N-ethyl-N-nitrosourea Research Articles

Mutagenicity evaluation of methyl tertiary- butyl ether in multiple tissues of transgenic rats following whole body inhalation exposure.

Methyl tertiary-butyl ether (MTBE) is used as a component of motor vehicle fuel to enhance combustion efficiency and to reduce emissions of carbon monoxide and nitrogen oxides. Although MTBE was largely negative in the in vitro and in vivo genotoxicity studies, isolated reports of positive findings along with the observation of tumors in the rat cancer bioassays raised concern for its in vivo mutagenic potential. To investigate this, transgenic male Big Blue Fischer 344 rats were exposed to 0 (negative control), 400, 1000, and 3000 ppm MTBE via whole body inhalation for 28 consecutive days, 6 h/day. Mutant frequencies (MF) at the cII locus of the transgene in the nasal epithelium (portal of entry tissue), liver (site of primary metabolism), bone marrow (rapidly proliferating tissue), and kidney (tumor target) were analyzed (5 rats/exposure group) following a 3-day post-exposure manifestation period. MTBE did not induce a mutagenic response in any of the tissues investigated. The adequacy of the experimental conditions to detect induced mutations was confirmed by utilizing tissue samples from animals treated with the known mutagen ethyl nitrosourea. These data provide support to the conclusion that MTBE is not an in vivo mutagen and male rat kidney tumors are not likely the result of a mutagenic mode of action.

Investigations on the genotoxic potential of styrene in Fischer 344 rats using multiple endpoints.

Genotoxicity of styrene monomer was evaluated in male Fischer 344 rats using the alkaline comet assay for DNA damage, micronucleus assay for cytogenetic damage and the Pig-a assay for gene mutations. In a dose range finding (DRF) study, styrene was administered by oral gavage in corn oil for 28 consecutive days at 0, 100, 500, and 1000 mg/kg/day. The bioavailability of styrene was confirmed in the DRF by measuring its plasma levels at approximately 7- or 15-min following dosing. The 1000 mg/kg/day group exceeded the maximum tolerated dose based on body weight and organ weight changes and signs of central nervous system depression. Based on these findings, doses of 0, 100, 250, and 500 mg/kg/day (for 28 or 29 days) were selected for the genotoxicity assays. Animals were sacrificed 3-4 h after treatment on Day 28 or 29 for assessing various genotoxicity endpoints. Pig-a mutant frequencies and micronucleus frequencies were determined in peripheral blood erythrocytes. The comet assay was conducted in the glandular stomach, duodenum, liver, lung, and kidney. These studies were conducted in accordance with the relevant OECD test guidelines. Oral administration of styrene did not lead to genotoxicity in any of the investigated endpoints. The adequacy of the experimental conditions was assured by including animals treated by oral gavage with the positive control chemicals ethyl nitrosourea and ethyl methane sulfonate. Results from these studies supplement to the growing body of evidence suggesting the lack of in vivo genotoxic potential for styrene.

Glutathione Peroxidase gpx1 to gpx8 Genes Expression in Experimental Brain Tumors Reveals Gender-Dependent Patterns.

Extensive research efforts in the field of brain tumor studies have led to the reclassification of tumors by the World Health Organization (WHO) and the identification of various molecular subtypes, aimed at enhancing diagnosis and treatment strategies. However, the quest for biomarkers that can provide a deeper understanding of tumor development mechanisms, particularly in the case of gliomas, remains imperative due to their persistently incurable nature. Oxidative stress has been widely recognized as a key mechanism contributing to the formation and progression of malignant tumors, with imbalances in antioxidant defense systems being one of the underlying causes for the excess production of reactive oxygen species (ROS) implicated in tumor initiation. In this study, we investigated the gene expression patterns of the eight known isoforms of glutathione peroxidase (GPx) in brain tissue obtained from male and female control rats, as well as rats with transplacental ethyl nitrosourea (ENU)-induced brain tumors. Employing the delta-delta Ct method for RT-PCR, we observed minimal expression levels of gpx2, gpx5, gpx6, and gpx7 in the brain tissue from the healthy control animals, while gpx3 and gpx8 exhibited moderate expression levels. Notably, gpx1 and gpx4 displayed the highest expression levels. Gender differences were not observed in the expression profiles of these isoforms in the control animals. Conversely, the tumor tissue exhibited elevated relative expression levels in all isoforms, except for gpx4, which remained unchanged, and gpx5, which exhibited alterations solely in female animals. Moreover, except for gpx1, which displayed no gender differences, the relative expression values of gpx2, gpx3, gpx6, gpx7, and gpx8 were significantly higher in the male animals compared to their female counterparts. Hence, the analysis of glutathione peroxidase isoforms may serve as a valuable approach for discerning the behavior of brain tumors in clinical settings.

