Effect of Aphidicolin, a Reversible Inhibitor of Eukaryotic Nuclear DNA Replication, on the Production of Genetically Modified Porcine Embryos by CRISPR/Cas9.

Mosaicism is the most important limitation for one-step gene editing in embryos by CRISPR/Cas9 because cuts and repairs sometimes take place after the first DNA replication of the zygote. To try to minimize the risk of mosaicism, in this study a reversible DNA replication inhibitor was used after the release of CRISPR/Cas9 in the cell. There is no previous information on the use of aphidicolin in porcine embryos, so the reversible inhibition of DNA replication and the effect on embryo development of different concentrations of this drug was first evaluated. The effect of incubation with aphidicolin was tested with CRISPR/Cas9 at different concentrations and different delivery methodologies. As a result, the reversible inhibition of DNA replication was observed, and it was concentration dependent. An optimal concentration of 0.5 µM was established and used for subsequent experiments. Following the use of this drug with CRISPR/Cas9, a halving of mosaicism was observed together with a detrimental effect on embryo development. In conclusion, the use of reversible inhibition of DNA replication offers a way to reduce mosaicism. Nevertheless, due to the reduction in embryo development, it would be necessary to reach a balance for its use to be feasible.

Ceftriaxone Reduced Susceptible Neisseria gonorrhoeae in the Netherlands, 2009 to 2017: From PenA Mosaicism to A501T/V Nonmosaicism.

OBJECTIVES: To compare molecular and epidemiological differences between ceftriaxone-reduced susceptible (CRO-RS) and ceftriaxone-susceptible (CRO-S) N. gonorrhoeae (Ng) and to study the genetic relatedness of CRO-RS isolates. METHODS: Demographic and clinical data and samples for cultures were routinely collected from gonorrhoea patients visiting the Amsterdam STI clinic in 2009 to 2017. Ng multiantigen sequence typing (NG-MAST) and penA types were compared between CRO-RS and CRO-S Ng (frequency matched on year of isolation and sexual risk group). Minimum spanning trees were produced based on multilocus variable number of tandem repeats analysis for Ng (NG-MLVA) genotypes. RESULTS: We selected 174 CRO-RS isolates (minimum inhibitory concentration, ≥0.064 mg/L) and 174 CRO-S isolates (minimum inhibitory concentration, ≤0.016 mg/L). Demographic and clinical characteristics of patients were overall comparable between those infected with CRO-RS Ng and CRO-S Ng. However, CRO-RS isolates were more often collected from the pharyngeal site (odds ratios [OR], 3.64; P < 0.001), and patients with CRO-RS Ng were less often human immunodeficiency virus (HIV) and syphilis positive (OR, 0.63; P = 0.041 and OR, 0.58; P = 0.028, respectively). We identified 12 clusters based on NG-MLVA genotypes, including 3 large (>25 isolates) clusters predominantly containing CRO-RS isolates. Those from cluster 1 (n = 32) were mostly from 2009 to 2012 (n = 24; 75.0%), with a mosaic penA XXXIV pattern (n = 27; 84.4%) and belonging to NG-MAST genogroup G1407 (n = 24; 75.0%). Isolates from cluster 2 (n = 29) were mostly from 2013 to 2015 (n = 24; 82.7%), had a nonmosaic penA IX + A501T mutation (n = 22; 75.9%) and NG-MAST G2400 (n = 14; 48.3%). Most isolates from cluster 3 (n = 37) were from 2015 to 2017 (n = 26; 70.2%), had a nonmosaic penA IV + A501V mutation (n = 24; 64.9%) and NG-MAST G2318 (n = 22; 59.5%). CONCLUSIONS: We observed a shift in the predominant penA (from mosaic toward nonmosaic plus A501T/V mutation), NG-MAST and NG-MLVA types among CRO-RS Ng over time. This indicates a successive spread of different CRO-RS Ng clones.

The effect of GM-CSF on development and aneuploidy in murine blastocysts.

