epidermal-growth-factor and Cleft-Palate

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is an environmental contaminant that produces adverse biological effects including developmental toxicity and teratogenesis. In the mouse embryo, TCDD induces cleft palate and hydronephrosis. The synthetic glucocorticoid, hydrocortisone (HC), induces cleft palate and a potent, synergistic interaction has been observed between TCDD and HC in C57BL/6N embryonic mice. The morphology and etiology of TCDD- and HC-induced clefts are distinctly different with formation of small palatal shelves following HC exposure and failure of normally-sized shelves to fuse after TCDD treatment. Each exposure also alters expression of several growth factors. When EGF, TGF alpha, EGF receptor, and the TGF beta's are considered as a combinatorial, interacting set of regulators, TCDD and HC each produce a unique pattern of increased and/or decreased expression across the set. The interaction of HC and TCDD results in a cleft palate whose etiology most closely resembles that observed after HC exposure, i.e. small palatal shelves. HC+TCDD-exposure also produces a pattern of growth factor expression which closely resembles that seen after HC. Both TCDD and HC act through receptor-mediated mechanisms and each compound has its own receptor. The Ah receptor (AhR) binds TCDD and the glucocorticoid receptor (GR) binds HC. On gestation day (GD) 14, in the embryonic palate exposed to TCDD, the AhR was downregulated and the GR expression increased. Conversely, following HC exposure, the GR was downregulated and AhR levels were elevated. HC+TCDD produced increased expression of both receptors and this pattern would be predicted to produce HC-like clefts as the GR-mediated responses would result in small palatal shelves. The observed cross-regulation of the receptors is believed to be important in the synergistic interaction between TCDD and HC for the induction of cleft palate.

Topics: Abnormalities, Drug-Induced; Animals; Cleft Palate; Drug Interactions; Drug Synergism; Epidermal Growth Factor; Female; Glucocorticoids; Mice; Mice, Inbred C57BL; Palate; Polychlorinated Dibenzodioxins; Pregnancy; Receptors, Aryl Hydrocarbon; Receptors, Glucocorticoid; Transforming Growth Factors

The purpose of this chapter has been to discuss glucocorticoid and EGF involvement in normal and abnormal palatal development. It is to be hoped that we have made clear the important point that these hormone/growth factors and their receptors are present during normal embryonic palatal development to provide for regulation of growth and cellular differentiation. When these hormone/growth factors are administered in pharmacological or large doses that result in teratogenesis, these potent chemicals and their receptors then become inducers of cleft palate. The primary reason for this is that the hormone/growth factor receptors have unique and special areas of localizations in target (embryonic and fetal) tissues, e.g., glucocorticoids in the palate. Therefore, large amounts of these chemicals are specifically bound to receptors in these target tissues and these high levels of hormone/growth factor-receptor complexes result in aberrant development, e.g., glucocorticoids cause inhibition of palatal mesenchymal cell growth. These effects are distinct from the interactions of physiological levels of these hormone/growth factors with their receptors in these target tissues during development, e.g., glucocorticoids cause induction of key enzymes and modulation of EGF receptor levels. The exact molecular mechanism(s) by which high levels of hormone/growth factors--receptor complexes exert harmful effects on embryos or fetuses is (are) unknown and remain(s) a challenge for the future. Interaction of hormone/growth factors and their receptors certainly cannot provide an explanation for the mechanism of all types of craniofacial teratogenesis, but this concept certainly appears capable of providing important information relating to the mechanisms of many animal and human teratogens. The fact that these chemicals and their receptors are involved in normal development makes them all the more important since subtle alterations in their levels or activities could result in teratogenesis without an exposure to pharmacological levels of these hormone/growth factors. It seems that progress in this area will develop quickly since the techniques of recombinant DNA research are available in conjunction with responsive in vitro cell systems such as the established line of human embryonic palatal mesenchymal cells. Clearly, the future looks very exciting for understanding the role that these hormone/growth factors and their receptors play in normal and abnormal palate developmen

Topics: Animals; Cells, Cultured; Cleft Palate; Cyclic AMP; Epidermal Growth Factor; ErbB Receptors; Glucocorticoids; H-2 Antigens; Mesoderm; Mice; Mice, Inbred Strains; Palate; Receptors, Cell Surface; Receptors, Glucocorticoid

Topics: Animals; Cell Division; Cleft Palate; Collagen; Dexamethasone; Epidermal Growth Factor; ErbB Receptors; Female; Humans; Mice; Palate; Pregnancy; Receptors, Cell Surface; Receptors, Glucocorticoid

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.. 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.. 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.. 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.

