Gene-teratogen interactions influence the penetrance of birth defects by altering Hedgehog signaling strength

Birth defects result from interactions between genetic and environmental factors, but the mechanisms remain poorly understood. We find that mutations and teratogens interact in predictable ways to cause birth defects by changing target cell sensitivity to Hedgehog (Hh) ligands. These interactions converge on a membrane protein complex, the MMM complex, that promotes degradation of the Hh transducer Smoothened (SMO). Deficiency of the MMM component MOSMO results in elevated SMO and increased Hh signaling, causing multiple birth defects. In utero exposure to a teratogen that directly inhibits SMO reduces the penetrance and expressivity of birth defects in Mosmo-/- embryos. Additionally, tissues that develop normally in Mosmo-/- embryos are refractory to the teratogen. Thus, changes in the abundance of the protein target of a teratogen can change birth defect outcomes by quantitative shifts in Hh signaling. Consequently, small molecules that re-calibrate signaling strength could be harnessed to rescue structural birth defects.

Developmental toxicity of Clerodendrum cyrtophyllum turcz ethanol extract in zebrafish embryo

ETHNOPHARMACOLOGICAL RELEVANCE

Clerodendrum cyrtophyllum Turcz has been used in traditional medicine for the treatment of various diseases. In spite of its therapeutic applications, research on its toxicity and teratogenicity is still limited.

AIM OF THE STUDY

The study aimed to investigate the developmental toxicity of the ethanol extract of C. cyrtophyllum (EE) in zebrafish embryo model.

MATERIAL AND METHODS

Major compounds from crude ethanol extract of Clerodendron cyrtophyllum Turcz leaves were determined using HPLC-DAD-Orbitrap-MS analysis. The developmental toxicity of EE were investigated using zebrafish embryo model. Zebrafish embryos at 6 h post-fertilization (hpf) were treated with EE at different concentrations. Egg coagulation, mortality, hatching, yolk sac edema, pericardial edema and teratogenicity were recorded each day for during a 5-day exposure. At time point 120 hpf, body length, pericardial area, heartbeat and yolk sac area were assessed. In order to elucidate molecular mechanisms for the developmental toxicity of EE, we further evaluated the effects of the EE on the expression of genes involved on signaling pathways affecting fish embryo's development such as heart development (gata5, myl7, myh6, has2, hand2, nkx 2.5), oxidative stress (cat, sod1, gpx4, gstp2), wnt pathway (β-catenin, wnt3a, wnt5, wnt8a, wnt11), or cell apoptosis (p53, bax, bcl2, casp3, casp8, casp9, apaf-1, gadd45bb) using qRT-PCR analysis.

RESULTS

Our results demonstrated that three major components including acteoside, cirsilineol and cirsilineol-4'-O-β-D-glucopyranoside were identified from EE. EE exposure during 6-96 h post-fertilization (hpf) at doses ranging from 80 to 200 μg/mL increased embryo mortality and reduced hatching rate. EE exposure at 20 and 40 μg/mL until 72-120 hpf induced a series of malformations, including yolk sac edema, pericardial edema, spine deformation, shorter body length. Based on two prediction models using a teratogenic index (TI), a 25% lethality concentration (LD25) and the no observed-adverse-effect level (NOAEL), EE is considered as teratogenic for zebrafish embryos with TI (LC50/EC50) and LD25/NOAEC values at 96 hpf reaching 3.87 and 15.73 respectively. The mRNA expression levels of p53, casp8, bax/bcl2, gstp2, nkx2.5, wnt3a, wnt11, gadd45bb and gata5 were significantly upregulated by EE exposure at 20 and 40 μg/mL while the expression of wnt5, hand2 and bcl2 were downregulated.

CONCLUSIONS

These results provide evidence for toxicity effects of EE to embryo stages and provide an insight into the potential toxicity mechanisms on embryonic development.

In Vivo Assessment of Drug-Induced Hepatotoxicity Using Xenopus Embryos

Failure to predict drug-induced toxicity reactions is a major problem contributing to a high attrition rate and tremendous cost in drug development. Drug screening in X. laevis embryos is high-throughput relative to screening in rodents, potentially making them ideal for this use. Xenopus embryos have been used as a toxicity model in the frog embryo teratogenesis assay on Xenopus (FETAX) for the early stages of drug safety evaluation. We previously developed compound-screening methods using Xenopus embryos and believe they could be used for in vitro drug-induced toxicity safety assessment before expensive preclinical trials in mammals. Specifically, Xenopus embryos could help predict drug-induced hepatotoxicity and consequently aid lead candidate prioritization. Here we present methods, which we have modified for use on Xenopus embryos, to help measure the potential for a drug to induce liver toxicity. One such method examines the release of the liver-specific microRNA (miRNA) miR-122 from the liver into the vasculature as a result of hepatocellular damage, which could be due to drug-induced acute liver injury. Paracetamol, a known hepatotoxin at high doses, can be used as a positive control. We previously showed that some of the phenotypes of mammalian paracetamol overdose are reflected in Xenopus embryos. Consequently, we have also included here a method that measures the concentration of free glutathione (GSH), which is an indicator of paracetamol-induced liver injury. These methods can be used as part of a panel of protocols to help predict the hepatoxicity of a drug at an early stage in drug development.

Warfarin-exposed zebrafish embryos resembles human warfarin embryopathy in a dose and developmental-time dependent manner - From molecular mechanisms to environmental concerns

Warfarin is the most worldwide used anticoagulant drug and rodenticide. Since it crosses placental barrier it can induce warfarin embryopathy (WE), a fetal mortality in neonates characterized by skeletal deformities in addition to brain hemorrhages. Although the effects of warfarin exposure in aquatic off target species were already described, the particular molecular toxicological mechanisms during early development are still unclear. Here, we used zebrafish (Danio rerio) to describe and compare the developmental effects of warfarin exposure (0, 15.13, 75.68 and 378.43 mM) on two distinct early developmental phases (embryos and eleuthero-embryos). Although exposure to both developmental phases induced fish mortality, only embryos exposed to the highest warfarin level exhibited features mimicking mammalian WE, e.g. high mortality, higher incidence of hemorrhages and altered skeletal development, among other effects. To gain insights into the toxic mechanisms underlying warfarin exposure, the transcriptome of embryos exposed to warfarin was explored through RNA-Seq and compared to that of control embryos. 766 differentially expressed (564 up- and 202 down-regulated) genes were identified. Gene Ontology analysis revealed particular cellular components (cytoplasm, extracellular matrix, lysosome and vacuole), biological processes (mainly amino acid and lipid metabolism and response to stimulus) and pathways (oxidative stress response and apoptosis signaling pathways) being significantly overrepresented in zebrafish embryos upon warfarin exposure. Protein-protein interaction further evidenced an altered redox system, blood coagulation and vasculogenesis, visual phototransduction and collagen formation upon warfarin exposure. The present study not only describes for the first time the WE in zebrafish, it provides new insights for a better risk assessment, and highlights the need for programming the rat eradication actions outside the fish spawning season to avoid an impact on off target fish community. The urge for the development of more species-specific anticoagulants for rodent pest control is also highlighted.

Metformin exposure in first trimester of pregnancy and risk of all or specific congenital anomalies: exploratory case-control study

OBJECTIVE

To investigate whether exposure to metformin during the first trimester of pregnancy, for diabetes or other indications, increases the risk of all or specific congenital anomalies.

DESIGN

Population based exploratory case-control study using malformed controls. Cases of 29 specific subgroups of non-genetic anomalies, and all non-genetic anomalies combined, were compared with controls (all other non-genetic anomalies or genetic syndromes).

SETTING

11 EUROmediCAT European congenital anomaly registries surveying 1 892 482 births in Europe between 2006 and 2013.

PARTICIPANTS

50 167 babies affected by congenital anomaly (41 242 non-genetic and 8925 genetic) including live births, fetal deaths from 20 weeks' gestation, and terminations of pregnancy for fetal anomaly.

MAIN OUTCOME MEASURE

Odds ratios adjusted for maternal age, registry, multiple birth, and maternal diabetes status.

RESULTS

168 babies affected by congenital anomaly (141 non-genetic and 27 genetic) were exposed to metformin, 3.3 per 1000 births. No evidence was found for a higher proportion of exposure to metformin during the first trimester among babies with all non-genetic anomalies combined compared with genetic controls (adjusted odds ratio 0.84, 95% confidence interval 0.55 to 1.30). The only significant result was for pulmonary valve atresia (adjusted odds ratio 3.54, 1.05 to 12.00, compared with non-genetic controls; 2.86, 0.79 to 10.30, compared with genetic controls).

