Retinoic acid-induced alterations in the expression of growth factors in embryonic mouse palatal shelves

Novel investigations in retinoic-acid-induced cleft palate about the gut microbiome of pregnant mice

Introduction

Cleft palate (CP) is one of the most common congenital birth defects in the craniofacial region, retinoic acid (RA) gavage is the most common method for inducing cleft palate model. Although several mechanisms have been proposed to illuminate RA-induced cleft palate during embryonic development, these findings are far from enough. Many efforts remain to be devoted to studying the etiology and pathogenesis of cleft palate. Recent research is gradually shifting the focus to the effect of retinoic acid on gut microbiota. However, few reports focus on the relationship between the occurrence of CP in embryos and gut microbiota.

Methods

In our research, we used RA to induce cleft palate model for E10.5 the feces of 5 RA-treated pregnant mice and 5 control pregnant mice were respectively metagenomics analysis.

Results

Compared with the control group, Lactobacillus in the gut microbiome the RA group was significantly increased. GO, KEGG and CAZy analysis of differentially unigenes demonstrated the most abundant metabolic pathway in different groups, lipopolysaccharide biosynthesis, and histidine metabolism.

Discussion

Our findings indicated that changes in the maternal gut microbiome palatal development, which might be related to changes in Lactobacillus and These results provide a new direction in the pathogenesis of CP induced by RA.

Perturbed development of cranial neural crest cells in association with reduced sonic hedgehog signaling underlies the pathogenesis of retinoic-acid-induced cleft palate

Cleft palate (CP) is one of the most common congenital craniofacial anomalies in humans and can be caused by either single or multiple genetic and environmental factor(s). With respect to environmental factors, excessive intake of vitamin A during early pregnancy is associated with increased incidence of CP in offspring both in humans and in animal models. Vitamin A is metabolized to retinoic acid (RA); however, the pathogenetic mechanism of CP caused by altered RA signaling during early embryogenesis is not fully understood. To investigate the detailed cellular and molecular mechanism of RA-induced CP, we administered all-trans RA to pregnant mice at embryonic day (E)8.5. In the RA-treated group, we observed altered expression of Sox10, which marks cranial neural crest cells (CNCCs). Disruption of Sox10 expression was also observed at E10.5 in the maxillary component of the first branchial arch, which gives rise to secondary palatal shelves. Moreover, we found significant elevation of CNCC apoptosis in RA-treated embryos. RNA-sequencing comparisons of RA-treated embryos compared to controls revealed alterations in Sonic hedgehog (Shh) signaling. More specifically, the expression of Shh and its downstream genes Ptch1 and Gli1 was spatiotemporally downregulated in the developing face of RA-treated embryos. Consistent with these findings, the incidence of CP in association with excessive RA signaling was reduced by administration of the Shh signaling agonist SAG (Smoothened agonist). Altogether, our results uncovered a novel mechanistic association between RA-induced CP with decreased Shh signaling and elevated CNCC apoptosis.

Characterizing cleft palate toxicants using ToxCast data, chemical structure, and the biomedical literature

Cleft palate has been linked to both genetic and environmental factors that perturb key events during palatal morphogenesis. As a developmental outcome, it presents a challenging, mechanistically complex endpoint for predictive modeling. A data set of 500 chemicals evaluated for their ability to induce cleft palate in animal prenatal developmental studies was compiled from Toxicity Reference Database and the biomedical literature, which included 63 cleft palate active and 437 inactive chemicals. To characterize the potential molecular targets for chemical-induced cleft palate, we mined the ToxCast high-throughput screening database for patterns and linkages in bioactivity profiles and chemical structural descriptors. ToxCast assay results were filtered for cytotoxicity and grouped by target gene activity to produce a "gene score." Following unsuccessful attempts to derive a global prediction model using structural and gene score descriptors, hierarchical clustering was applied to the set of 63 cleft palate positives to extract local structure-bioactivity clusters for follow-up study. Patterns of enrichment were confirmed on the complete data set, that is, including cleft palate inactives, and putative molecular initiating events identified. The clusters corresponded to ToxCast assays for cytochrome P450s, G-protein coupled receptors, retinoic acid receptors, the glucocorticoid receptor, and tyrosine kinases/phosphatases. These patterns and linkages were organized into preliminary decision trees and the resulting inferences were mapped to a putative adverse outcome pathway framework for cleft palate supported by literature evidence of current mechanistic understanding. This general data-driven approach offers a promising avenue for mining chemical-bioassay drivers of complex developmental endpoints where data are often limited.

[Influence of dexamethasone on the cell polarity and PAR complex of the embryonic epithelial cells in the palate]

OBJECTIVE

This study aims to investigate whether dexamethasone (DEX) can down-regulate the PAR complex and disrupt the cell polarity in the palatal epithelium during palatal fusion.

METHODS

Pregnant rats were randomly divided into control and DEX groups, which were injected intraperitoneally with 0.9% sodium chloride (0.1 mL) and DEX (6 mg·kg ⁻¹), respectively, every day from E10 to E12. The palatal epithelial morphology was observed using hematoxylin and eosin staining and scanning electron microscopy. Immunofluorescence staining, Western Blot analysis, and real-time polymerase chain reaction were performed to detect the expression of PAR3, PAR6, and aPKC.

RESULTS

The incidence of cleft palate in DEX group (46.15%) was significantly higher than that in control group (3.92%), and the difference was statistically significant (χ2=24.335, P=0.00). DEX can also retard the growth of the palatal shelves and the short palatal shelves. The morphology and arrangement of MEE cells changed from polarized bilayer cells to nonpolarized monolayer ones. Additionally, the spherical structure decreased, which caused the cleft palate. PAR3 and PAR6 were only detected in the palatal epithelium, and aPKC was expressed in the palatal epithelium and mesenchyme. DEX can reduce the expression levels of PAR3, PAR6, and aPKC in the protein and gene levels.

CONCLUSIONS

DEX can down-regulate the complex gene expression in the MEE cells, thereby destroying the cell polarity and causing cleft palate.

Development of an organotypic stem cell model for the study of human embryonic palatal fusion

BACKGROUND

Cleft palate (CP) is a common birth defect, occurring in an estimated 1 in 1,000 births worldwide. The secondary palate is formed by paired palatal shelves, consisting of a mesenchymal core with an outer layer of epithelial cells that grow toward each other, attach, and fuse. One of the mechanisms that can cause CP is failure of fusion, that is, failure to remove the epithelial seam between the palatal shelves to allow the mesenchyme confluence. Epidermal growth factor (EGF) plays an important role in palate growth and differentiation, while it may impede fusion.

METHODS

We developed a 3D organotypic model using human mesenchymal and epithelial stem cells to mimic human embryonic palatal shelves, and tested the effects of human EGF (hEGF) on proliferation and fusion. Spheroids were generated from human umbilical-derived mesenchymal stem cells (hMSCs) directed down an osteogenic lineage. Heterotypic spheroids, or organoids, were constructed by coating hMSC spheroids with extracellular matrix solution followed by a layer of human progenitor epithelial keratinocytes (hPEKs). Organoids were incubated in co-culture medium with or without hEGF and assessed for cell proliferation and time to fusion.

RESULTS

Osteogenic differentiation in hMSC spheroids was highest by Day 13. hEGF delayed fusion of organoids after 12 and 18 hr of contact. hEGF increased proliferation in organoids at 4 ng/ml, and proliferation was detected in hPEKs alone.

CONCLUSION

Our results show that this model of human palatal fusion appropriately mimics the morphology of the developing human palate and responds to hEGF as expected.