Topics: Bone Development; Cell Proliferation; Cells, Cultured; Cleft Palate; Epidermal Growth Factor; Epithelial Cells; Humans; Mesenchymal Stem Cells; Osteogenesis; Palate; Spheroids, Cellular; Umbilical Veins

Non-syndromic cleft lip with or without cleft palate (NSCL/P) is a common orofacial congenital anomaly. The objective of the present study was to analyze the association of single nucleotide polymorphisms (SNPs) in the NAT2 and EGF61genes with NSCL/P in a Chinese population.. The frequencies of NAT2 (rs1799929)and EGF61 (rs4444903) gene variations were examined in a group of 285 NSCL/P patients and in 315 controls. Peripheral venous blood samples were collected for DNA extraction. Genotyping of the 2 SNPs was carried out using a mini sequencing (SNaPshot) method. Data were analyzed using the chi-square test.. We found a significant association between the EGF61 (rs4444903) and NSCL/P (P = .01) genes.Conversely, NAT2 (rs1799929) was not significantly different between the cases and the control group.The genotype frequencies of rs4444903GA showed a significant difference compared with GG genotype as a reference (odds ratio = 0.59; 95% confidence interval: 0.42-0.84, P = .01).. Our study showed that the EGF61 rs4444903GA genotype had a decreased risk of NSCL/P. Our data provides further evidence regarding the role of EGF61 variations in the development of NSCL/P in families of the studied populations.

Topics: Arylamine N-Acetyltransferase; Asian People; Cleft Lip; Cleft Palate; Epidermal Growth Factor; Genotype; Humans; Nucleotides; Polymorphism, Single Nucleotide

Cleft of the secondary palate is one of the most common congenital birth defects in humans. The primary cause of cleft palate formation is a failure of fusion of bilateral palatal shelves, but rupture of the once fused palate has also been suggested to take place in utero. The possibility of post-fusion rupture of the palate in humans has hardly been accepted, mainly because in all the cleft palate cases, the cleft palatal edge is always covered with intact epithelium. To verify whether the intrauterine environment of the fetus plays roles in wound healing when the once fused palate is torn apart, we artificially tore apart fetal mouse palates after fusion and cultivated them in culture medium with or without mouse or human amniotic fluid. We thereby found that the wounded palatal edge became completely covered with flattened epithelium after 36 hours in culture with amniotic fluid, but not in culture without amniotic fluid. Using histological and scanning electron microscopic analyses of the healing process, it was revealed that the epithelium covering the wound was almost exclusively derived from the adjacent nasal epithelium, but not from the oral epithelium. Such actions of amniotic fluid on the fetal wound were never simulated by exogenous epidermal growth factor (EGF), albumin, or both. In addition, the rapid epithelialization induced by amniotic fluid was not prevented by either PD168393 (an inhibitor of the EGF receptor-specific tyrosine kinase) or SB431542 (a specific inhibitor of TGFbeta receptor type I/ALK5). The present study provides new insights into the unique biological actions of amniotic fluid in the repair of injured fetal palate.

Topics: Activin Receptors, Type I; Amniotic Fluid; Animals; Cleft Palate; Epidermal Growth Factor; Epithelium; ErbB Receptors; Female; Fetus; Humans; Male; Mice; Mice, Inbred ICR; Microscopy, Electron, Scanning; Nasal Mucosa; Organ Culture Techniques; Palate; Protein Serine-Threonine Kinases; Receptor, Transforming Growth Factor-beta Type I; Receptors, Transforming Growth Factor beta; Rupture; Wound Healing

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.. 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.. 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.. 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.