Vernonia amygdalina Extract Reverts Hematological and Biochemical Alterations in Rats Exposed to N-Nitroso-N-Ethyl Urea

Environmental carcinogens or exogenous carcinogens includes chemical, biological, and physical agents that have the potential to increase cancer risk because of prolonged high prevalence of exposure. Exposure can be through the respiratory, digestive, cutaneous or other possible contamination routes. N-Nitroso-N-ethyl urea (NEU), an ethylating agent has been described as a very potent transplacental teratogen and carcinogen in rodents. Plants have been investigated to protect against the effect of environmental carcinogens due to their arrays of phytochemicals. 35Female albino rats of average ages 10weeks were rats exposed to freshly prepared 3 fractionated doses of 50 mg/kg N-Nitroso-N-ethyl urea dissolved in 1/15 M phosphate buffer, given intraperitoneally and treated with varying concentrations of Vernonia amygdalina leaf aqueous extracts. At the end of the test period, hematological and biochemical parameters were determined in blood samples. Compared to the control group, the NEU exposed rats treated group showed significances in several hematological parameters, including decreases in white blood cell (WBC), red blood cell (RBC), and platelet (PLT) counts. Furthermore, in comparison to the control group, the NEU exposed rats showed significantly (p<0.05) increased blood glucose, serum total cholesterol, low density lipoprotein (LDL-cholesterol), triacylglycerols levels and igh density lipoprotein (HDL-cholesterol) level. The hematological and biochemical parameters in the NEU exposed rats treated group were similar to control group. V. amygdalina extract significantly (P<0.05) restored the hematological and biochemical parameters in N-Nitroso-N-ethyl urea exposed rats

Ethylnitrosourea-induced gliomas: a song in the attic?

It is essential to seek the underlying molecular mechanisms of glioma development, and critical to discover interventions that reduce the incidence and attenuate the growth of gliomas using a well-established in vivo experimental model because glioma is clinically one of the most difficult malignant tumors to treat. Ethylnitrosourea (ENU)-induced glioma in the rat has been extensively utilized as an experimental brain tumor model since the mid-1960s, however, the scientific value of ENU-induced glioma has been underappreciated mainly due to the recent development of transgenic mouse glioma models. Because of the pathophysiological characteristics, which are similar to the high grade human malignant gliomas, ENU-induced glioma is an excellent in vivo model to: a) examine the cell origin, development, and pathophysiology of gliomas; b) investigate anti-tumor effects of calorie restriction (CR) and its underlying mechanisms; and c) discover new preventive and/or therapeutic interventions of glioma. Further exploration of genetic changes during initiation, malignant transformation of glial cells, and progression of glioma as well as CR's anti-tumor effects on cellular processes using cutting edge technology, e.g., spatial transcriptomics, could provide more insight and a deeper understanding of the pathophysiology of gliomas.

Reconstructed human intestinal comet assay, a possible alternative in vitro model for genotoxicity assessment.

The aim of the present study was to evaluate the compatibility of reconstructed 3D human small intestinal microtissues to perform the in vitro comet assay. The comet assay is a common follow-up genotoxicity test to confirm or supplement other genotoxicity data. Technically, it can be performed utilizing a range of in vitro and in vivo assay systems. Here, we have developed a new reconstructed human intestinal comet (RICom) assay protocol for the assessment of orally ingested materials. The human intestine is a major site of food digestion and adsorption, first-pass metabolism as well as an early site of toxicant first contact and thus is a key site for evaluation. Reconstructed intestinal tissues were dosed with eight test chemicals: ethyl methanesulfonate (EMS), ethyl nitrosourea (ENU), phenformin hydrochloride (Phen HCl), benzo[a]pyrene (BaP), 1,2-dimethylhydrazine hydrochloride (DMH), potassium bromate (KBr), glycidamide (GA), and etoposide (Etop) over a span of 48 h. The RICom assay correctly identified the genotoxicity of EMS, ENU, KBr, and GA. Phen HCl, a known non-genotoxin, did not induce DNA damage in the 3D reconstructed intestinal tissues whilst showing high cytotoxicity as assessed by the assay. The 3D reconstructed intestinal tissues possess sufficient metabolic competency for the successful detection of genotoxicity elicited by BaP, without the use of an exogenous metabolic system. In contrast, DMH, a chemical that requires liver metabolism to exert genotoxicity, did not induce detectable DNA damage in the 3D reconstructed intestinal tissue system. The genotoxicity of Etop, which is dependent on cellular proliferation, was also undetectable. These results suggest the RICom assay protocol is a promising tool for further investigation and safety assessment of novel ingested materials. We recommend that further work will broaden the scope of the 3D reconstructed intestinal tissue comet assay and facilitate broader analyses of genotoxic compounds having more varied modes of actions.