Involvement of RBP4 in all‑trans retinoic acid induced cleft palate

The current study was designed to elucidate the mechanism of retinol binding protein 4 (RBP4) in cleft palate induced by all‑trans retinoic acid (atRA). To establish a cleft palate model in C57BL/6J mice, pregnant mice were administered atRA (100 mg/kg) by gavage at the tenth embryonic stage (E10.0). Control groups were given the equivalent volume of corn oil. Pregnant mice were dissected at E12.5, E13.5 and E14.5 to obtain the embryonic palates. The expression levels of RBP4 in the embryonic palatal mesenchyme (EPM) were determined by immunohistochemistry, reverse transcription‑quantitative polymerase chain reaction (RT‑qPCR) and western blotting. Human embryonic palatal mesenchymal cells were exposed to atRA to detect the variation in RBP4 induced by atRA in vitro. Small interfering RNA was used to suppress the expression of RBP4, and a plasmid overexpressing RBP4 was used to examine upregulated expression. The cell counting kit‑8 assay was used to evaluate the effect of RBP4 on cell proliferation. The expression levels of p27 and cyclin D1 were determined by RT‑qPCR and western blotting, while the expression levels of extracellular signal‑related kinase (ERK) 1/2 and protein kinase B (AKT) were assessed by western blotting. At E14.5, RBP4 was strongly expressed in the EPM, while it was downregulated following atRA treatment, which induced cleft palate in vivo. In vitro experiments indicated that atRA suppressed the expression of RBP4 and altered the expression of p27 and cyclin D1 to cause growth inhibition. Knockdown of RBP4 resulted in decreased expression of cyclin D1 and increased p27, and suppressed proliferation. Overexpression of RBP4 reversed the inhibitory effect of atRA and promoted proliferation via the ERK1/2 and AKT signaling pathways. These results suggested that RBP4 was involved in cleft palate induced by atRA and it can be suppressed by atRA to cause growth inhibition in the embryonic palate.

Transmission analysis of TGFB1 gene polymorphisms in non-syndromic cleft lip with or without cleft palate

OBJECTIVES

Transforming growth factor beta1 (TGF-β1) plays a significant role in craniofacial development. Previous linkage studies reported that the TGF-β1-locus at 19q13.1 harbour predisposing genes for non-syndromic oral clefts. In the present study case parents triads were evaluated to find the transmission effects of genetic variants in TGF- β1 towards non-syndromic cleft lip or palate (NSCL/P).

METHODS

Using allelic discrimination method148 families (case-parent triads) were assessed for single nucleotide polymorphisms (SNPs) in TGF-β1 gene. The SNPs were checked for mendelian errors and Hardy-Weinberg equilibrium (HWE). Transmission disequilibrium test and haplotype frequencies were estimated.

RESULTS

The TGF-β1 SNPs showed very low minor allele frequencies (MAFs) and observed heterozygosity (Hobs). The transmission disequilibrium test (TDT) and parent-of-origin likelihood ratio tests (PO-LRT) were not significant for any of the SNPs tested. Strong linkage disequilibrium (r² = 0.722) was found between rs1800469 and rs1800470 SNPs. Haplotype analysis ignoring parent of origin showed strong evidence of excess transmission but it is not significant (p-value = 0.293).

CONCLUSION

Transmission of minor alleles were not observed from either parent indicating that the TGF-β1 gene polymorphisms by themselves do not confer risk for non-syndromic oral clefts but, rather, modify the stability and the activation process of TGF-β1. As the number of families included in the study are less, results must be considered still preliminary and require replication using more families.

Copy Number Changes Identified Using Whole Exome Sequencing in Nonsyndromic Cleft Lip and Palate in a Honduran Population

BACKGROUND

The majority of cleft lip with or without cleft palate cases appear as an isolated, nonsyndromic entity (NSCLP). With the advent of next generation sequencing, whole exome sequencing (WES) has been used to identify single nucleotide variants and insertion/deletions which cause or increase the risk of NSCLP. However, to our knowledge, there are no published studies using WES in NSCLP to investigate copy number changes (CNCs), which are a major component of human genetic variation. Our study aimed to identify CNCs associated with NSCLP in a Honduran population using WES.

METHODS

WES was performed on two to four members of 27 multiplex Honduran families. CNCs were identified using two algorithms, CoNIFER and XHMM. Priority was given to CNCs that were identified in more than one patient and had variant frequencies of less than 5% in reference data sets.

RESULTS

WES completion was defined as >90% of the WES target at >8 × coverage and >80% of the WES target at >20 × coverage. Twenty-four CNCs that met our inclusion criteria were identified by both CoNIFER and XHMM. These CNCs were confirmed using quantitative PCR. Pedigree analysis produced three CNCs corresponding to ADH7, AHR, and CRYZ segregating with NSCLP. Two of the three CNCs implicate genes, AHR and ADH7, whose known biological functions could plausibly play a role in NSCLP.

CONCLUSION

WES can be used to detect candidate CNCs that may be involved in the pathophysiology of NSCLP. Birth Defects Research 109:1257-1267, 2017. © 2017 Wiley Periodicals, Inc.

Excessive retinoic acid inhibit mouse embryonic palate mesenchymal cell growth through involvement of Smad signaling

All-trans retinoic acid (atRA), the oxidative metabolite of retinoic acid (RA), is essential for palatogenesis. Overdose RA is capable of inducing cleft palate in mice and humans. Normal embryonic palatal mesenchymal (EPM) cell growth is crucial for shelf growth. Smad signaling is involved in many biological processes. However, it is not much clear if atRA could affect Smad signaling during EPM cells growth. In this study, the timed pregnant mice with maternal administration of 100 mg/kg body weight of RA by gastric intubation were cervical dislocation executed to evaluate growth changes of palatal shelves by hematoxylin and eosin (H&E) staining. At the same time, a primary mouse EPM (MEPM) cell culture model was also established. MEPM cells were treated with atRA (0.1, 0.5, 1, 5 and 10 μM) for 24, 48 and 72 h. The results indicated that the sizes of the shelves were smaller than those in control. AtRA inhibited MEPM cell growth with both increasing concentration and increasing incubation time, especially at 72 h in vitro. Moreover, atRA significantly increased the mRNA and protein expression levels of Smad7 (P < .05), but the mRNA and protein expression levels of PCNA were reduced (P < .05). We also found atRA inhibited phosphorylation of Smad2 compared with untreated group (P < .05). However, the protein and mRNA levels of Smad2 did not change both in atRA-treated and untreated group (P > .05). We demonstrated that RA induced inhibition of MEPM cell growth that could cause cleft palate partly by down-regulation of Smad pathway.

My Winding Road: From Microbiology to Toxicology and Environmental Health

I would certainly never have predicted that I would become the director of the National Institute of Environmental Health Sciences (NIEHS) and the National Toxicology Program (NTP) when I was a Jewish girl growing up in Teaneck, New Jersey. My family stressed the importance of education. Yet for a girl there were many not-so-subtle suggestions that the appropriate careers were in teaching or nursing, and the most important thing was to be a wife and mother. Well, I can't disagree with the latter, although I would have to add grandmother to that list of achievements. My parents were both college graduates, but my mom only taught high school English for one year before leaving the field to start our family. My dad returned from World War II and joined his brother in accounting. After my first sister was born, my father joined my mother's family jewelry business and helped to open a second retail store. My mother helped my dad out during the busy times—Christmas and wedding season—but otherwise focused on our growing family of three girls and one boy. This became increasingly challenging when it became clear that my little brother was severely retarded and would require extra care.

Cephalometric Analysis of Craniofacial Malformations in Newborn Mice with Cleft Palate Induced by Retinoic Acid

Objective

To determine changes on craniofacial growth morphometrically in newborn mice with cleft palate induced by retinoic acid.

Design, Setting, Participants, Interventions

Gestation day 10 or 12 pregnant female C57BL/6N mice were given a single dose of all-trans retinoic acid (atRA) by gastric intubations via oral gavage. Sixty newborn mice with cleft palate (CP), 52 without CP from the experimental group, and 30 without CP from the control group were collected, and lateral cephalograms were taken of all of the mice.

Main Outcome Measures

Cephalometric analysis of the craniofacial skeleton was performed by means of a personal computer.

Results

Inhibition of craniofacial growth was found in the experimental groups but not in the control groups. In the maxillary bone and mandible, the amount of growth was significantly reduced.

Conclusions

These results suggest that craniofacial growth is inhibited in newborn mice with cleft palate induced by retinoic acid.