CONCLUSIONS

No evidence was found for an increased risk of all non-genetic congenital anomalies combined following exposure to metformin during the first trimester, and the one significant association was no more than would be expected by chance. Further surveillance is needed to increase sample size and follow up the cardiac signal, but these findings are reassuring given the increasing use of metformin in pregnancy.

The effects of microduplication 1q21.1 and in-utero isotretinoin exposure

The impact of in-utero isotretinoin exposure has been widely reported, with many affected pregnancies failing to reach term.^{1 2} Due to the low numbers of in-utero isotretinoin exposed pregnancies, the interactions between this drug and rare genetic defects such as microduplication 1q21.1 are unclear, particularly how they might manifest phenotypically. We present this case of in-utero isotretinoin exposure occurring in a child with microduplication 1q21.1. The child was born with congenital abnormalities which did not fit into a single syndrome. Regrettably in-utero exposure to isotretinoin continues to occur. We hope this case will trigger further discussion on the dangers of dispensing Isotretinoin without ensuring stringent pregnancy testing and its potential interaction with genetic abnormalities, in particular with microduplication 1q21.1.

Retinoid acid-induced microRNA-31-5p suppresses myogenic proliferation and differentiation by targeting CamkIIδ

BACKGROUND

We previously reported that Wnt5a/CaMKIIδ (calcium/calmodulin-dependent protein kinase II delta) pathway was involved in the embryonic tongue deformity induced by excess retinoic acid (RA). Our latest study found that the expression of miR-31-5p, which was predicted to target the 3'UTR of CamkIIδ, was raised in the RA-treated embryonic tongue. Thus, we hypothesized that the excess RA regulated Wnt5a/CaMKIIδ pathway through miR-31-5p in embryonic tongue.

METHODS

C2C12 myoblast line was employed as an in vitro model to examine the suppression of miR-31-5p on CamkIIδ expression, through which RA impaired the myoblast proliferation and differentiation in embryonic tongue.

RESULTS

RA stimulated the expression of miR-31-5p in both embryonic tongue and C2C12 myoblasts. Luciferase reporter assay confirmed that the 3'UTR of CamkIIδ was a target of miR-31-5p. MiR-31-5p mimics disrupted CamkIIδ expression, C2C12 proliferation and differentiation as excess RA did, while miR-31-5p inhibitor partially rescued these defects in the presence of RA.

CONCLUSIONS

Excess RA can stimulate miR-31-5p expression to suppress CamkIIδ, which represses the proliferation and differentiation of tongue myoblasts.

Maternal and infant genetic variants, maternal periconceptional use of selective serotonin reuptake inhibitors, and risk of congenital heart defects in offspring: population based study

Objective To evaluate whether the association between maternal periconceptional use of selective serotonin reuptake inhibitors (SSRIs) and increased risk of congenital heart defects in offspring is modified by maternal or infant genetic variants in folate, homocysteine, or transsulfuration pathways.Design Population based study. DNA from mothers, fathers, and infants was genotyped with an Illumina GoldenGate custom single nucleotide polymorphism panel. A hybrid design based on a log linear model was used to calculate relative risks and Bayesian false discovery probabilities (BFDP) to identify polymorphisms associated with congenital heart defects modified by SSRI use.Data sources Data from the US National Birth Defects Prevention Study on 1180 liveborn infants with congenital heart defects and 1644 controls, born 1997-2008.Main outcome measures Cases included infants with selected congenital heart defects and control infants had no major defects. SSRI use was obtained from telephone interviews with mothers.Results For women who reported taking SSRIs periconceptionally, maternal SHMT1 (rs9909104) GG and AGgenotypes were associated with a 5.9 and 2.4 increased risk of select congenital heart defects in offspring, respectively, versus the AA genotype (BFDP=0.69). Compared with the AA genotype, BHMT (rs492842 and rs542852) GG and AG genotypes were associated with twice the riskof congenital heart defects (BFDP=0.74 and 0.79, respectively). MGST1 (rs2075237) CC and ACgenotypes were associated with an increased risk compared with the GG genotype (8.0 and 2.8, respectively; BFDP=0.79). Single nucleotide polymorphism in infant genes in the folate (MTHFS rs12438477), homocysteine (TRDMT1 rs6602178 and GNMT rs11752813) and transsulfuration (GSTP1 rs7941395 and MGST1 rs7294985) pathways were also associated with an increased risk of congenital heart defects.Conclusions Common maternal or infant genetic variants in folate, homocysteine, or transsulfuration pathways are associated with an increased risk of certain congenital heart defects among children of women taking SSRIs during cardiogenesis.

DNA methyltransferase expressions in Japanese rice fish (Oryzias latipes) embryogenesis is developmentally regulated and modulated by ethanol and 5-azacytidine

We aimed to investigate the impact of the epigenome in inducting fetal alcohol spectrum disorder (FASD) phenotypes in Japanese rice fish embryogenesis. One of the significant events in epigenome is DNA methylation which is catalyzed by DNA methyltransferase (DNMT) enzymes. We analyzed DNMT enzyme mRNA expressions in Japanese rice fish development starting from fertilized eggs to hatching and also in embryos exposed for first 48h of development either to ethanol (300mM) or to 5-azacytidine (5-azaC; 2mM), an inhibitor of DNMT enzyme activity. As observed in FASD phenotypes, 5-azaC exposure was able to induce microcephaly and craniofacial cartilage deformities in Japanese rice fish. Moreover, we have observed that expression of DNMTs (dnmt1, dnmt3aa, and dnmt3bb.1) are developmentally regulated; high mRNA copies were found in early stages (1-2day-post-fertilization, dpf), followed by gradual reduction until hatched. In ethanol-treated embryos, compared to controls, dnmt1 mRNA is in reduced level in 2dpf and in enhanced level in 6dpf embryos. While dnmt3aa and 3bb.1 remained unaltered. In contrast, embryos exposed to 5-azaC have an enhanced level of dnmt1 and dnmt3bb.1 mRNAs both in 2 and 6dpf embryos while dnmt3aa is enhanced only in 6dpf embryos. Moreover, endocannabinoid receptor 1a (cnr1a) mRNA which was found to be reduced by ethanol remained unaltered and cnr1b and cnr2 mRNAs, which were remained unaltered by ethanol, were increased significantly by 5-azaC in 6dpf embryos. This study indicates that the craniofacial defects observed in FASD phenotypes are the results of dysregulations in DNMT expressions.

Developmental toxicity and DNA damage from exposure to parking lot runoff retention pond samples in the Japanese medaka (Oryzias latipes)

Parking lot runoff retention ponds (PLRRP) receive significant chemical input, but the biological effects of parking lot runoff are not well understood. We used the Japanese medaka (Oryzias latipes) as a model to study the toxicity of water and sediment samples from a PLRRP in Morehead City, NC. Medaka exposed in ovo to a dilution series of PLRRP water had increased odds of death before hatching, but not teratogenesis or delayed hatching. Next, we adapted a long-amplicon quantitative PCR (LA-QPCR) assay for DNA damage for use with the Japanese medaka. We employed LA-QPCR to test the hypotheses that PLRRP water and sediments would cause nuclear and mitochondrial DNA damage with and without full-spectrum, natural solar radiation. Fluoranthene with and without natural sunlight was a positive control for phototoxic polycyclic aromatic hydrocarbon-induced DNA damage. Fluoranthene exposure did not result in detectable DNA damage by itself, but in combination with sunlight caused significant DNA damage to both genomes. PLRRP samples caused DNA damage to both genomes, and this was not increased by sunlight exposure, suggesting the DNA damage was unlikely the result of PAH phototoxicity. We report for the first time that PLRRP-associated pollutants cause both nuclear and mitochondrial DNA damage, and that fluoranthene-mediated phototoxicity results in similar levels of damage to the nuclear and mitochondrial genomes. These effects may be especially significant in sensitive marine ecosystems.

