Arsenic inhibits hedgehog signaling during P19 cell differentiation

Possible role of lncRNAs in amelioration of Parkinson's disease symptoms by transplantation of dopaminergic cells

Long non-coding RNAs (lncRNAs) are biomarkers for diagnosis and treatment of Parkinson's disease (PD). Since dopaminergic cell transplantation is a clinical method to treat PD, this study investigated the effects of dopaminergic cell therapy on the expression of some lncRNAs and genes related to PD. In this study, Twenty-eight rats were randomly assigned to four experimental groups. The control group (Sal group) received saline injections. The Par group was a PD rat model with 6-hydroxydopamine (6-OHDA) injection in right striatum (ST). PD animals were transplanted by undifferentiated P19 stem cells (Par-E group), and P19-derived dopaminergic cells (Par-N group). Cell transplant effects were evaluated using behavioral tests (cylinder, open field, and rotarod tests), and histological methods (H&E and Nissl staining, and immunohistochemistry). Moreover, the expression of lncRNAs MALAT1, MEG3, and SNHG1, alongside specific neuronal (synaptophysin) and dopaminergic (tyrosine hydroxylase) markers was evaluated by qRT-PCR. Behavioral and histopathological examinations revealed that cell transplantation partially compensated dopaminergic cell degeneration in ST and substantia nigra (SN) of PD rats. The expression of MALAT1, SNHG1, and MEG3 was decreased in the ST of the Par group, while MEG3 and SNHG1 gene expression was increased in PBMC relative to the Sal group. In PBMC of the Par-N group, all three lncRNAs showed a reduction in their expression. Conversely, MALAT1 and SNHG1 expression was increased in ST tissue, while MEG3 gene expression was decreased compared to the Sal group. In conclusion, dopaminergic cell transplantation could change the lncRNAs expression. Furthermore, it partially improves symptoms in PD rats.

Identification of novel NRF2-dependent genes as regulators of lead and arsenic toxicity in neural progenitor cells

Lead (Pb) and arsenic (As) are prevalent metal contaminants in the environment. Exposures to these metals are associated with impaired neuronal functions and adverse effects on neurodevelopment in children. However, the molecular mechanisms by which Pb and As impair neuronal functions remain poorly understood. Here, we identified F2RL2, TRIM16L, and PANX2 as novel targets of Nuclear factor erythroid 2-related factor 2 (NRF2)-the master transcriptional factor for the oxidative stress response-that are commonly upregulated with both Pb and As in human neural progenitor cells (NPCs). Using a ChIP (Chromatin immunoprecipitation)-qPCR assay, we showed that NRF2 directly binds to the promoter region of F2RL2, TRIM16L, and PANX2 to regulate expression of these genes. We demonstrated that F2RL2, PANX2, and TRIM16L have differential effects on cell death, proliferation, and differentiation of NPCs in both the presence and absence of metal exposures, highlighting their roles in regulating NPC function. Furthermore, the analyses of the transcriptomic data on NPCs derived from autism spectrum disorder (ASD) patients revealed that dysregulation of F2RL2, TRIM16L, and PANX2 was associated with ASD genetic backgrounds and ASD risk genes. Our findings revealed that Pb and As induce a shared NRF2-dependent transcriptional response in NPCs and identified novel genes regulating NPC function. While further in vivo studies are warranted, this study provides a novel mechanism linking metal exposures to NPC function and identifies potential genes of interest in the context of neurodevelopment.

Use of Microbial Consortia in Bioremediation of Metalloid Polluted Environments

Metalloids are released into the environment due to the erosion of the rocks or anthropogenic activities, causing problems for human health in different world regions. Meanwhile, microorganisms with different mechanisms to tolerate and detoxify metalloid contaminants have an essential role in reducing risks. In this review, we first define metalloids and bioremediation methods and examine the ecology and biodiversity of microorganisms in areas contaminated with these metalloids. Then we studied the genes and proteins involved in the tolerance, transport, uptake, and reduction of these metalloids. Most of these studies focused on a single metalloid and co-contamination of multiple pollutants were poorly discussed in the literature. Furthermore, microbial communication within consortia was rarely explored. Finally, we summarized the microbial relationships between microorganisms in consortia and biofilms to remove one or more contaminants. Therefore, this review article contains valuable information about microbial consortia and their mechanisms in the bioremediation of metalloids.