A preliminary study on the teratogenesis of dexamethasone and the preventive effect of vitamin B12 on murine embryonic palatal shelf fusion in vitro

Excessive dexamethasone (Dex) administrated into pregnant mice during critical periods of palatal development can produce a high incidence of cleft palate. Its mechanisms remain unknown. Vitamin B12 has been shown to antagonize the teratogenic effects of Dex, which, however, remains controversial. In this study, we investigated the effects of Dex and vitamin B12 on murine embryonic palatal shelf fusion using organ culture of murine embryonic shelves. The explanted palatal shelves on embryonic day 14 (E14) were cultured for 24, 48, 72 or 96 h in different concentrations of Dex and/or vitamin B12. The palatal shelves were examined histologically for the morphological alterations on the medial edge epithelium (MEE) and fusion rates among different groups. It was found that the palatal shelves were not fused at 72 h or less of culture in Dex group, while they were completely fused in the control and vitamin B12-treated groups at 72 and 96 h, respectively. The MEE still existed and proliferated. In Dex+vitamin B12 group the palatal shelves were fused at each time point in a similar rate to controls. These results may suggest that Dex causes teratogenesis of murine embryonic palatal shelves and vitamin B12 prevents the teratogenic effect of Dex on palatogenesis on murine embryos in vitro.

The Intersection Between the Aryl Hydrocarbon Receptor (AhR)‐ and Retinoic Acid‐Signaling Pathways

Data from a variety of animal and cell culture model systems have demonstrated an interaction between the aryl hydrocarbon receptor (AhR)- and retinoic acid (RA)-signaling pathways. The AhR(1) was originally identified as the receptor for the polycyclic aromatic hydrocarbon family of environmental contaminants; however, recent data indicate that the AhR binds to a variety of endogenous and exogenous compounds, including some synthetic retinoids. In addition, activation of the AhR pathway alters the function of nuclear hormone-signaling pathways, including the estrogen, thyroid, and RA pathways. Activation of the AhR pathway through exposure to environmental compounds results in significant changes in RA synthesis, catabolism, transport, and excretion. Some effects on retinoid homeostasis mediated by the AhR pathway may result from the interactions of these two pathways at the level of activating or repressing the expression of specific genes. This chapter will review these two pathways, the evidence demonstrating a link between them, and the data indicating the molecular basis of the interactions between these two pathways.

Nutrition and Genes in the Development of Orofacial Clefting

Clefts of the lip, alveolus, and/or palate, which are called orofacial clefts (OFC), occur in 0.5 to 3 per 1000 live and stillbirths. The pathogenesis of these congenital malformations remains largely unknown, but evidence is increasing that both nutritional and genetic factors are involved. Unlike genetic factors, nutritional causes can be corrected and may therefore contribute to the prevention of OFC. The goal of this review is to summarize the embryogenesis and genes involved in OFC, and to give an overview of the nutrients and related genes in humans. Improving our knowledge of the role of nutrition, genes, and their interactions in the pathogenesis of OFC may stimulate the development of nutritional interventions for OFC prevention in the future.

PDGF-C Controls proliferation and is down-regulated by retinoic acid in mouse embryonic palatal mesenchymal cells

BACKGROUND

Platelet-derived growth factor C (PDGF-C) was recently identified as a member of the PDGF ligand family. Some observation suggests that PDGF-C could play an important role in palatogenesis highlighted by the Pdgfc(-/-) mouse with cleft palate, which led us to examine the mechanism of PDGF-C signaling in palatogenesis. It is well known that retinoic acid (RA) is a teratogen that can effectively induce cleft palate in the mouse. Due to the critical roles of PDGF-C and RA in cleft palate, the link between cleft palate induced by RA and loss of PDGF-C was investigated.

METHODS

Retarded mesenchymal proliferation is an important cause for cleft palate. To clarify the mechanism of PDGF-C in palatogenesis, we evaluated the effects of PDGF-C and anti-PDGF-C neutralizing antibody on proliferation activity in mouse embryonic palatal mesenchymal (MEPM) cells.

RESULTS

Briefly, our results show PDGF-C promotes proliferation, anti-PDGF-C antibody inhibits it in MEPM cells, and RA downregulates the PDGF-C expression both at the mRNA and protein levels.

CONCLUSIONS

These demonstrate that PDGF-C is a potent mitogen for MEPM cells, implying that inactivated PDGF-C by gene-targeting or reduced PDGF-C by RA may both cause inhibition of proliferation in palatal shelves, which might account for the pathogenesis of cleft palate in Pdgfc(-/-) mouse or RA-treated mouse. In conclusion, our results suggest that PDGF-C signaling is a new mechanism of cleft palate induced by RA.

Transforming growth factor-beta1 signaling participates in the physiological and pathological regulation of mouse inner ear development by all-trans retinoic acid

BACKGROUND

Retinoic acid (RA) is a vitamin A derivative that participates in patterning and regulation of inner ear development. Either excess RA or RA deficiency during a critical stage of inner ear development can produce teratogenic effects. Previous studies have shown that in utero exposure of the developing mouse inner ear to a high dose of all-trans RA (atRA) results in severe malformations of the inner ear that are associated with diminished levels of endogenous transforming growth factor-beta1 (TGF-beta(1)) protein.

METHODS

In this study, the effects of a teratogenic level of atRA on levels and patterns of expression of TGFbeta receptor II (TGFbetaRII) and Smad2, a downstream component of the TGFbeta signal transduction pathway, are investigated in the developing mouse inner ear. The expression pattern of endogenous RA receptor alpha (RARalpha) and the ability of an RARalpha(1)-specific antisense oligonucleotide (AS) to modulate otic capsule chondrogenesis are demonstrated in the inner ear and in culture.

RESULTS

Endogenous TGFbetaRII and Smad2 are downregulated in the inner ear following in utero atRA treatment. In addition, a reduction in endogenous TGFbeta(1) and a marked suppression of chondrogenesis occur in RARalpha(1) AS-treated cultures in comparison to untreated or oligonucleotide-treated control cultures. This chondrogenic suppression can be partially overcome by supplementation of RARalpha(1) AS-treated cultures with exogenous TGFbeta(1) protein.

CONCLUSIONS

Our findings support a role for TGFbeta in the physiological and pathological effects of RA on inner ear development.

Teratogenic effects of retinoic acid are modulated in mice lacking expression of epidermal growth factor and transforming growth factor-alpha

BACKGROUND

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGFalpha) regulate cell proliferation and differentiation in the embryo. The induction of cleft palate (CP) by all trans-retinoic acid (RA) was associated with altered expression of TGFalpha, EGF receptor, and binding of EGF. This study uses knockout (KO) mice to examine the roles of EGF and TGFalpha in teratogenic responses of embryos exposed to RA.

METHODS

Pregnant wild-type (WT) mice of mixed genetic background, EGF KO, C57BL/6J, and TGFalpha KO mice were given a single oral dose of RA (100 mg/kg, 10 ml/kg) or corn oil on GD 10 at 12 PM, GD 11 at 12 PM or 4 PM, or GD 12 at 8 AM or 12 PM (plug day = GD 0). GD 18 fetuses were examined for external, visceral, and skeletal effects.

RESULTS

After exposure to RA on GD 12, the incidence of CP in EGF KO was significantly reduced relative to WT. In TGFalpha KO fetuses, RA exposure on GD 10 increased the incidence of CP versus C57BL/6J. The incidence of skeletal defects in the limbs, vertebrae, sternebrae, and ribs were also affected by lack of expression of EGF or TGFalpha with region-specific amelioration or exacerbation of the effects of RA. In TGFalpha KO fetuses, incidences of forelimb long bone and digit defects increased relative to C57BL/6J. In EGF KO fetuses, relative to WT, the incidence of hindlimb oligodactyly was increased. In EGF KO, but not WT, RA produced short, bent radius, humerus, and ulna. Both TGFalpha and EGF KO mice had increased incidences of dilation of the renal pelvis and this was reduced by RA.

CONCLUSIONS

RA exposure produced skeletal and visceral defects in all genotypes; however, EGF or TGFalpha KO influenced the incidence and severity of defects. This study supports a role for EGF and TGFalpha in the response to RA.