Valproate-induced teratogenesis in Japanese rice fish (Oryzias latipes) embryogenesis

Fertilized eggs of Japanese rice fish (medaka) at three developmental stages (Iwamatsu stages 4-30) were exposed to waterborne valproic acid (VPA) (0-80 mM) in hatching solution for 48 h. The amount of valproate to cause 50% mortality (IC(50)) is found to be developmental stage-specific. The embryos were more sensitive to valproate at early stages of development (Iwamatsu stages 4-10) than in the embryos in late stages (Iwamatsu stages 17-30). Valproate exposed embryos have microcephaly and disrupted cardiovasculature with delayed vessel circulation, thrombus formation, and slow heart rate. The hatching efficiency is also reduced by valproate exposure due to developmental delay. The mRNA analysis of nine genes belong to oxidative stress (catalase, gsr, gst), neurogenesis (iro3, wnt1, shh, otx2, nlgn3b) and cell cycle regulation (ccna2) have been done. It was observed that the genes belong to oxidative stress remained unaltered after valproate exposure. However, some of the genes belong to neurogenesis (wnt1,shh, otx2 and nlgn3b) and cell cycle (ccna2) showed developmental stage-specific alteration after valproate exposure. This study indicates that valproate is able to induce some of the phenotypic features which are analogous to human fetal valproate syndrome (FVS). Modulation of genes expressed in neural tissues indicates that this fish can be used to analyze the mechanisms of many neurobehavioral disorders like Autism spectrum disorder (ASD) in human.

Ethanol exposure induces upregulation of specific microRNAs in zebrafish embryos

Prenatal exposure to ethanol leads to a myriad of developmental disorders known as fetal alcohol spectrum disorder, often characterized by growth and mental retardation, central nervous system damage, and specific craniofacial dysmorphic features. The mechanisms of ethanol toxicity are not fully understood, but exposure during development affects the expression of several genes involved in cell cycle control, apoptosis, and transcriptional regulation. MicroRNAs (miRNAs) are implicated in some of these processes, however, it is not yet clear if they are involved in ethanol-induced toxicity. In order to clarify this question, we have exposed zebrafish embryos to ethanol and evaluated whether a miRNA deregulation signature could be obtained. Zebrafish embryos were exposed to 1 and 1.5% of ethanol from 4 h postfertilization (hpf) to 24 hpf. The miRNA expression profiles obtained reveal significant miRNA deregulation and show that both ethanol concentrations upregulate miR-153a, miR-725, miR-30d, let-7k, miR-100, miR-738, and miR-732. Putative gene targets of deregulated miRNAs are involved in cell cycle control, apoptosis, and transcription, which are the main processes affected by ethanol toxicity. The conservation of affected mechanisms among vertebrates leads us to postulate that similar miRNA deregulation occurs in humans, highlighting a relevant role of miRNAs in ethanol toxicology.

MicroRNA expression changes during zebrafish development induced by perfluorooctane sulfonate

Perfluorooctane sulfonate (PFOS), a kind of widely distributed environmentally organic compound, has been found to cause developmental toxicity. Although microRNAs (miRNAs) play an important role in many metabolic tasks, whether and how they are involved in the process of PFOS-induced toxicity is largely unknown. To address this problem, PFOS-induced changes in miRNAs and target gene expression in zebrafish embryos, and the potential mechanism of PFOS-induced toxic action were studied in this research. Zebrafish embryos were exposed to 1 µg ml(-1) PFOS or DMSO control from 6 h post-fertilization (hpf) to 24 or 120 hpf. Subsequently, RNA was isolated from the embryo pool and the expression profiles of 219 known zebrafish miRNAs were analyzed using microarray. Finally, quantitative real-time polymerase chain reaction was used to validate several miRNAs expression of microarray data. The analysis revealed that PFOS exposure induced significant changes in miRNA expression profiles. A total of 39 and 81 miRNAs showed significantly altered expression patterns after PFOS exposure 24 and 120 hpf. Of the changed miRNAs, 20 were significantly up-regulated and 19 were significantly down-regulated (p < 0.01) at 24 hpf, whereas 41 were significantly up-regulated and 40 were significantly down-regulated (p < 0.01) at 120 hpf. These miRNAs were involved in development, apoptosis and cell signal pathway, cell cycle progression and proliferation, oncogenesis, adipose metabolism and hormone secretion, whereas there is still little functional information available for 32 miRNAs. Our results demonstrate that PFOS exposure alters the expression of a suite of miRNAs and may induce developmental toxicity.

In utero beta 2 adrenergic agonist exposure and adverse neurophysiologic and behavioral outcomes

Beta 2 adrenergic receptor overstimulation during critical periods of prenatal development can induce a permanent shift in the balance of sympathetic-to-parasympathetic tone. This is a biologically plausible mechanism whereby beta 2 adrenergic agonists can induce functional and behavioral teratogenesis, which explains their association with increases in autism spectrum disorders, psychiatric disorders, poor cognitive, motor function and school performance, and changes in blood pressure in the offspring. The use of beta 2 adrenergic agonists should be limited to proven indications when alternate drugs are ineffective or unavailable; the risks of untreated disease to the mother and fetus are greater than the risk of the beta 2 adrenergic agonist.

6-mercaptopurine (6-MP) induces p53-mediated apoptosis of neural progenitor cells in the developing fetal rodent brain

6-mercaptopurine (6-MP), a DNA-damaging agent, induces apoptosis of neural progenitor cells, and causes malformation in the fetal brain. The aim of the present study is to clarify the molecular pathway of 6-MP-induced apoptosis of neural progenitor cells in the fetal telencephalon of rats and mice. p53 protein is activated by DNA damage and induces apoptosis through either the intrinsic pathway involving the mitochondria or the extrinsic pathway triggered by death receptors. In this study, the expression of puma and cleaved caspase-9 proteins, which are specific intrinsic pathway factors, increased in the rat telencephalon after 6-MP treatment. 6-MP-induced apoptosis of neural progenitor cells was completely absent in p53-deficient mice. On the other hand, the expression of Fas protein, an extrinsic pathway factor, did not change throughout the experimental period in the rat telencephalon treated with 6-MP. The number of apoptotic neural progenitor cells was similar among Fas-mutated lpr/lpr and wild-type mice, suggesting that the Fas pathway does not play a significant role in 6-MP-induced apoptosis of neural progenitor cells. These results may suggest that the p53-mediated intrinsic pathway is essential for 6-MP-induced apoptosis of neural progenitor cells in the developing telencephalon of rats and mice.

Molecular basis for skeletal variation: insights from developmental genetic studies in mice

Skeletal variations are common in humans, and potentially are caused by genetic as well as environmental factors. We here review molecular principles in skeletal development to develop a knowledge base of possible alterations that could explain variations in skeletal element number, shape or size. Environmental agents that induce variations, such as teratogens, likely interact with the molecular pathways that regulate skeletal development.

Perturbation of retinoic acid (RA)-mediated limb development suggests a role for diminished RA signaling in the teratogenesis of ethanol

BACKGROUND

A proposed mechanism for ethanol teratogenicity entails ethanol-mediated reductions in retinoic acid (RA). This premise was investigated utilizing a mouse model, with limb reduction defects as the teratogenic end point.

METHODS

Ethanol, Disulfiram, or BMS-189453 was administered to C57BL/6J mice on the 9(th) day of pregnancy. Forelimb morphology was assessed on gestation day 18 using Alcian blue and Alizarin red staining. Nile blue sulfate or LysoTracker Red (LTR) vital staining identified cell death in the limb bud. The ability of RA to prevent ethanol-induced cell death was assessed by coadministration followed by laser scanning confocal microscopic examination of LTR-staining. In situ hybridization and qPCR were used to examine gene expression in treated limb buds.

RESULTS

Ethanol, Disulfiram, and BMS-189453 resulted in postaxial ectrodactyly, intermediate ectrodactyly, and other digital defects. Excessive Nile blue sulfate staining was evident in the presumptive AER following each of the three exposures. Ethanol-induced LTR staining was prevented by RA supplementation. Both in situ hybridization and qPCR illustrated decreases in Shh and Tbx5 in ethanol-exposed embryos as compared to control.

CONCLUSIONS

Contrary to studies of prolonged RA deficiency, acute exposure to functional antagonists of RA results in limb defects that are morphologically similar to those caused by ethanol. The rescue of ethanol-induced cell death by RA and similar changes in Shh transcription further suggest that RA contributes to ethanol-induced limb dysmorphology. Moreover, the repression of key mediators of limb development soon after ethanol exposure adds to the existing knowledge of the pathogenic effects of ethanol.