Long-term arsenic exposure impairs differentiation in mouse embryonal stem cells

Arsenic is a contaminant found in many foods and drinking water. Exposure to arsenic during development can cause improper neuronal progenitor cell development, differentiation, and function, while in vitro studies have determined that acute arsenic exposure to stem and progenitor cells reduced their ability to differentiate. In the current study, P19 mouse embryonal stem cells were exposed continuously to 0.1-μM (7.5 ppb) arsenic for 32 weeks. A cell lineage array examining messenger RNA (mRNA) changes after 8 and 32 weeks of exposure showed that genes involved in pluripotency were increased, whereas those involved in differentiation were reduced. Therefore, temporal changes of select pluripotency and neuronal differentiation markers throughout the 32-week chronic arsenic exposure were investigated. Sox2 and Oct4 mRNA expression were increased by 1.9- to 2.5-fold in the arsenic-exposed cells, beginning at Week 12. Sox2 protein expression was similarly increased starting at Week 16 and remained elevated by 1.5-fold to sixfold. One target of Sox2 is N-cadherin, whose expression is a hallmark of epithelial-mesenchymal transitions (EMTs). Exposure to arsenic significantly increased N-cadherin protein levels beginning at Week 20, concurrent with increased grouping of N-cadherin positive cells at the perimeter of the embryoid body. Expression of Zeb1, which helps increase the expression of Sox2, was also increased started at Week 16. In contrast, Gdf3 mRNA expression was reduced by 3.4- to 7.2-fold beginning at Week 16, and expression of its target protein, phospho-Smad2/3, was also reduced. These results suggest that chronic, low-level arsenic exposure may delay neuronal differentiation and maintain pluripotency.

Recent Advances in Arsenic Research: Significance of Differential Susceptibility and Sustainable Strategies for Mitigation

Arsenic contamination in drinking water and associated adverse outcomes are one of the major health issues in more than 50 countries worldwide. The scenario is getting even more detrimental with increasing number of affected people and newer sites reported from all over the world. Apart from drinking water, the presence of arsenic has been found in various other dietary sources. Chronic arsenic toxicity affects multiple physiological systems and may cause malignancies leading to death. Exposed individuals, residing in the same area, developed differential dermatological lesion phenotypes and varied susceptibility toward various other arsenic-induced disease risk, even after consuming equivalent amount of arsenic from the similar source, over the same duration of time. Researches so far indicate that differential susceptibility plays an important role in arsenic-induced disease manifestation. In this comprehensive review, we have identified major population-based studies of the last 20 years, indicating possible causes of differential susceptibility emphasizing arsenic methylation capacity, variation in host genome (single nucleotide polymorphism), and individual epigenetic pattern (DNA methylation, histone modification, and miRNA expression). Holistic multidisciplinary strategies need to be implemented with few sustainable yet cost-effective solutions like alternative water source, treatment of arsenic-contaminated water, new adaptations in irrigation system, simple modifications in cooking strategy, and dietary supplementations to combat this menace. Our review focuses on the present perspectives of arsenic research with special emphasis on the probable causes of differential susceptibility toward chronic arsenic toxicity and sustainable remediation strategies.

Sonic hedgehog signaling pathway in Myelodysplastic Syndrome: Abnormal activation and jervine intervention

OBJECTIVE

This study aims to investigate the roles of Sonic hedgehog (Shh) signaling pathway in the occurrence and progression of Myelodysplastic Syndrome (MDS) and further evaluate using jervine as therapeutic strategy for MDS by inhibiting Shh pathway.

METHODS

CD34+ cells from the bone marrow of 53 MDS patients were counted by flow cytometry and isolated by magnetic bead sorting. Shh, Smo, Ptch-1 and Gli-1 (involved in Shh pathway) in CD34+ cells were examined by RT-qPCR. Besides, the relationship between Shh pathway-related genes and the clinical features or prognosis of MDS were analyzed. Further, the effects of jervine on MUTZ-1 cells regarding their proliferation, apoptosis and cell cycle as well as Shh pathway-related gene and protein expression were analyzed.

RESULTS

Gene expression level of Shh, Gli-1 and Smo was significantly increased in MDS patients. Herein, Smo and Gli-1 were correlated with chromosome karyotype classification and IPSS. MDS patients with high expression of Smo or Gli-1 had a poor prognosis. Jervine inhibited gene and protein expression of Shh, Smo, Ptch-1 and Gli-1. Besides, jervine suppressed the proliferation and promoted the apoptosis of MUTZ-1 cells, as well as inhibited the transition of cells from G1 to S phase.