Effect of valproic acid on fetal and maternal organs in the mouse: a morphological study

Valproic acid (VPA) is an antiepileptic drug used clinically. Because of its known teratogenic properties VPA is not recommended for women of child bearing age. The present study was designed to assess the effects of VPA on both fetal and maternal organs. Randomized groups of pregnant mice were treated as follows: Group 1 (n = 10) 500 mg/kg VPA/day on gestation days 8-11; Group 2 (n = 10) 600 mg/kg VPA/day on gestation days 8-11; and Group 3 (n = 4) saline-injected controls. On gestation day 18, the pregnant mice were euthanized, fetuses collected and prepared for scanning electron microscopy. In addition, fetal and maternal organs were processed for routine histology, immunohistochemistry for growth factors (TGF alpha, beta-1, beta-2 and EGF) and transmission electron microscopy. Scanning microscopy revealed specific lesions induced by VPA in the fetus, namely spina bifida occulta, exencephaly, and exophthalmia. On the other hand, there were no detectable morphological changes in fetal or maternal organs by routine histology, immunohistochemistry or electron microscopy. The data suggest that the lesions present in the fetus are due to a direct effect by VPA on retinoic acid, a ubiquitous compound that has a role in normal development, rather than the lack of transport of sufficient nutrients to the fetus as a result of placental insufficiency due to VPA-induced toxicity.

Combination therapy with folic acid and methionine in the prevention of retinoic acid-induced cleft palate in mice

BACKGROUND

During formation of the secondary palate, clefting may result when critical developmental events are altered. The purpose of this study was to reduce the incidence of retinoic acid (RA)-induced cleft palate (CP) in mice by the co-administration of folic acid (FA), methionine (ME) or a combination of both.

METHODS

Four groups of time-pregnant Swiss Webster mice were injected intraperitoneally with 50 mg/kg RA on gestational day (GD) 10. Likewise, 4.0 mg/kg FA and 187 mg/kg ME were administered on GD 8-11. The experiment included a control group (RA plus H2O) and three experimental groups, (RA plus therapeutic doses of FA, ME, or FA + ME). Necropsies were carried out on GD 18 and pups were analyzed for teratogenic effects.

RESULTS

Litters that received no therapy exhibited 100% CP with individual pups showing 76% susceptibility. Each therapy administered separately reduced the frequency of CP to approximately 6%, and the combination of FA and ME completely prevented the occurrence of RA-induced cleft palate (0%). A second experiment was conducted in which therapy levels were decreased by 25%. Litters that did not receive therapy experienced 100% clefting and individual pups exhibited CP at 86%. These therapies administered separately did not alter significantly the frequency of cleft palate. The combined doses of FA and ME, however, lowered significantly the frequency of cleft palate to 46%. Decreases in limb and tail defects with FA + ME therapy were also observed in both experiments.

CONCLUSIONS

Although FA and ME, at appropriate levels, can reduce individually the frequency of RA-induced cleft palate and other defects in mice, the results from the present study suggest that there is an additive interaction between the two therapeutic agents that can reduce further the teratogenic impact of RA. Further studies are needed to assess the mechanism of action of concomitant doses of FA and ME in the reduction of drug-induced birth defects.

Chromosome 17: gene mapping studies of cleft lip with or without cleft palate in Chinese families

OBJECTIVE

Involvement of loci on chromosome 17, including retinoic acid receptor alpha (RARA) in nonsyndromic oral clefts has been reported in Caucasian populations, although never investigated in Asian populations. The purpose of the present study was to investigate several loci on chromosome 17, including RARA, in Chinese families.

PARTICIPANTS

Thirty-six multiplex families (310 individuals), ascertained through nonsyndromic cleft lip with or without cleft palate surgical probands from hospitals in Shanghai, China, participated in the present study. There were 23 families whose probands had cleft lip and cleft palate (CLP) and 13 with cleft lip alone (CL).

RESULTS

Seventeen markers, spanning chromosome 17 and about 10 cM apart were assessed. Logarithm of odds ratio (LOD) scores (two point and multipoint), model-free linkage analyses, and allelic association tests (transmission/disequilibrium, Fisher's exact tests, and chi-square) were performed on the total family sample, families with CLP probands (CLP subgroup), and families with CL probands (CL subgroup). LOD scores from the two-point analyses were inconclusive. Multipoint analyses rejected linkage except for a few regions in the CL subgroup. However, positive results were found using the model-free linkage and association methods (p < .05). The markers with positive results varied across the CL and CLP subgroups. However, the RARA region and loci nearby yielded consistently positive results.

CONCLUSION

Genetic variation within the RARA locus or nearby appears to be involved in the pathogenesis of nonsyndromic oral clefts in this population. Furthermore, based on the differing pattern of results in the CL versus CLP subgroups, it appears that the formation of CL and CLP is because of either differing alleles at the same genetic locus or different but related (and/or linked) genes that modify the severity and expression of oral clefting.

Availability of NMR microscopic observation of mouse embryo disorder: examination in malformations induced by maternal administration of retinoic acid

Nuclear magnetic resonance (NMR) microscopy is a magnetic resonance imaging method with enhanced spatial resolution due to the use of a high static magnetic field and high magnetic field gradients. It is considered to be a useful tool for non-invasive and continuous investigation of tissue and organs at the histological level. In this study, we applied NMR microscopy to assessment of morphology in mouse embryos using a developmental disorder model induced by retinoic acid administration. Pregnant mice were given 50 mg/kg all-trans retinoic acid at 8.5 dpc. Embryos were collected at several time points after treatment and examined by NMR microscopy after fixation. Two-dimensional and three-dimensional spin echo sequences were used. Tissue contrast on two-dimensional images changed according to length of repetition time and echo time, and also to developmental stage of embryos. Two-dimensional and three-dimensional images nondestructively demonstrated defects in development of the skeleton and soft tissue, e.g. hypoplasia of vertebrae in the lumbar and tail regions and dysplasia of the spinal cord, in embryos exposed to retinoic acid. These morphological abnormalities were confirmed by conventional assessment after imaging. Although further improvements are required, NMR microscopy will provide a new approach for multi-parameter assessment of embryonic development under physiological and pathological conditions.

Teratogenicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in mice lacking the expression of EGF and/or TGF-alpha

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) exposure produces hydronephrosis and cleft palate in mice. These responses are correlated with disruption of expression of epidermal growth factor (EGF) receptor ligands, primarily EGF and transforming growth factor-alpha (TGF-alpha), and altered epithelial cell proliferation and differentiation. This research examined the role of these growth factors in TCDD-induced teratogenicity by using wild type (WT) and knockout (-/-) mice that do not express EGF, TGF-alpha, or both EGF and TGF-alpha. Pregnant females were weighed on GD 12 and dosed by gavage with either corn oil or TCDD at 24 microg/kg, 5 ml/kg. On GD 17.5, the maternal parameters evaluated included body weight, body weight gain, liver weight (absolute and adjusted for body weight). The number of implantations, live and dead fetuses, early or late resorptions, the proportion of males, fetal body weight, fetal absolute and relative liver weight, placenta weight, incidence of cleft palate, and the severity and incidence of hydronephrosis were recorded. TCDD did not affect maternal weight gain, fetal weight, or survival, but maternal and fetal liver weights and liver-to-body weight ratios were increased in all genotypes. The WT and TGF-alpha (-/-), but not the EGF (-/-) and EGF + TGF-alpha (-/-) fetuses, developed cleft palate after exposure to 24 microg TCDD/kg. Hydronephrosis was induced by TCDD in all genotypes, with the incidence in EGF + TGF-alpha (-/-) fetuses comparable to that of the WT. The incidence and severity of this defect was substantially increased in EGF (-/-) and TGF-alpha (-/-). In conclusion, this study demonstrated that expression of EGF influences the induction of cleft palate by TCDD. Also, EGF and TGF-alpha are not required for the induction of hydronephrosis, but when either is absent the response of the fetal urinary tract to TCDD is enhanced.

