Biology subjects

Schimenti, J. C.

Publications and source records attributed to Schimenti, J. C..

24 records · Page 2Linked to original sources

bioRxiv2019

Signaling to TRP53 and TAp63 from CHK1/CHK2 is responsible for elimination of most oocytes defective for either chromosome synapsis or recombination

Eukaryotic organisms have evolved mechanisms to prevent the accumulation of cells bearing genetic aberrations. This is especially crucial for the germline, because fecundity, and fitness of progeny would be adversely affected by an excessively high mutational incidence. The process of meiosis poses unique problems for mutation avoidance, due to the requirement for SPO11-induced programmed double strand breaks (DSBs) in recombination-driven pairing and segregation of homologous chromosomes. Mouse meiocytes bearing unrepaired meiotic DSBs or unsynapsed chromosomes are eliminated before completing meiotic prophase I. In previous work, we showed that checkpoint kinase 2 (CHK2; CHEK2), a canonical DNA damage response protein, is crucial for eliminating not only oocytes defective in meiotic DSB repair (e.g. Trip13Gt mutants), but also asynaptic Spo11-/- oocytes that accumulate a threshold level of spontaneous DSBs. However, rescue of such oocytes by Chk2 deficiency was incomplete, raising the possibility that a parallel checkpoint pathway(s) exists. Here, we show that mouse oocytes lacking both TAp63 and TRP53 protects nearly all Spo11-/- and Trip13Gt/Gt oocytes from elimination. We present evidence that checkpoint kinase I (CHK1; CHEK1), which is known to signal to TRP53, also becomes activated by persistent DSBs in oocytes, and to an increased degree when CHK2 is absent. The combined data indicate that nearly all oocytes reaching a threshold level of unrepaired DSBs are eliminated by a semi-redundant pathway of CHK1/CHK2 signaling to TRP53/TAp63.

genetics↗

bioRxiv2019

A segregating human allele of SPO11 modeled in mice disrupts timing and amounts of meiotic recombination, causing oligospermia and a decreased ovarian reserve.

A major challenge in medical genetics is to characterize variants of unknown significance (VUS), so as to better understand underlying causes of disease and design customized treatments. Infertility has presented an especially difficult challenge with respect to not only determining if a given patient has a genetic basis, but also to identify the causative genetic factor(s). Though genome sequencing can identify candidate variants, in silico predictions of causation are not always sufficiently reliable so as to be actionable. Thus, experimental validation is crucial. Here, we describe the phenotype of mice containing a nonsynonymous (proline-to-threonine at position 306) change in Spo11, corresponding to human SNP rs185545661. SPO11 is a topoisomerase-like protein that is essential for meiosis because it induces DNA double stranded breaks (DSBs) that stimulate pairing and recombination of homologous chromosomes.\n\nAlthough both male and female Spo11P306T/P306T mice were fertile, they had reduced sperm and oocytes, respectively. Spermatocyte chromosomes exhibited synapsis defects (especially between the X and Y chromosomes), elevated apoptotic cells, persistent markers of DSBs, and most importantly, fewer Type 1 crossovers that causes some chromosomes to have none. Spo11P306T/- mice were sterile and made fewer meiotic DSBs than Spo11+/- animals, suggesting that the Spo11P306T allele is a hypomorph and likely is delayed in making sufficient DSBs in a timely fashion. If the consequences are recapitulated in humans, it would predict phenotypes of premature ovarian failure, reduced sperm counts, and possible increased number of aneuploid gametes. These results emphasize the importance of deep phenotyping in order to accurately assess the impact of VUSs in reproduction genes.

genetics↗

bioRxiv2018

Female-biased embryonic death from genomic instability-induced inflammation

Genomic instability (GIN) can trigger cellular responses including checkpoint activation, senescence, and inflammation. Though extensively studied in cell culture and cancer paradigms, little is known about the impact of GIN during embryonic development, a period of rapid cellular proliferation. We report that GIN-causing mutations in the MCM2-7 DNA replicative helicase render female mouse embryos to be dramatically more susceptible than males to embryonic lethality. This bias was not attributable to X-inactivation defects, differential replication licensing, or X vs Y chromosome size, but rather \"maleness,\" since XX embryos could be rescued by transgene-mediated sex reversal or testosterone (T) administration. The ability of exogenous or endogenous T to protect embryos was related to its anti-inflammatory properties. The NSAID ibuprofen rescued female embryos containing mutations not only in MCM genes but also Fancm, which have elevated GIN from compromised replication fork repair. Additionally, deficiency for the anti-inflammatory IL10 receptor was synthetically lethal with the GIN-causing Mcm4Chaos3 helicase mutant. Our experiments indicate that embryonic and maternal GIN arising from DNA replication-associated DNA damage induces embryonic inflammation likely via the cGAS-STING response, preferentially killing female embryos while male embryos are protected by high levels of intrinsic T.