Genotoxicity evaluation of orally administered styrene monomer in mice using comet, micronucleus, and Pig-a endpoints.

Male B6C3F1 mice were administered styrene monomer by oral gavage for 29 consecutive days at dose levels of 0, 75, 150, or 300 mg/kg/day. The highest dose level represented the maximum tolerated dose based on findings in a 28-day dose range-finding study, in which the bioavailability of orally administered styrene was also confirmed. The positive control group received ethyl nitrosourea (ENU; 51.7 mg/kg/day) on Study Days 1-3 and ethyl methanesulfonate (EMS; 150 mg/kg/day) on Study Days 27-29 by oral gavage. Approximately 3 h following the final dose, blood was collected to assess erythrocyte Pig-a mutant and micronucleus frequencies. DNA strand breakage was assessed in glandular stomach, duodenum, kidney, liver, and lung tissues using the alkaline comet assay. The %tail DNA for stomach, liver, lung, and kidney in the comet assay among the styrene-treated groups was neither significantly different from the respective vehicle controls nor was there any dose-related increasing trend in any of the tissues; results for duodenum were interpreted to be inconclusive because of technical issues. The Pig-a and micronucleus frequencies among styrene-treated groups also did not show significant increases relative to the vehicle controls and there was also no evidence for a dose-related increasing trend. Thus, orally administered styrene did not induce DNA damage, mutagenesis, or clastogenesis/aneugenesis in these Organization of Economic Co-operation and Development test guideline-compliant genotoxicity studies. Data from these studies can contribute to the overall assessment of genotoxic hazard and risk posed to humans potentially exposed to styrene.

Immunotherapeutic potential of ethanolic olive leaves extract (EOLE) and IL-28B combination therapy in ENU induced animal model of leukemia.

Cytokine therapies have shown promising results against cancers. Cytokines are secreted naturally from different bodily cells. These have fewer side effects but higher specificity than chemotherapy and radiation therapy. In leukemia, changes in normal hematopoiesis and defective leukocyte production limit the efficacy of immunotherapy by reducing the count of functional immune cells. Therefore, the treatment of leukemia needs advanced therapeutics that can target multiple cancer sustaining mechanisms. In combination therapy, using two different therapeutic agents affect cancer growth in many ways and sometimes gives synergistic effects. Here, we examined the effect of the ethanolic olive leaf extract (EOLE) and IL-28B in combination. N-N' Ethyl-nitrosourea (ENU) induced leukemia in Swiss albino mice was treated with EOLE for four weeks and IL-28B for one week after confirming the development of leukemia. The combination of EOLE and IL-28B significantly reduced the blast cell and total WBC counts in the peripheral blood, altered the levels of various cytokines in plasma, and induced the functional activity of NK cells in leukemic mice. The induced NK activity correlates with increased expression of perforin and granzyme studied at the gene level through real-time (RT)-PCR. The treatment of leukemic mice with combined EOLE and IL-28B has also caused an increased serum IL-10 and IFN-γ level, and reduced serum TGF-β indicates improved overall immunity. Altogether, the combination of EOLE and IL-28B has given substantial therapeutic activity against leukemia.

Abstract 1171: Genotoxic preventive potential of ethanol leaves extract of Annona muricata on N-Nitroso-N-ethylurea pro-leukaemia carcinogen in mice by bone marrow micronucleus assay

Abstract Background: Genotoxicity which is an important indicator of DNA damage, repair and cell rejuvenation has been a predisposing factor to cancer development evidenced by bone marrow suppression in leukemia and studies have proven the effect of several agents inclusive of natural products to induce, prevent and treat genotoxicity through experimental models and clinical trials. Aim:The genotoxic preventive potential of Annona muricata ethanol leaves extract on N-nitroso-N-ethylurea (NEU) pro-leukemia carcinogen in mice model using micronuclei formation in bone marrow was assessed. Materials and Methods: 48 mice weighing 18-24g were randomly divided into six groups of eight mice each comprising of the; mice intravenously administered 20mg/kg of NEU 48 hourly 3 times (A); 80mg/kg of NEU 48 hourly 3 times (B); negative control fed with feed and water only (C); 0.2ml (0.1g/ml) ethanolic leaves extract of Annona muricata for 3 weeks prior to administration of low dose of NEU (D); 0.2ml (0.1g/ml) ethanolic extract of Annona muricata for 3 weeks prior to administration of high dose of NEU (E); and Annona muricata (ethanolic leaves extract) and commercial diet for adverse/toxicity group (F). After six weeks of last exposure, animals were ethically sacrificed, bone marrow harvested, smeared, stained using MayGrumwald and number of micronucleus polychromatic erythrocyte (MNPCEs) were determined microscopically.Result: Groups exposed to various dosage of the NEU yielded significantly increased MNPCEs with group B producing higher MNPCEs than A. The groups treated with extract displayed a significant reduction in the MNPCEs despite the prior exposure concentrations of NEU. The adverse group displayed no difference in MNPCEs when compared with the negative control (Table 1). Conclusion: The extract displayed profound capacity to prevent genotoxicity thereby alleviating leukemia condition and it is well tolerated. Week Number Groups (Mean±Standard deviation of MNPCE) A B C D E F 2 14.13±0.56 50.45±2.31 4.52±0.34 6.15±0.49 17.11±1.11 4.53±0.45 3 15.01±0.18 53.77±1.95 4.61±0.67 7.85±0.98 20.34±2.34 4.62±0.23 4 16.11±0.22 56.95±2.01 4.91±0.88 8.01±1.01 25.11±1.67 5.63±0.45 5 19.64±1.68 68.23±1.56 4.82±0.75 10.07±0.67 30.54±2.34 5.92±0.67 Citation Format: Olufemi Emmanuel Akanni, Eunice Oluwaseyi Bamisaye, Sunday Anthony Fashina, Fatai Adesina Abdulraheem, Solomon Olufemi Fadiora. Genotoxic preventive potential of ethanol leaves extract of Annona muricata on N-Nitroso-N-ethylurea pro-leukaemia carcinogen in mice by bone marrow micronucleus assay [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1171.