CONCLUSION

Shh signaling pathway of MDS patients is abnormally activated and participated in the occurrence and progression of MDS. Jervine intervention is a potential therapeutic strategy for MDS.

Recent Advances in Arsenic Research: Significance of Differential Susceptibility and Sustainable Strategies for Mitigation

Arsenic contamination in drinking water and associated adverse outcomes are one of the major health issues in more than 50 countries worldwide. The scenario is getting even more detrimental with increasing number of affected people and newer sites reported from all over the world. Apart from drinking water, the presence of arsenic has been found in various other dietary sources. Chronic arsenic toxicity affects multiple physiological systems and may cause malignancies leading to death. Exposed individuals, residing in the same area, developed differential dermatological lesion phenotypes and varied susceptibility toward various other arsenic-induced disease risk, even after consuming equivalent amount of arsenic from the similar source, over the same duration of time. Researches so far indicate that differential susceptibility plays an important role in arsenic-induced disease manifestation. In this comprehensive review, we have identified major population-based studies of the last 20 years, indicating possible causes of differential susceptibility emphasizing arsenic methylation capacity, variation in host genome (single nucleotide polymorphism), and individual epigenetic pattern (DNA methylation, histone modification, and miRNA expression). Holistic multidisciplinary strategies need to be implemented with few sustainable yet cost-effective solutions like alternative water source, treatment of arsenic-contaminated water, new adaptations in irrigation system, simple modifications in cooking strategy, and dietary supplementations to combat this menace. Our review focuses on the present perspectives of arsenic research with special emphasis on the probable causes of differential susceptibility toward chronic arsenic toxicity and sustainable remediation strategies.

Melarsomine suppresses canine osteosarcoma cell survival via inhibition of Hedgehog-GLI signaling

The Hedgehog-GLI signaling pathway is activated in human and canine osteosarcoma (OSA) and represents a potential therapeutic target for cancers, including OSA. Arsenic trioxide represses GLI expression. Melarsomine, an arsenic compound-containing drug, has been approved for the treatment of canine heartworm disease. Hence, we hypothesized that melarsomine inhibits GLI signaling in canine OSA cell lines. The present study aimed to assess this hypothesis. Cell viability and colony formation were decreased in the canine OSA cell lines Abrams and D17 after treatment with melarsomine. Melarsomine-induced apoptotic cell death was assessed via cell cycle analysis using propidium iodide staining. Quantitative real-time reverse transcription polymerase chain reaction and western blot analyses revealed a downregulation of genes downstream of the Hedgehog signaling pathway, including GLI1, GLI2, and PTCH, after melarsomine treatment. The present results suggest that melarsomine exerts antitumor effects and serves as a GLI inhibitor in canine OSA cells. Additional studies are required to evaluate and confirm the anticancer effect and relevant therapeutic dose of melarsomine in vivo.

Metabolic and epigenetic reprogramming in the arsenic-induced cancer stem cells

At present, the belief that genetic mutations control every aspect of tumorigenesis is still very popular. Even for the highly debated "bad luck" theory of cancers, it ascertained that random mutation of genes during the self-renewal of somatic stem cells is responsible for cancer initiation. Logically, most of the new therapeutic strategies so far, from molecular targeting to precision medicine or personalized medicine, are genome-obsessed and focused on identifying and targeting these mutated genes. Accordingly, a rather simplified therapeutic regimen was formulated: cancers with the same mutations, e.g., lung cancer, pancreatic cancer, breast cancer, ovarian cancer, etc, were managed with the same chemo or targeting medicine, whereas for a particular cancer, such as breast cancer or lung cancer, with different mutational spectrums was treated with different, so-called personalized medicine. The outcomes of this strategy, however, are mixed with encouraging and disappointing findings. In this review article, we will address the importance of non-genetic factors, the metabolic and epigenetic reprogramming, during the induction of cancer stem cells in response to arsenic, a major environmental human carcinogen. The information provided may not only advance our understanding of carcinogenic mechanism to a new level but also help in designing new strategies through targeting the metabolic and epigenetic signaling pathways for cancer therapy.