Immunolocalization of fibroblast growth factor receptors 1 and 2 in mouse palate development

Recent evidence has implicated mutations of fibroblast growth factor receptors (FGF-R) in the pathogenesis of craniosynostotic syndromes. Cleft palate can be a component of such syndromes. The expression of FGF-R1 and FGF-R2 has been delineated in normally developing cranium, where they seem to regulate cellular differentiation and proliferation, respectively. The specific role of fibroblast growth factor signaling in mammalian palate development is unclear. The authors investigated the patterns of expression of FGF-R1 and FGF-R2 throughout mouse palatal development in the embryo. Time-dated CD-1 mouse heads (n = 135) were harvested at embryonic ages 12.5, 13.5, 14.5, 15.5, and 16.5 days (term gestation = 19.5 days), fixed in paraformaldehyde, embedded in paraffin, and sectioned. In addition, paired palatal shelves (n = 30) were isolated by means of microdissection from embryonic day--13.5 embryos, grown on Millipore filters in serum-free medium in vitro for 24, 48, 72, or 96 hours and processed for histological analysis. Immunohistochemical analysis for FGF-R1 and FGF-R2 was performed on the in vivo and in vitro specimens. FGF-R1 and FGF-R2 were found to be specifically expressed in the epithelium of the developing palatal shelves from the time of their outgrowth from the maxillary processes through completion of fusion in vivo and in vitro. Expression of both receptors was particularly strong during the phases of medial epithelial-medial epithelial contact between the individual shelves, through the formation of the medial epithelial seam, to the ultimate dissolution of the seam. Such a pattern of expression seems to implicate fibroblast growth factor signaling in the regulation of the critical phase of fusion of the bilateral shelves. The expression of both FGF-R1 and FGF-R2 in the lateral palatal mesenchyme, where such secondary structures as tooth primordia and bone begin to appear, also suggests a role for fibroblast growth factor signaling in the induction of ongoing differentiation and maturation of the palate after fusion. These data suggest that fibroblast growth factor signaling may play a role in the epithelial-mesenchymal interactions that dictate fusion and maturation of the developing palate. Furthermore, the data are consistent with the correlation of cleft palate formation with aberrant fibroblast growth factor signaling.

Synergistic teratogenic effects induced by retinoids in mice by coadministration of a RARalpha- or RARgamma-selective agonist with a RXR-selective agonist

To study the interaction of retinoid-induced limb defects and cleft palate on day 11 of gestation, a RXR-selective agonist (AGN191701, an arylpropenyl-thiophene-carboxylic acid derivative, 20 mg/kg orally) was coadministered with a RARalpha-agonist (Am580, an arylcarboxamidobenzoic acid derivative, 5 mg/kg orally) to NMRI mice. AGN191701 was neither fetotoxic nor teratogenic at the dose used but potentiated Am580-induced limb defects and cleft palate and prevented Am580-induced fetal weight retardation. These results suggest that Am580-induced limb defects and probably cleft palate on day 11 of gestation may be mediated via RARalpha-RXR heterodimerization, particularly in the absence of toxicokinetic interactions. AGN191701 was also coadministered with a RARgamma-agonist (CD437, an adamantyl-hydroxyphenyl naphthoic acid derivative, 15 mg/kg orally) on days 8 and 11 of gestation to investigate which CD437-induced defects are mediated via RARgamma-RXR heterodimerization. On day 8 of gestation, AGN191701 potentiated CD437-induced embryolethality, exencephaly, spina bifida aperta, cleft palate, and tail defects, as well as visceral and skeletal defects, but not micrognathia. On day 11 of gestation, the incidence of CD437-induced cleft palate and limb defects was also potentiated when coadministered with the RXR agonist. These results suggest that synergistic teratogenic effects can be induced by coadministration of two receptor-selective retinoids, indicating the importance of RARalpha-RXR and RARgamma-RXR heterodimers in producing structural defects during organogenesis.

Secalonic acid D alters the nature of and inhibits the binding of the transcription factors to the phorbol 12-O-tetradecanoate-13 acetate-response element in the developing murine secondary palate

Secalonic acid D (SAD), a mycotoxin produced by Penicillium oxalicum in corn, induces cleft palate (CP) in the offspring of exposed dams. Results of recent studies suggest that protein kinase C (PKC) inhibition by SAD may be relevant to its CP-induction. Downstream effects of PKC are determined by the nature of transcription factors (TF) that form the activator protein-1 (AP-1) and the binding of AP-1 (and other TF) to the phorbol 12-O-tetradecanoate-13 acetate-response element (TRE) to form AP-1-TRE complex, neither of which have been studied in the palate. The aims of the present study were to identify the components of the murine palatal AP-1-TRE complex during development and to uncover the effects of SAD on this complex. Western blots and gel mobility shift assays of control palatal nuclear extracts revealed that, although all relevant TF are present in the palate throughout development, only cyclic-AMP response element (CRE) binding protein (CREB) and CRE-modulator protein-1 (CREM-1) and activating transcription factor-1 bound to TRE on Gestation Day (GD) 12. The pattern shifted to c-Jun and c-Fos (known AP-1 components) on GD 13 and 14. In SAD-treated offspring, however, CREM-1 alone; c-Jun, c-Fos, and CREB; and c-Jun and c-Fos bound to TRE on GD 12, 13, and 14, respectively. Binding of TF to TRE was inhibited by SAD on both GD 12 and 13. These results suggest that a dynamic shift in the binding of TF to TRE from PKA- to PKC-responsive TF occurs during palate development and that teratogens such as SAD can alter both the nature and extent of TF binding to TRE.

Histological observations of palatal malformations in rat embryos induced by retinoic acid treatment

Malformations of the palate were induced in white rat embryos following maternal exposure to retinoic acid (tretinoin). Five experimental groups and the controls were treated by the following protocol: Group 1: pregnant rats received 100 mg retinoic acid (RA)/kg b.w. suspended in corn oil on gestational day (GD) 11.5; Group 2: 20 mg RA/kg b.w. from GD 8-12; Group 3: 20 mg RA/kg b.w. from GD 7.5-11.5; Group 4: 100 mg RA/kg b.w. on GD 10-11; Group 5: 100 mg RA/kg b.w. on GD 10 and 12; Group 6 received corn oil vehicle from GD 7-14.5; and Group 6: served as non-injected controls. In all retinoic acid treated groups, varying degrees of clefts with occasional attempts of fusion were noted. The severity and frequency of the malformations were dependent on dosage or gestational day of drug treatment. Our results indicate that RA, even at the lowest dose tested (20 mg/kg b.w.) severely affects the various tissues constituting the embryonic palatal shelves by altering cell interaction and possibly programmed cell death. These events would then result in lack of or inadequate differentiation with subsequent formation of aberrant craniofacial architecture.

Treatment with all-trans-retinoic acid decreases levels of endogenous TGF-beta(1) in the mesenchyme of the developing mouse inner ear

BACKGROUND

Previous studies have shown that in utero exposure of the mouse embryo to high doses of all-trans-retinoic acid (atRA) produces defects of the developing inner ear and its surrounding cartilaginous capsule, while exposure of cultured periotic mesenchyme plus otic epithelium to high doses of exogenous atRA results in an inhibition of otic capsule chondrogenesis.

METHODS

In this study, we examine the effects of atRA exposure on the endogenous expression of transforming growth factor-beta(1) (TGF-beta(1)), a signaling molecule that mediates the epithelial-mesenchymal interactions that guide the development of the capsule of the inner ear.

RESULTS

Our results demonstrate a marked reduction in immunostaining for TGF-beta(1) in the periotic mesenchyme of atRA-exposed embryos of age E10.5 and E12 days in comparison with control specimens. Consistent with these in vivo findings, high-density cultures of E10.5 periotic mesenchyme plus otic epithelium, treated with doses of atRA that suppress chondrogenesis, showed significantly decreased levels of TGF-beta(1), as compared with TGF-beta(1) levels in untreated control cultures. Furthermore, we demonstrate a rescue of cultured periotic mesenchyme plus otic epithelium from atRA-induced chondrogenic suppression by supplementation of cultures with excess TGF-beta(1).

CONCLUSIONS

Our results support the hypothesis that TGF-beta(1) plays a role in mechanisms of atRA teratogenicity during inner ear development.