Topics: Abnormalities, Drug-Induced; Animals; Bone and Bones; Cleft Palate; Epidermal Growth Factor; Female; Fetus; Kidney Pelvis; Mice; Mice, Knockout; Phenotype; Pregnancy; Prenatal Injuries; Transforming Growth Factor alpha; Tretinoin

Triamcinolone acetonide (TAC), a synthetic glucocorticoid, induces cleft palate resulting from poor development of palatal shelves in mice. However, TAC has no effect on medial edge epithelial cells (MEE cells) in secondary palatal shelves. In the present study, we examined the relationship between the pathogenesis of cleft palate and the effects on MEE cells and palatal mesenchymal cells in rat embryos/fetuses exposed to TAC. Pregnant Wistar Hannover rats were given TAC intramuscularly at 0.5 mg/kg at gestation days (Day) 12, 13, and 14, then embryos/fetuses were harvested on Days 14.5, 15, 16 and 20. The effects of TAC were as follows; an inhibition of palatal mesenchymal cell proliferation on Day 14.5, a decrease in the density of palatal mesenchymal cells and MEE cells, and expression of epidermal growth factor (EGF) receptors in MEE cells on Day 15, and stratified squamous differentiation of MEE cells with expression of cytokeratin and EGF receptors on Day 16. These findings indicated that TAC inhibited the proliferation of mesenchymal cells and affected the differentiation of MEE cells into stratified squamous epithelia in the palatal shelves of rat embryos. However, these stratified squamous MEE cells partially fused with each other. Thus, we suspected that a major contributing factor to the formation of TAC-induced cleft palate might not be the altered differentiation of MEE cells, but the inhibition of mesenchymal cell proliferation.

Topics: Animals; Cleft Palate; Embryo, Mammalian; Epidermal Growth Factor; Epithelial Cells; Female; Immunohistochemistry; In Situ Nick-End Labeling; Mesoderm; Palate; Pregnancy; Rats; Rats, Wistar; Triamcinolone Acetonide

The environmental toxicant 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) produces cleft palate (CP) and hydronephrosis (HN) in mice. The etiology of these defects involves hyperproliferation of epithelial cells of the secondary palatal shelf and ureter, respectively. These effects correlate with altered expression of the epidermal growth factor receptor (EGFR), epidermal growth factor (EGF), and transforming growth factor-alpha (TGF-alpha). In this study, the developmental toxicity of TCDD was examined in EGF, TGF-alpha, and double EGF + TGF-alpha knockout (-/-) and wild type (WT) mice. The influence of background genetics in responsiveness to TCDD was examined using liver 7-ethoxyresorufin-O-deethylase (EROD) activity. Animals were dosed by gavage with 0, 0.2, 1, 5, 24, 50, 100, or 150 micro g TCDD/kg (5 ml/kg) body weight on gestation day 12. The mixed genetic background of WT, EGF (-/-), and EGF + TGF-alpha (-/-) made these mice less responsive to TCDD relative to C57BL/6J and TGF-alpha (-/-), which have a C57BL background. These results show that EGF and TGF-alpha are not required for response to TCDD; however, the specific ligand available to bind EGFR affects the responsiveness to TCDD. EGF (-/-) mice are less responsive for CP, but more sensitive to HN. TGF-alpha (-/-) mice were similar to WT in sensitivity for induction of CP and HN. The responses of EGF + TGF-alpha (-/-) mice were like the WT except at higher doses where sensitivity to CP increased, suggesting that the responses may be mediated by alternative ligands for EGFR that are not functional equivalents of EGF or TGF-alpha. In conclusion, the EGFR pathway is mechanistically important in responses of the embryo to TCDD. Specific ligands confer sensitivity or resistance that are target tissue-dependent.

