Early molecular effects of ethanol during vertebrate embryogenesis

Alcohol induces neural tube defects by reducing retinoic acid signaling and promoting neural plate expansion

Introduction: Neural tube defects (NTDs) are among the most debilitating and common developmental defects in humans. The induction of NTDs has been attributed to abnormal folic acid (vitamin B9) metabolism, Wnt and BMP signaling, excess retinoic acid (RA), dietary components, environmental factors, and many others. In the present study we show that reduced RA signaling, including alcohol exposure, induces NTDs. Methods: Xenopus embryos were exposed to pharmacological RA biosynthesis inhibitors to study the induction of NTDs. Embryos were treated with DEAB, citral, or ethanol, all of which inhibit the biosynthesis of RA, or injected to overexpress Cyp26a1 to reduce RA. NTD induction was studied using neural plate and notochord markers together with morphological analysis. Expression of the neuroectodermal regulatory network and cell proliferation were analyzed to understand the morphological malformations of the neural plate. Results: Reducing RA signaling levels using retinaldehyde dehydrogenase inhibitors (ethanol, DEAB, and citral) or Cyp26a1-driven degradation efficiently induce NTDs. These NTDs can be rescued by providing precursors of RA. We mapped this RA requirement to early gastrula stages during the induction of neural plate precursors. This reduced RA signaling results in abnormal expression of neural network genes, including the neural plate stem cell maintenance genes, geminin, and foxd4l1.1. This abnormal expression of neural network genes results in increased proliferation of neural precursors giving rise to an expanded neural plate. Conclusion: We show that RA signaling is required for neural tube closure during embryogenesis. RA signaling plays a very early role in the regulation of proliferation and differentiation of the neural plate soon after the induction of neural progenitors during gastrulation. RA signaling disruption leads to the induction of NTDs through the mis regulation of the early neuroectodermal network, leading to increased proliferation resulting in the expansion of the neural plate. Ethanol exposure induces NTDs through this mechanism involving reduced RA levels.

Genetically programmed retinoic acid deficiency during gastrulation phenocopies most known developmental defects due to acute prenatal alcohol exposure in FASD

Fetal Alcohol Spectrum Disorder (FASD) arises from maternal consumption of alcohol during pregnancy affecting 2%-5% of the Western population. In Xenopus laevis studies, we showed that alcohol exposure during early gastrulation reduces retinoic acid (RA) levels at this critical embryonic stage inducing craniofacial malformations associated with Fetal Alcohol Syndrome. A genetic mouse model that induces a transient RA deficiency in the node during gastrulation is described. These mice recapitulate the phenotypes characteristic of prenatal alcohol exposure (PAE) suggesting a molecular etiology for the craniofacial malformations seen in children with FASD. Gsc ^+/Cyp26A1 mouse embryos have a reduced RA domain and expression in the developing frontonasal prominence region and delayed HoxA1 and HoxB1 expression at E8.5. These embryos also show aberrant neurofilament expression during cranial nerve formation at E10.5 and have significant FASD sentinel-like craniofacial phenotypes at E18.5. Gsc ^+/Cyp26A1 mice develop severe maxillary malocclusions in adulthood. Phenocopying the PAE-induced developmental malformations with a genetic model inducing RA deficiency during early gastrulation strongly supports the alcohol/vitamin A competition model as a major molecular etiology for the neurodevelopmental defects and craniofacial malformations seen in children with FASD.

HCN2 Channel-induced Rescue of Brain, Eye, Heart, and Gut Teratogenesis Caused by Nicotine, Ethanol, and Aberrant Notch Signaling

Organogenesis is a complex process that can be disrupted by embryonic exposure to teratogens or mutation-induced alterations in signaling pathways, both of which result in organ mispatterning. Building on prior work in Xenopus laevis that showed that increased HCN2 ion channel activity rescues nicotine-induced brain & eye morphogenesis, we demonstrate much broader HCN2-based rescue of organ patterning defects. Induced HCN2 expression in both local or distant tissues can rescue CNS (brain & eye) as well as non-CNS (heart, & gut) organ defects induced by three different teratogenic conditions: nicotine exposure, ethanol exposure, or aberrant Notch protein. Rescue can also be induced by small-molecule HCN2 channel activators, even with delayed treatment initiation. Our results suggest that HCN2 (likely mediated by bioelectric signals) can be an effective regulator of organogenesis from all three germ layers (ectoderm, mesoderm, and endoderm) and reveal non-cell-autonomous influences on organ formation that work at considerable distance during embryonic development. These results suggest molecular bioelectric strategies for repair that could be explored in the future for regenerative medicine. This article is protected by copyright. All rights reserved.

Retinoic Acid is Required for Normal Morphogenetic Movements During Gastrulation

Retinoic acid (RA) is a central regulatory signal that controls numerous developmental processes in vertebrate embryos. Although activation of Hox expression is considered one of the earliest functions of RA signaling in the embryo, there is evidence that embryos are poised to initiate RA signaling just before gastrulation begins, and manipulations of the RA pathway have been reported to show gastrulation defects. However, which aspects of gastrulation are affected have not been explored in detail. We previously showed that partial inhibition of RA biosynthesis causes a delay in the rostral migration of some of the earliest involuting cells, the leading edge mesendoderm (LEM) and the prechordal mesoderm (PCM). Here we identify several detrimental gastrulation defects resulting from inhibiting RA biosynthesis by three different treatments. RA reduction causes a delay in the progression through gastrulation as well as the rostral migration of the goosecoid-positive PCM cells. RA inhibition also hampered the elongation of explanted dorsal marginal zones, the compaction of the blastocoel, and the length of Brachet’s cleft, all of which indicate an effect on LEM/PCM migration. The cellular mechanisms underlying this deficit were shown to include a reduced deposition of fibronectin along Brachet’s cleft, the substrate for their migration, as well as impaired separation of the blastocoel roof and involuting mesoderm, which is important for the formation of Brachet’s cleft and successful LEM/PCM migration. We further show reduced non-canonical Wnt signaling activity and altered expression of genes in the Ephrin and PDGF signaling pathways, both of which are required for the rostral migration of the LEM/PCM, following RA reduction. Together, these experiments demonstrate that RA signaling performs a very early function critical for the progression of gastrulation morphogenetic movements.

Reduced Retinoic Acid Signaling During Gastrulation Induces Developmental Microcephaly

Retinoic acid (RA) is a central signaling molecule regulating multiple developmental decisions during embryogenesis. Excess RA induces head malformations, primarily by expansion of posterior brain structures at the expense of anterior head regions, i.e., hindbrain expansion. Despite this extensively studied RA teratogenic effect, a number of syndromes exhibiting microcephaly, such as DiGeorge, Vitamin A Deficiency, Fetal Alcohol Syndrome, and others, have been attributed to reduced RA signaling. This causative link suggests a requirement for RA signaling during normal head development in all these syndromes. To characterize this novel RA function, we studied the involvement of RA in the early events leading to head formation in Xenopus embryos. This effect was mapped to the earliest RA biosynthesis in the embryo within the gastrula Spemann-Mangold organizer. Head malformations were observed when reduced RA signaling was induced in the endogenous Spemann-Mangold organizer and in the ectopic organizer of twinned embryos. Two embryonic retinaldehyde dehydrogenases, ALDH1A2 (RALDH2) and ALDH1A3 (RALDH3) are initially expressed in the organizer and subsequently mark the trunk and the migrating leading edge mesendoderm, respectively. Gene-specific knockdowns and CRISPR/Cas9 targeting show that RALDH3 is a key enzyme involved in RA production required for head formation. These observations indicate that in addition to the teratogenic effect of excess RA on head development, RA signaling also has a positive and required regulatory role in the early formation of the head during gastrula stages. These results identify a novel RA activity that concurs with its proposed reduction in syndromes exhibiting microcephaly.