Effects of EGF and TGFbeta1 on c-myc gene expression and DNA synthesis in embryonic hamster palate mesenchymal cells

Previous work has shown that cell proliferation is a major contributor to the early palate morphogenesis in mammals. The present study was undertaken to examine the effect of EGF, TGFbeta1 and their combination on proliferation (measured by DNA synthesis) and on the expression of a growth related proto-oncogene, c-myc, in embryonic hamster palate mesenchymal cells (HPMC). Vertically developing hamster palatal shelves were dissected on day 11 of gestation, and trypsinized, and primary cultures were grown in DMEM + 10% serum at 37 degrees C and 5% CO2. Following appropriate growth factor treatment of HPMC, DNA synthesis was measured by scintillation counting and extracted RNA was subjected to Northern blot analysis. In serum-starved, pre-confuent cultures treated with EGF (20 ng/ml), DNA synthesis was stimulated in the presence of 2.5% serum. In contrast, treatment of HPMC with TGFbeta1 (10 ng/ml) in the presence or absence of EGF/serum for 24 hr, or HPMC pre-treatment with TGFbeta1 (30 min) followed by EGF/serum (24 hr), resulted in an arrest of DNA synthesis. Northern blot analysis of RNA extracted from HPMC showed that as serum-starved, growth-arrested cells progressed through G0 to G1 phase of the cell cycle, following EGF treatment, c-myc was expressed by 1 hr and declined thereafter. In contrast, TGFbeta1 did not support expression of c-myc. Following pre- or co-treatment with TGFbeta1, the EGF +/- serum-induced expression of c-myc was seen between 1 and 6 hr. It appears that EGF-induced expression of c-myc may be involved in advancing the HPMC in G1, and thus may contribute to the onset of DNA synthesis in HPMC. Since co- or pre-treatment with TGFbeta1 did not inhibit EGF/serum induced expression of c-myc, it is possible that growth arresting effect of TGFbeta1 may not be exerted directly through inhibition or blockage of c-myc expression.

Retinoid-induced limb defects 2: involvement of TGF-beta 2 in retinoid-induced inhibition of limb bud development

We previously demonstrated that retinoid-induced inhibition of chondrogenesis in the forelimb bud may be mediated by TGF-beta2 (1). The present study was conducted to examine whether TGF-beta2 is involved in the inhibition of forelimb bud development caused by all-trans-retinoic acid (RA). Expression of TGF-beta2 was examined immunohistochemically in forelimb buds of embryos 24 h after dosing to the mother on Day 12 of gestation in the rat. In the control and 50 mg/kg group, TGF-beta2 was expressed in the epithelium and prechondrogenic area around dead cells in the forelimb bud. In the 100 mg/kg group, a dose at which RA caused reduction defects of forearm bones, TGF-beta2 expression was observed in the distal margin of forelimb buds, in which no expression was observed in the control and 50 mg/kg group. Immunohistologic studies also indicated that in the 100 mg/kg group, the expression of TGF-beta2 was enhanced in forearm-bone prechondrocytes around the dead cells. In a whole embryo culture system, exposure to RA for 24 h reduced the proximodistal length and protein content in forelimb buds at concentrations of 3 microg/mL or more. The whole embryo culture system also showed that the expression of TGF-beta2 was induced at the concentration of 3 microg/mL in the same region as found in forelimb buds of embryos from dams administered a teratogenic dosage of RA in vivo. Local application of TGF-beta2 to the distal margin of the forelimb bud in Day 12 embryos reduced proximodistal growth and protein content in forelimb buds for 24 h in culture even without RA treatment. We also found that exogenous TGF-beta2 inhibited DNA synthesis of forelimb bud cells in culture in a concentration-dependent manner. Neutralization of TGF-beta2 with its antibody in the distal margin of forelimb buds partially prevented the RA-induced inhibition of forelimb bud growth in the whole embryo culture system. These results suggest that RA-induced TGF-beta2 in the distal margin of forelimb buds may be involved in RA-induced inhibition of forelimb bud growth via reduction of cell proliferation in the distal margin, and RA-induced TGF-beta2 in the prechondrogenic area may inhibit chondrogenesis in the future forearm bones, followed by reduction defects of the forearm bones.

Phenytoin-induced alterations in craniofacial gene expression

In utero exposure to the anticonvulsant drug phenytoin has been shown to alter normal embryonic development, leading to a pattern of dysmorphogenesis known as the Fetal Hydantoin Syndrome. This embryopathy is characterized by growth retardation, microcephaly, mental deficiency, and craniofacial malformations, although the precise mechanism(s) by which phenytoin alters normal developmental pathways remains unknown. To better understand the molecular events involved in the pathogenesis of phenytoin-induced congenital defects, alterations in gene expression were examined during critical periods of craniofacial development. Pregnant SWV mice were administered phenytoin (60 mg/kg/day) from gestational day 6.5 until they were sacrificed at selected developmental time points. Tissue from the craniofacial region of control and exposed embryos was isolated, and samples were subjected to in situ transcription, antisense RNA amplification, and hybridization on reverse Northern blots to quantitatively assess expression of 36 candidate genes. Chronic phenytoin exposure significantly altered expression of several genes at distinct times during morphogenesis. Results of these studies show that expression of the retinoic acid receptors (RAR) alpha, beta, and gamma were significantly increased by phenytoin exposure. Elevations in gene expression of laminin beta 1, and the growth factors IGF-2, TGF alpha, and TGF beta 1, were also demonstrated in the craniofacial region of phenytoin-exposed embryos. As several of these genes are transcriptionally regulated by retinoic-acid-responsive elements in their promoter regions, phenytoin-induced alterations in expression of the RAR isoforms may have severe downstream consequences in the regulation of events necessary for normal craniofacial development. Such alterations occurring coordinately at critical times during craniofacial development may account for the dysmorphogenesis often associated with phenytoin exposure.

Role of TGF-beta in RA-induced cleft palate in CD-1 mice

Retinoic acid (RA) plays an important role in embryogenesis, by regulating morphogenesis, cell proliferation, differentiation, and extracellular matrix production. RA exposure on gestational day (GD) 12 in CD-1 mice results in delayed palatal shelf elevation and subsequent clefts in the secondary palate. Given the dynamic and complex nature of palate development, it is not surprising that this system is susceptible to changes in retinoid levels. There is evidence that experimental manipulation of retinoid status during development alters normal transforming growth factor-beta (TGF-beta) status. To study the role of perturbation in TGF-beta levels in RA-induced cleft palate, gravid CD-1 mice were treated with 70 mg/kg RA on GD 12. We examined changes in TGF-beta proteins and the steady-state level of TGF-beta mRNA within the first 24 hr after exposure. The interactions between RA and TGF-beta s were very complex. RA differentially regulated the mRNA and protein levels of TGF-beta 1. Changes in mRNA steady-state levels were rapid and transient in nature, indicating a direct mediation by RA. Differential regulation was evident, because RA treatment resulted in an increase in TGF-beta 1 mRNA steady levels followed by a decrease in the intracellular and extracellular forms of TGF-beta 1 protein. Moreover, the patterns of localization and levels of TGF-beta 2 and TGF-beta 3 proteins were not dramatically affected, although there was an increase in TGF-beta 3 mRNA steady-state levels. The increases in mRNA steady-state levels for TGF-beta 2 and TGF-beta 3, as for TGF-beta 1, were rapid and transient in nature, again arguing for direct mediation by RA. These data provide evidence for interactions between RA and TGF-beta s, and indicate that RA is capable of differentially regulating TGF-beta isoforms through processes involving different stages of TGF-beta synthesis and secretion. Further, changes in TGF-beta isoforms were observed prior to changes in mesenchyme morphology and must be considered as mediators of RA's effects on mesenchyme development.

Differential expression and biological activity of retinoic acid-induced TGFbeta isoforms in embryonic palate mesenchymal cells

The effect of retinoic acid (RA) on TGF-beta mRNA expression and protein production in murine embryonic palate mesenchymal (MEPM) cells was examined by Northern blotting and TGF-beta bioassay in association with TGF-beta isoform-specific neutralizing antibodies. Heat or acid activation was used to distinguish between latent and active TGF-beta protein released into the culture medium. RA had little or no effect on TGF-beta1 mRNA expression and protein production. In contrast, RA increased TGF-beta2 and beta3 protein released into the culture medium, the protein being mostly in an inactive or latent form. The amount of active TGF-beta released was increased relative to the total increase in TGF-beta released, suggesting that RA treatment stimulated activation of latent TGF-beta. RA also increased TGF-beta2 mRNA expression; we have previously shown that RA upregulates TGF-beta3 mRNA in these cells. RA and TGF-beta individually inhibited 3H-thymidine incorporation into MEPM cell DNA, while, when administered simultaneously, they inhibited proliferative activity to a greater extent. Heat- or acid-activated conditioned medium (CM) from MEPM cells treated with RA was able to inhibit 3H-thymidine incorporation into MEPM cell DNA to an extent greater than seen with RA treatment alone. Coincubation of heat-activated CM from RA-treated MEPM cells with pan-specific or TGF-beta2 or beta3-specific neutralizing antibodies partially relieved the inhibitory effect on 3H-thymidine incorporation, suggesting that this proliferative response was due to RA-induced TGF-beta. Simultaneous treatment with RA and TGF-beta also stimulated gycosaminoglycan (GAG) synthesis to an extent greater than that seen with TGF-beta treatment alone, this despite the ability of RA to inhibit GAG synthesis. These data demonstrate a role for RA and RA-induced TGF-beta in the regulation of palate cell proliferation and GAG synthesis and suggest a role for TGF-beta in retinoid-induced cleft palate.

