Unravelling the function of TEX15 during piRNA-mediated transposable element silencing
Final Report Abstract
Infertility is a common disease affecting around 10-15% of all couples. In around one third of cases a male factor is the reason for the couple’s infertility. Azoospermia is the most severe phenotype of male infertility and affected individuals have no chance to reproduce in a natural way. However, they can decide to undergo a testicular biopsy with the aim of testicular sperm extraction. If sperm are gained through the biopsy, these can be used for a medically assisted reproduction. In recent years it was shown that a genetic analysis prior to the biopsy can help to predict the chances of successful sperm retrieval. A crucial gene for male fertility is TEX15. It is involved in the piRNA pathway, which consists of PIWI proteins and small non-coding PIWI-interaction RNAs (piRNAs). This pathway ensures that transposable elements (TEs), which are part of the genome of mammals, are suppressed. This is especially important in foetal germ cells, as these undergo a genetic reprogramming and de novo methylation. This procedure re-activates TEs. The piRNA pathway ensure targeted re-methylation of TE sites. TEX15 is likely involved in transcriptional gene silencing (TGS), which ensures long term silencing of TEs. Genetic analyses in infertile men frequently reveal variants in TEX15, which are difficult to interpret. In many cases it remains unknown whether the detected variant is the cause of the man’s infertility. Using a reporter assay in mouse embryonic stem cells, we tested variants in TEX15 and analysed if the variants impair the function of TEX15 in silencing transposable elements. We found that the variants c.2709_2711del p.(Glu903del) and c.3319G>C p.(Ala1107Pro) did not influence TGS in vitro. In an independent approach, we looked for further genes, which might be involved in the piRNA pathway and associated with azoospermia. Previous experiments have shown that the piRNA factor MIWI2 associates with the protein HSP90AA1. Fittingly, we found the homozygous missense variant c.971G>A p.(Arg324Lys) in HSP90AA1 in an azoospermic man. We created a knock-out mouse line for Hsp90aa1 as well as a knock-in mouse line harbouring the variant found in the infertile man. Our analyses show that mice lacking HSP90AA1 show male specific infertility due to meiotic arrest predominantly at leptotene cell stage. However, HSP90AA1 is not crucial for methylation of TEs in mice as revealed by total RNA-sequencing and enzymatic methylationsequencing of mouse germ cells. Its function in the piRNA pathway is probably redundant with the highly similar HSP90AB1. Our experiments highlight HSP90AA1 as a novel gene associated with azoospermia in humans. If validated, this gene can be included into clinical diagnostic testing of infertile men. We are currently phenotyping the mouse line harbouring the variant found in the azoospermic man, which will likely enable us to describe the first (likely) pathogenic variant in HSP90AA1 in humans.
Publications
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The Human Phenotype Ontology in 2024: phenotypes around the world. Nucleic Acids Research, 52(D1), D1333-D1346.
Gargano, Michael A.; Matentzoglu, Nicolas; Coleman, Ben; Addo-Lartey, Eunice B.; Anagnostopoulos, Anna V.; Anderton, Joel; Avillach, Paul; Bagley, Anita M.; Bakštein, Eduard; Balhoff, James P.; Baynam, Gareth; Bello, Susan M.; Berk, Michael; Bertram, Holli; Bishop, Somer; Blau, Hannah; Bodenstein, David F.; Botas, Pablo; Boztug, Kaan ... & Robinson, Peter N.
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Reproductive genetics and health. Medizinische Genetik, 36(3), 179-188.
Wyrwoll, Margot J. & Steingröver, Johanna
