Biology subjects

Schimenti, J.

Publications and source records attributed to Schimenti, J..

4 recordsLinked to original sources

bioRxiv2023

A novel mouse allele of the DNA/RNA helicase senataxin (Setxspcar3) 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, Setxspcar3 mutant mice do not show any apparent neural phenotype, but instead exhibit male infertility and female subfertility. Histology of the Setxspcar3mutant testes revealed absence of spermatids and mature spermatozoa in the seminiferous tubules. Cytological analysis of chromosome spread preparations of the Setxspcar3 mutant spermatocytes revealed normal synapsis, but aberrant DNA damage in the autosomes, and defective formation of the sex body. Furthermore, Setxspcar3 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.

cell biology↗

bioRxiv2019

A predicted deleterious allele of the essential meiosis gene MND1, present in ~3% of East Asians, does not disrupt reproduction in mice.

Infertility is a major health problem affecting ~15% of couples worldwide. Except for cases involving readily-detectable chromosome aberrations, confident identification of a causative genetic defect is problematic. Despite the advent of genome sequencing for diagnostic purposes, the preponderance of segregating genetic variants complicates identification of culprit genetic alleles or mutations. Many algorithms have been developed to predict the effects of \"variants of unknown significance\" (VUS), typically SNPs (single nucleotide polymorphisms), but these predictions are not sufficiently accurate for clinical action. As part of a project to identify population variants that impact fertility, we have been generating CRISPR-Cas9 edited mouse models of suspect SNPs in genes that are known to be required for fertility in mice. Here, we present data on a non-synonymous (amino acid altering) SNP (rs140107488) in the meiosis gene Mnd1, which is predicted bioinformatically to be deleterious to protein function. We report that when modeled in mice, this allele (MND1K85M), which is present allele frequency of ~3% in East Asians, has no discernable effect upon fertility, fecundity, or gametogenesis, although it may cause sex skewing of progeny from homozygous males. In sum, this appears to be a benign allele that can be eliminated or de-prioritized in clinical genomic analyses of infertility patients.

genetics↗

bioRxiv2019

CDK2 kinase activity is a regulator of male germ cell fate

The ability of men to remain fertile throughout their lives depends upon establishment of a spermatogonial stem cell (SSC) pool from gonocyte progenitors, and also maintaining the proper balance between SSC renewal and spermatogenic differentiation throughout life. Depletion of SSCs causes infertility with a Sertoli Cell Only Syndrome (SCOS) phenotype. We previously created a mouse strain in which an inhibitory phosphorylation site (Tyr15) of Cyclin-dependent kinase 2 (Cdk2) was altered. Juvenile males homozygous for this allele (Cdk2Y15S) initiate the first round of spermatogenesis, which originates from prospermatogonia, but meiocytes arrest due to chromosomal defects resembling those in Cdk2-/- mice. Subsequent waves of spermatogonial differentiation and meiosis were largely absent, leading to an SCOS-like phenotype. Here, we demonstrate that Cdk2Y15S/Y15S mice possess mitotically active GFRa1+ SSC-like cells, but they are impaired in their ability to differentiate. Marker analysis and single cell RNA-seq revealed defective differentiation of gonocytes into SSCs. Biochemical and genetic data demonstrated that Cdk2Y15S is a gain-of-function allele causing deregulated kinase activity, and its phenotypic effects could be reversed by mutating the Thr160 positive regulatory site in cis. These results demonstrate that precise temporal regulation of CDK2 activity in male germ cell development and in the cell cycle is critical for long-term spermatogenic homeostasis.

genetics↗

bioRxiv2017

A Single Checkpoint Pathway Eliminates Mouse Oocytes With DNA Damage Or Chromosome Synapsis Failure

Pairing and synapsis of homologous chromosomes during meiosis is crucial for producing genetically normal gametes, and is dependent upon repair of SPO11-induced double stranded breaks (DSBs) by homologous recombination. To prevent transmission of genetic defects, diverse organisms have evolved mechanisms to eliminate meiocytes containing unrepaired DSBs or unsynapsed chromosomes. Here, we show that the CHK2 (CHEK2)-dependent DNA damage checkpoint culls not only recombination-defective mouse oocytes, but also SPO11-deficient oocytes that are severely defective in homolog synapsis. The checkpoint is triggered by spontaneous DSBs that arise in late prophase I, accumulating above the checkpoint activation threshold ([~]10 DSBs) because presence of HORMAD1/2 on unsynapsed chromosome axes prevents their repair. Furthermore, Hormad2 deletion rescued fertility and meiotic DSB repair of oocytes containing a synapsis-proficient, non-crossover recombination defective mutation in a gene (Trip13) required for removal of HORMADs from synapsed chromosomes, indicating that a substantial fraction of meiotic DSBs are normally repaired by intersister recombination in mice.

genetics↗