Pharmacological activation of the Sonic hedgehog pathway with a Smoothened small molecule agonist ameliorates the severity of alcohol-induced morphological and behavioral birth defects in a zebrafish model of fetal alcohol spectrum disorder

Ethanol exposure during the early stages of embryonic development can lead to a range of morphological and behavioral differences termed fetal alcohol spectrum disorders (FASDs). In a zebrafish model, we have shown that acute ethanol exposure at 8-10 hr postfertilization (hpf), a critical time of development, produces birth defects similar to those clinically characterized in FASD. Dysregulation of the Sonic hedgehog (Shh) pathway has been implicated as a molecular basis for many of the birth defects caused by prenatal alcohol exposure. We observed in zebrafish embryos that shh expression was significantly decreased by ethanol exposure at 8-10 hpf, while smo expression was much less affected. Treatment of zebrafish embryos with SAG or purmorphamine, small molecule Smoothened agonists that activate Shh signaling, ameliorated the severity of ethanol-induced developmental malformations including altered eye size and midline brain development. Furthermore, this rescue effect of Smo activation was dose dependent and occurred primarily when treatment was given after ethanol exposure. Markers of Shh signaling (gli1/2) and eye development (pax6a) were restored in embryos treated with SAG post-ethanol exposure. Since embryonic ethanol exposure has been shown to produce later-life neurobehavioral impairments, juvenile zebrafish were examined in the novel tank diving test. Our results further demonstrated that in zebrafish embryos exposed to ethanol, SAG treatment was able to mitigate long-term neurodevelopmental impairments related to anxiety and risk-taking behavior. Our results indicate that pharmacological activation of the Shh pathway at specific developmental timing markedly diminishes the severity of alcohol-induced birth defects.

Zebrafish models of fetal alcohol spectrum disorders

Fetal alcohol spectrum disorder (FASD) describes a wide range of structural deficits and cognitive impairments. FASD impacts up to 5% of children born in the United States each year, making ethanol one of the most common teratogens. Due to limitations and ethical concerns, studies in humans are limited in their ability to study FASD. Animal models have proven critical in identifying and characterizing the mechanisms underlying FASD. In this review, we will focus on the attributes of zebrafish that make it a strong model in which to study ethanol-induced developmental defects. Zebrafish have several attributes that make it an ideal model in which to study FASD. Zebrafish produced large numbers of externally fertilized, translucent embryos. With a high degree of genetic amenability, zebrafish are at the forefront of identifying and characterizing the gene-ethanol interactions that underlie FASD. Work from multiple labs has shown that embryonic ethanol exposures result in defects in craniofacial, cardiac, ocular, and neural development. In addition to structural defects, ethanol-induced cognitive and behavioral impairments have been studied in zebrafish. Building upon these studies, work has identified ethanol-sensitive loci that underlie the developmental defects. However, analyses show there is still much to be learned of these gene-ethanol interactions. The zebrafish is ideally suited to expand our understanding of gene-ethanol interactions and their impact on FASD. Because of the conservation of gene function between zebrafish and humans, these studies will directly translate to studies of candidate genes in human populations and allow for better diagnosis and treatment of FASD.

Alcohol and the Eye

In this article, we present a review of ocular conditions related to alcohol consumption. A search of the literature published from 1952 to March 2020 was performed. The titles and abstracts were screened and the eligible studies were selected. PubMed, ISI Web of Knowledge database, Scopus, Embase, and the Cochrane Library were searched. We categorized the relationship between alcohol intake and ocular conditions by the type of ocular exposure to alcohol. Accordingly, ocular findings following acute alcohol intoxication, optic neuropathy following methanol toxicity, congenital conditions related to maternal alcohol consumption, and ocular disease related to chronic alcoholism are discussed. The main feature of alcohol intoxication in the eye is abnormal eye movement. Acute optic neuropathy secondary to methyl alcohol consumption is a serious ocular disease with permanent vision loss or scotoma. Prenatal exposure to ethanol may end in fetal alcohol spectrum disease, where ocular findings are a constant component. The association between chronic alcohol consumption and increased risks of cataract, age-related macular degeneration, diabetic retinopathy, different types of optic neuropathy, impairment of visual quality, retinal vascular disease, and ocular surface disease has also been reported. Along with detrimental medical and social effects, the role of alcohol consumption in different ocular conditions should be considered, as alcohol-induced visual disturbances may contribute to the heavy burden of alcohol abuse on the healthcare system and overall quality of life.

Xenopus in revealing developmental toxicity and modeling human diseases

The Xenopus model offers many advantages for investigation of the molecular, cellular, and behavioral mechanisms underlying embryo development. Moreover, Xenopus oocytes and embryos have been extensively used to study developmental toxicity and human diseases in response to various environmental chemicals. This review first summarizes recent advances in using Xenopus as a vertebrate model to study distinct types of tissue/organ development following exposure to environmental toxicants, chemical reagents, and pharmaceutical drugs. Then, the successful use of Xenopus as a model for diseases, including fetal alcohol spectrum disorders, autism, epilepsy, and cardiovascular disease, is reviewed. The potential application of Xenopus in genetic and chemical screening to protect against embryo deficits induced by chemical toxicants and related diseases is also discussed.

Folic acid supplement rescues ethanol-induced developmental defects in the zebrafish embryos

Fetal alcohol syndrome (FASD) describes a range of birth defects. Mechanisms of FASD-associated defects are not well understood. It has great significance to investigate whether nutrient supplements like folic acid (FA) can effectively rescue ethanol-induced defects. Moreover, it is very important to determine the optimal time for FA supplementation when it can most effectively antagonize the teratogenic effects of ethanol during embryonic development. Our results indicated that ethanol exposure interrupted the development of zebrafish embryos and induced multiple defects in cardiac function, pharyngeal arch arteries, vessel, craniofacial cartilage, pharyngeal arches, brain, somite and hemoglobin formation. The expressions of critical genes that play important roles in above organs such as tbx1, flk-1, hand2, ngn1, huc, titin, gata-1 and c-myb were reduced, and the apoptosis was increased in ethanol-treated group. FA supplementation could reverse ethanol-induced defects, improve the decreased expressions of above genes and reduce the apoptosis. We also found that giving FA at 6-12 h post-fertilization (hpf), which is at the gastrula period (5.25-10 hpf), can obviously prevent the teratogenicity of ethanol. This research provides clues for elucidating the mechanism of fetal abnormalities caused by alcohol intake and for preventing FASD.

Fetal Alcohol Spectrum Disorder: Embryogenesis Under Reduced Retinoic Acid Signaling Conditions

Fetal Alcohol Spectrum Disorder (FASD) is a complex set of developmental malformations, neurobehavioral anomalies and mental disabilities induced by exposing human embryos to alcohol during fetal development. Several experimental models and a series of developmental and biochemical approaches have established a strong link between FASD and reduced retinoic acid (RA) signaling. RA signaling is involved in the regulation of numerous developmental decisions from patterning of the anterior-posterior axis, starting at gastrulation, to the differentiation of specific cell types within developing organs, to adult tissue homeostasis. Being such an important regulatory signal during embryonic development, mutations or environmental perturbations that affect the level, timing or location of the RA signal can induce multiple and severe developmental malformations. The evidence connecting human syndromes to reduced RA signaling is presented here and the resulting phenotypes are compared to FASD. Available data suggest that competition between ethanol clearance and RA biosynthesis is a major etiological component in FASD.