Topics: Abnormalities, Drug-Induced; Administration, Oral; Animals; Cleft Palate; Cytochrome P-450 CYP1A1; Dose-Response Relationship, Drug; Environmental Pollutants; Epidermal Growth Factor; Female; Genetic Predisposition to Disease; Hydronephrosis; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Microsomes, Liver; Polychlorinated Dibenzodioxins; Pregnancy; Teratogens; Transforming Growth Factor alpha

To investigate the morphologic changes of embryonic palatal development exposed to retinoic acid (RA) in mouse, and to detect the significance of the expression of TGFbeta1, TGFbeta3, EGF and BCL2.. The stage of palatal development was examined by light microscopy. S-P immunohistochemistry and in-situ hybridization was used to detect spatio-temporal patterns of expression of TGFbeta1, TGFbeta3, EGF and BCL2 in embryonic palate.. The fetus exposed to RA resulted in formation of small palatal shelves without contact and fusion of each other to form and intact palate. RA can regulate the embryonic palatal expression of genes involved in RA-induced cleft palate.. RA can inhibit the proliferation of MEPM cell to form small palatal shelves and induce abnormal differentiation of MEE cell causing the bi-palatal shelves no contact and fuse with each other, then induce the formation of cleft palate. RA can regulate the spatio-temporal patterns of expression of TGFbeta1, TGFbeta3 and EGF in embryonic palatal processes and the change of special expression of these genes in embryonic palatal processes are involved in RA-induced cleft palate.

Topics: Abnormalities, Drug-Induced; Animals; Cleft Palate; Embryo, Mammalian; Epidermal Growth Factor; Female; Mice; Mice, Inbred C57BL; Palate; Transforming Growth Factor beta; Tretinoin

During mammalian palatal fusion, the medial edge epithelial (MEE) cells must stop DNA synthesis prior to the initial contact of opposing palatal shelves and thereafter selectively disappear from the midline. Exogenous EGF has been shown to inhibit the cessation of DNA synthesis and induce cleft palate; however, the precise intracellular mechanism has not been determined. We hypothesized that EGF signaling acting via ERK1/2 would maintain MEE DNA synthesis and cell proliferation and consequently inhibit the process of palatal fusion. Palatal shelves from E13 mouse embryos were maintained in organ cultures and stimulated with EGF. EGF-treated palates failed to fuse with intact MEE and had significant ERK1/2 phosphorylation. Both EGF-induced ERK1/2 phosphorylation and BrdU-incorporation were localized in the nucleus of MEE cells. Subsequent inhibition assays using U0126, a specific inhibitor of ERK1/2 phosphorylation, were conducted. U0126 inhibited EGF-induced ERK1/2 phosphorylation in a dose-dependent manner and consequently MEE cells stopped proliferation. The threshold of ERK1/2 inactivation to stop MEE DNA synthesis coincides with the level required to rescue the EGF-induced cleft palate phenotype. These results indicate that EGF-induced inhibition of palatal fusion is dependent on nuclear ERK1/2 activation and that this mechanism must be tightly regulated during normal palatal fusion.

Topics: Active Transport, Cell Nucleus; Animals; Butadienes; Cell Division; Cleft Palate; Enzyme Inhibitors; Epidermal Growth Factor; Epithelial Cells; Mice; Mitogen-Activated Protein Kinase 1; Mitogen-Activated Protein Kinase 3; Mitogen-Activated Protein Kinases; Nitriles; Organ Culture Techniques; Palate; Phosphorylation; Signal Transduction

To investigate the molecular mechanism of congenital cleft palate induced by Dexamethasone (DEX) and the counteractive effect of Vitamin B12.. The RT-PCR was used to detect the independent and joint effects of DEX and Vitamin B12 on the gene expressions of A/J embryonic mouse palatal cells.. DEX stimulated the gene expressions of EGF and TGFbeta1, while the expression of TGFalpha left unchanged in the palatal cells. Vitamin B12 had no direct effects on the gene expressions of EGF, TGFalpha, and TGFbeta1; however, it counteracted the effects of DEX on the palate cells.. DEX induces cleft palate through increasing some gene expressions of growth factors, which can be inhibited by Vitamin B12.

Topics: Animals; Cells, Cultured; Cleft Palate; Dexamethasone; Embryo, Mammalian; Epidermal Growth Factor; Mice; Palate; Transforming Growth Factor alpha; Transforming Growth Factor beta; Vitamin B 12

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.