Embryonic arsenic exposure reduces intestinal cell proliferation and alters hepatic IGF mRNA expression in killifish (Fundulus heteroclitus)

Arsenic (As) is a toxicant found in food and water throughout the world, and studies suggested that exposure early in life reduces growth. Thus, the goal of this study was to examine mechanisms by which As impacted organismal growth. Killifish (Fundulus heteroclitus) were exposed to 0, 10, 50, or 200 ppb As as embryos and, after hatching, were reared in clean water for up to 40 weeks. Metabolism studies revealed that killifish biotransform As such that monomethylated and dimethylated arsenicals account for 15-17% and 45-61%, respectively, of the total metal. Growth, as measured by condition factor (CF), was significantly and dose-dependently reduced at 8 weeks of age but was similar to controls by 40 weeks. To determine mechanisms underlying the observed initial decrease, intestinal proliferation and morphology were examined. Arsenic-exposed fish exhibited significant 1.3- to 1.5-fold reduction in intestinal villus height and 1.4- to 1.6-fold decrease in proliferating cell nuclear antigen (PCNA+) intestinal cells at all weeks examined. In addition, there were significant correlations between CF, PCNA+ cells, and intestinal villus height. Upon examining whether fish might compensate for the intestinal changes, it was found that hepatic mRNA expression of insulin-like growth factor 1 (IGF-1) and its binding protein (IGFBP-1) were dose-dependently increased. These results indicate that embryonic exposure initially diminished growth, and while intestinal cell proliferation remained reduced, fish appear to compensate by enhancing transcript levels of hepatic IGF-1 and IGFBP-1.

Arsenic Induces Members of the mmu-miR-466-669 Cluster Which Reduces NeuroD1 Expression

Chronic arsenic exposure can result in adverse development effects including decreased intellectual function, reduced birth weight, and altered locomotor activity. Previous in vitro studies have shown that arsenic inhibits stem cell differentiation. MicroRNAs (miRNAs) are small noncoding RNAs that regulate multiple cellular processes including embryonic development and cell differentiation. The purpose of this study was to examine whether altered miRNA expression was a mechanism by which arsenic inhibited cellular differentiation. The pluripotent P19 mouse embryonal carcinoma cells were exposed to 0 or 0.5 μM sodium arsenite for 9 days during cell differentiation, and changes in miRNA expression was analyzed using microarrays. We found that the expression of several miRNAs important in cellular differentiation, such as miR-9 and miR-199 were decreased by 1.9- and 1.6-fold, respectively, following arsenic exposure, while miR-92a, miR-291a, and miR-709 were increased by 3-, 3.7-, and 1.6-fold, respectively. The members of the miR-466-669 cluster and its host gene, Scm-like with 4 Mbt domains 2 (Sfmbt2), were significantly induced by arsenic from 1.5- to 4-fold in a time-dependent manner. Multiple miRNA target prediction programs revealed that several neurogenic transcription factors appear to be targets of the cluster. When consensus anti-miRNAs targeting the miR-466-669 cluster were transfected into P19 cells, arsenic-exposed cells were able to more effectively differentiate. The consensus anti-miRNAs appeared to rescue the inhibitory effects of arsenic on cell differentiation due to an increased expression of NeuroD1. Taken together, we conclude that arsenic induces the miR-466-669 cluster, and that this induction acts to inhibit cellular differentiation in part due to a repression of NeuroD1.

Mechanism of arsenite toxicity in embryonic stem cells

Environmental arsenite exposure has been linked to cancer as well as other diseases, presenting an important and serious public health problem. Toxicity of inorganic arsenite (iAs) has been investigated using animal models and cell culture, yet its developmental effects are poorly understood. This study investigated the molecular mechanism of iAs toxicity to ascertain insight into development and differentiation processes using mouse embryonic stem cells (ESCs). The results showed that iAs exposure affected morphology and integrity of ESC colonies as well as inhibited cell growth in a concentration-dependent manner, excluding concentrations <1 μM iAs which stimulated ESC growth. ESCs self-renewal and pluripotency was also affected as evident from the downregulation of transcription circuitry, Oct4, Nanog, Sox2 and Klf4 resulting in non-specific differentiation. ESCs exposed to iAs randomly differentiated into three germ layers, mesoderm, endoderm and ectoderm, as judged by transcriptional expression of Brachyury, Gata4 and FGF2, as well as translational expression of BRACHYURY, GATA4 and TUJ1 respectively. The differentiated cells represented osteogenic, chondrogenic, myogenic and neurogenic lineages as evident from upregulation of Col1, Sox9, Col2, Myog, Notch, Nes and Nef. Although iAs caused slight apoptosis with a concomitant increase in ROS levels, the exposed ESCs had significant Bcl2 expression, which could be involved in the protection against apoptosis. Further analysis revealed upregulation of Jun and P38 in ESCs with an increase in iAs concentration. These observations indicated that iAs stress caused random differentiation of ESCs via JNK/P38 pathways. These findings suggest that iAs exposure may cause teratogenicity during early fetal development. Copyright © 2017 John Wiley & Sons, Ltd.