The role of multiple drug resistance proteins in fetal and/or placental protection against teratogen-induced orofacial clefting

Previous studies have shown a role for multiple drug resistance proteins in protecting the fetus from a limited number of teratogens. We have expanded the number of proteins and teratogens examined by comparing the influence of the mdr1a and mdr2 proteins on teratogen-induced orofacial clefting using their respective knockouts in crosses with the A/J, high susceptibility strain. Western blots identified the presence of mdr1a and possibly mdr2 in the placenta and fetus. The mdr1a knockout, on its unique genetic background showed lower, similar, and higher incidences of clefting compared to A/J for Dilantin, hydrocortisone (HC), and 6-aminonicotinamide (6-AN), respectively. The mdr2 knockout did not affect 6-AN clefting when compared to A/J. In reciprocal crosses, when corrected for increased spontaneous clefting, maternally inherited A/J susceptibility genes predominated over the effects of the maternal absence of mdr1a (with 6-AN). Unlike mdr1a, which had a direct effect in the fetus as shown by genotyping of affected versus unaffected fetuses, an effect of mdr2 in the fetus was not found. The mdr1a knockout was backcrossed to the A/J inbred strain for 11 generations (congenics) to eliminate genetic background effects. Reciprocal crosses showed no maternal effect from the lack of mdr1a, confirming that mdr1a expression in the fetus, rather than the placenta, protects the fetus from teratogens. Mdr2 seems not to be involved in the protection of the fetus from teratogens.

Altered localization of gene expression in both ectoderm and mesoderm is associated with a murine strain difference in retinoic acid-induced forelimb ectrodactyly

BACKGROUND

Defects in digit number or fusion as a teratogenic response are well documented in humans and intensively studied in various mouse models. Maternal exposure to excess levels of all-trans-retinoic acid (RA) at gestational day 9.5 induces postaxial ectrodactyly (digit loss) in the murine C57BL/6N strain but not in the SWV/Fnn strain.

METHODS

Whole-mount in situ hybridization was used to examine the differential expression of limb patterning genes at the transcriptional level between the two mouse strains following the maternal exposure to a teratogenic level of RA. The detection of a gene with altered expression was followed by either the evaluation of other genes that were synexpressed or with an assessment of downstream genes.

RESULTS

In the C57BL/6N limb bud following maternal RA administration, gene-specific perturbations were observed within hours of the RA injection in the posterior pre-AER (apical ectodermal ridge) (Fgf8, Dlx3, Bmp4, Sp8, but not Dlx2 or p63), whereas these genes were normally expressed in the SWV/Fnn limb bud. Furthermore, although RA caused comparable reductions of Shh expression between the strains in the 12 h after administration, some Shh downstream genes were differentially expressed (e.g., Gli1, Ptc, and Hoxd13), whereas others were not (e.g., Fgf4, Bmp4, and Gremlin).

CONCLUSIONS

It is proposed that altered gene expression in both pre-AER and mesoderm is involved in the pathogenesis of postaxial digit loss, and that because the alterations in the pre-AER occur relatively early in the temporal sequence of events, those changes are candidates for an initiating factor in the malformation.

Antiepileptic medication during pregnancy: does fetal genotype affect outcome?

Congenital abnormalities and impaired development in childhood are attributable to fetal exposure to antiepileptic drugs (AEDs). Pregnancy registries set up to obtain information about the potential risks of fetal exposure to AEDs, in particular major congenital malformations (MCMs), suggest that valproate exposure increases the frequency of congenital malformations more than other AEDs. Furthermore, follow-up studies have drawn attention to cognitive impairments in later childhood after prenatal exposure to valproate. Fetal exposure to AEDs may be influenced by drug transporting proteins in the placenta, including P-glycoprotein (P-gp), multidrug resistance protein (MRP) 1, and breast cancer resistance protein (BCRP). Their location in the syncytiotrophoblast plasma membrane, at the interface of the maternal and fetal circulations, allows these transport proteins to efflux xenobiotics back to the mother and offers the fetus protection from medications taken during pregnancy. Genetic variations in the expression and activity of these transport proteins may influence fetal exposure to AEDs and thus the risk of teratogenicity. Identification of a hierarchy of haplotypes ranging from susceptible to protective of congenital abnormalities could assist genetic counseling, in assessing fetal risks from exposure to AEDs.

A new paradigm in toxicology and teratology: altering gene activity in the absence of DNA sequence variation

'Epigenetics' is a heritable phenomenon without change in primary DNA sequence. In recent years, this field has attracted much attention as more epigenetic controls of gene activities are being discovered. Such epigenetic controls ensue from an interplay of DNA methylation, histone modifications, and RNA-mediated pathways from non-coding RNAs, notably silencing RNA (siRNA) and microRNA (miRNA). Although epigenetic regulation is inherent to normal development and differentiation, this can be misdirected leading to a number of diseases including cancer. All the same, many of the processes can be reversed offering a hope for epigenetic therapies such as inhibitors of enzymes controlling epigenetic modifications, specifically DNA methyltransferases, histone deacetylases, and RNAi therapeutics. 'In utero' or early life exposures to dietary and environmental exposures can have a profound effect on our epigenetic code, the so-called 'epigenome', resulting in birth defects and diseases developed later in life. Indeed, examples are accumulating in which environmental exposures can be attributed to epigenetic causes, an encouraging edge towards greater understanding of the contribution of epigenetic influences of environmental exposures. Routine analysis of epigenetic modifications as part of the mechanisms of action of environmental contaminants is in order. There is, however, an explosion of research in the field of epigenetics and to keep abreast of these developments could be a challenge. In this paper, we provide an overview of epigenetic mechanisms focusing on recent reviews and studies to serve as an entry point into the realm of 'environmental epigenetics'.

Thoracic skeletal defects and cardiac malformations: a common epigenetic link?

Congenital heart defects (CHDs) are the most common birth defects in humans. In addition, cardiac malformations represent the most frequently identified anomaly in teratogenicity experiments with laboratory animals. To explore the mechanisms of these drug-induced defects, we developed a model in which pregnant rats are treated with dimethadione, resulting in a high incidence of heart malformations. Interestingly, these heart defects were accompanied by thoracic skeletal malformations (cleft sternum, fused ribs, extra or missing ribs, and/or wavy ribs), which are characteristic of anterior-posterior (A/P) homeotic transformations and/or disruptions at one or more stages in somite development. A review of other teratogenicity studies suggests that the co-occurrence of these two disparate malformations is not unique to dimethadione, rather it may be a more general phenomenon caused by various structurally unrelated agents. The coexistence of cardiac and thoracic skeletal malformations has also presented clinically, suggesting a mechanistic link between cardiogenesis and skeletal development. Evidence from genetically modified mice reveals that several genes are common to heart development and to formation of the axial skeleton. Some of these genes are important in regulating chromatin architecture, while others are tightly controlled by chromatin-modifying proteins. This review focuses on the role of these epigenetic factors in development of the heart and axial skeleton, and examines the hypothesis that posttranslational modifications of core histones may be altered by some developmental toxicants.

DEHP, bis(2)-ethylhexyl phthalate, alters gene expression in human cells: possible correlation with initiation of fetal developmental abnormalities

Diethylhexylphthalate (DEHP) is a widely distributed phthalate, to which humans are exposed to due to its variety of commercial and manufacturing uses. As a plasticiser, it is found in a wide number of products, and metabolites of DEHP have been detected in urine samples from a high percentage of the people screened for phthalates. We utilised DNA microarray analysis to evaluate DEHP for gene expression disrupting activity using the human cell line MCF-7, and found that DEHP significantly dysregulated approximately 34% of the 2400 genes spotted on the NEN2400 chip we used. The results suggest that DEHP, a known estrogen agonist and probable androgen antagonist, alters the expression of a number of genes, many of which are critical for fetal development. Down-regulation of two genes, FGD1 and PAFAH1B1, related in that both are essential for fetal brain development, was corroborated using quantitative real time PCR. These studies show DEHP to be a highly effective human gene expression-altering chemical, and that, at appropriate concentrations, it has the possibility of altering fetal central nervous system development, resulting in the birth defects lissencephaly and/or faciodigitogenital dysplasia.

Application of pharmacogenomic strategies to the study of drug-induced birth defects

Approximately 3% of all infants are born with one or more major birth defects, resulting in >150,000 affected babies each year in the US alone. At present, birth defects account for more than 21% of all infant deaths, making them the leading cause of infant mortality. Although the etiology and determinants of individual susceptibility are largely unknown for most congenital malformations, pharmacogenomic analyses offer promise for the future.

