A novel mouse allele of the DNA/RNA helicase senataxin ( Setx ^spcar3 ) causing meiotic arrest of spermatocytes and male infertility

An unbiased screen for discovering novel genes for fertility identified the spcar3, spermatocyte arrest 3, mutant phenotype. The spcar3 mutation identified a new allele of the Setx gene, encoding senataxin, a DNA/RNA helicase that regulates transcription termination by resolving DNA/RNA hybrid R-loop structures. Although mutations in the human SETX gene cause neural disorders, Setx ^spcar3 mutant mice do not show any apparent neural phenotype, but instead exhibit male infertility and female subfertility. Histology of the Setx ^spcar3 mutant testes revealed absence of spermatids and mature spermatozoa in the seminiferous tubules. Cytological analysis of chromosome spread preparations of the Setx ^spcar3 mutant spermatocytes revealed normal synapsis, but aberrant DNA damage in the autosomes, and defective formation of the sex body. Furthermore, Setx ^spcar3 testicular cells exhibited abnormal accumulation of R-loops compared to wild type testicular cells. Transient expression assays identified regions of the senataxin protein required for sub-nuclear localization. Together, these results not only confirm that senataxin is required for normal meiosis and spermatogenesis but also provide a new resource for determination of its role in maintaining R-loop formation and genome integrity.