Structural and Functional Characterisation of the MIWI2 Silencing Complex

The piRNA pathway is composed of PIWI proteins and small RNA guides termed piRNAs. The murine nuclear piRNA pathway, orchestrated by the PIWI protein MIWI2, safeguards the developing germline against the deleterious activity of transposons. MIWI2, guided by piRNA, target-engages nascent transposon transcripts and initiates transcriptional inhibition via the recruitment of transcriptional repressor proteins to form the MIWI2-piRNA-induced silencing complex (MIWI2-piRISC). Our lab has recently identified a host of MIWI2 interactors; however, we have not established how these proteins contribute to the MIWI2-piRISC, nor how these proteins achieve transcriptional inhibition at a mechanistic level. To address this knowledge gap, I will first determine the structure of target engaged MIWI2 and assess how this structure supports its role as a structural scaffold. I will then characterise the MIWI2-piRISC in vivo and examine its structure using a biochemical approach. Concurrently, I will explore the how TEX15, one of the putative MIWI2-piRISC components, induces transcriptional inhibition and whether this possible function of TEX15 is essential for piRNA pathway function in vivo. By taking both a structural and functional approach, this work will provide novel insights into how the piRNA pathway defends the mammalian germline from the threat of transposons during germline development.