSSs, indicating differential TSSs usage. The majority of the alternative TSSs do not increase proteome complexity suggesting that the function of thousands of alternative TSSs is associated with the fine regulation of mRNA isoform expression from a gene due to the transcription factor-specific activation of various alternative TSSs. We identified individual muscle promoter regions for each TSS using muscle open chromatin data (ATAC-seq and DNase-seq). Then, using the positional weight matrix approach we predicted time course activation of “classic” transcription factors involved in response of skeletal muscle to contractile activity, as well as diversity of less/un-investigated factors. Transcriptome response induced by acute stress related to activation of the alternative TSSs indicates that differential TSSs usage is an essential mechanism of fine regulation of gene response to stress stimulus. A comprehensive resource of accurate TSSs and individual promoter regions for each TSS in muscle was created. This resource together with the positional weight matrix approach can be used to accurate prediction of TFs in any gene(s) of interest involved in the response to various stimuli, interventions or pathological conditions in human skeletal muscle.

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Piwi regulates the usage of alternative transcription start sites in the Drosophila ovary via interaction with the FACT complex component Ssrp

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