Modification of stem cell states by alcohol and acetaldehyde

Ethanol (EtOH) is a recreationally ingested compound that is both teratogenic and carcinogenic in humans. Because of its abundant consumption worldwide and the vital role of stem cells in the formation of birth defects and cancers, delineating the effects of EtOH on stem cell function is currently an active and urgent pursuit of scientific investigation to explicate some of the mechanisms contributing to EtOH toxicity. Stem cells represent a primordial, undifferentiated phase of development; thus encroachment on normal physiologic processes of differentiation into terminal lineages by EtOH can greatly alter the function of progenitors and terminally differentiated cells, leading to pathological consequences that manifest as fetal alcohol spectrum disorders and cancers. In this review we explore the disruptive role of EtOH in differentiation of stem cells. Our primary objective is to elucidate the mechanisms by which EtOH alters differentiation-related gene expression and lineage specifications, thus modifying stem cells to promote pathological outcomes. We additionally review the effects of a reactive metabolite of EtOH, acetaldehyde (AcH), in causing both differentiation defects in stem cells as well as genomic damage that incites cellular aging and carcinogenesis.

Preventing Ethanol-Induced Brain and Eye Morphology Defects Using Optogenetics

Background: Embryonic exposure to the teratogen ethanol leads to dysmorphias, including eye and brain morphology defects associated with fetal alcohol spectrum disorder (FASD). Exposure of Xenopus laevis embryos to ethanol leads to similar developmental defects, including brain and eye dysmorphism, confirming our work and the work of others showing Xenopus as a useful system for studies of the brain and eye birth defects associated with FASD. Several targets of ethanol action have been hypothesized, one being regulation of Kir2.1 potassium channel. Endogenous ion fluxes and membrane voltage variation (bioelectric signals) have been shown to be powerful regulators of embryonic cell behaviors that are required for correct brain and eye morphology. Disruptions to these voltage patterns lead to spatially correlated disruptions in gene expression patterns and corresponding morphology. Materials and Methods: Here, we use controlled membrane voltage modulation to determine when and where voltage modulation is sufficient to rescue ethanol-induced brain and eye defects in Xenopus embryos. Results: We found (1) that modulating membrane voltage using light activation of the channelrhodopsin-2 variant D156A rescues ethanol exposed embryos, resulting in normal brain and eye morphologies; (2) hyperpolarization is required for the full duration of ethanol exposure; (3) hyperpolarization of only superficial ectoderm is sufficient for this effect; and(4) the rescue effect acts at a distance. Conclusions: These results, particularly the last, raise the exciting possibility of using bioelectric modulation to treat ethanol-induced brain and eye birth defects, possibly with extant ion channel drugs already prescribed to pregnant women. This may prove to be a simple and cost-effective strategy for reducing the impact of FASD.

What's retinoic acid got to do with it? Retinoic acid regulation of the neural crest in craniofacial and ocular development

Retinoic acid (RA), the active derivative of vitamin A (retinol), is an essential morphogen signaling molecule and major regulator of embryonic development. The dysregulation of RA levels during embryogenesis has been associated with numerous congenital anomalies, including craniofacial, auditory, and ocular defects. These anomalies result from disruptions in the cranial neural crest, a vertebrate-specific transient population of stem cells that contribute to the formation of diverse cell lineages and embryonic structures during development. In this review, we summarize our current knowledge of the RA-mediated regulation of cranial neural crest induction at the edge of the neural tube and the migration of these cells into the craniofacial region. Further, we discuss the role of RA in the regulation of cranial neural crest cells found within the frontonasal process, periocular mesenchyme, and pharyngeal arches, which eventually form the bones and connective tissues of the head and neck and contribute to structures in the anterior segment of the eye. We then review our understanding of the mechanisms underlying congenital craniofacial and ocular diseases caused by either the genetic or toxic disruption of RA signaling. Finally, we discuss the role of RA in maintaining neural crest-derived structures in postembryonic tissues and the implications of these studies in creating new treatments for degenerative craniofacial and ocular diseases.

Ethanol promotes differentiation of embryonic stem cells through retinoic acid receptor-γ

Ethanol (EtOH) is a teratogen, but its teratogenic mechanisms are not fully understood. The alcohol form of vitamin A (retinol/ROL) can be oxidized to all-trans-retinoic acid (RA), which plays a critical role in stem cell differentiation and development. Using an embryonic stem cell (ESC) model to analyze EtOH's effects on differentiation, we show here that EtOH and acetaldehyde, but not acetate, increase differentiation-associated mRNA levels, and that EtOH decreases pluripotency-related mRNAs. Using reporter assays, ChIP assays, and retinoic acid receptor-γ (RARγ) knockout ESC lines generated by CRISPR/Cas9 and homologous recombination, we demonstrate that EtOH signals via RARγ binding to RA response elements (RAREs) in differentiation-associated gene promoters or enhancers. We also report that EtOH-mediated increases in homeobox A1 (Hoxa1) and cytochrome P450 family 26 subfamily A member 1 (Cyp26a1) transcripts, direct RA target genes, require the expression of the RA-synthesizing enzyme, aldehyde dehydrogenase 1 family member A2 (Aldh1a2), suggesting that EtOH-mediated induction of Hoxa1 and Cyp26a1 requires ROL from the serum. As shown with CRISPR/Cas9 knockout lines, the retinol dehydrogenase gene Rdh10 and a functional RARE in the ROL transporter stimulated by retinoic acid 6 (Stra6) gene are required for EtOH induction of Hoxa1 and Cyp26a1 We conclude that EtOH stimulates stem cell differentiation by increasing the influx and metabolism of ROL for downstream RARγ-dependent transcription. In stem cells, EtOH may shift cell fate decisions to alter developmental outcomes by increasing endogenous ROL/RA signaling via increased Stra6 expression and ROL oxidation.

Retinoic acid signaling reduction recapitulates the effects of alcohol on embryo size

Intrauterine growth restriction (IUGR) is commonly observed in human pregnancies and can result in severe clinical outcomes. IUGR is observed in Fetal Alcohol Syndrome (FAS) fetuses as a result of alcohol (ethanol) exposure during pregnancy. To further understand FAS, the severe form of Fetal Alcohol Spectrum Disorder, we performed an extensive quantitative analysis of the effects of ethanol on embryo size utilizing our Xenopus model. Ethanol-treated embryos exhibited size reduction along the anterior-posterior axis. This effect was evident primarily from the hindbrain caudally, while rostral regions appeared refractive to ethanol-induced size changes, also known as asymmetric IUGR. Interestingly, some embryo batches in addition to shortening from the hindbrain caudally also exhibited an alcohol-dependent reduction of the anterior head domain, known as symmetric IUGR. To study the connection between ethanol exposure and reduced retinoic acid levels we treated embryos with the retinaldehyde dehydrogenase inhibitors, DEAB and citral. Inhibition of retinoic acid biosynthesis recapitulated the growth defects induced by ethanol affecting mainly axial elongation from the hindbrain caudally. To study the competition between ethanol clearance and retinoic acid biosynthesis we demonstrated that, co-exposure to alcohol reduces the teratogenic effects of treatment with retinol (vitamin A), the retinoic acid precursor. These results further support the role of retinoic acid in the regulation of axial elongation.