Environmental pollutant N-N'ethylnitrosourea-induced leukemic NLRP3 inflammasome activation and its amelioration by Eclipta prostrata and its active compound wedelolactone.

Environmental exposure of N-nitroso compounds (NOCs) from various sources like tobacco smoke, pesticides, smoked meat, and rubber manufacturing industries has been an alarming cause of carcinogenesis. Neonatal exposure to the carcinogenic N-N'ethylnitrosourea (ENU), a NOC has been established to cause leukemogenesis. Our world is constantly battling against cancer with consistent investigations of new anti-cancer therapeutics. Plant derived compounds have grasped worldwide attention of researchers for their promising anti-cancer potentials. Eclipta prostrata is one such ayurvedic herb, renowned for its anti-inflammatory properties. Currently, it has been explored in various cancer cell lines to establish its anti-cancer effect, but rarely in in-vivo cancer models. Wedelolactone (WDL), the major coumestan of E. prostrata is recognized as an inhibitor of IKK, a master regulator of the NF-kB inflammatory pathway. As persistent inflammation and activated inflammasome contribute to leukemogenesis, we tried to observe anti-leukemogenic efficacy of E. prostrata and its active compound WDL on the marrow cells of ENU induced experimental leukemic mice. Treatment groups were administered an oral gavage at a dose of 1200 mg/kg and 50 mg/kg b.w of crude extract and WDL respectively for 4 weeks. Various parameters like hemogram, survivability, cytological and histological investigations, migration assay, cell culture, flowcytometry and confocal microscopy were taken into consideration pre- and post-treatment. Interestingly, the plant concoction portrayed maximum effects in comparison to WDL alone. The study suggests E. prostrata and WDL as vital complementary adjuncts for anti-inflammasome mechanism in ENU-induced leukemia.

Environmental pollutant ENU induced leukemic NF-kB signaling amelioration by Eclipta alba in murine model

ABSTRACT Exposure to N-nitroso compounds (NOCs) in our environment via pesticides, tobacco, and smoked meat can be potentially carcinogenic. The induction of N-N’ ethylnitrosourea (ENU), a genotoxic NOC, leads to leukemogenesis. The study aimed to explore the ameliorating effect of the Ayurvedic herb Eclipta alba on the bone marrow cells of ENU-induced leukemic mice. Eclipta alba is investigated for its anti-cancer effect on various cell lines, but never on haematological malignant models. Theefficacy of the extract was explored on leukemia by changes in body weight, survivability, peripheral blood hemogram, bone marrow cytological, histological, and cell culture studies pre-and post-treatment. The treated group revealed significant immunomodulation of the expressional profile of NF-kB family and IL-1β in marrow cells, by flow-cytometry, and immunofluorescence study. Through our experimental endeavour we depicted the cellular mechanism, signaling modality and tried to establish the anti-cancer potency of Eclipta alba on ENU-induced leukemia.