genetics↗

bioRxiv2018

A putative human infertility allele of the meiotic recombinase DMC1 does not affect fertility in mice

Whole exome or genome sequencing is becoming routine in clinical situations for identifying mutations underlying presumed genetic causes of disease, including infertility. While this is a powerful approach for implicating polymorphisms or de novo mutations in genes plausibly related to the phenotype, a greater challenge is to definitively prove causality. This is a crucial requisite for treatment, especially for infertility, in which validation options are limited. In this study, we created a mouse model of a putative infertility allele, DMC1M200V. DMC1 encodes a RecA homolog essential for meiotic recombination and fertility in mice. This allele was originally implicated as being responsible for sterility of a homozygous African woman, a conclusion supported by subsequent biochemical analyses of the mutant protein and by studies of yeast with the orthologous amino acid change. Here, we found that Dmc1M200V/M200V male and female mice are fully fertile and do not exhibit any gonadal abnormalities. Detailed immunocytological analysis of meiosis revealed no defects suggestive of compromised fertility. This study serves as a cautionary tale for making conclusions about consequences of genetic variants, especially with respect to infertility, and emphasizes the importance of conducting relevant biological assays for making accurate diagnoses in the era of genomic medicine.

genetics↗

bioRxiv2017

Pharmacological inhibition of the DNA damage checkpoint prevents radiation-induced oocyte death

Ovarian function is directly correlated with survival of the primordial follicle reserve. Women diagnosed with cancer have a primary imperative of treating the cancer, but since the resting oocytes are hypersensitive to the DNA-damaging modalities of certain chemo- and radiotherapeutic regimens, such patients face the collateral outcome of premature loss of fertility and ovarian endocrine function. Current options for fertility preservation primarily include collection and cryopreservation of oocytes or in vitro fertilized oocytes, but this necessitates a delay in cancer treatment and additional assisted reproductive technology (ART) procedures. Here, we evaluated the potential of pharmacological preservation of ovarian function by inhibiting a key element of the oocyte DNA damage checkpoint response, checkpoint kinase 2 (CHK2; CHEK2). Whereas non-lethal doses of ionizing radiation (IR) eradicate immature oocytes in wild type mice, irradiated Chk2-/- mice retain their oocytes and thus, fertility. Using an ovarian culture system, we show that transient administration of the CHK2 inhibitor 2-(4-(4-Chlorophenoxy)phenyl)-1H-benzimidazole-5-carboxamide-hydrate (\"CHK2iII\") blocked activation of the CHK2 targets TRP53 and TRP63 in response to sterilizing doses of IR, and preserved oocyte viability. After transfer into sterilized host females, these ovaries proved functional and readily yielded normal offspring. These results provide experimental evidence that chemical inhibition of CHK2 is a potentially valid treatment for preserving fertility and ovarian endocrine function of women exposed to DNA-damaging cancer therapies such as IR.\n\nSummary sentenceOocytes, which are highly sensitive to DNA damage caused by certain cancer treatments, can be protected from radiation-induced death by an inhibitor of the checkpoint protein CHK2.

cancer biology↗

bioRxiv2016

Mcmdc2, a minichromosome maintenance (MCM) paralog, is required for repair of meiotic DNA breaks and homolog pairing in mouse meiosis

The mammalian Mcm-domain containing 2 (Mcmdc2) gene encodes a protein of unknown function that is homologous to the mini-chromosome maintenance family of DNA replication licensing and helicase factors. Drosophila melanogaster contains two separate genes, the \"Mei-MCMs,\" that appear to have arisen from a single ancestral Mcmdc2 gene. The Mei-MCMs are involved in promoting meiotic crossovers by blocking the anti-crossover activity of BLM helicase, a function performed by MSH4 and MSH5 in metazoans. Here, we report that MCMDC2-deficient mice of both sexes are viable but sterile. Males fail to produce spermatozoa, and formation of primordial follicles is disrupted in females. Histology and immunocytological analyses of mutant testes revealed that meiosis is arrested in Prophase I, and is characterized by persistent meiotic double-stranded DNA breaks (DSBs), failure of homologous chromosome synapsis and XY body formation, and an absence of crossing over. These phenotypes essentially phenocopy those of MSH4/5 deficient meiocytes. The data indicate that MCMDC2 is essential for invasion of homologous sequences by RAD51- and DMC1-coated ssDNA filaments, or stabilization of recombination intermediates following strand invasion, both of which are needed to drive stable homolog pairing and DSB repair via recombination in mice.

genetics↗