Ethanol and cannabinoids interact to alter behavior in a zebrafish fetal alcohol spectrum disorder model

BACKGROUND

Recent work suggests that endocannabinoids (eCBs) may signal through the sonic hedgehog signaling pathway. We therefore hypothesized that combined ethanol and eCB exposure during defined stages of zebrafish embryogenesis will produce deficits comparable to human fetal alcohol spectrum disorder (FASD).

METHODS

Zebrafish embryos were exposed to ethanol or cannabinoid agonists alone or in combination at defined developmental stages and assessed for changes in brain morphology or expression of marker genes such as pax6a. Juvenile fish were then assessed for risk-taking/anxiety-like behavior using the novel tank dive test.

RESULTS

Either chronic or acute exposure to high doses of the CB1R agonist ACEA resulted in FASD phenotypes. However, acute subthreshold doses of CB1R agonist alone, or combined with 0.5% ethanol, did not induce morphological phenotypes, but did induce dysmorphogenesis when combined with acute 1% ethanol. Phenotypes were rescued using the CB1R antagonist SR141716A. In addition, JZL195, a dual inhibitor of FAAH and MAGL, two degradative enzymes for eCBs, induced FASD phenotypes in the presence of subthreshold ethanol, confirming the activation of common signaling pathways by ethanol and eCBs. We next analyzed the effects of ethanol and CB1R agonist on juvenile zebrafish behavior and show that ACEA or ethanol alone did not alter behavior, but combined ACEA and ethanol increased risk-taking behavior.

CONCLUSIONS

These studies demonstrate that pathological and behavioral phenotypes associated with FASD are induced by exposure to CB1R agonists and suggest that combined exposure to lower levels of alcohol and marijuana may be capable of inducing FASD-like morphological and behavioral impairments.

Adaptive correction of craniofacial defects in pre-metamorphic Xenopus laevis tadpoles involves thyroid hormone-independent tissue remodeling

While it is well-established that some organisms can regenerate lost structures, the ability to remodel existing malformed structures has been less well studied. Thus, in this study we examined the ability of pre-metamorphic Xenopus laevis tadpoles to self-correct malformed craniofacial tissues and found that tadpoles can adaptively improve and normalize abnormal craniofacial morphology caused by numerous developmental perturbations. We then investigated the tissue-level and molecular mechanisms that mediate the self-correction of craniofacial defects in pre-metamorphic X. laevis tadpoles. Our studies revealed that this adaptive response involves morphological changes and the remodeling of cartilage tissue, prior to metamorphosis. RT-qPCR and RNA-Seq analysis of gene expression suggests a thyroid hormone-independent endocrine signaling pathway as the potential mechanism responsible for triggering the adaptive and corrective remodeling response in these larvae that involves mmp1 and mmp13 upregulation. Thus, investigating how malformed craniofacial tissues are naturally corrected in X. laevis tadpoles has led us to valuable insights regarding the maintenance and manipulation of craniofacial morphology in a vertebrate system. These insights may help in the development of novel therapies for developmental craniofacial anomalies in humans.

FASD: folic acid and formic acid — an unholy alliance in the alcohol abusing mother

Alcohol consumption during pregnancy remains a significant cause of preventable birth defects and developmental disabilities; however, the mechanism of toxicity remains unclear. Methanol is present as a congener in many alcoholic beverages and is formed endogenously. Because ethanol is preferentially metabolized over methanol, it has been found in the sera and cerebro-spinal fluid of alcoholics. Toxicity resulting from methanol has been attributed to formic acid. Formic acid is present in significantly higher quantities in the biofluids of alcoholics. These higher levels can be cytotoxic and cause neuronal cell death. However, the adverse effects can be mitigated by adequate levels of hepatic folic acid, because formic acid elimination depends on folic acid. During pregnancy, folate concentrations are at least 2-fold higher in cord blood then in maternal blood, owing to increased folate requirements. The reverse has been demonstrated in pregnancies with alcohol abuse, suggesting downregulation of folate transporters and low fetal folate levels. Moreover, formic acid can cross the placenta and its adverse effects can be mitigated by folic acid. Thus, the combination of low fetal folate levels and presence of formic acid form a potent cytotoxic combination that may play a significant role in the etiology of fetal alcohol spectrum disorder.

Xenopus embryos to study fetal alcohol syndrome, a model for environmental teratogenesis

Vertebrate model systems are central to characterize the outcomes of ethanol exposure and the etiology of fetal alcohol spectrum disorder (FASD), taking advantage of their genetic and morphological closeness and similarity to humans. We discuss the contribution of amphibian embryos to FASD research, focusing on Xenopus embryos. The Xenopus experimental system is characterized by external development and accessibility throughout embryogenesis, large clutch sizes, gene and protein activity manipulation, transgenesis and genome editing, convenient chemical treatment, explants and conjugates, and many other experimental approaches. Taking advantage of these methods, many insights regarding FASD have been obtained. These studies characterized the malformations induced by ethanol including quantitative analysis of craniofacial malformations, induction of fetal growth restriction, delay in gut maturation, and defects in the differentiation of the neural crest. Mechanistic, biochemical, and molecular studies in Xenopus embryos identified early gastrula as the high alcohol sensitivity window, targeting the embryonic organizer and inducing a delay in gastrulation movements. Frog embryos have also served to demonstrate the involvement of reduced retinoic acid production and an increase in reactive oxygen species in FASD. Amphibian embryos have helped pave the way for our mechanistic, molecular, and biochemical understanding of the etiology and pathophysiology of FASD.

Comparison of molecular marker expression in early zebrafish brain development following chronic ethanol or morpholino treatment

This study was undertaken to ascertain whether defined markers of early zebrafish brain development are affected by chronic ethanol exposure or morpholino knockdown of agrin, sonic hedgehog, retinoic acid, and fibroblast growth factors, four signaling molecules that are suggested to be ethanol sensitive. Zebrafish embryos were exposed to 2% ethanol from 6 to 24 hpf or injected with agrin, shha, aldh1a3, or fgf8a morpholinos. In situ hybridization was employed to analyze otx2, pax6a, epha4a, krx20, pax2a, fgf8a, wnt1, and eng2b expression during early brain development. Our results showed that pax6a mRNA expression was decreased in eye, forebrain, and hindbrain of both chronic ethanol exposed and select MO treatments. Epha4a expression in rhombomere R1 boundary was decreased in chronic ethanol exposure and aldh1a3 morphants, lost in fgf8a morphants, but largely unaffected in agrin and shha morphants. Ectopic pax6a and epha4a expression in midbrain was only found in fgf8a morphants. These results suggest that while chronic ethanol induces obvious morphological change in brain architecture, many molecular markers of these brain structures are relatively unaffected by ethanol exposure.