In utero exposure to tributyltin chloride differentially alters male and female fetal gonad morphology and gene expression profiles in the Sprague–Dawley rat

Tributyltin (TBT) is an environmental contaminant commonly used in anti-fouling agents for boats, as well as a by-product from several industrial processes. It has been shown to accumulate in organisms living in areas with heavy maritime traffic thereby entering the food chain. Here, we determined the consequences of in utero exposure to TBT on the developing fetal gonads in the Sprague-Dawley rat. Timed pregnant rats were gavaged either with vehicle or TBT (0.25, 2.5, 10 or 20 mg/kg) from days 0 to 19 or 8 to 19 of gestation. On gestational day 20, dams were sacrificed; fetal testes and ovaries were processed for light (LM) or electron microscopic (EM) evaluation and RNA was prepared for gene expression profiling. At the highest doses of TBT the number of Sertoli cells and gonocytes was reduced, there were large intracellular spaces between Sertoli cells and gonocytes and there was an increased abundance of lipid droplets in the Sertoli cells; EM studies revealed abnormally dilated endoplasmic reticulum in Sertoli cells and gonocytes. In the intertubular region between adjacent interstitial cells, immunostaining for the gap junctional protein connexin 43 was strong in controls, whereas it was reduced or completely absent in treated rats. In the ovaries, TBT (20 mg/kg, days 0-19; 10 mg/kg, days 8-19) reduced the number of germ cells by 44% and 46%, respectively. On examining gene expression profiles in the testis, 40 genes out of 1176 tested were upregulated more than two-fold over control. While no genes were upregulated in the TBT exposed fetal ovary, eight genes were downregulated. In conclusion, in utero exposure to TBT resulted in gender-specific alterations in gonadal development and gene expression profiles suggesting that there may be different adaptive changes to toxicity in developing male and female rats.

Intake of high levels of vitamin A and polyunsaturated fatty acids during different developmental periods modifies the expression of morphogenesis genes in European sea bass (Dicentrarchus labrax)

The effect of the feeding period on larval development was investigated in European sea bass larvae by considering the expression level of some genes involved in morphogenesis. Larvae were fed a control diet except during three different periods (period A: from 8 to 13 d post-hatching (dph); period B: from 13 to 18 dph; period C: from 18 to 23 dph) with two compound diets containing high levels of vitamin A or PUFA. European sea bass morphogenesis was affected by these two dietary nutrients during the early stages of development. The genes involved in morphogenesis could be modulated between 8 and 13 dph, and our results indicated that retinoids and fatty acids influenced two different molecular pathways that in turn implicated two different gene cascades, resulting in two different kinds of malformation. Hypervitaminosis A delayed development, reducing the number of vertebral segments and disturbing bone formation in the cephalic region. These malformations were correlated to an upregulation of retinoic acid receptor gamma, retinoid X receptor (RXR) alpha and bone morphogenetic protein (BMP)4. An excess of PUFA accelerated the osteoblast differentiation process through the upregulation of RXRalpha and BMP4, leading to a supernumerary vertebra. These results suggest that the composition of diets devoted to marine fish larvae has a particularly determining effect before 13 dph on the subsequent development of larvae and juvenile fish.

For dioxin-induced birth defects, mouse or human CYP1A2 in maternal liver protects whereas mouse CYP1A1 and CYP1B1 are inconsequential

Dioxin (2,3,7,8-tetrachlorodibenzo-p-dioxin) induces cleft palate and hydronephrosis in mice, when exposed in utero; these effects are mediated by the aryl hydrocarbon receptor. The Cyp1a1, Cyp1a2, and Cyp1b1 genes are up-regulated by the aryl hydrocarbon receptor. To elucidate their roles in dioxin-induced teratogenesis, we compared Cyp1a1(-/-), Cyp1a2(-/-), and Cyp1b1(-/-) knock-out mice with Cyp1(+/+) wild-type mice. Dioxin was administered (25 microg/kg, gavage) on gestational day 10, and embryos were examined on gestational day 18. The incidence of cleft palate and hydronephrosis was not significantly different in fetuses from Cyp1a1(-/-), Cyp1b1(-/-), and Cyp1(+/+) wild-type mice. To fetuses carried by Cyp1a2(-/-) dams, however, this dose of dioxin was lethal; this effect was absolutely dependent on the maternal Cyp1a2 genotype and independent of the embryonic Cyp1a2 genotype. Dioxin levels were highest in adipose tissue, mammary gland, and circulating blood of Cyp1a2(-/-) mothers, compared with that in the Cyp1(+/+) mothers, who showed highest dioxin levels in liver. More dioxin reached the embryos from Cyp1a2(-/-) dams, compared with that from Cyp1(+/+) dams. Fetuses from Cyp1a2(-/-) dams exhibited a approximately 6-fold increased sensitivity to cleft palate, hydronephrosis, and lethality. Using the humanized hCYP1A1_1A2 transgenic mouse (expressing the human CYP1A1 and CYP1A2 genes in the absence of mouse Cyp1a2 gene), the teratogenic effects of dioxin reverted to the wild-type phenotype. These data indicate that maternal mouse hepatic CYP1A2, by sequestering dioxin and thus altering the pharmacokinetics, protects the embryos from toxicity and birth defects; substitution of the human CYP1A2 trans-gene provides the same protection. In contrast, neither CYP1A1 nor CYP1B1 appears to play a role in dioxin-mediated teratogenesis.

Gene-environment interactions in rare diseases that include common birth defects

Rare syndromes often feature specific types of birth defects that frequently are major diagnostic clues to the presence of a given disorder. Despite this specificity, not everyone with the same syndrome is equally or comparably affected, and not everyone with a specific birth defect manifests the same syndrome or is affected with all the features of a particular syndrome. A symposium sponsored by the National Institutes of Health Office of Rare Diseases, and the National Toxicology Program Center for the Evaluation of Risks to Human Reproduction attempted to explore how much of this variability is due to genetic factors and how much is due to environmental factors. The specific types of birth defects examined included cardiovascular defects, holoprosencephaly, clefts of the lip and/or palate, neural tube defects, and diaphragmatic hernias.

Valproic acid-induced skeletal malformations: associated gene expression cascades

OBJECTIVES

Valproic acid (VPA) is a widely used anticonvulsant medication with well-known teratogenic effects in both humans and in experimental animal model systems. The most commonly observed malformations induced by VPA in experimental animals include neural and skeletal defects. In this study the potential alterations in somitic tissue gene expression relative to the development of observed axial skeletal defects were examined.

METHODS

SWV mice were treated at 8.5 days post coitum (d.p.c.) with 1.36 mmol/kg or 2.72 mmol/kg VPA by i.p. injection. At 18.5 d.p.c., animals were killed and stained for morphological and skeletal examination. Cervical malformations consisting of vertebral fusions and cervical ribs were consistently observed. Phenotypic analysis confirmed the presence of dose-dependent axial skeletal malformations induced by in-utero VPA-exposure. Using antisense RNA amplification and cDNA microarrays, we examined the expression of approximately 5700 genes in the first six postotic somites of control and treated embryos at 6, 12, 18 and 24 h after the 8.5 d.p.c. VPA treatment.

RESULTS

Analysis indicated that several ontological groups (e.g. histone deacetylase complex, guanosine triphosphatases, cell proliferation and cytoskeletal) have significantly enriched gene expression changes in response to the teratogenic insult. The RNA from 6 h post-treatment was also subjected to a microarray cross-platform validation, and genes identified on both platforms are presented.

CONCLUSION

These data were then used to deduce candidate cellular pathways that may be responsible for the VPA-induced teratogenic skeletal phenotypes.

Transgenerational effects of radiation and chemicals in mice and humans

Parental exposure of mice to radiation and chemicals causes a variety of adverse effects (e.g., tumors, congenital malformations and embryonic deaths) in the progeny and the tumor-susceptibility phenotype is transmissible beyond the first post-radiation generation. The induced rates of tumors were 100-fold higher than those known for mouse specific locus mutations. There were clear strain differences in the types of naturally-occurring and induced tumors and most of the latter were malignant. Another important finding was that germ-line exposure elicited very weak tumorigenic responses, but caused persistent hypersensitivity in the offspring for the subsequent development of cancer by the postnatal environment. Activations of oncogenes, ras, mos, abl, etc. and mutations in tumor suppressor genes such as p53 were also detected in specific tumors in cancer-prone descendants. However, the majority of tumors observed in the progeny were those commonly observed in the strains that were used and oncogene activations were rarely observed in these tumors. It can be hypothesized that genetic instability modifies tumor occurrence in a transgenerational manner, but so far no links could be established between chromosomal and molecular changes and transmissible tumor risks. Our data are consistent with the hypothesis that cumulative changes in many normal but cancer-related genes affecting immunological, biochemical and physiological functions may slightly elevate the incidence of tumors or fasten the tumor development. This hypothesis is supported by our GeneChip analyses which showed suppression and/or over-expression of many such genes in the offspring of mice exposed to radiation. In humans, a higher risk of leukemia and birth defects has been reported in the children of fathers who had been exposed to radionuclides in the nuclear reprocessing plants and to diagnostic radiation. These findings have not been supported in the children of atomic bomb survivors in Hiroshima and Nagasaki, who were exposed to higher doses of atomic radiation. However, it will be important to follow the human subjects, especially for adult type cancers and chronic diseases throughout their lives to determine whether the mouse studies can predict human responses.