High-Level EVI1 Perturbs Hematopoietic Function By Skewing Cells Towards Myeloid Phenotype Via Induction of PU.1/ Spi1 Â Transcription

Inv(3q26) and t(3:3)(q21;q26) are specific to poor prognosis acute myeloid leukemia (AML) and myelodysplastic syndrome, and result in marked overexpression of EVI1 isoforms. Despite extensive study, the mechanism by which this induces myeloid malignancy is unclear. We describe a mouse model that mimics the transcriptional effects of 3q26 rearrangement, and study of this has revealed a novel mechanism of leukemogenesis, specifically myeloid skewing with concomitant suppression of erythropoiesis and lymphopoiesis. In an effort to characterize the effects of high-level EVI1 expression on hematopoietic cells in vivo, we created a tetracycline (Tet)-inducible allele of Evi1 (termed Evi1TO) in the mouse by inserting seven repeats of the Tet operon within the first exon of Evi1. The advantage of this design is that it allows for the induction of all spliced isoforms of the locus, of which at least three exist, those encoding 135, 123, and 103 kDa. To assess whether Evi1 can be induced in vivo, we tested induction in mice harboring Evi1TO/TO / Rosa26rtTA/rtTA alleles: treatment of these mice with DOX results in dramatic up-regulation of the major Evi1 transcript in hematopoietic cells to levels commonly seen in leukemic cells. This accurately models the pattern of Mecom gene expression most commonly seen in human AML with rearrangements at 3q26, in which setting the EVI1 isoforms are upregulated, but typically not the longer, MDS1-EVI1/PRDM3 isoform; and this particular expression pattern is associated with the poorest prognosis. To determine the direct effect of EVI1 overexpression on hematopoietic stem/progenitor cells (HSPCs) and to minimize secondary and non-cell autonomous effects, we enumerated HSPCs in Evi1TO/TO / Rosa26rtTA/rtTA mice following three days of induction administered by DOX chow. This revealed a doubling of LSK cells, due primarily to increases in HSCs and MPP3 cells, the latter representing myeloid-poised progenitors. In long-term competitive transplantation experiments, EVI1 overexpression resulted in marked suppression of both erythropoiesis and lymphopoiesis, due to both increases in apoptosis and decreases in proliferation. In the same setting, there was a marked expansion of myeloid cells, such that EVI1-overexpressing cells constituted the majority of myeloid cells in the marrow, despite the presence of normal competitor bone marrow. Our data indicate that when Evi1 is induced in vivo in an admixture with normal hematopoietic cells, there is expansion of the Evi1 -expressing cells indicating they have a proliferative and/or survival advantage, with specific predilection for myeloid differentiation; we found that EVI1 overexpression led to significant increases in both bone marrow and circulating granulocytes and their progenitors, and marked decreases in erythrocytes and T and B lymphocytes; monocytes and platelets were largely unaffected. To understand the mechanism, we employed EML cells, which are immortalized progenitor cells. EVI1 overexpression caused marked upregulation of Sca-1, a marker of myeloid skewing, with concomitant inhibition of erythropoiesis; these effects are dependent on EVI1 binding to DNA. This myeloid skewing correlated with a two-fold increase in PU.1 expression. ChIP-seq experiments revealed several binding sites for EVI1 upstream of PU.1, and knock-out of one of these sites in vivo led to blunting of PU.1 induction by EVI1, and abrogated EVI1-mediated upregulation of Sca-1; in vitro knockdown studies showed similar results. These data are consistent with a mechanism whereby EVI1 overexpression upregulates PU.1, and together these factors suppress erythropoiesis and promote myelopoiesis. However, by itself EVI1 overexpression does not result in leukemia. To see if leukemia would result if additional mutations were induced, we treated competitively transplanted mice with the mutagen, ethylnitrosourea (ENU). This induced myeloid leukemias in 100% of the mice, and all were derived from EVI1-overexpressing cells. These data suggest that EVI1 overexpression requires additional cooperating genetic events for induction of leukemia. DisclosuresNo relevant conflicts of interest to declare.

Differential exposure to N-ethyl N-nitrosourea during pregnancy is relevant to the induction of glioma and PNSTs in the brain

Exposure to N-nitroso compounds (NOCs) during pregnancy has been associated with an increase in brain tumors in the progeny. This study investigated the brain tumorigenic effect of N-ethyl N-nitrosourea (ENU) after differential exposure of rats during pregnancy.Sprague Dawley rats were exposed to a single dose of ENU (80 mg/kg) in three different circumstances: 1) at first, second or third week of gestation; 2) at the 15th embryonic day (E15) in consecutive litters and 3) at E15 in three successive generations. Location and characterization of the offspring's brain tumors were performed by magnetic resonance imaging and histopathological studies. Finally, tumor incidence and latency and the animals' survival were recorded.ENU-exposure in the last two weeks of pregnancy induced intracranial tumors in over 70% of the offspring rats, these being mainly gliomas with some peripheral nerve sheath tumors (PNSTs). Tumors appeared in young adults; glioma-like small multifocal neoplasias converged on large glioblastomas in senescence and PNSTs in the sheath of the trigeminal nerve, extending to cover the brain convexity. ENU-exposure at E15 in subsequent pregnancies lead to an increase in glioma and PNST incidence. However, consecutive generational ENU-exposure (E15) decreased the animals' survival due to an early onset of both types of tumors. Moreover, PNST presented an inheritable component because progeny, which were not themselves exposed to ENU but whose progenitors were, developed PNSTs.Our results suggest that repeated exposure to ENU later in pregnancy and in successive generations favours the development of intracranial gliomas and PNSTs in the offspring.