Ethanol itself is a holoprosencephaly-inducing teratogen

Ethanol is a teratogen, inducing a variety of structural defects in developing humans and animals that are exposed in utero. Mechanisms of ethanol teratogenicity in specific defects are not well understood. Oxidative metabolism of ethanol by alcohol dehydrogenase or cytochrome P450 2E1 has been implicated in some of ethanol's teratogenic effects, either via production of acetaldehyde or competitive inhibition of retinoic acid synthesis. Generalized oxidative stress in response to ethanol may also play a role in its teratogenicity. Among the developmental defects that ethanol has been implicated in is holoprosencephaly, a failure to define the midline of the forebrain and midface that is associated with a deficiency in Sonic hedgehog pathway function. Etiologically, holoprosencephaly is thought to arise from a complex combination of genetic and environmental factors. We have developed a gene-environment interaction model of holoprosencephaly in mice, in which mutation of the Sonic hedgehog coreceptor, Cdon, synergizes with transient in utero exposure to ethanol. This system was used to address whether oxidative metabolism is required for ethanol's teratogenic activity in holoprosencephaly. We report here that t-butyl alcohol, which is neither a substrate nor an inhibitor of alcohol dehydrogenases or Cyp2E1, is a potent inducer of holoprosencephaly in Cdon mutant mice. Additionally, antioxidant treatment did not prevent ethanol- or t-butyl alcohol-induced HPE in these mice. These findings are consistent with the conclusion that ethanol itself, rather than a consequence of its metabolism, is a holoprosencephaly-inducing teratogen.

Long-term behavioral change as a result of acute ethanol exposure in zebrafish: Evidence for a role for sonic hedgehog but not retinoic acid signaling

BACKGROUND

Developmental exposure to ethanol is recognized to produce long-term neurobehavioral impairment in multiple animal models. However, the molecular mechanisms underlying these deficits remain poorly understood. The present study was undertaken to ascertain whether two well-characterized targets of prenatal alcohol exposure, sonic hedgehog (Shh) and retinoic acid (RA), that induce the hallmark morphological phenotypes of fetal alcohol spectrum disorders (FASD), are involved in the generation of behavioral alterations as a result of alcohol exposure.

METHODS

Zebrafish embryos were exposed to ethanol (0%, 1%, 3%) at either 8-10 or 24-27h post-fertilization (hpf) and then evaluated during adolescence in the novel tank dive test to assess anxiety and risk-taking behavior. Overt signs of dysmorphogenesis were also scored and behavioral and morphological changes were compared for embryos treated with alcohol alone or in combination with subthreshold doses of shh or alhh1a3 morpholinos (MOs).

RESULTS

Ethanol treated fish displayed altered tank diving behavior that was not exacerbated by combined MO treatment. While treatment of embryos with either shha mRNA or RA prior to ethanol exposure only ameliorated the altered tank diving response in the case of shha mRNA overexpression, dysmorphogenesis was rescued by both treatments.

CONCLUSION

These results suggest that the effects of ethanol exposure on changes in anxiety and risk-taking behavior in adolescent zebrafish is manifested by a blunting of Shh, but not RA, signaling during early development.

Modeling human craniofacial disorders in Xenopus

PURPOSE OF REVIEW

Craniofacial disorders are among the most common human birth defects and present an enormous health care and social burden. The development of animal models has been instrumental to investigate fundamental questions in craniofacial biology and this knowledge is critical to understand the etiology and pathogenesis of these disorders.

RECENT FINDINGS

The vast majority of craniofacial disorders arise from abnormal development of the neural crest, a multipotent and migratory cell population. Therefore, defining the pathogenesis of these conditions starts with a deep understanding of the mechanisms that preside over neural crest formation and its role in craniofacial development.

SUMMARY

This review discusses several studies using Xenopus embryos to model human craniofacial conditions, and emphasizes the strength of this system to inform important biological processes as they relate to human craniofacial development and disease.

Neurotransmitter signaling pathways required for normal development in Xenopus laevis embryos: a pharmacological survey screen

Neurotransmitters are not only involved in brain function but are also important signaling molecules for many diverse cell types. Neurotransmitters are widely conserved, from evolutionarily ancient organisms lacking nervous systems through man. Here, results are reported from a loss- and gain-of-function survey, using pharmacological modulators of several neurotransmitter pathways to examine possible roles for these pathways in normal embryogenesis. Applying reagents targeting the glutamatergic, adrenergic and dopaminergic pathways to embryos of Xenopus laevis from gastrulation to organogenesis stages, we observed and quantified numerous malformations, including craniofacial defects, hyperpigmentation, muscle mispatterning and miscoiling of the gut. These data implicate several key neurotransmitters in new embryonic patterning roles, reveal novel earlier stages for processes involved in eye development, suggest new targets for subsequent molecular-genetic investigation, and highlight the necessity for in-depth toxicology studies of psychoactive compounds to which human embryos might be exposed during pregnancy.

The chick embryo as a model for the effects of prenatal exposure to alcohol on craniofacial development

Prenatal exposure to ethanol results in fetal alcohol spectrum disorder (FASD), a syndrome characterised by a broad range of clinical manifestations including craniofacial dysmorphologies and neurological defects. The characterisation of the mechanisms by which ethanol exerts its teratogenic effects is difficult due to the pleiotropic nature of its actions. Different experimental model systems have been employed to investigate the aetiology of FASD. Here, I will review studies using these different model organisms that have helped to elucidate how ethanol causes the craniofacial abnormalities characteristic of FASD. In these studies, ethanol was found to impair the prechordal plate-an important embryonic signalling centre-during gastrulation and to negatively affect the induction, migration and survival of the neural crest, a cell population that generates the cartilage and most of the bones of the skull. At the cellular level, ethanol appears to inhibit Sonic hedgehog signalling, alter levels of retionoic acid activity, trigger a Ca(2+)-CamKII-dependent pathway that antagonises WNT signalling, affect cytoskeletal dynamics and increase oxidative stress. Embryos of the domestic chick Gallus gallus domesticus have played a central role in developing a working model for the effects of ethanol on craniofacial development because they are easily accessible and because key steps in craniofacial development are particularly well established in the avian embryo. I will finish this review by highlighting some potential future avenues of fetal alcohol research.

Analysis of crosstalk between retinoic acid and sonic hedgehog pathways following ethanol exposure in embryonic zebrafish

BACKGROUND

Ethanol is a teratogen affecting numerous regions of the developing nervous system. The present study was undertaken to ascertain whether ethanol independently disrupts distinct signaling pathways or rather disrupts interactive pathways that regulate development of ethanol-sensitive tissues.

METHODS

Zebrafish embryos were exposed to ethanol in the absence or presence of aldh1a3 or Shh morpholino oligonucleotides (MOs), which disrupt retinoic acid (RA) or sonic hedgehog (Shh) function, respectively. Morphological analysis of ocular or midbrain-hindbrain boundary (MHB) development was conducted, and the ability to rescue ethanol and MO-induced phenotypes was assessed. In situ hybridization was used to analyze Pax6a expression during ocular development.

RESULTS

Chronic ethanol exposure, or combined ethanol and MO treatment, results in perturbed MHB formation and microphthalmia. While RA can rescue the MHB phenotype following ethanol combined with either MO, Shh mRNA is unable to rescue the disrupted MHB with combined ethanol and aldh1a3 MO treatment. RA also is unable to rescue microphthalmia induced by ethanol and Shh MO.

CONCLUSION

These studies demonstrate that while reduction of either RA or Shh signaling produces the same disruption of MHB or ocular development, that can be phenocopied using ethanol combined with either MO, RA overexpression can only rescue disrupted MHB, but not microphthalmia, in combined subthreshold Shh MO and ethanol. Our data suggest that MHB development may involve crosstalk between RA and Shh signaling, while ocular development depends on RA and Shh signaling that both are targets of ethanol in fetal alcohol spectrum disorders but do not depend on a mechanism involving crosstalk.

