Unravelling the function of TEX15 during piRNA-mediated transposable element silencing

• Applicant: Dr. Margot Julia Wyrwoll
• Subject Area: Human Genetics
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 508316270

Infertility affects around 7% of all men. The most severe male infertility phenotype is azoospermia, which can be due to meiotic arrest. Bi-allelic loss-of-function (LoF) variants in TEX15 have been described as causal for male infertility due to meiotic arrest. However, the interpretation of missense variants in TEX15 is challenging as nothing is known about the critical regions of the TEX15 protein. Based on data obtained from mice, it is assumed that TEX15 is involved in transposable element (TE) silencing. During foetal development of mammals, germ cells undergo de novo methylation of the genome. This leads to demethylation of TEs, which are commonly repressed to ensure genomic integrity. Next, the TEs are re-methylated, to prevent these loci from transcription. However, many TE copies of the long interspersed nuclear element-1 (LINE1) type manage to escape the first round of DNA methylation. The interaction of PIWI proteins and small non-coding PIWI-interacting RNAs (piRNAs) counters TE expression. The recruitment of the protein MIWI2 to the nascent transcript likely initiates co-transcriptional gene silencing (CTGS), causing inhibition of further transcription of these sites, followed by transcriptional gene silencing (TGS) and ultimately DNA methylation. The protein TEX15 is a highly likely candidate protein for TGS. Within this project, we aim to elucidate the underlying mechanisms by which TEX15 is involved in the piRNA pathway and how it directs de novo DNA methylation of TEs. We will investigate the mechanism of piRNA guided DNA methylation in the mouse foetal testis using immunoprecipitation coupled mass-spectrometry analysis and a newly established reporter assay for CTGS/TGS. The impact of TEX15 recruitment on chromatin structure and histone modification will be investigated, revealing its impact on chromatin accessibility at transposon loci. Next, we will investigate the effect of human TEX15 missense variants detected in infertile men. The proposed project will, thus, advance our understanding of TE silencing in mammals. It will further help to understand genetic causes of human male infertility. Our findings may therefore directly translate into clinics, improving assessment of TEX15 missense variants, which will result in improved genetic counselling and patient care. Hence my period at the O’Carroll lab will teach me state-of-the-art methods. When combined with my previous clinical work, I will be able to establish a translational approach, which will present a unique position in the field of reproductive genetics.

• DFG Programme: WBP Fellowship
• International Connection: United Kingdom
• Host: Professor Dónal O' Carroll, Ph.D.