BACKGROUND: Growth factors and cytokines are present in small quantities in the oviduct and uterus and some are synthesized by the growing embryo. Granulocytes-macrophage colony-stimulating factor (GM-CSF) is known as an important regulator, which enhances cell proliferation and reduces apoptosis in developing blastocysts, during normal fetal and placental development. The purpose of this study is to investigate whether adding GM-CSF to the culture media affects blastulation or the chromosomal status of mouse embryos. METHODS: Murine embryos were cultured in vitro from the 2-cell stage until the blastocyst stage in the presence of different concentrations of GM-CSF of 0 ng/ml (control), 1, 2, 5 and 10 ng/ml. The development of each embryo was noted and the embryos were then spread for fluorescence in situ hybridization (FISH) using locus-specific probes (LSI) for chromosomes 2, 11 and 16 in all embryos. RESULTS: No difference in the blastulation potential was noted with the addition of 1 and 2 ng/ml of GM-CSF compared with the controls, but there was a significant decrease (P < 0.001) in the blastulation rate in the 5 and 10 ng/ml concentrations. The rate of mosaicism/aneuploidy noted in all GM-CSF groups (1, 2, 5 and 10 ng/ml) was slightly higher than in the control group (0 ng/ml GM-CSF) but the differences were not significant. In the mosaic embryos from the GM-CSF cultured groups, the percentage of aneuploid cells was statistically higher than in the control group. CONCLUSIONS: GM-CSF exerted a negative impact on blastocyst development at higher concentrations. GM-CSF did not affect the rates of mosaicism/aneuploidy, but did increase the percentage of aneuploid cells within the mosaic embryos. Adding GM-CSF to the culture media for clinical use requires further studies either on human or animal models to evaluate its long-term effects.

Somatic mosaicism caused by monoallelic reversion of a mutation in T cells of a patient with ADA-SCID and the effects of enzyme replacement therapy on the revertant phenotype.

Patients with adenosine deaminase (ADA) deficiency exhibit spontaneous and partial clinical remission associated with somatic reversion of inherited mutations. We report a child with severe combined immunodeficiency (T-B- SCID) due to ADA deficiency diagnosed at the age of 1 month, whose lymphocyte counts including CD4+ and CD8+ T and NK cells began to improve after several months with normalization of ADA activity in Peripheral blood lymphocytes (PBL), as a result of somatic mosaicism caused by monoallelic reversion of the causative mutation in the ADA gene. He was not eligible for haematopoietic stem cell transplantation (HSCT) or gene therapy (GT); therefore he was placed on enzyme replacement therapy (ERT) with bovine PEG-ADA. The follow-up of metabolic and immunologic responses to ERT included gradual improvement in ADA activity in erythrocytes and transient expansion of most lymphocyte subsets, followed by gradual stabilization of CD4+ and CD8+ T (with naïve phenotype) and NK cells, and sustained expansion of TCRγδ+ T cells. This was accompanied by the disappearance of the revertant T cells as shown by DNA sequencing from PBL. Although the patient's clinical condition improved marginally, he later developed a germinal cell tumour and eventually died at the age of 67 months from sepsis. This case adds to our current knowledge of spontaneous reversion of mutations in ADA deficiency and shows that the effects of the ERT may vary among these patients, suggesting that it could depend on the cell and type in which the somatic mosaicism is established upon reversion.

In utero Exposure to Genotoxicants Leading to Genetic Mosaicism: An Overlooked Window of Susceptibility in Genetic Toxicology Testing?