AH receptor, ARNT, glucocorticoid receptor, EGF receptor, EGF, TGF alpha, TGF beta 1, TGF beta 2, and TGF beta 3 expression in human embryonic palate, and effects of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD)

Protein and mRNA for epidermal growth factor (EGF), transforming growth factor-alpha (TGF alpha), EGF receptor, transforming growth factor-beta 1 (TGF beta 1), TGF beta 2, TGF beta 3, glucocorticoid receptor (GR), the aryl hydrocarbon receptor (AhR), and the Ah receptor nuclear translocator (ARNT) were localized in gestational days (GD) 49-59 human embryonic secondary palates. The response to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) was determined for expression of these genes following palatal organ culture. Craniofacial tissues were shipped in medium from the Human Embryology Laboratory, University of Washington, Seattle, WA. Half of each specimen was cultured in control medium and half in medium containing TCDD at either 1 x 10(-8) or 1 x 10(-10) M. After fixation and paraffin-embedding, sections were examined either immunohistochemically or by in situ hybridization. Expression patterns were determined for each gene for the major stages of palatogenesis and in response to TCDD and compared to previously determined patterns of expression in the same developmental stages of palatogenesis for the mouse (GD49-59 in human palatogenesis corresponds to GD12-16 in the mouse). Human and mouse palates were dissimilar in particular spatiotemporal patterns of expression of these genes. Relative to patterns in mouse palatal development, human tissues demonstrated expression of EGF at early palatal stages, expression of EGF receptor and TGF alpha throughout fusion events, and uniform expression of TGF beta 3 in all epithelial regions without specifically higher levels in the medial cells. The responses to TCDD also differed in patterns of gene expression as well as in concentration required to induce hyperplasia of the medial epithelium. In summary, human palates expressed all of these regulatory genes, responses to TCDD were detected, and comparison between mouse and human palates revealed interspecies variation that may be a factor in each species' response to TCDD, as well as other teratogenic exposures.

Effect of retinoic acid on otic capsule chondrogenesis in high-density culture suggests disruption of epithelial-mesenchymal interactions

Previous studies have shown that in utero exposure of the mouse embryo to nonphysiological levels of all-trans retinoic acid (RA) produces malformations of the epithelial-derived auditory and vestibular receptors of the inner ear and its surrounding cartilaginous capsule. In this study, we demonstrate the effects of all-trans RA in high-density cultures of the periotic mesenchyme fated to form the otic capsule. Our results demonstrate an inhibition of chondrogenesis in cultured periotic mesenchyme + otic epithelium of embryonic age E10.5 days (E10.5) in response to all-trans RA exposure. However, at later stages of development (i.e., E12, E14), when epithelial-mesenchymal interactions are no longer required for initiation of chondrogenesis, exposure to this teratogen has no effect on the chondrogenic process. Two analogues of all-trans RA, i.e., cis-RA and trans-retinol, were investigated for their biological activity in chondrogenic cultures of inner ear mesenchyme + epithelium. Moreover, we tested the inductive capability and responsiveness of in utero RA-exposed inner ear tissues when cultured with inner ear tissues that were not exposed to this teratogen. Our results support the hypothesis that all-trans RA disrupts otic capsule formation by interfering with the tissue interactions required for its normal differentiation and development.

TGFbeta2 knockout mice have multiple developmental defects that are non-overlapping with other TGFbeta knockout phenotypes

The growth and differentiation factor transforming growth factor-beta2 (TGFbeta2) is thought to play important roles in multiple developmental processes. Targeted disruption of the TGFbeta2 gene was undertaken to determine its essential role in vivo. TGFbeta2-null mice exhibit perinatal mortality and a wide range of developmental defects for a single gene disruption. These include cardiac, lung, craniofacial, limb, spinal column, eye, inner ear and urogenital defects. The developmental processes most commonly involved in the affected tissues include epithelial-mesenchymal interactions, cell growth, extracellular matrix production and tissue remodeling. In addition, many affected tissues have neural crest-derived components and simulate neural crest deficiencies. There is no phenotypic overlap with TGFbeta1- and TGFbeta3-null mice indicating numerous non-compensated functions between the TGFbeta isoforms.

Glycosaminoglycan biosynthesis during 5-fluoro-2-deoxyuridine-induced palatal clefts in the rat

The biosynthesis and hydration of glycosaminoglycans (GAG) has been implicated in the generation of palatal shelf-elevating force(s) in mammals, although the nature of the palatal shelf extracellular matrices during cleft palate formation remains poorly understood. This study quantifies the GAG composition in the palatal shelves of Wistar rat fetuses at various periods of palatogenesis where clefts were induced experimentally using 5-fluoro-2-deoxyuridine (FUDR). For both normal and cleft palatal shelves, hyaluronan, heparan sulphate and chondroitin-4-sulphate were detected but not dermatan sulphate or chondroitin-6-sulphate. Throughout the period of cleft development studied, the total amount of GAG was significantly decreased (by approx. 30%) compared with normal development, this decrease being particularly marked at a time equivalent to post-elevation during normal development (approx. 75%). Furthermore, and unlike normal palatogenesis, no significant differences were recorded between the anterior and posterior parts of the palatal shelves during cleft formation. As for normal palatogenesis, however, the percentages of each GAG were not altered at any stage. The findings are consistent with the view that suppression of GAG biosynthesis is related to the development of cleft palate in FUDR-treated rat fetuses and can therefore be interpreted as providing evidence of a role for the mesenchymal glycoconjugates in shelf elevation during normal palatogenesis.

Mice devoid of gamma-aminobutyrate type A receptor beta3 subunit have epilepsy, cleft palate, and hypersensitive behavior

gamma-Aminobutyric acid type A receptors (GABA(A)-Rs) mediate the bulk of rapid inhibitory synaptic transmission in the central nervous system. The beta3 subunit is an essential component of the GABA(A)-R in many brain regions, especially during development, and is implicated in several pathophysiologic processes. We examined mice harboring a beta3 gene inactivated by gene targeting. GABA(A)-R density is approximately halved in brain of beta3-deficient mice, and GABA(A)-R function is severely impaired. Most beta3-deficient mice die as neonates; some neonatal mortality, but not all, is accompanied by cleft palate. beta3-deficient mice that survive are runted until weaning but achieve normal body size by adulthood, although with reduced life span. These mice are fertile but mothers fail to nurture offspring. Brain morphology is grossly normal, but a number of behaviors are abnormal, consistent with the widespread location of the beta3 subunit. The mice are very hyperactive and hyperresponsive to human contact and other sensory stimuli, and often run continuously in tight circles. When held by the tail, they hold all paws in like a ball, which is frequently a sign of neurological impairment. They have difficulty swimming, walking on grids, and fall off platforms and rotarods, although they do not have a jerky gait. beta3-deficient mice display frequent myoclonus and occasional epileptic seizures, documented by electroencephalographic recording. Hyperactivity, lack of coordination, and seizures are consistent with reduced presynaptic inhibition in spinal cord and impaired inhibition in higher cortical centers and/or pleiotropic developmental defects.

Relation of TGF-beta 2 to inhibition of limb bud chondrogenesis by retinoid in rats

A newly synthesized retinoid, Am-80 (4-[5,6,7,8-tetrahydro-5,5,8,8-tetramethyl-2-naphthalenyl] carbamoxyl) benzoic acid, induced limb reduction defects in rats in vivo. The present study was designed to investigate the mechanisms of its teratogenic action and also to examine whether transforming growth factor-beta (TGF-beta) is involved in limb reduction defects by using a rat limb bud cell culture system. Am-80 inhibited DNA synthesis and chondrogenesis of limb bud cells from day 12 embryos at concentrations of 1-4 ng/ml in a concentration-dependent manner. Quantities of TGF-beta 1 and 2 in culture medium from limb bud cells treated with Am-80 were evaluated using sandwich ELISAs. Although TGF-beta 1 was not detected in conditioned medium with or without Am-80, TGF-beta 2 increased in a concentration-dependent manner at drug concentrations that inhibited DNA synthesis and chondrogenesis. In addition, when TGF-beta 2 was exogenously added to limb bud cell culture medium, the synthesis of glycosaminoglycan (GAGs) was reduced even without Am-80 treatment. Neutralization of TGF-beta 2 with antibody prevented the inhibition of GAGs synthesis induced by Am-80. These results suggest that TGF-betas, especially beta 2, are involved in the inhibition of chondrogenesis caused by Am-80 in limb bud cells.