Prenatal arsenic exposure alters REST/NRSF and microRNA regulators of embryonic neural stem cell fate in a sex-dependent manner

Exposure to arsenic, a common environmental toxin found in drinking water, leads to a host of neurological pathologies. We have previously demonstrated that developmental exposure to a low level of arsenic (50ppb) alters epigenetic processes that underlie deficits in adult hippocampal neurogenesis leading to aberrant behavior. It is unclear if arsenic impacts the programming and regulation of embryonic neurogenesis during development when exposure occurs. The master negative regulator of neural-lineage, REST/NRSF, controls the precise timing of fate specification and differentiation of neural stem cells (NSCs). Early in development (embryonic day 14), we observed increased expression of Rest, its co-repressor, CoREST, and the inhibitory RNA binding/splicing protein, Ptbp1, and altered expression of mRNA spliced isoforms of Pbx1 that are directly regulated by these factors in the male brain in response to prenatal 50ppb arsenic exposure. These increases were concurrent with decreased expression of microRNA-9 (miR-9), miR-9*, and miR-124, all of which are REST/NRSF targets and inversely regulate Rest expression to allow for maturation of NSCs. Exposure to arsenic decreased the formation of neuroblasts in vitro from NSCs derived from male pup brains. The female response to arsenic was limited to increased expression of CoREST and Ptbp2, an RNA binding protein that allows for appropriate splicing of genes involved in the progression of neurogenesis. These changes were accompanied by increased neuroblast formation in vitro from NSCs derived from female pups. Unexposed male mice express transcriptomic factors to induce differentiation earlier in development compared to unexposed females. Thus, arsenic exposure likely delays differentiation of NSCs in males while potentially inducing precocious differentiation in females early in development. These effects are mitigated by embryonic day 18 of development. Arsenic-induced dysregulation of the regulatory loop formed by REST/NRSF, its target microRNAs, miR-9 and miR-124, and RNA splicing proteins, PTBP1 and 2, leads to aberrant programming of NSC function that is perhaps perpetuated into adulthood inducing deficits in differentiation we have previously observed.

Cryptolepine derivative-6h inhibits liver fibrosis in TGF-β1-induced HSC-T6 cells by targeting the Shh pathway

Liver fibrosis is a worldwide problem with a significant morbidity and mortality. Cryptolepis sanguinolenta (family Periplocaceae) is widely used in West African countries for the treatment of malaria, as well as for some other diseases. However, the role of C. sanguinolenta in hepatic fibrosis is still unknown. It has been reported that Methyl-CpG binding protein 2 (MeCP2) had a high expression in liver fibrosis and played a central role in its pathobiology. Interestingly, we found that a cryptolepine derivative (HZ-6h) could inhibit liver fibrosis by reducing MeCP2 expression, as evidenced by the dramatic downregulation of α-smooth muscle actin (α-SMA) and type I collagen alpha-1 (Col1α1) in protein levels in vitro. Meanwhile, we also found that HZ-6h could reduce the cell viability and promote apoptosis of hepatic stellate cells (HSCs) treated with transforming growth factor beta 1(TGF-β1). Then, we investigated the potential molecular mechanisms and found that HZ-6h blocked Shh signaling in HSC-T6 cells, resulting in the decreased protein expression of Patched-1 (PTCH-1), Sonic hedgehog (Shh), and glioma-associated oncogene homolog 1 (GLI1). In short, these results indicate that HZ-6h inhibits liver fibrosis by downregulating MeCP2 through the Shh pathway in TGF-β1-induced HSC-T6 cells.