Nutrition implications for fetal alcohol spectrum disorder

Prenatal alcohol exposure produces a multitude of detrimental alcohol-induced defects in children collectively known as fetal alcohol spectrum disorder (FASD). Children with FASD often exhibit delayed or abnormal mental, neural, and physical growth. Socioeconomic status, race, genetics, parity, gravidity, age, smoking, and alcohol consumption patterns are all factors that may influence FASD. Optimal maternal nutritional status is of utmost importance for proper fetal development, yet is often altered with alcohol consumption. It is critical to determine a means to resolve and reduce the physical and neurological malformations that develop in the fetus as a result of prenatal alcohol exposure. Because there is a lack of information on the role of nutrients and prenatal nutrition interventions for FASD, the focus of this review is to provide an overview of nutrients (vitamin A, docosahexaenoic acid, folic acid, zinc, choline, vitamin E, and selenium) that may prevent or alleviate the development of FASD. Results from various nutrient supplementation studies in animal models and FASD-related research conducted in humans provide insight into the plausibility of prenatal nutrition interventions for FASD. Further research is necessary to confirm positive results, to determine optimal amounts of nutrients needed in supplementation, and to investigate the collective effects of multiple-nutrient supplementation.

A comparison of the different animal models of fetal alcohol spectrum disorders and their use in studying complex behaviors

Prenatal ethanol exposure (PNEE) has been linked to widespread impairments in brain structure and function. There are a number of animal models that are used to study the structural and functional deficits caused by PNEE, including, but not limited to invertebrates, fish, rodents, and non-human primates. Animal models enable a researcher to control important variables such as the route of ethanol administration, as well as the timing, frequency and amount of ethanol exposure. Each animal model and system of exposure has its place, depending on the research question being undertaken. In this review, we will examine the different routes of ethanol administration and the various animal models of fetal alcohol spectrum disorders (FASD) that are commonly used in research, emphasizing their strengths and limitations. We will also present an up-to-date summary on the effects of prenatal/neonatal ethanol exposure on behavior across the lifespan, focusing on learning and memory, olfaction, social, executive, and motor functions. Special emphasis will be placed where the various animal models best represent deficits observed in the human condition and offer a viable test bed to examine potential therapeutics for human beings with FASD.

Eye-specific gene expression following embryonic ethanol exposure in zebrafish: roles for heat shock factor 1

The mechanisms through which ethanol exposure results in developmental defects remain unclear. We used the zebrafish model to elucidate eye-specific mechanisms that underlie ethanol-mediated microphthalmia (reduced eye size), through time-series microarray analysis of gene expression within eyes of embryos exposed to 1.5% ethanol. 62 genes were differentially expressed (DE) in ethanol-treated as compared to control eyes sampled during retinal neurogenesis (24-48 h post-fertilization). The EDGE (extraction of differential gene expression) algorithm identified >3000 genes DE over developmental time in ethanol-exposed eyes as compared to controls. The DE lists included several genes indicating a mis-regulated cellular stress response due to ethanol exposure. Combined treatment with sub-threshold levels of ethanol and a morpholino targeting heat shock factor 1 mRNA resulted in microphthalmia, suggesting convergent molecular pathways. Thermal preconditioning partially prevented ethanol-mediated microphthalmia while maintaining Hsf-1 expression. These data suggest roles for reduced Hsf-1 in mediating microphthalmic effects of embryonic ethanol exposure.

Fetal Alcohol Spectrum Disorder (FASD) Associated Neural Defects: Complex Mechanisms and Potential Therapeutic Targets

Fetal alcohol spectrum disorder (FASD), caused by prenatal alcohol exposure, can result in craniofacial dysmorphism, cognitive impairment, sensory and motor disabilities among other defects. FASD incidences are as high as 2% to 5 % children born in the US, and prevalence is higher in low socioeconomic populations. Despite various mechanisms being proposed to explain the etiology of FASD, the molecular targets of ethanol toxicity during development are unknown. Proposed mechanisms include cell death, cell signaling defects and gene expression changes. More recently, the involvement of several other molecular pathways was explored, including non-coding RNA, epigenetic changes and specific vitamin deficiencies. These various pathways may interact, producing a wide spectrum of consequences. Detailed understanding of these various pathways and their interactions will facilitate the therapeutic target identification, leading to new clinical intervention, which may reduce the incidence and severity of these highly prevalent preventable birth defects. This review discusses manifestations of alcohol exposure on the developing central nervous system, including the neural crest cells and sensory neural placodes, focusing on molecular neurodevelopmental pathways as possible therapeutic targets for prevention or protection.

Sonic hedgehog expression is disrupted following in ovo ethanol exposure during early chick eye development

The eye is particularly sensitive to ethanol's teratogenic effects. Our previous work, using a chick embryo model system, has shown that ethanol acts rapidly to perturb vital processes of early eye development producing defects of the lens and retina. Ethanol-induced disruption of the midline ventral telencephalon, a key site for expression of ocular morphogens such as sonic hedgehog (Shh), was further established. Consequently, in this study we have examined the effects of ethanol on the Shh pathway during the period of optic vesicle/optic cup formation. Chick embryos were injected in ovo with 125μL of a 20% ethanol solution directly into the yolk-sac at HH-stage 7, resulting in peak ethanol uptake of 0.294g/dL. Subsequent molecular analysis at 12, 24 and 48h post-treatment revealed that ethanol had no affect on Shh transcription, while, a significant reduction in the expression of the active signalling Shh protein was found. Surprisingly, none of the downstream Shh pathway members (Ptc, Gli1 and Gli3) were significantly altered by ethanol exposure. Overall, our results indicate that ethanol's disruption of Shh may be mediated through some alternative mechanism independent of the classical signalling pathway. However, the precise role of Shh in relation to ethanol teratogenicity continues to be debated. Thus, in conclusion, our findings are discussed in relation to the varied and often conflicting reports of ethanol-induced Shh perturbation found in the literature.

Connexin26-mediated transfer of laterality cues in Xenopus

A cilia-driven leftward flow of extracellular fluid breaks bilateral symmetry in the dorsal midline of the neurula stage vertebrate embryo. The left-specific Nodal signaling cascade in the lateral plate mesoderm (LPM) is key to asymmetric morphogenesis and placement of organs during subsequent development. The nature of the initial asymmetric cue(s) as well as the transfer of information from the midline to the left side has remained elusive. Gap junctional communication has been previously involved in Xenopus left-right (LR) development, however a function at cleavage stages was inferred from inhibitor experiments. Here we show by heptanol-mediated block of connexin function that flow stages during neurulation represent the critical time window. Flow in Xenopus occurs at the gastrocoel roof plate (GRP), a ciliated sheath of cells of mesodermal fate transiently positioned within the dorsal epithelial lining of the forming archenteron. We reasoned that endodermal cells immediately adjacent to the GRP are important for transfer of asymmetry. A systematic screen identified two connexin genes, Cx26 and Cx32, which were co-expressed in these lateral endodermal cells. Gain- and loss-of-function experiments pinpointed Cx26 as the critical connexin for LR development, while Cx32 had no effect on laterality. Importantly, GRP morphology, ciliation and flow were not affected in Cx26 morphants. Our results demonstrate a decisive role of Cx26 in the transfer of laterality cues from the GRP to the left LPM, providing a novel access to the identification of the initial asymmetric signal generated by flow.