Postembryonic screen for mutations affecting spine development in zebrafish

The spine gives structural support for the adult body, protects the spinal cord, and provides muscle attachment for moving through the environment. The development and maturation of the spine and its physiology involve the integration of multiple musculoskeletal tissues including bone, cartilage, and fibrocartilaginous joints, as well as innervation and control by the nervous system. One of the most common disorders of the spine in human is adolescent idiopathic scoliosis (AIS), which is characterized by the onset of an abnormal lateral curvature of the spine of <10° around adolescence, in otherwise healthy children. The genetic basis of AIS is largely unknown. Systematic genome-wide mutagenesis screens for embryonic phenotypes in zebrafish have been instrumental in the understanding of early patterning of embryonic tissues necessary to build and pattern the embryonic spine. However, the mechanisms required for postembryonic maturation and homeostasis of the spine remain poorly understood. Here we report the results from a small-scale forward genetic screen for adult-viable recessive and dominant zebrafish mutations, leading to overt morphological abnormalities of the adult spine. Germline mutations induced with N-ethyl N-nitrosourea (ENU) were transmitted and screened for dominant phenotypes in 1229 F1 animals, and subsequently bred to homozygosity in F3 families; from these, 314 haploid genomes were screened for adult-viable recessive phenotypes affecting general body shape. We cumulatively found 40 adult-viable (3 dominant and 37 recessive) mutations each leading to a defect in the morphogenesis of the spine. The largest phenotypic group displayed larval onset axial curvatures, leading to whole-body scoliosis without vertebral dysplasia in adult fish. Pairwise complementation testing of 16 mutant lines within this phenotypic group revealed at least 9 independent mutant loci. Using massively-parallel whole genome or whole exome sequencing and meiotic mapping we defined the molecular identity of several loci for larval onset whole-body scoliosis in zebrafish. We identified a new mutation in the skolios/kinesin family member 6 (kif6) gene, causing neurodevelopmental and ependymal cilia defects in mouse and zebrafish. We also report multiple recessive alleles of the scospondin and a disintegrin and metalloproteinase with thrombospondin motifs 9 (adamts9) genes, which all display defects in spine morphogenesis. Our results provide evidence of monogenic traits that are essential for normal spine development in zebrafish, that may help to establish new candidate risk loci for spine disorders in humans.

Tripartite-motif family protein 35-28 regulates microglia development by preventing necrotic death of microglial precursors in zebrafish

Microglia are tissue-resident macrophages in the central nervous system (CNS) that play essential roles in the regulation of CNS development and homeostasis. Yet, the genetic networks governing microglia development remain incompletely defined. Here, we report the identification and characterization of a microglia-defective zebrafish mutant wulonghkz12 (wulhkz12 ) isolated from an ethylnitrosourea (ENU)-based genetic screen. We show that wulhkz12 mutants harbors a missense point mutation in the gene region encoding the PRY/SPRY domain of the tripartite-motif family protein 35-28 (trim35-28) gene. Time-lapse imaging revealed that the loss of Trim35-28 function causes lytic necrosis of microglial precursors/peripheral macrophages, as indicated by cytoplasmic swelling and membrane rupture of these precursors and accompanied by neutrophil infiltration and systemic inflammation. Intriguingly, the lytic necrosis of microglial precursors in trim35-28-deficient mutants appeared to depend neither on the canonical pyroptotic nor necroptotic pathways, as inhibition of the key component in each pathway could not rescue the microglia phenotype in trim35-28-deficient mutants. Finally, results from tissue-specific rescue experiments suggested that Trim35-28 acts cell-autonomously in the survival of microglial precursors. Taken together, the findings of our study reveal Trim35-28 as a regulatory protein essential for microglia development.