Cocaïne et trisomie 8 associées au diagnostic prénatal d’agénésie du corps calleux

We report the case of a newborn presenting an agenesis of corpus callosum (ACC) discovered in the prenatal period and initially related to cocaine exposure during the first trimester of gestation. The cytogenetic analysis revealed a trisomy 8 mosaicism. The putative role of prenatal cocaine exposure and mosaicism for chromosome 8 in ACC are discussed. This report emphasizes the specific analysis of chromosome 8 by using fluorescence in situ hybridization as a complement to routine cytogenetic analysis for prenatal diagnosis of ACC.

Hypervitaminosis A resulting in DNA aberration in fetal transgenic mice (Muta Mouse)

Treatment with excessive amounts of Vitamin A during maternity induces fetal malformations. However, it is unclear whether these malformations are due to gene mutations or not. Using transgenic mice (containing lacZ gene showing beta-galactosidase enzymatic activity), we planned to observe whether gene mutations occur in the fetal tissues after treatment during maternity with Vitamin A (retinol palmitate). On the 11th day of pregnancy, mothers were given 30 mg (group 2), 150 mg (group 3) and 300 mg (group 4) of Vitamin A/kg body weight orally. Fetuses obtained on the 18th day of gestation showed malformations, such as cleft palate, origodactyly, brachydactyly and ectromeria. Most notably, cleft palate occurred dose dependently. The incidental rates were 100% in group 4, 58% in group 3 and 6% in group 2. The number of dead and absorbed fetuses also increased dose dependently with the treatments. DNA (integrated vectors containing lacZ genes) extracted from each fetus showed Vitamin A-induced lacZ mutations, especially in the malformed fetuses. The mutation frequencies were 4.99x10(-5) in group 4, 5.28x10(-5) in group 3 and 4.26x10(-5) in group 2. The frequencies of group 3 were significantly higher (p<0.05) than that of the controls (group 1), 2.79x10(-5). Maternal treatment with Vitamin A (150 mg/kg of body weight) was carried out on the 11th day of pregnancy. Fetuses obtained on the 14th day of gestation showed a much higher incidence of mutation, approximately 8.91x10(-5) (group 6) that was significantly higher (p<0.0001) than those from the controls (group 5), 2.94x10(-5). The present study indicates a possibility that hypervitaminosis A-induced fetal malformation and death might be caused by gene mutations.

Identification of early-responsive genes correlated to valproic acid-induced neural tube defects in mice

BACKGROUND

Valproic acid (VPA) causes the failure of neural tube closure in newborn mice. However, the molecular mechanism of its teratogenesis is unknown. This study was conducted to investigate the genomewide effects of VPA disruption of normal neural tube development in mice.

METHODS

Microarray analysis was performed on the head part of NMRI mouse embryos treated for 1 hr with VPA on gestational day (GD) 8. Subsequently, we attempted to isolate genes that changed in correlation with the teratogenic action of VPA by employing reduced teratogenic VPA analogs, valpromide (VPD) and valnoctamide (VCD), in a real-time PCR study.

RESULTS

Microarray results demonstrated that during neurulation, many genes, some of whose functions are known and some unknown, were either increased or decreased after VPA injection. Some genes were affected by VPD or VCD in the same way as VPA, but others were not changed by the analogs. In this way, our system identified 11 increased and 20 decreased genes. Annotation analysis revealed that the increased genes included gadd45b, ier5, per1, phfl3, pou3f1, and sox4, and the decreased genes included ccne2, ccnl, gas5, egr2, sirt1, and zfp105.

CONCLUSIONS

These findings demonstrate that expression changes in genes having roles in the cell cycle and apoptosis pathways of neural tube cells were strongly expected to relate to the teratogenic, but not antiepileptic, activity of VPA. Our approach has allowed the expansion of the catalog of molecules immediately affected by VPA in the developing neural tube.

Vertebral malformations induced by sodium salicylate correlate with shifts in expression domains of Hox genes

Several embryotoxic agents, which includes sodium salicylate, were reported to induce vertebral variations in the form of supernumerary ribs (SNR) when administered to pregnant rodents. Because the biological significance of SNR in toxicological studies is still a matter of debate, we investigated the molecular basis of this defect by analyzing the possible involvement of Hox genes, known to specify vertebrae identity. Sodium salicylate (300mg/kg) was administered to pregnant rats on gestational day 9 (GD 9). On GD 13, the expression of several Hox genes, selected according to the position of their anterior limit of expression, namely upstream (Hoxa9), at the level (Hoxa10) and downstream (Hoxd9) to the morphological alteration, were analyzed. Posterior shifts in the anterior limit of expression of Hoxa10 and Hoxd9 were observed following exposure to salicylate, which could explain an effect at the level of the axial skeleton. This finding suggests that the appearance of ectopic ribs can be attributed to an anterior transformation of lumbar vertebrae identity into thoracic vertebrae identity. Whether this transformation occurs with all compounds inducing SNR in rats remains to be determined.

Insulinlike growth factor I gene expression is increased in the fetal lung after tracheal ligation

BACKGROUND/PURPOSE

The mortality and morbidity in congenital diaphragmatic hernia are mainly caused by pulmonary hypoplasia. To improve clinical results, further methods inducing lung growth may have to be used. The aim of this report was to evaluate the expression of insulinlike growth factor I (IGF-I), estrogen receptor alpha, estrogen receptor beta, growth hormone receptor, and thioredoxin in a rat model of hypoplastic, hyperplastic, and normal fetal lungs to improve understanding of lung growth.

METHODS

Hypoplastic diaphragmatic hernia lungs were created by giving nitrofen by gavage to pregnant rats on day 9.5. Hyperplastic lungs were achieved by intrauterine tracheal ligation of rat fetuses on day 19. All lungs were harvested on gestational day 21. Total nucleic acids were extracted by proteinase K digestion and extraction in phenol/chloroform. The total nucleic acids mixture was hybridized with radioactively labeled RNA probes, and the radioactivity of the hybrids was compared with the respective standard curve of known amounts of in vitro synthesized mRNA. Immunohistochemistry staining was performed for IGF-I.

RESULTS

The IGF-I mRNA was significantly (P < .01) higher in hyperplastic lungs compared with control and hypoplastic lungs. The latter 2 did not differ. No difference was found between the other mRNA levels in the study groups.

CONCLUSIONS

IGF-I is involved in the accelerated lung growth seen after intrauterine tracheal ligation.

Platinum toxicity and gene expression in Xenopus embryos: analysis by FETAX and differential display

Since the level of platinum in the environment is destined to increase, because of its use in vehicle catalytic converters, the toxicity of platinum needs further investigation. In this study, the frog embryo teratogenesis assay-Xenopus (FETAX) was used to compare the embryotoxicity and teratogenicity of two common platinum species, (NH4)2PtCl4 and (NH4)2PtCl6. The uptake rates of the two platinum species were studied, and also their effects on the expression of genes encoding metallothionein and heat-shock protein 70, which are known to be induced by several stress factors. In addition, the differential display technique was used to search for genes that were specifically induced by platinum. A gene for the type I collagen alpha-chain and a novel gene were identified.

Evaluation of two methods for assessing gene-environment interactions using data from the Danish case-control study of facial clefts

BACKGROUND

Epidemiological investigations have begun to consider gene-environment (GE) interactions as potential risk factors for many diseases, including several different birth defects. However, traditional methodological approaches for the analysis of case-control data tend to have low power for detection of interaction effects. A log-linear approach that can impose the assumption that the genotype and exposure of interest occur independently in the population has been proposed as a potentially more powerful method for assessing GE interactions but has not been widely applied in the published literature.