Arsenic inhibits stem cell differentiation by altering the interplay between the Wnt3a and Notch signaling pathways

data indicates that arsenic exposure inhibits stem cell differentiation. This study investigated whether arsenic disrupted the Wnt3a signaling pathway, critical in the formation of myotubes and neurons, during the differentiation in P19 mouse embryonic stem cells. Cells were exposed to 0, 0.1, or 0.5 μM arsenite, with or without exogenous Wnt3a, for up to 9 days of differentiation. Arsenic exposure alone inhibits the differentiation of stem cells into neurons and skeletal myotubes, and reduces the expression of both β-catenin and GSK3β mRNA to ~55% of control levels. Co-culture of the arsenic-exposed cells with exogenous Wnt3a rescues the morphological phenotype, but does not alter transcript, protein, or phosphorylation status of GSK3β or β-catenin. However, arsenic exposure maintains high levels of Hes5 and decreases the expression of MASH1 by 2.2-fold, which are anti- and pro-myogenic and neurogenic genes, respectively, in the Notch signaling pathway. While rescue with exogenous Wnt3a reduced Hes5 levels, MASH1 levels stay repressed. Thus, while Wnt3a can partially rescue the inhibition of differentiation from arsenic, it does so by also modulating Notch target genes rather than only working through the canonical Wnt signaling pathway. These results indicate that arsenic alters the interplay between multiple signaling pathways, leading to reduced stem cell differentiation.

Melittin induces PTCH1 expression by down-regulating MeCP2 in human hepatocellular carcinoma SMMC-7721 cells

Hepatocellular carcinoma (HCC) has a high mortality rate worldwide and still remains to be a noticeable public health problem. Therefore, new remedies are urgently needed. Melittin, a major component of bee venom, is known to suppress cell growth in various cancers including HCC. However, the mechanism of the anticancer effect of melittin on HCC has not been fully elucidated. It has been reported that Methyl-CpG binding protein 2 (MeCP2) plays a key role in tumor proliferation, apoptosis, migration and invasion. In the present study, we found the high expression of MeCP2 in human HCC tissues and in the SMMC-7721 cell line. MeCP2 silencing inhibited cell proliferation, while over-expression of MeCP2 promoted cell growth in SMMC-7721 cells. It indicates that MeCP2 may be an attractive target for human HCC. We further found that melittin could inhibit cell proliferation by reducing MeCP2 expression in vitro. Interestingly, the inhibitory effect of melittin on cell proliferation was due to a delay in G0/G1 cell cycle progression, without influencing cell apoptosis. Next, we investigated the potential molecular mechanisms and found that MeCP2 could modulate Shh signaling in SMMC-7721 cells. Further study indicates that melittin may induce the demethylation of PTCH1 promoter, resulting in the increased expression of PTCH1. Furthermore, the expression of Shh and GLI1 was significantly lowered upon treatment of melittin. These results suggest that melittin can block Shh signaling in vitro. In short, these results indicate that melittin inhibits cell proliferation by down-regulating MeCP2 through Shh signaling in SMMC-7721 cells.

Arsenic and Its Methylated Metabolites Inhibit the Differentiation of Neural Plate Border Specifier Cells

Exposure to arsenic in food and drinking water has been correlated with adverse developmental outcomes, such as reductions in birth weight and neurological deficits. Additionally, studies have shown that arsenic suppresses sensory neuron formation and skeletal muscle myogenesis, although the reason why arsenic targets both of these cell types in unclear. Thus, P19 mouse embryonic stem cells were used to investigate the mechanisms by which arsenic could inhibit cellular differentiation. P19 cells were exposed to 0, 0.1, or 0.5 μM sodium arsenite and induced to form embryoid bodies over a period of 5 days. The expression of transcription factors necessary to form neural plate border specifier (NPBS) cells, neural crest cells and their progenitors, and myocytes and their progenitors were examined. Early during differentiation, arsenic significantly reduced the transcript and protein expression of Msx1 and Pax3, both needed for NPBS cell formation. Arsenic also significantly reduced the protein expression of Sox 10, needed for neural crest progenitor cell production, by 31-50%, and downregulated the protein and mRNA levels of NeuroD1, needed for neural crest cell differentiation, in a time- and dose-dependent manner. While the overall protein expression of transcription factors in the skeletal muscle lineage was not changed, arsenic did alter their nuclear localization. MyoD nuclear translocation was significantly reduced on days 2-5 between 15 and 70%. At a 10-fold lower concentration, monomethylarsonous acid (MMA III) appeared to be just as potent as inorganic arsenic at reducing the mRNA levels Pax3 (79% vs84%), Sox10 (49% vs 65%), and Msx1 (56% vs 56%). Dimethylarsinous acid (DMA III) also reduced protein and transcript expression, but the changes were less dramatic than those with MMA or arsenite. All three arsenic species reduced the nuclear localization of MyoD and NeuroD1 in a similar manner. The early changes in the differentiation of neural plate border specifier cells may provide a mechanism for arsenic to suppress both neurogenesis and myogenesis.