NEW STRAIN OF MUTANT MICE CHARACTERIZED BY SELECTIVE RESISTANCE TO ONE OF TWO SEPTIC SHOCK PROTOCOLS

More than 40 years ago ethyl nitrosoеurea was identified as a powerful mutagen for mammalian germ cells resulting in random point mutations in gamete DNA. This feature allowed the use of this mutagen for genetic studies on the mechanisms of various pathological and physiological processes in model organisms. In our study genome-wide mutagenesis in C3H mice by ethyl nitrosourea followed in generation F3 by selection of animals resistant to acute lethal hepatotoxicity caused by a combination of E. coli lipopolysaccharide (LPS) and D-galactosamine (D-gal). Tumor necrosis factor (TNF) is known to be a critical mediator of this pathology. Exposure to D-galactosamine increases sensitivity of hepatocytes to TNF leading to their necrosis and/or apoptosis. After double LPS/D-gal screening in F3 several mice resistant to LPS/D-gal-induced hepatotoxicity were identified, and became the founders of the corresponding “mutant” families. Using outcrossing to C57BL6 background followed by intercrossing, generations F5 and F7 were obtained. Among families of mutant animals only one family showed the resistance to the combination of LPS and D-gal, but sensitivity to TNF-D-galactosamine. This phenotype showed approximately Mendelian inheritance consistent with the recessive mutation hypothesis. This latter fact was confirmed by the sensitivity of mice from “heterozygous generations” (F4 and F6) to lethal LPS/Dgal hepatotoxicity. Primary bone marrow macrophages obtained from half of the mutant mice showed significantly reduced levels of TNF after LPS stimulation in vitro. At the same time, the serum TNF levels 1 hour after the administration of a non-lethal LPS dose did not differ in the mutant family mice and wild-type mice. These results implicate a recessive mutation either in innate TLR4-mediated signaling pathway, including proteins associated with LPS transfer, adapter molecules, components of kinase signaling cascades, transcription factors, or in enzymes involved in regulation of TLR4 cascades, such as components of the ubiquitin cycle, or in genomic regulatory sequences that control the expression of one of these genes, including the tnf gene.

Finding the Unicorn, a New Mouse Model of Midfacial Clefting.

Human midfacial clefting is a rare subset of orofacial clefting and in severe cases, the cleft separates the nostrils splitting the nose into two independent structures. To begin to understand the morphological and genetic causes of midfacial clefting we recovered the Unicorn mouse line. Unicorn embryos develop a complete midfacial cleft through the lip, and snout closely modelling human midfacial clefting. The Unicorn mouse line has ethylnitrosourea (ENU)-induced missense mutations in Raldh2 and Leo1. The mutations segregate with the cleft face phenotype. Importantly, the nasal cartilages and surrounding bones are patterned and develop normal morphology, except for the lateral displacement because of the cleft. We conclude that the midfacial cleft arises from the failure of the medial convergence of the paired medial nasal prominences between E10.5 to E11.5 rather than defective cell proliferation and death. Our work uncovers a novel mouse model and mechanism for the etiology of midfacial clefting.

The Establishment of a Three-color Flow Cytometry Approach for the Scoring of Micronucleated Reticulocytes in Rat Bone Marrow

To develop and verify a flow cytometric measurement of reticulocytes (RETs) micronucleus in rat bone marrow. In our flow cytometric protocol, reticulocytes, leukocytes and DNA were labeled by anti-CD71-fluorescein isothiocyanate (FITC), anti-CD45-phycoerythrin (PE) and DRAQ5, respectively. Sprague-Dawley (SD) rats were assigned to four treatment groups randomly, and were exposed to ethyl methanesulfonate (EMS), cyclophosphamide (CP), ethyl nitrosourea (ENU) and colchicine (COL) respectively. Each treatment group was divided into four subgroups (5 rats per subgroup) according to different exposure dosage. A exposure dose of 0 was used as vehicle control for each group. Rats were administered with testing mutagens by gavage twice with a 24 h interval. Bone marrow from both femurs were collected 24 h after the last administration. The frequency of micronucleated reticulocytes (MN-RETs) and the percentage of reticulocytes (RETs%) were determined by flow cytometric measurement established in this study. And the manual counting method with microscope (by Giemsa staining) was conducted at the same time. A method for detection of reticulocyte micronucleus in bone marrow based on flow cytometry was successfully established. The MN-RETs in rat bone marrow of 20 SD rats treated by vehicle (i.e., background value of MN-RETs) was 0.83‰±0.12‰ by this method. The background value of MN-RETs in manual enumeration method was 1.43‰±0.44‰. It was obvious that the flow cytometric method had lower background value and more stable results. The trend, in which MN-RETs ascended and RETs% descended with increasing dose, can be detected by both methods in rats that exposed to EMS, CP, ENU and COL. Both methods were good to detect the correlation of induced-MN-RETs with four testing mutagens (the correlation coefficients were ranged from 0.834 3 to 0.913 7). With its sensitivity, rapidity, easy operation and low background value, the three-color flow cytometric enumerative protocol established in our laboratory can be used as a good substitute for manual micronucleus counting method and used in genotoxicity assessment of chemical substances.

The 3D reconstructed skin micronucleus assay: considerations for optimal protocol design.