In utero development represents a sensitive window for the induction of mutations. These mutations may subsequently expand clonally to populate entire organs or anatomical structures. Although not all adverse mutations will affect tissue structure or function, there is growing evidence that clonally expanded genetic mosaics contribute to various monogenic and complex diseases, including cancer. We posit that genetic mosaicism is an underestimated potential health problem that is not fully addressed in the current regulatory genotoxicity testing paradigm. Genotoxicity testing focuses exclusively on adult exposures and thus may not capture the complexity of genetic mosaicisms that contribute to human disease. Numerous studies have shown that conversion of genetic damage into mutations during early developmental exposures can result in much higher mutation burdens than equivalent exposures in adults in certain tissues. Therefore, we assert that analysis of genetic effects caused by in utero exposures should be considered in the current regulatory testing paradigm, which is possible by harmonization with current reproductive/developmental toxicology testing strategies. This is particularly important given the recent proposed paradigm change from simple hazard identification to quantitative mutagenicity assessment. Recent developments in sequencing technologies offer practical tools to detect mutations in any tissue or species. In addition to mutation frequency and spectrum, these technologies offer the opportunity to characterize the extent of genetic mosaicism following exposure to mutagens. Such integration of new methods with existing toxicology guideline studies offers the genetic toxicology community a way to modernize their testing paradigm and to improve risk assessment for vulnerable populations. Environ. Mol. Mutagen. 61:55-65, 2020. © 2019 The Authors. Environmental and Molecular Mutagenesis published by Wiley Periodicals, Inc. on behalf of Environmental Mutagen Society.

Mifepristone-inducible LexPR system to drive and control gene expression in transgenic zebrafish.

Effective transgenesis methods have been successfully employed in many organisms including zebrafish. However, accurate spatiotemporal control of transgene expression is still difficult to achieve. Here we describe a system for chemical-inducible gene expression and demonstrate its feasibility for generating transgenic driver lines in zebrafish. The key element of this system is a hybrid transcription factor engineered by fusion of the DNA-binding domain of the bacterial LexA repressor, a truncated ligand-binding domain of the human progesterone receptor, and the activation domain of the human NF-kappaB/p65 protein. This hybrid transcription factor (LexPR transactivator) binds to the synthetic steroid, mifepristone (RU-486), and functions in a ligand-dependent manner to induce expression of the gene(s) placed under the control of a synthetic operator-promoter sequence that harbors LexA binding sites. Transgene expression is strictly controlled and can be induced at any stage of the life cycle through administration of mifepristone in the water. To demonstrate the utility of this system, we generated stable transgenic lines which allow inducible tissue-specific expression of activated K-ras(V12). Combined with the Ac/Ds-mediated transgenesis, the LexPR expression system has many potential applications in the fields of genetics and biotechnology.

Effect of gonadotropins on chromosome aneuploidy, chromosome mosaicism & sex ratio in mouse preimplantation embryos.

BACKGROUND & OBJECTIVE: There are potential risks of major birth defect in IVF (in vitro fertilization) pregnancy as well as IVF-ICSI (intra cytoplasmic sperm injection) pregnancies in comparison with naturally conceived human pregnancies. This increase risk could be due to either gonadotropins used for ovarian stimulation or in vitro culture conditions or multiple pregnancy or combinations of all the factors. The effects of gonadotropins on chromosome aneuploidy, chromosome mosaicism and sex ratio on mouse preimplantation embryos were evaluated through the use of fluorescence in situ hybridization (FISH). METHODS: The study material consisted of 111 preimplantation mouse embryos (2-16 cell stage) in control group and 405 preimplantation mouse embryos in gonadotropin stimulated group from genetically identical Swiss Albino young (6-8 wk) mouse kept in a similar environmental conditions. The study was designed to investigate effect of gonadotropins on chromosome aneuploidy, chromosome mosaicism and sex ratio through the use of FISH technique using chromosome X, Y and 19 probes. All blastomeres of embryos in both groups were assessed. RESULTS: Interpretable FISH results were obtained in 66 embryos in control group and 128 embryos in gonadotropin stimulated group. There was no excess of chromosome aneuploidy (only one case of sex chromosome trisomy in study group; 19, 19, X, Y, Y) or chromosome mosaicism or deviations in sex ratio between the two groups. However, deviation (1.36 M: 1 F in control group & 1.25 M : 1 F in study group) was seen from expected sex ratio (1 M : 1 F) i.e., skewed sex ratio in both the groups. INTERPRETATION & CONCLUSION: Our results showed that gonadotropins used for ovarian stimulation had no effects in causing increase in chromosome X, Y, 19 aneuploidy and mosaicism and skewing of sex ratio in mouse model. A large scale study with more FISH probes on a larger sample size need to be done to confirm the findings.

