Periodic Reporting for period 4 - PIWI-Chrom (Understanding small RNA-mediated transposon control at the level of chromatin in the animal germline)
Okres sprawozdawczy: 2021-01-01 do 2022-06-30
1. How do nuclear Argonaute proteins, once targeted via small RNAs complementarity to a transposon transcript, orchestrate local heterochromatin formation?
2. How do cells re-interpret heterochromatin at selected loci, where transposon sequence information is stored, in order to transcribe the precursor transcripts for piRNA biogenesis.
The co-evolution between eukaryotic genomes and selfish genetic elements such as transposons is one of the oldest genetic conflicts. It is central not only for species survival, but also for evolution: transposons contribute to genetic and genomic innovation at multiple levels thanks to their rapid diversification and mobility. It also becomes increasingly clear that transposons have major impact on human biology and disease. Uncontrolled transposon activity in the germline leads to sterility, and transposition events can lead to several human disease phenotypes. A deep conceptual and mechanistic understanding of transposon control is therefore of central importance. Despite the fact that genome defense systems in eukaryotes vary widely, recent years have uncovered striking similarities in the molecular mechanisms that are being exploited over and over again. This is why studying genome defense pathways in highly established and powerful model systems such as the fruit fly has been and will continue to be key.
Within Aim 2, we discovered (A) the molecular machinery that underlies heterochromatin transcription at piRNA source loci, (B) the machinery that exports piRNA precursors to the cytoplasmic piRNA biogenesis sites, and (C) the principle of piRNA cluster definition on chromatin. In all three projects, we combined fly genetics with in vivo studies, cell-biology, molecular biology, and biochemistry to reveal the conceptual logic and the mechanistic principles underlying heterochromatic piRNA clusters. Our work provides major examples of how gene/protein functions can be altered through duplication and subsequent adaptation processes. Within part C, we discovered the first known example of HP1 protein guidance to chromatin via a protein that binds the chromodomain of an HP1 family protein. Finally, we succeeded in establishing the first stable cell line derived from ovarian germline stem cells. This major achievement (publication in preparation) will enable us and the field to study the complete piRNA pathway with new and powerful experimental approaches.
The results from our work have been disseminated in the form of several major primary publications, a methods publication, as well as conference presentations and invited seminars by me or students/postdocs in my group.