Implementation of the seventh amendment to the EU Cosmetics Directive has driven much research into suitable in vitro alternative assays to support satisfactory risk assessments. One such assay is the reconstructed skin micronucleus (RSMN) assay. First reported in 2006, further development occurred and a standard protocol was published in 2011. To evaluate and optimise the assay at Covance Laboratories, we tested nine chemicals [4-nitrophenol (4-NP), cyclohexanone (CH), 2-ethyl-1,3-hexanediol (2-EHD), methyl methansulfonate (MMS), mitomycin C (MMC), ethyl nitrosourea (ENU), benzo[a]pyrene (BaP), cyclophosphamide (CPA) and vinblastine (VIN)] using the EpiDerm™ 3D skin model (MatTek Corporation®, IVLSL, Bratislava, Slovakia) and compared the data using the standard 48-h treatment regimen and also an emerging 72-h treatment protocol. The EpiDerm™ tissue has reportedly some metabolic capacity but data using 48-h treatments has provided mixed results. Our investigations demonstrate that the two chemicals requiring metabolic activation (BaP and CPA) were negative following the 48-h protocol but were clearly positive following 72-h treatment. Furthermore, Replication Index (RI) data showed higher RI values in vehicle control treatments (indicating increased cell division) across the treatment set following 72-h treatments. A general greater magnitude of micronucleus (MN) induction was also observed following test chemical treatment. These data suggest that the 72-h treatment protocol is more suitable as a standard approach for the detection of clastogenic, aneugenic and metabolically activated chemicals in the RSMN assay. For further assay optimisation, we compare the statistical power of scoring cells from duplicate or triplicate cultures per treatment concentration and provide recommendations.

Identification of a Spontaneous Noncoding Mutation on Chromosome 18 Which Suppresses Thrombosis in Factor V Leiden Homozygous, TFPI Deficient Mice

Factor V Leiden (FVL) is an incompletely penetrant thrombosis susceptibility variant common in humans. This incomplete penetrance suggests there are modifiers of FVL (F5L) that alter the susceptibility to a thrombotic event. To identify modifiers, we performed a sensitized ethylnitrosourea (ENU) mutagenesis screen in mice to induce mutations suppressing the F5L/LTfpi+/- perinatal lethal thrombotic phenotype. Although we identified thrombosuppressor mutations in two of our 22 independent MF5L mouse lines thus far, the others are still unknown. Our mouse line MF5L16 has produced a large, highly penetrant (77.2%), multigenerational pedigree containing 136 viable F5L/LTfpi+/- mice. We performed the Prothrombin Time (PT) assay on plasma from a subset of these mice and observed a significantly longer PT in MF5L16F5L/LTfpi+/- mice compared to F5+/LTfpi+/- and Tfpi+/- control mice (q&amp;lt;0.01). The aim of our study was to identify the MF5L16 thrombosuppressor. First, we analyzed four mice by whole genome sequencing and identified a total of 44 candidate ENU mutations. Sanger re-sequencing analysis determined that 22 were false-positive calls. Seven arose in our F5L/L breeding colony and were introduced into MF5L16 by these mice. Three arose on the Tfpi- mouse background. The remaining 12 candidates could not be analyzed as they were in repetitive/low complexity regions. Due to the lack of ENU-induced mutations segregating in MF5L16, we next analyzed the seven mutations entering the pedigree from the F5L/L breeders in all 136 MF5L16 F5L/LTfpi+/- mice. We identified a significant association between a Chromosome 18 intergenic variant (Chr18 G to A, Chr18A) and F5L/LTfpi+/- mouse survival (p=0.0031). Two additional mutations within intronic regions on Chromosomes 9 and 13 were also significantly associated with survival when co-inherited with the Chromosome 18 mutation (p=0.000113). Importantly, no coding variants were linked to these variants. To re-create the suppression of the lethal F5L/LTfpi+/- phenotype, we bred a F5L/L Chr18A/A mouse onto the Tfpi- background to produce F5+/L Chr18+/ATfpi+/- mice. We then bred these F5+/L Chr18+/ATfpi+/- triple heterozygous mice to F5L/L Chr18A/ATfpi+/+ mice to observe the effects of Chr18A on F5L/LTfpi+/- mouse survival. The first litter of six mice from this cross yielded one F5L/LTfpi+/- mouse that was also heterozygous for Chr18 (F5L/LTfpi+/- Chr18+/A: expected ratio ~1:8). This suggests that the Chr18A variant suppresses F5L/LTfpi+/- lethal thrombosis and that noncoding genomic variants can act as potent thrombosuppressors. Our genetic analyses suggest that thrombosuppressor variants arose in our F5L mouse colony due to positive selective pressure for the best F5L breeders. In addition, the genomic interactions between the putative thrombosuppressor variants described here illuminate the complexities of thrombosis genomics and could provide insights into human thrombosis. Disclosures No relevant conflicts of interest to declare.