Topics: Abnormalities, Drug-Induced; Administration, Oral; Animals; Body Weight; Cleft Palate; Environmental Pollutants; Epidermal Growth Factor; Female; Hydronephrosis; Liver; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Organ Size; Polychlorinated Dibenzodioxins; Pregnancy; Reproduction; Teratogens; Toxicity Tests; Transforming Growth Factor alpha

Retinoic acid (RA) is teratogenic in many species, producing multiple malformations, including cleft palate. The effects of RA which lead to cleft palate vary depending on the stage of development exposed. After exposure of embryonic mice to RA on gestation day (GD) 10, abnormally small palatal shelves form. After exposure on GD 12 shelves of normal size form, but fail to fuse, as the medial cells proliferate and differentiate into a nasal-like epithelium. Growth factors and their receptors play an important role in regulating development, and the expression of EGF receptors, EGF, TGF-alpha, TFG-beta 1, and TGF-beta 2 has been reported in the mouse embryo. In a variety of cell types in culture, these growth factors are capable of regulating proliferation, differentiation, expression of matrix proteins, and other cellular events including epithelial-mesenchymal transformations. The present study examines immunohistochemically the expression of EGF, TGF-alpha, TGF-beta 1, and TGF-beta 2 in the control embryonic palatal shelves from GD 12 to 15 and the effects of RA treatment on GD 10 or 12 on their expression on GD 14 and 16. These growth factors were shown to have specific temporal and spatial expression in the palatal shelf. With advancing development the levels of TGF-alpha decreased while the expression of EGF increased. TGF-beta 2 localization became regional by GD 14-15, with higher levels found in epithelial cells and chondrogenic mesenchyme. TGF-beta 1 occurred in epithelial and mesenchymal cells and distribution did not change substantially with advancing development. RA exposure altered the expression of TFG-alpha, TGF-beta 1, and TGF-beta 2, but significant effects on EGF were not found. The effects on TGF-alpha and TGF-beta 1 expression were dependent on the gestational age exposed. Levels of TGF-alpha on GD 14 decreased after RA exposure on GD 10, but increased after GD 12 exposure. TGF-beta 1 expression in the mesenchyme was increased after exposure on GD 12, but was unaffected by RA on GD 10. After exposure on either day, the levels of TGF-beta 2 increased in GD 14 nasal epithelial cells. Acting in concert, growth factors could regulate events critical to formation of the secondary palate, including cessation of medial epithelial cell proliferation, synthesis of extracellular matrix proteins in the mesenchyme, programmed cell death of medial epithelial peridermal cells, and transformation of basal epithelial medial cells to mesenchymal cells.

Topics: Abnormalities, Drug-Induced; Animals; Cell Differentiation; Cleft Palate; Epidermal Growth Factor; Female; Gene Expression Regulation; Male; Mice; Mice, Inbred C57BL; Morphogenesis; Palate; Pregnancy; Transforming Growth Factors; Tretinoin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is teratogenic in mice, inducing cleft palate and hydronephrosis at doses which are not overtly maternally toxic or embryotoxic. After TCDD exposure the palatal shelves of normal size come into contact, but fail to fuse due to altered differentiation of the medial epithelial cells. These cells continue to express EGF receptors, proliferate, and differentiate into an oral-like stratified squamous epithelium. The present study examines the effect of TCDD on the expression of growth factors which are believed to regulate differentiation and proliferation in the palate. This study also examined the combined effect of TCDD and retinoic acid (RA), since in teratology studies coadministration of these agents results in an enhancement of cleft palate incidence. Embryos were exposed in vivo on Gestation Day (GD) 10 or 12 to TCDD ot TCDD + RA and the palatal shelves were dissected on GD 14-16. Growth factor expression was determined immunohistochemically using antibodies to TGF-alpha, EGF, TGF-beta 1, or TGF-beta 2. The growth factors displayed specific spatial and temporal expression in the palatal shelves. TCDD reduced the expression of TGF-alpha, EGF, and TGF-beta 1 in epithelial and mesenchymal cells. The degree of reduction was generally greater after exposure on GD 10 to TCDD alone or in combination with RA when compared to that on GD 12. The abnormal proliferation and differentiation of TCDD-exposed medial cells may be a response to reduced expression of EGF and TGF-alpha. Low levels of these factors may be related to the previously observed elevated levels of EGF receptors in medial cells. In other systems, low levels of ligand have resulted in upregulation of the EGF receptor. Continued proliferation and altered differentiation could also be attributable to decreased levels of TGF-beta 1, a factor inhibitory to epithelial proliferation. Since TGF-beta 1 stimulates mesenchymal growth and TGF-alpha and EGF stimulate epithelial proliferation, the formation of small shelves after exposure to TCDD + RA on GD 10 may be due to the severe reduction in these factors. Only a slight to moderate reduction in growth factor expression occurs after exposure to TCDD + RA on GD 12 and in this case shelves of normal size form. Since TCDD and RA appear to act in part through pathways that involve TGF-beta 1, in vitro experiments were designed to examine the involvement of TGF-beta 1 in TCDD teratogenicity.(ABSTRACT TRUNCATED AT 400