Ethanol-induced microphthalmia is not mediated by changes in retinoic acid or sonic hedgehog signaling during retinal neurogenesis

BACKGROUND

Microphthalmia (reduced eye size), generally accompanied by vision defects, is a hallmark of fetal alcohol spectrum disorder (FASD) in humans. In zebrafish, embryonic ethanol exposure over the time of retinal neurogenesis also results in microphthalmia. This microphthalmia is in part the consequence of reduced retinal cell differentiation, including photoreceptors. Here we pursue 2 signaling pathways implicated in other aspects of FASD pathogenesis: retinoic acid (RA) and Sonic hedgehog (Shh).

METHODS

We evaluated markers for RA and Shh signaling within the eyes of embryos treated with ethanol during the period of retinal neurogenesis. We also performed rescue experiments using administration of exogenous RA and microinjection of cholesterol, which augments Shh signaling.

RESULTS

Using sequential or co-treatments, RA did not rescue ethanol-induced microphthalmia at any concentration tested. In addition, RA itself caused microphthalmia, although the underlying mechanisms were distinct from those of ethanol. Interestingly, RA treatment appeared to recover photoreceptor differentiation in a concentration-dependent manner. This may be an independent effect of exogenous RA, as ethanol treatment alone did not alter RA signaling in the eye. Cholesterol injection also did not rescue ethanol-induced microphthalmia at any concentration tested, and ethanol treatments did not alter expression of shh, or of ptc-2, which is normally regulated by Shh signaling.

CONCLUSIONS

Together these findings indicate that, during the time of retinal neurogenesis, effects of ethanol on eye development are likely independent of the RA and Shh signaling pathways. These studies suggest that FASD intervention strategies based upon augmentation of RA or Shh signaling may not prevent ethanol-induced microphthalmia.

Ethanol exposure during the early first trimester equivalent impairs reflexive motor activity and heightens fearfulness in an avian model

Prenatal alcohol exposure is a leading cause of childhood neurodevelopmental disability. The adverse behavioral effects of alcohol exposure during the second and third trimester are well documented; less clear is whether early first trimester-equivalent exposures also alter behavior. We investigated this question using an established chick model of alcohol exposure. In ovo embryos experienced a single, acute ethanol exposure that spanned gastrulation through neuroectoderm induction and early brain patterning (19-22h incubation). At 7 days posthatch, the chicks were evaluated for reflexive motor function (wingflap extension, righting reflex), fearfulness (tonic immobility [TI]), and fear/social reinstatement (open-field behavior). Chicks exposed to a peak ethanol level of 0.23-0.28% were compared against untreated and saline-treated controls. Birds receiving early ethanol exposure had a normal righting reflex and a significantly reduced wingflap extension in response to a sudden descent. The ethanol-treated chicks also displayed heightened fearfulness, reflected in increased frequency of TI, and they required significantly fewer trials for its induction. In an open-field test, ethanol treatment did not affect latency to move, steps taken, vocalizations, defecations, or escape attempts. The current findings demonstrate that early ethanol exposure can increase fearfulness and impair aspects of motor function. Importantly, the observed dysfunctions resulted from an acute ethanol exposure during the period when the major brain components are induced and patterned. The equivalent period in human development is 3-4 weeks postconception. The current findings emphasize that ethanol exposure during the early first trimester equivalent can produce neurodevelopmental disability in the offspring.

Zebrafish fetal alcohol syndrome model: effects of ethanol are rescued by retinoic acid supplement

This study was designed to develop a zebrafish experimental model to examine defects in retinoic acid (RA) signaling caused by embryonic ethanol exposure. RA deficiency may be a causative factor leading to a spectrum of birth defects classified as fetal alcohol spectrum disorder (FASD). Experimental support for this hypothesis using Xenopus showed that effects of treatment with ethanol could be partially rescued by adding retinoids during ethanol treatment. Previous studies show that treating zebrafish embryos during gastrulation and somitogenesis stages with a pathophysiological concentration of ethanol (100mM) produces effects that are characteristic features of FASD. We found that treating zebrafish embryos with RA at a low concentration (10(-9)M) and 100mM ethanol during gastrulation and somitogenesis stages significantly rescued a spectrum of defects produced by treating embryos with 100mM ethanol alone. The rescued phenotype that we observed was quantitatively more similar to embryos treated with 10(-9)M RA alone (RA toxicity) than to untreated or 100mM ethanol-treated embryos. RA rescued defects caused by 100mM ethanol treatment during gastrulation and somitogenesis stages that include early gastrulation cell movements (anterior-posterior axis), craniofacial cartilage formation, and ear development. Morphological evidence also suggests that other characteristic features of FASD (e.g., neural axis patterning) are rescued by RA supplement.

Impact of ethanol on the developing GABAergic system

Alcohol intake during pregnancy has a tremendous impact on the developing brain. Embryonic and early postnatal alcohol exposures have been investigated experimentally to elucidate the fetal alcohol spectrum disorders' (FASD) milieu, and new data have emerged to support a devastating effect on the GABAergic system in the adult and developing nervous system. GABA is a predominantly inhibitory neurotransmitter that during development excites neurons and orchestrates several developmental processes such as proliferation, migration, differentiation, and synaptogenesis. This review summarizes and brings new data on neurodevelopmental aspects of the GABAergic system with FASD in experimental telencephalic models.

Developmental toxicity of ethanol in chick heart in ovo and in micromass culture can be prevented by addition of vitamin C and folic acid

The teratogenic effects of ethanol include malformations of the cardiovascular system, which may be abrogated by multivitamin therapy. Chick cardiomyocytes in micromass culture were treated with ethanol alone or with supplementation with folate or vitamin C. Ethanol alone caused a loss of cell viability and differentiation (beating) whereas those cells treated in addition with vitamins were comparable to the control. Chick embryos were injected on day 3 of incubation with PBS, ethanol alone or with additional vitamin C or folic acid. On day 9 embryos were examined for viability, growth retardation and gross malformation and the hearts were processed for histology. Results showed that ethanol significantly decreased survival of embryos or caused growth retardation and gross malformation (p<0.05). Embryos incubated with addition of vitamin C or folic acid were comparable to the control. Data obtained in this study suggest that supplementation with vitamin C or folic acid during pregnancy may prevent defects in heart development brought about by ethanol.

Ethanol induces embryonic malformations by competing for retinaldehyde dehydrogenase activity during vertebrate gastrulation

Human embryos exposed to alcohol (ethanol) develop a complex developmental phenotype known as fetal alcohol spectrum disorder (FASD). In Xenopus embryos, ethanol reduces the levels of retinoic acid (RA) signaling during gastrulation. RA, a metabolite of vitamin A (retinol), is required for vertebrate embryogenesis, and deviation from its normal levels results in developmental malformations. Retinaldehyde dehydrogenase 2 (RALDH2) is required to activate RA signaling at the onset of gastrulation. We studied the effect of alcohol on embryogenesis by manipulating retinaldehyde dehydrogenase activity in ethanol-treated embryos. In alcohol-treated embryos, we analyzed RA signaling levels, phenotypes induced and changes in gene expression. Developmental defects that were characteristic of high ethanol concentrations were phenocopied by a low ethanol concentration combined with partial RALDH inhibition, whereas Raldh2 overexpression rescued the developmental malformations induced by high ethanol. RALDH2 knockdown resulted in similar RA signaling levels when carried out alone or in combination with ethanol treatment, suggesting that RALDH2 is the main target of ethanol. The biochemical evidence that we present shows that, at the onset of RA signaling during early gastrulation, the ethanol effect centers on the competition for the available retinaldehyde dehydrogenase activity. In light of the multiple regulatory roles of RA, continued embryogenesis in the presence of abnormally low RA levels provides an etiological explanation for the malformations observed in individuals with FASD.