Developmental expression and CORT-regulation of TGF-beta and EGF receptor mRNA during mouse palatal morphogenesis: correlation between CORT-induced cleft palate and TGF-beta 2 mRNA expression

Glucocorticoids (CORT) have been shown to induce cleft palate in mice. Although the pathogenetic pathway of CORT-induced cleft palate has been investigated for several decades, the molecular details remain to be elucidated. Since growth factors have been shown to regulate palate morphogenesis, and the expression of several growth factors or their receptors, e.g. TGF-beta, EGF receptor (EGF-R), are known to be modulated by CORT, we postulate that CORT modulation of growth factor (or receptor) gene expression is a key mechanism involved in CORT-induced cleft palate. To test this hypothesis, we analyzed the steady-state levels (Northern and RNase protection) and developmental expression (in situ hybridization) of four CORT-responsive genes--TGF-Beta 1, TGF- beta 2, TGF-beta 3, and EGF receptor (EGF-R)--in developing mouse palates in the presence or absence of exogenous CORT. Pregnant B10.A dams were injected on day 12 of gestation with CORT or sham-injected and embryonic palates were collected at 1, 2, and 3 days postinjection (E13-E15). During mouse palate development, significant increases in TGF-beta 1 and TGF-beta 3 mRNA levels, as well as significant decrease in TGF-beta 2 mRNA levels, are detected; no significant difference in EGF-R transcript level is observed with progressive development. In CORT-exposed palates, we demonstrate no significant differences in the direction or magnitude of change with time in TGF-beta 1, TGF-beta 3, and EGF-R mRNA levels compared to controls. However, CORT delays by 1 day the down-regulation of palatal TGF-beta 2 transcript normally seen on day 14 of gestation. TGF-beta 2 is known to inhibit cell proliferation. The level of TGF-beta 2 mRNA, the only isoform primarily expressed in the palatal mesenchyme, significantly decreases with progressive palatal development; this down-regulation of TGF-beta 2 expression is associated with increased mesenchymal cell proliferation and palatal shelf growth. CORT, at a critical stage of palatogenesis, induces a delay in the normal down-regulation of TGF-beta 2 gene expression. Given that CORT is known to inhibit mesenchymal cell proliferation and palatal shelf growth, we conclude that the CORT-induced delay in the normal down-regulation of TGF-beta 2 gene expression is probably key event in the pathogenesis of CORT-induced cleft palate.

Prenatal craniofacial development: new insights on normal and abnormal mechanisms

Technical advances are radically altering our concepts of normal prenatal craniofacial development. These include concepts of germ layer formation, the establishment of the initial head plan in the neural plate, and the manner in which head segmentation is controlled by regulatory (homeobox) gene activity in neuromeres and their derived neural crest cells. There is also a much better appreciation of ways in which new cell associations are established. For example, the associations are achieved by neural crest cells primarily through cell migration and subsequent cell interactions that regulate induction, growth, programmed cell death, etc. These interactions are mediated primarily by two groups of regulatory molecules: "growth factors" (e.g., FGF and TGF alpha) and the so-called steroid/thyroid/retinoic acid superfamily. Considerable advances have been made with respect to our understanding of the mechanisms involved in primary and secondary palate formation, such as growth, morphogenetic movements, and the fusion/merging phenomenon. Much progress has been made on the mechanisms involved in the final differentiation of skeletal tissues. Molecular genetics and animal models for human malformations are providing many insights into abnormal development. A mouse model for the fetal alcohol syndrome (FAS), a mild form of holoprosencephaly, demonstrates a mid-line anterior neural plate deficiency which leads to olfactory placodes being positioned too close to the mid-line, and other secondary changes. Work on animal models for the retinoic acid syndrome (RAS) shows that there is major involvement of neural crest cells. There is also major crest cell involvement in similar syndromes, apparently including hemifacial microsomia. Later administration of retinoic acid prematurely and excessively kills ganglionic placodal cells and leads to a malformation complex virtually identical to the Treacher Collins syndrome. Most clefts of the lip and/or palate appear to have a multifactorial etiology. Genetic variations in TGF alpha s, RAR alpha s, NADH dehydrogenase, an enzyme involved in oxidative metabolism, and cytochrome P-450, a detoxifying enzyme, have been implicated as contributing genetic factors. Cigarette smoking, with the attendant hypoxia, is a probable contributing environmental factor. It seems likely that few clefts involve single major genes. In most cases, the pathogenesis appears to involve inadequate contact and/or fusion of the facial prominences or palatal shelves. Specific mutations in genes for different FGF receptor molecules have been identified for achondroplasia and Crouzon's syndrome, and in a regulatory gene (Msx2) for one type of craniosynostosis. Poorly co-ordinated control of form and size of structures, or groups of structures (e.g., teeth and jaws), by regulatory genes should do much to explain the very frequent "mismatches" found in malocclusions and other dentofacial "deformities". Future directions for research, including possibilities for prevention, are discussed.

Spatial and temporal distribution of sonic hedgehog mRNA in the embryonic mouse mandible by reverse transcription/polymerase chain reaction and in situ hybridization analysis

Hedgehog genes have recently been implicated in the control of pattern formation in many developing organ system. Vertebrate homologues of the Drosophila hedgehog have been identified in mouse and rate embryos. The temporal regulation of sonic hedgehog (mouse homologue) has previously been studied by Northern analysis of whole embryos with varying results. Sonic hedgehog transcript expression in the mouse mandibular process was now characterized using polymerase chain reaction (PCR) an in situ hybridization techniques. PCR analysis revealed transcripts at gestational days 10 and 11, before the formation of the dental lamina, but not at days 12-14, after tooth buds have formed. Transcripts were localized to, primarily, the epithelium in the presumptive incisor region of the mandibular midline at gestational day 10. No mRNA was detected by in situ hybridization techniques in the presumptive molar regions of odontogenic epithelium. Sonic hedgehog expression may be involved in the regulation of pattern formation through establishment of an incisor-molar axis of polarity.

Blockade of the initiation of murine odontogenesis in vitro by citral, an inhibitor of endogenous retinoic acid synthesis

Endogenous retinoids are present in the embryonic mouse mandible and reach a concentration peak immediately before the formation of the dental lamina. Because exogenous retinoids alter the pattern of the dental lamina and the expression of epidermal growth factor mRNA (a transcript necessary for initiation of odontogenesis), the role of retinoic acid in the initiation of odontogenesis was studied here. Citral (3,7-dimethyl-2,6-octadienal), a known inhibitor of retinoic acid synthesis, was used to block the endogenous synthesis of retinoic acid in the mouse embryonic mandible before the formation of the dental lamina (gestational day 9). A 24-h exposure to citral totally blocked tooth formation in 7/10 mandibles. Reductions of endogenous retinoic acid concentrations were confirmed by high-performance liquid chromatography. Tooth formation was restored by simultaneous treatment with all-trans retinoic acid or 9-cis retinoic acid during the citral exposures (first 24 h of culture). Endogenous retinoic acid is necessary for the initiation of odontogenesis.

Instruction by retinoic acid of incisor morphology in the mouse embryonic mandible

Endogenous retinoids are present in the embryonic mouse mandible and reach a peak in concentration at the time of the formation of the dental lamina. All-trans retinoic acid is present in a 10-fold higher concentration in the future incisor region of the mouse embryonic mandible at day 11.5. It was found here that exogenous all-trans retinoic acid has pleiotropic effects on the pattern of odontogenesis when applied before the formation of the dental lamina. These effects include a change in the pattern of the dental lamina, supernumerary buds and incisors in the diastema region, and replacement of molars with incisors in the molar region. Thus retinoic acid appears to instruct incisor morphology in the mouse embryonic mandible.