METHODS

The present analyses were undertaken to compare the results obtained when stratified analyses and a log-linear approach were used to assess potential GE interactions. The analyses were conducted using data from a population-based, case-control study conducted in Denmark and considered associations between nonsyndromic cleft lip with or without cleft palate (CL+/-P), infant genotype for variants of RAR-alpha, TGF-alpha, TGF-beta3, and MSX1, and maternal exposure to smoking, alcohol, and multivitamins.

RESULTS

Neither the stratified nor the log-linear analyses provided evidence that that risk of CL+/-P is influenced by any of the GE interactions that were evaluated, despite the potential increase in power offered by the latter approach. Further, the analyses highlight concerns regarding the power to reject the assumption of independence of the genetic and environmental factor of interest in the controls and related concerns regarding the validity of results obtained using the log-linear approach when the underlying assumption is violated.

CONCLUSIONS

The potential increase in power offered by the log-linear approach is offset by concerns regarding the validity of this approach when the independence assumption is violated.

ARNT2 is not required for TCDD developmental toxicity in zebrafish

ZfAHR2 has been identified as the receptor that is essential for mediating the developmental toxicity caused by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in zebrafish. One form of zfARNT2, zfARNT2b, forms a functional heterodimer with zfAHR2 that specifically recognizes XREs in gel shift experiments and induces XRE-driven transcription in COS-7 cells treated with TCDD. However, it has not been demonstrated that zfARNT2b acts as the physiological dimerization partner for zfAHR2 to mediate TCDD toxicity in developing zebrafish. An antisense morpholino targeted against zfARNT2 (zfarnt2-MO) along with a line of mutant zebrafish lacking expression of the zfarnt2 gene have been used to test the hypothesis that zfARNT2 mediates the developmental toxicity of TCDD. Injection of the zfarnt2-MO decreased expression of the zfARNT2 protein but did not provide any protection against the formation of pericardial edema at 72 hpf. In addition, in TCDD dose response studies the zfarnt2(-/-) embryos showed no protection against three endpoints of TCDD toxicity observed at 96 hpf: pericardial edema, reduced trunk blood flow, and shortened lower jaw. Finally, immunostaining results at 96 hpf demonstrate that the zfarnt2(-/-) embryos show a similar pattern of TCDD-induced zfCYP1A expression as WT embryos. These results demonstrate that zfARNT2 is not essential for mediating TCDD developmental toxicity in zebrafish and suggest that alternate dimerization partner(s) exist for zfAHR2 in vivo.

Clinical aspects of the MDR1 (ABCB1) gene polymorphism

Transporter proteins, in particular P-glycoprotein (Pgp), are important determinants in absorption, tissue targeting, and elimination of drugs. In addition to physiological and environmental factors, its expression and function are modified by genetic polymorphisms of the MDR1 gene. So far, several MDR1 SNPs have been identified, and mutations at positions 2677 and 3435 were associated with alteration of Pgp expression and/or function. In contrast to drug-metabolizing enzymes (eg, CYP2D6), for which loss of function mutations or gene amplification manifests as distinct phenotypes in the population, the impact of MDR1 polymorphisms on pharmacokinetics and pharmacodynamics of Pgp substrates is moderate. Clinical studies on the effects of the C3435T polymorphism and drug treatment with cardiac glycosides, the immunosuppressants cyclosporine and tacrolimus, HIV protease inhibitors, and tricyclic antidepressants are discussed.

Transgenerational transmission of radiation- and chemically induced tumors and congenital anomalies in mice: studies of their possible relationship to induced chromosomal and molecular changes

This article provides a broad overview of our earlier studies on the induction of tumors and congenital anomalies in the progeny of X-irradiated or chemically treated mice and our subsequent (published, hitherto unpublished and on-going) investigations aimed at identifying potential relationships between genetic changes induced in germ cells and the adverse effects manifest as tumors and congenital anomalies using cytogenetic and molecular approaches. The earlier studies document the fact that tumors and congenital anomalies can be induced by irradiation or treatment with certain chemicals such as urethane and that these phenotypes are heritable i.e., transmitted to generations beyond the first generation. These findings support the view that transmissible induced genetic changes are involved. The induced rates of congenital abnormalities and tumors are about two orders of magnitude higher than those recorded in the literature from classical mutation studies with specific locus mutations. The cytogenetic studies addressed the question of whether there were any relationships between induced translocations and induced tumors. The available data permit the inference that gross chromosomal changes may not be involved but do not exclude smaller induced genetic changes that are beyond the resolution of the techniques used in these studies. Other work on possible relationship between visible chromosomal anomalies (in bone marrow preparations) and tumors were likewise negative. However, there were indications that some induced cytogenetic changes might underlie induced congenital anomalies, i.e., trisomies, deletions and inversions were observed in induced and transmissible congenital anomalies (such as dwarfs, tail anomalies). Studies that explored possible relationships between induction of minisatellite mutations at the Pc-3 locus and tumors were negative. However, gene expression analysis of tumor (hepatoma)-susceptible offspring of progeny descended from irradiated male mice showed abnormal expression of many genes. Of these, only very few were oncogenes. This lends some support to our hypothesis that cumulative changes in gene expression of many genes, which perform normal cellular functions, may contribute to the occurrence of tumors in the offspring of irradiated or chemically treated mice.

Adriamycin induces notochord hypertrophy with conservation of sonic hedgehog expression in abnormal ectopic notochord in the adriamycin rat model

BACKGROUND/PURPOSE

The Adriamycin rat model (ARM) is a well-established model of the Vertebral, Anorectal, Cardiac, Tracheoesophageal, Renal, Limb (VACTERL) association. The notochord, which expresses Sonic Hedgehog (Shh), has been found to be grossly malformed with ventral ectopic branches in the foregut region of embryos in the ARM. The authors designed this study to test the hypothesis that Shh-expressing ectopic notochord could contribute to an increased volume of notochord relative to total embryo volume, resulting in an increased concentration of Shh in the notochord of affected embryos.

METHODS

Adriamycin was administered intraperitoneally to rats on days 7 (E7), E8, and E9 of gestation and saline to control animals. Embryos recovered at E12 and E14 were examined immunohistochemically for Shh expression. Quantitative morphology using the Cavalieri technique was performed to determine embryo and notochord volume.

RESULTS

Embryos in both Adriamycin and control groups at E12 and E14 showed comparable levels of Shh expression in notochord at all locations. The percentage of notochord per embryo was significantly increased in Adriamycin embryos at E12 and E14 compared with equivalent controls.

CONCLUSIONS

These data suggest that Adriamycin induces notochord hypertrophy. With all regions of the notochord secreting Shh, this could result in a higher concentration gradient of Shh in close abnormal proximity to the foregut, possibly contributing to the malformations found in the VACTERL association.

Gene-Teratogen Interactions in Chemically Induced Congenital Malformations

Exposure of the embryo to environmental chemicals can result in congenital malformations or abortion. Although experimental teratology data are considered sufficient for risk assessment, only knowledge of their mechanisms of action permits a justifiable extrapolation of animal data to humans. Mechanistic studies of some teratogenic agents such as retinoic acids, valproic acid, diethylstilbestrol, and cyclopamine provided evidence of interference with regulation of genes controlling the embryonic development. The new genomic technologies are important tools in this field and may represent a real improvement in understanding the mechanisms of action of chemical teratogens.

Reproductive toxicity evaluation of dietary butyl benzyl phthalate (BBP) in rats

Butyl benzyl phthalate (BBP) was administered in the diet at 0, 750, 3750, and 11,250 ppm ad libitum to 30 rats per sex per dose for two offspring generations, one litter/breeding pair/generation, through weaning of F2 litters. Adult F0 systemic toxicity and adult F1 systemic and reproductive toxicity were present at 11,250 ppm (750 mg/kg per day). At 11,250 ppm, there were reduced F1 and F2 male anogenital distance (AGD) and body weights/litter during lactation, delayed acquisition of puberty in F1 males and females, retention of nipples and areolae in F1 and F2 males, and male reproductive system malformations. At 3750 ppm (250 mg/kg per day), only reduced F1 and F2 offspring male AGD was present. There were no effects on parents or offspring at 750 ppm (50 mg/kg per day). The F1 parental systemic and reproductive toxicity no observable adverse effect level (NOAEL) was 3750 ppm. The offspring toxicity NOAEL was 3750 ppm. The offspring toxicity no observable effect level (NOEL) was 750 ppm, based on the presence of reduced AGD in F1 and F2 males at birth at 3750 ppm, but no effects on reproductive development, structures, or functions.