Topics: Animals; Cleft Palate; Drug Synergism; Epidermal Growth Factor; Female; Immunohistochemistry; Male; Mice; Mice, Inbred C57BL; Polychlorinated Dibenzodioxins; Teratogens; Transforming Growth Factors; Tretinoin

Retinoic acid (RA) has been shown to be teratogenic in many species, and 13-cis-RA is teratogenic in humans. Exposure to RA during embryonic morphogenesis produced a variety of malformations including limb defects and cleft palate. The type and severity of malformation depended on the stage of development exposed. The purpose of this study was to compare the effects of RA exposure in vivo on different stages of palate development. These results were compared to effects observed after exposure in organ culture. The vehicle used in RA dosing was also shown to be a major factor in the incidence of RA-induced cleft palate. For the in vivo studies, RA (100 mg/kg) in 10 ml corn oil/kg was given p.o. on gestation day (GD) 10 or 12, and the embryos were examined on GD 14 and 16. Exposure to RA in an oil:DMSO vehicle resulted in much higher incidences of cleft palate than were observed after dosing with RA in oil only. After exposure on GD 10, to RA, small palatal shelves formed which did not make contact and fuse on GD 14. The medial cells did not undergo programmed cell death. Instead, the medial cells differentiated into a stratified, squamous, oral-like epithelium. The RA-exposed medial cells did not incorporate 3H-TdR on GD 14 or 16, but the cells expressed EGF receptors and bound 125I-EGF. In contrast, RA-induced clefting after exposure on GD 12 did not involve growth inhibition. Shelves of normal size formed and made contact, but because of altered medial cell differentiation did not fuse. Medial cells differentiated into a pseudostratified, ciliated, nasal-like epithelium. This response was produced in vivo at exposure levels which produced cleft palate, and after exposure of palatal shelves to RA in vitro from GD 12-15. The medial cells exposed on GD 12 incorporated 3H-TdR on GD 14, expressed EGF receptors, and bound 125I-EGF. The responses to RA which lead to cleft palate differed after exposure on GD 10 or 12, and the pathways of differentiation which the medial cells followed depended on the developmental stage exposed.

Topics: Animals; Cleft Palate; Corn Oil; Dimethyl Sulfoxide; Epidermal Growth Factor; Gestational Age; Mice; Mice, Inbred C57BL; Microscopy, Electron; Organ Culture Techniques; Palate; Pharmaceutical Vehicles; Tretinoin

Epidermal growth factor (EGF) injected into pregnant mice increased the frequency of cleft palate (CP) in cortisone-treated mouse fetuses. EGF alone produced proliferation and thickening of the epithelium of the palatal processes, but CP was not significantly increased over saline injected controls. Cortisone alone produced thinning of the palatal epithelium and caused CP in 61 percent of formed fetuses. The combination of EGF and cortisone treatment induced CP in 100 percent of formed fetuses; epithelial thickening still occurred with the combination treatment. Thus, EGF may be teratogenic under special circumstances. These observations suggest that the relative thickness of the palatal shelf epithelium may not be a critical factor in the fusion of the palatal shelves.

Topics: Abnormalities, Drug-Induced; Animals; Cleft Palate; Cortisone; Drug Synergism; Epidermal Growth Factor; Female; Mice; Palate; Peptides; Pregnancy; Teratogens