Philadelphia chromosome mosaicism at diagnosis in chronic myeloid leukemia: clinical correlates and effect on imatinib mesylate treatment outcome.

In chemotherapy-treated patients with chronic myeloid leukemia (CML), the karyotypic detection of Philadelphia chromosome (Ph)-negative metaphases at diagnosis (i.e. Ph mosaicism) is not considered significant as a prognostic factor for survival. In the current retrospective study, clinical correlates and prognostic relevance of Ph mosaicism were evaluated in 63 Ph-positive patients with CML, including 59 in chronic phase and 4 in accelerated phase, receiving imatinib mesylate as either first (n = 46) or second (n = 17) line therapy. Thirteen patients (21%) displayed Ph-negative metaphases at diagnosis and, compared to the other 50 patients with 100% Ph-positive metaphases, presented with significantly lower leukocyte count (p = 0.0004), circulating blast percentage (p = 0.02), and incidence of palpable splenomegaly (p = 0.02). Ph mosaicism did not correlate with other CML-pertinent prognostic factors including Sokal score (p = 0.4) or the presence of additional chromosome changes (p = 0.96) found in 10 patients (16%). Neither Ph mosaicism nor the presence of additional chromosome changes affected complete or partial cytogenetic remission rates to IM. Multivariable analysis identified Ph mosaicism as a risk factor for shortened survival. Due to the small sample size, the current preliminary observations require validation in a larger group of patients.

Gonadal Mosaicism Induced by Chemical Treatment of Sperm in Drosophila melanogaster.

Accurate interpretation of forward genetic screens of chromosomes exposed in mature spermatozoa to a mutagenic chemical requires understanding-incomplete to date-of how exposed chromosomes and their replicas proceed through early development stages from the fertilized ovum to establishment of the germline of the treated male's offspring. We describe a model for early embryonic development and establishment of the germline of Drosophila melanogaster and a model-validating experiment. Our model proposes that, barring repair, DNA strands modified by treatment with alkylating agents are stable and mutagenic. Each replication of an alkylated strand can result in misreplication and a mutant-bearing daughter nucleus. Daughter nuclei thenceforth replicate faithfully and their descendants comprise the embryonic syncytium. Of the 256 nuclei present after the eighth division, several migrate into the polar plasm at the posterior end of the embryo to found the germline. Based upon distribution of descendants of the alkylated strands, the misreplication rate, and the number of nuclei selected as germline progenitors, the frequency of gonadal mosaicism is predictable. Experimentally, we tracked chromosomes 2 and 3 from EMS-treated sperm through a number of generations, to characterize autosomal recessive lethal mutations and infer gonadal genetic content of the sons of treated males. Over 50% of 106 sons bore germlines that were singly, doubly, or triply mosaic for chromosome 2 or chromosome 3. These findings were consistent with our model, assuming a rate of misreplication between 0.65 and 0.80 at each replication of an alkylated strand. Crossing treated males to mismatch-repair-deficient females had no apparent effect on mutation rate.

Somatic activating mutations in Pik3ca cause sporadic venous malformations in mice and humans.

Venous malformations (VMs) are painful and deforming vascular lesions composed of dilated vascular channels, which are present from birth. Mutations in the TEK gene, encoding the tyrosine kinase receptor TIE2, are found in about half of sporadic (nonfamilial) VMs, and the causes of the remaining cases are unknown. Sclerotherapy, widely accepted as first-line treatment, is not fully efficient, and targeted therapy for this disease remains underexplored. We have generated a mouse model that faithfully mirrors human VM through mosaic expression of Pik3ca(H1047R), a constitutively active mutant of the p110α isoform of phosphatidylinositol 3-kinase (PI3K), in the embryonic mesoderm. Endothelial expression of Pik3ca(H1047R)resulted in endothelial cell (EC) hyperproliferation, reduction in pericyte coverage of blood vessels, and decreased expression of arteriovenous specification markers. PI3K pathway inhibition with rapamycin normalized EC hyperproliferation and pericyte coverage in postnatal retinas and stimulated VM regression in vivo. In line with the mouse data, we also report the presence of activating PIK3CA mutations in human VMs, mutually exclusive with TEK mutations. Our data demonstrate a causal relationship between activating Pik3ca mutations and the genesis of VMs, provide a genetic model that faithfully mirrors the normal etiology and development of this human disease, and establish the basis for the use of PI3K-targeted therapies in VMs.