Axial skeletal and hox expression domain alterations induced by retinoic acid, valproic acid, and bromoxynil during murine development

Retinoic acid (RA) alters the developmental fate of the axial skeletal anlagen. "Anteriorizations" or "posteriorizations," the assumption of characteristics of embryonic areas normally anterior or posterior to the affected tissues, are correlated with altered embryonal expression domains of Hox genes after in utero RA treatment. These "homeotic" changes have been hypothesized to result from alterations of a "Hox cod" which imparts positional identity in the axial skeleton. To investigate whether such developmental alterations were specific to RA, or were a more general response to xenobiotic exposure, CD-1 pregnant mice were exposed to RA, valproic acid (VA), or bromoxynil (Br) during organogenesis. Additionally, the expression domains of two Hox genes, Hoxa7 and Hoxa10, were examined in gestation day (GD) 12.5 embryos obtained from control, RA, VA, or Br, treated gravid dams exposed on GD 6, 7, or 8. The anterior expression boundary of Hoxa7 is at the level of the C7/T1 vertebrae and that of Hoxa10 is at L6/S1. Compound-induced changes in the incidence of skeletal variants were observed. These included supernumerary cervical ribs (CSNR) lateral to C7, 8 vertebrosternal ribs, supernumerary lumbar ribs (LSNR) lateral to L1, extra presacral vertebrae, and the induction of vertebral and/or rib malformations. RA and VA administration on GD 6 caused posteriorization in the cervico-thoracic region (CSNR) while GD 8 exposure to any of the three compounds resulted in anteriorizations in the thoraco-lumbar area (LSNR and an increase in the number of presacral vertebrae). These effects occurred across regions of the axial skeleton. Analysis of gene expression demonstrated changes in the anterior boundaries of Hoxa7 expression domains in embryos treated on GD 6 and 8 with RA. VA and Br did not induce any statistically significant alterations in Hoxa7 and none of the compounds caused alterations in Hoxa10 expression domains. The studies indicate that RA GD 6 treatment-induced Hoxa7 shifts were rostral (posteriorization) while the RA-induced GD 8 anterior expression boundary shift was caudal (anteriorization), correlating with the axial skeletal changes noted. These data suggest that xenobiotic compounds such as VA and Br may induce similar axial skeletal changes by affecting different components of the developmental processes involved in the patterning of the axial skeleton.

Role of aryl hydrocarbon receptor in mesencephalic circulation failure and apoptosis in zebrafish embryos exposed to 2,3,7,8-tetrachlorodibenzo-p-dioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a persistent and potent developmental toxicant in various animals, with developing fish being the most sensitive organisms. Although the expression of aryl hydrocarbon receptor (AHR) as well as the partner molecule, AHR nuclear translocator (ARNT) in the brain has been reported, the effect of TCDD on the brain remains to be clarified in detail. Previously, we reported local circulation failure and apoptosis in dorsal midbrain caused by TCDD in developing zebrafish. In the present experiments, we investigated the effects of morpholino antisense oligos against aryl hydrocarbon receptor 2 (zfAHR2) (AHR2-MO) on toxicological endpoints caused by TCDD in developing zebrafish. AHR2-MO but not its negative homologue (4mis-AHR2-MO) improved TCDD-evoked circulation failure in mesencephalic vein and reduced the occurrence of apoptosis in dorsal midbrain, with concomitant inhibition of CYP1A induction in vascular endothelium. Injection of bovine serum albumin (BSA) into the general circulation, followed by immunohistochemistry with anti-BSA, showed that TCDD raised vascular permeability to albumin in dorsal midbrain, which was blocked by AHR2-MO and N-acetlycystein. In the absence of TCDD, development of embryos injected with AHR2-MO appeared normal at least until 60 h after fertilization. It is concluded that AHR2 activation in the vascular endothelium of the zebrafish embryo midbrain is involved in the mesencephalic circulation failure and apoptosis elicited by TCDD. This is the further evidence that vascular endothelium is the target of TCDD in relation to local circulation failure and apoptosis in dorsal midbrain.

Lack of Expression of EGF and TGF- in the Fetal Mouse Alters Formation of Prostatic Epithelial Buds and Influences the Response to TCDD

In utero, 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure causes abnormal ventral, dorsolateral, and anterior prostate development in C57BL/6J mice. Androgens, mesenchymal-epithelial interactions, and growth factor expression all have roles in initiating and regulating development and growth of the prostate. Epidermal growth factor (EGF) and transforming growth factor alpha (TGF-alpha), both of which bind the EGF receptor (EGFR), are expressed in human and rodent developing prostate. This study examines the influence of null expression of EGF and/or TGF-alpha on prostatic bud development and on the ability of TCDD to inhibit prostatic budding. Growth factor knockout (-/-) and wild-type (WT) mice were exposed either to vehicle or to TCDD (0, 0.2, 1, 5, 10, 50, 100, or 150 microg/kg) on gestation day (GD) 12. The number of anterior, dorsal, and lateral prostatic buds (ADLB) and ventral buds (VB) were counted on GD 17.5. Control WT and EGF (-/-) fetuses had similar numbers of ADLB and VB. In control TGF-alpha (-/-) fetuses, the number of ADLBs was higher relative to the C57BL/6J. Control EGF + TGF-alpha (-/-) had poor bud outgrowth, especially in the ADL region. TCDD induced a dose-related decrease in bud formation in all strains with the formation of VBs being more sensitive than ADLBs. The severity of the response depended on growth factor expression, with the most severe effects on VBs in the EGF (-/-) and on ADLBs in the EGF + TGF-alpha (-/-) fetuses. TGF-alpha (-/-) and C57BL/6J fetuses responded to TCDD similarly. In conclusion, EGF and TGF-alpha expression are important for the formation of ADLBs and VBs, and expression of EGF and TGF-alpha affects the ability of TCDD to inhibit prostatic bud formation in a region-specific manner.

Developmental toxicity evaluation of the new fluoroquinolone antibacterial DW-116 in rats

We have recently reported that the fluoroquinolone antibacterial DW-116 induces a significant developmental toxicity in rat. The present study was conducted to better understand the teratogenic effects of DW-116 at several developmental toxic doses in rats. DW-116 was orally administered to pregnant rats from gestational day (GD) 6 through 16 at dose levels of 0, 320, 400, and 500 mg/kg/day. All dams were subjected to caesarean section on GD 20 and their fetuses were examined for external, visceral, and skeletal abnormalities. At above 400 mg/kg, severe decreases in maternal body weight gain, food consumption, litter size, fetal weight and placental weight, and severe increases in resorption rate and fetal morphological alterations were observed. At 320 mg/kg, mild decreases in maternal body weight gain, food consumption, fetal weight and placental weight, and mild increases in fetal variations and retardations were observed. These results suggest that DW-116 is embryotoxic at above 320 mg/kg/day and is embryolethal and teratogenic at above 400 mg/kg in pregnant rats and that DW-116 is a selective developmental toxicant in rat conceptuses.

Modulation of p53 after maternal exposure to all-trans-retinoic acid in Swiss Webster mouse fetuses

The response to exposure of all-trans-retinoic acid (RA) during development varies from physiologic to severe teratogenic outcomes and is dependent upon the dose and the stage of development in all species. Effects of RA-mediated teratogenesis may be due to its ability to cause apoptosis. We have recently reported the modulation of p53 in murine stem cells by RA. The aim of this study was to characterize the temporal and spatial pattern of p53 expression in Swiss Webster mouse fetuses following maternal treatment with a single oral dose of 100 mg/kg body weight of RA during organogenesis. RA treatment resulted in a decreased p53 mRNA level in fetuses 24, 48, and 72 h after maternal treatment as detected by semiquantitative reverse transcriptase polymerase chain reaction. Western blot analysis showed a decrease in p53 protein at 24 and 48 h. Immunohistochemistry revealed decreased localization of p53 in the neuroepithelium of fetuses exposed to RA in utero. RA treatment also resulted in decreased nuclear p21 and decreased expression of cytosolic as well as nuclear p27 at 72 h in the fetuses. These results demonstrated that RA-mediated teratogenesis is accompanied by a reduction in the temporal and spatial pattern of p53 gene and protein expression in addition to the disruption of the cell cycle by modulation of p21 and p27.