Black ginseng inhibits ethanol-induced teratogenesis in cultured mouse embryos through its effects on antioxidant activity

Fetal alcohol syndrome is caused by excessive ethanol consumption during pregnancy. We investigated the effect of black ginseng (red ginseng that is subjected to 9 cycles of 95-100 degrees C for 2-3h) on ethanol-induced teratogenesis using an in vitro whole embryo culture system. Postimplantational mouse embryos at embryonic day 8.5 were exposed to ethanol (1 microl/ml) in the presence or absence of black ginseng (1, 10, and 100 microg/ml) for 2 days, and then morphological scoring and real-time PCR analysis were carried out. In ethanol-treated embryos, the total morphological score and individual scores for flexion, heart, fore-, mid-, and hindbrains, otic, optic, and olfactory systems, branchial bars, maxillary and mandibular processes, caudal neural tube, and somites were significantly lower than the control group (p<0.05). Treatment with black ginseng improved most of the morphological scores significantly as compared to ethanol-treated embryos (p<0.05). The mRNA levels of the antioxidant enzymes cytosolic glutathione peroxidase (GPx), phospholipid hydroperoxide GPx, and selenoprotein P were significantly decreased in ethanol-treated embryos, but co-treatment with black ginseng restored the mRNA levels to those of control embryos. These results indicate that black ginseng has a protective effect on ethanol-induced teratogenesis through the augmentation of antioxidative activity in embryos.

Comparing quantitative trait Loci and gene expression data

We develop methods to compare the positions of quantitative trait loci (QTL) with a set of genes selected by other methods, such as microarray experiments, from a sequenced genome. We apply our methods to QTL for addictive behavior in mouse, and a set of genes upregulated in a region of the brain associated with addictive behavior, the nucleus accumbens (NA). The association between the QTL and NA genes is not significantly stronger than expected by chance. However, chromosomes 2 and 16 do show strong associations suggesting that genes on these chromosomes might be associated with addictive behavior. The statistical methodology developed for this study can be applied to similar studies to assess the mutual information in microarray and QTL analyses.

Fetal ethanol exposure activates protein kinase A and impairs Shh expression in prechordal mesendoderm cells in the pathogenesis of holoprosencephaly

BACKGROUND

In humans, fetal ethanol exposure can cause holoprosencephaly (HPE), one of the most common birth defects that is characterized by brain, facial, and oral abnormalities. However, the pathogenesis of HPE is not clear. In the present study, we investigated the teratogenic mechanism of ethanol-induced brain and facial malformations in mice.

METHODS

Pregnant C57BL/6J mice were administered ethanol on E7 and facial and brain malformations were characterized on E10.5. We examined the effect of fetal ethanol exposure on Shh expression and activation of protein kinase A (PKA) because mutations in the human Shh gene are the most frequent cause of autosomal-dominant inherited HPE and PKA is a potent endogenous antagonist of Shh signaling.

RESULTS

Fetal ethanol exposure on E7 induced severe midline defects characteristic of HPE. Ethanol exposure impaired Shh expression and induced excessive apoptosis only along the anterior edge of the prechordal mesendoderm (PME). In addition, ethanol activated PKA in anterior PME cells. Pretreatment of embryos with antioxidants, such as vitamins C or E, prevented the development of ethanol-induced HPE.

CONCLUSIONS

Shh expression in PME cells is involved in the pathogenesis of ethanol-induced HPE. Ethanol may impair Shh expression indirectly by activating PKA. The inhibition of excessive apoptosis in PME cells by antioxidants implies that oxidative stress may underlie the teratogenic actions of ethanol. Thus, antioxidant treatment may be a simple preventative measure that could reduce the incidence of HPE following fetal ethanol exposure.

Genetic influence on dysmorphogenesis in embryos from different rat strains exposed to ethanol in vivo and in vitro

BACKGROUND

The aim was to investigate the susceptibility of embryos from 2 rat strains (U and H) to a 48 hours ethanol exposure in early pregnancy, both in vivo and in vitro.

METHODS

The embryos were studied on gestational days 9 to 11. We used 1 ethanol dose in vivo (6 g/kg x 2), 3 different ethanol concentrations in vitro (88 mM, 132 mM, 176 mM) and also attempted to diminish the teratogenic effect in vitro by supplying the antioxidant N-acetylcysteine (NAC, 0.5 mM) to the culture medium.

RESULTS

The U embryos were more damaged by ethanol than the H embryos, both in vivo and in vitro. NAC addition diminished, but failed to completely normalize, the embryonic maldevelopment. Ethanol increased the Bax/Bcl-2 ratio in the U embryos both in vivo and in vitro, but not in the H embryos. Furthermore, ethanol caused increased Caspase-3 immunostaining in U embryos, but not in H embryos. Ethanol exposure in vivo did not alter CuZnSOD and MnSOD mRNA levels in U and H embryos. In vitro, however, the ethanol-exposed U embryos increased their CuZnSOD and MnSOD mRNA levels, whereas the CuZnSOD mRNA was unchanged and MnSOD mRNA decreased in the H embryos, in neither strain did NAC exert any effect. The U embryos increased catalase gene expression in response to ethanol in vivo, but decreased catalase mRNA levels in vitro, changes normalized by NAC. The H embryos did not alter catalase mRNA levels in vivo, but increased gene expression in vitro, with no NAC effect. Ethanol affected the gene expression of the other ROS scavenging enzymes and the developmental genes studied - Bmp-4, Ret, Shh, Pax-6 - similarly in the 2 strains.

CONCLUSIONS

The findings support a role for genetic predisposition, oxidative stress, and apoptosis in ethanol teratogenicity, and suggest that the teratogenic predisposition of the more susceptible U rats may reside, at least in part, in the regulation of the ROS scavenging enzymes in the U embryos.

The effects of ethanol on CNS development in the chick embryo

Human and animal studies show that the central nervous system (CNS) is particularly vulnerable to developmental exposure to alcohol across all stages of development. New critical periods of ethanol sensitivity continue to be defined. The aim of this study was to further examine the stage-specific effects of ethanol on CNS development using a relatively simple programme of neuronal migration and differentiation, the chick embryo spinal cord, and treating at the immediate post-neurulation stage. Embryos (HH-stage 10-12) were explanted into shell-less culture and treated with ethanol (20 microl/40%) or saline (20 microl). At 6,12, 24 and 48 h post-treatment specimens were processed for resin histology. In addition, levels of cell death were analysed using Lysotracker Red, neural crest cell migration patterns were examined using HNK-1 staining and effects on DNA synthesis were evaluated on autoradiographs prepared 1h after exposure to 3H-TdR. This treatment protocol produced significant growth retardation in ethanol specimens examined at 48 h post-treatment. This effect was shown to involve increased levels of cell death, perturbation of DNA synthesis and an abnormal translocation and subsequent loss of cells into the neural tube lumen. No gross malformations were observed. We conclude that these results further highlight the stage-specific effects of ethanol on neurodevelopment.