The health effects of diethylstilbestrol revisited.

Although diethylstilbestrol has not been prescribed commonly for more than 25 years, its effects on the health of exposed persons are still important. In this article, we summarize current information about the major health effects of diethylstilbestrol exposure and delineate implications for nurses. Nurses can help to identify persons at risk from prior diethylstilbestrol exposure, facilitate comprehensive assessments of persons exposed to diethylstilbestrol, and share current information about diethylstilbestrol.

Change of mosaic pattern by androgens during prostatic bud formation in XTfm/X+ heterozygous female mice.

The testicular feminization (Tfm) gene, which is characterized by a deficiency in androgen receptors, is located on the X-chromosome. Using steroid autoradiography, the mosaicism of the Tfm gene has been demonstrated in the androgen target tissues of XTfm/X+ heterozygous female mouse fetuses and the effects of androgens on the mosaic pattern analysed. In the mesenchyme of urogenital sinuses of wild-type female fetuses (X+/X+), more than 95% of the cells were androgen-receptor positive (labelled with [3H]testosterone) while in that of heterozygous fetuses (XTfm/X+), only half of the cells were receptor positive (Tfm gene inactive), and receptor-positive cells and -negative cells formed small irregular patches. When the heterozygous sinuses were cultured in vitro in the presence of androgens, the sinuses underwent male sexual development and formed epithelial buds (prostate gland rudiments) projecting into the surrounding mesenchyme. Autoradiographic analysis revealed that the mosaicism of the mesenchyme disappeared around the developing epithelial buds: almost all the mesenchymal cells in close vicinity to the buds were receptor positive while in the outer layers receptor-positive and -negative cells coexisted. The proportion of receptor-positive cells was greatly increased in the mesenchyme beneath the non-budding area of the sinus epithelium. This androgen-induced increase was observed before the onset of bud formation. The results obtained in the thymidine incorporation experiments suggest that the increase of receptor-positive cells beneath the sinus epithelium might be explained by the migratory behaviour of the androgen-incorporating cells rather than by their selective proliferation.

Somatic mosaicism in plants with special reference to somatic crossing over.

Plant systems in use for the detection of environmental mutagens appear capable of detecting all types of genetic effects which can be studied in animals. The study of somatic mosaicism, however, is better developed in plants than in higher animals. A case is presented here which shows the ability of plant systems in analyzing a host of genetic end points, including chromosome aberrations like deletions, somatic crossing over, numerical inequality, gene conversion, paramutations and point mutations. The systems in general use utilize certain varieties of Tradescantia, Glycine max, Nicotiana tabacum, Antirrhinum majus, Petunia hybrida, and Arabidopsis thaliana. Heterozygous plants or their homozygous counterparts with gene markers affecting chlorophyll development or anthocyanin in floral parts are exploited in these studies. Mutagens produce different frequencies of different types of spots typical of the mode of action of the agent. Analysis of these parameters may be used to predict, at least qualitatively, the kind of genetic damage that might be produced in man. Besides, one can test the validity of interpretation by traditional progeny tests of plants raised from tissue culture from sectors as in Nicotiana and/or by precursor analysis as done in Antirrhinum. The study of mosaicism in plants offers quite inexpensive, rapid, and reliable tests of mutagenicity at least as a preliminary eukaryotic test system.

Analysis of the genotoxic activity of four N-nitroso compounds by the Drosophila mosaic test.

Mutagenic activity of 4 nitroso compounds of environmental importance - N-nitroso-morpholine, dinitrosopiperazine, N,N'-dinitroso-pyridinol-carbamate and N-methyl-N-nitroso-p-toluenesulfonamide - was tested by the Drosophila mosaic test. Larvae were fed with the nitroso-compound-containing food for 2-4 days, and when they had developed into adults, their wings were screened for mosaic spots. All 4 compounds were positive. This finding supports the conclusion that the mosaic test - besides other test procedures - may become a tool for identifying mutagens.

Testing the mutagenicity of malondialdehyde and formaldehyde by the Drosophila mosaic and the sex-linked recessive lethal tests.

The mutagenicities of malondialdehyde and formaldehyde were tested by screening each for genetic mosaics of Drosophila melanogaster and by the Muller-5 test for sex-linked recessive lethal mutations. For comparison, the effects of X-rays were also assayed by the above technique. Malondialdehyde, a degradation product of polyunsaturated fatty acids, was found to be a weak mutagen by the above criteria; it induced point mutations and chromosome exchanges at low frequency, as proved by the mosaic test, but failed to induce detectable sex-linked lethality. Formaldehyde was more mutagenic than malondialdehyde; beside induction of mosaic spots it induced sex-linked recessive lethal mutations, but only in the larval testes of Drosophila. Formaldehyde also induced disintegration of the clones. Formaldehyde treatment (feeding larvae with formaldehyde-containing food for about 4 days) was 5 times more mutagenic than malondialdehyde treatment and 5 times less effective than irradiation by 1000 R of X-rays. Wing mosaicism offers a more sensitive way to detect mutagenesis as compared with eye mosaicism. It is suggested that aldehyde-induced mosaic spots derive from mitotic recombination and point mutations.

Effects of treating drosophila females with TEM on their mortality, and the yields of mutation recovered from x-irradiated sperm.

Ring-X-bearing Drosophila males were irradiated with 0, 1000, 2000 or 3000 R of X-rays and mated to females that had been injected with saline or 10(-4) M TEM. The mortality and the fertility of the treated females were recorded. The rate of dominant lethals, of entire sex chromosome loss and partial loss of the Y chromosome, the sex ratio, and the rate of mosaics were determined on the progency. TEM slightly increased the rate of mortality of the females. But it did not influence the yield of mutations recovered from the irradiated spermatozoa.

Analysis of genotoxic activity of 16 compounds and mixtures by the Drosophila mosaic test.

The mutagenicity of 16 compounds and mixtures were tested by the Drosophila melanogaster wing mosaic test. Fourteen of them gave negative results, two proved to be mutagenic. The positive compounds were chlor-diamino-toluene and 2-(2,4-dichlorophenoxy) propionic acid. Chlor-diamino-toluene increased the frequency of mitotic recombinations and gene mutations although it was found negative by the sex linked recessive lethal test. 2-(2,4-dichlorophenoxy) propionic acid caused only mitotic recombinations.

[Role of propionic acid, yeasts and ethyl alcohol in regulating the activity of H-factor in Drosophila simulans]. / O roli propionovoi kisloty, drozhzhei i étilovogo spirta v reguliatsii aktivnosti H-faktora u Drosophila simulans.

Effects of yeast, propionic acid and ethanol on the activity of H-factor, which sharply increases the frequency of somatic recombination in X-chromosomes of dorsal prothoracal disc cells in Drosophila simulans are studied. The frequency of yellow and singed mosaic spots in heterozygous yw ++/++sn1vHD. melanogaster females, inherited H-factor from the father (the stock sn1v) is estimated. The results of the varience analysis have shown that yeast and propionic acid regulate the activity of H-factor in cells of dorsal prothoracal disc, the interaction of yeast and propionic acid being also observed. Yeasts (or some unknown product of their metabolism) are the activator of H-factor; thus, when larvae eat much yeast, the frequency of yellow and singed mosaic spots in humeral region becomes high. A decrease of mosaic spot frequency under the increase of propionic acid content in nutrition medium is a result of the inhibitory effect of propionic acid on the yeast growth, but not of the direct repression of H-factor activity. So, propionic acid may be considered as a regulator of the second order. Ethanol does not activate H-factor. Changes in the content of yeast and propionic acid in nutrition medium do not affect the frequency of yellow and singed mosaic spots in other regions of D. simulans body, except humeral.