Sites of serotonin uptake in epithelia of the developing mouse palate, oral cavity, and face: possible role in morphogenesis

With the method of whole mouse embryo culture, together with immunocytochemistry with an antiserum to serotonin (5-HT), sites of 5-HT uptake were found to be transiently expressed in the epithelia of the developing palate, tongue, nasal septum, and maxillary and mandibular prominences during the period of active morphogenesis (embryonic days 12-14; or E12-14). These sites had the ability to take up 5-HT when added to the culture medium in the presence of the MAO inhibitor nialamide and an antioxiant, L-cysteine (NC), and could also be seen after exposure of embryos to the 5-HT precursor L-tryptophan (L-TRP) + NC. These sites were also visible after culturing embryos without any additives, which may have been due to the presence of L-TRP in one component of the culture medium (DMEM) or to 5-HT itself, which is present in relatively high amounts in fetal calf serum. At E12-13, the appearance of 5-HT immunoreactivity (IR) at these sites after treatment with 5-HT + NC was blocked by the 5-HT uptake inhibitor fluoxetine, providing further evidence that these are true sites of 5-HT uptake. However, fluoxetine did not completely block the appearance of these sites in E14 embryos after 5-HT + NC or L-TRP + NC although it was effective with NC alone. This finding could mean that at E14 5-HT uptake into these sites occurs by mechanisms not completely blocked by fluoxetine or that there is some limited capacity for 5-HT synthesis. Taken together with results from previous studies where 1) 5-HT has been reported to stimulate palatal shelf reorientation and palatal mesenchyme cell motility in vitro [Wee et al., J Embryol Exp Morphol 53:75-90, 1979; Zimmerman et al., J Craniofac Genet Dev Biol 3:371-385, 1983] and 2) long-term culturing of mouse embryos in the presence of 5-HT or fluoxetine has been shown to cause malformations of the craniofacial region (Lauder, Thomas, and Sadler, in preparation), the results of the present study suggest that 5-HT could act as a developmental signal in the palate, oral cavity, and face during the period of active morphogenesis.     

Effects of (R)-deoxycoformycin (pentostatin) on intrauterine nucleoside catabolism and embryo viability in the pregnant mouse.

The viability of early mouse embryos is acutely sensitive to (R)-deoxycoformycin (pentostatin), a tight-binding inhibitor of adenosine deaminase (ADA). Previous studies have shown that a single 5-mg/kg dose on day 7 (plug = day 0) of gestation fully inhibits uteroplacental ADA activity within 0.5 h; causes massive cell death in the neural plate and primary mesenchyme by 6 h, major craniofacial anomalies by day 10, and resorption by day 12 (Knudsen et al., '89; Airhart et al., '91). The present study has examined further the developmental toxicity and early effects of this inhibitor on ADA metabolism. (R)-Deoxycoformycin was administered to pregnant CD-1 (ICR) mice as a single intraperitoneal dose of 0.5-10 mg/kg total body weight on days 6-11 of gestation. The major adverse effect, early resorption, was dose dependent and specific to day 7-8 exposure. Treatment with 5 mg/kg on day 7 resulted in 85% resorptions, 15% malformations, and a 24% reduction in mean fetal weight, whereas the same dose of (S)-deoxycoformycin had no effect. Levels of adenosine and 2'-deoxyadenosine, which are the endogenous substrates of ADA, were monitored in the embryo/decidual unit (E/D) by reversed-phase high-performance liquid chromatography (RP-HPLC). In response to the inhibitor, both nucleosides increased transiently in the antimesometrial compartment (antimesometrial decidua + embryo). Peak levels (Cmax) of adenosine and 2'-deoxyadenosine were dose dependent over the range tested (0.05-10 mg/kg). Exposure to 5 mg/kg on day 7 raised adenosine levels within 0.5 h to 42-fold over the basal level of 0.06 nmol/mg protein. There was an even stronger effect on 2'-deoxyadenosine levels, which were elevated 674-fold over the detection limit of 0.0005 nmol/mg protein. Direct exposure to the inhibitor in serum-free E/D culture produced similar results: 50 microM (R)-deoxycoformycin within 1 h raised adenosine levels 26-fold and 2'-deoxyadenosine levels 410-fold. In vivo studies also showed a general correlation between embryolethality and the length of adenine nucleoside pool expansion, apparent for exposure on day 7, 8, or 9 but not on day 6, suggesting that the embryo becomes sensitive to adenosine or 2'-deoxyadenosine once the neural plate has formed.     

Serotonin and morphogenesis. I. Sites of serotonin uptake and -binding protein immunoreactivity in the midgestation mouse embryo

The possible involvement of the neurotransmitter serotonin (5-HT) in morphogenesis of the craniofacial region in the mouse embryo has been investigated using the method of whole-embryo culture. Day-12 embryos were incubated for 3-4 h in the presence of 5-HT or its precursors L-tryptophan (L-TRP) or 5-hydroxytryptophan (5-HTP), followed by fixation, sectioning and staining with a specific antiserum to 5-HT. Sites of 5-HT immunoreactivity were found in a variety of locations in tissues of the head and neck, which are either epithelia derived from the non-neural ectoderm or are non-neuronal midline brain structures. These sites include the surface epithelia of the head, face, nasal prominences, branchial arches, oral cavity and associated parts of the nasal epithelium, the epithelium covering the eye, parts of the otic vesicle, the epiphysis and roof of the diencephalon. With the exception of the oral cavity, sites of immunoreactivity for serotonin-binding protein were identified in the mesenchyme adjacent to these sites. This mesenchyme consists of ectodermally derived neural crest cells, which are known to receive inductive influences from the epithelia with which they interact during their migration through the craniofacial region. The presence of 5-HT uptake sites in epithelia and adjacent sites of SBP in the underlying mesenchyme raises the possibility that 5-HT might be involved in those epithelial-mesenchymal interactions known to be important for the development of structures in the craniofacial region.     

Isotretinoin teratogenicity in mouse whole embryo culture

Recent clinical observations strongly suggest that isotretinoin [13-cis-retinoic acid (cis RA)] is a human teratogen causing primarily heart and craniofacial malformations including ear and palatal defects. The purpose of the present study was to determine if cis RA could induce similar craniofacial malformations in mouse embryo culture. Day 8 CD-1 mouse embryos were cultured for 48 hours in rat serum in the presence or absence of various concentrations of cis RA dissolved in DMSO. DMSO by itself had no effect on embryonic development; however, cis RA at 2 X 10(-5) M (6 micrograms/ml) was clearly toxic. At 2 X 10(-6) M cis RA, growth retardation was minimal, and approximately one-third of the embryos exhibited very specific defects including a dramatic reduction in the size of the first and second visceral arches, which eventually give rise to the maxilla, mandible, and ear. Similar observations were also made with 4-oxo-13-cis RA, which is a major metabolite of cis RA in the mouse and human. These malformations would be expected to result in defects similar to those observed in the human, and preliminary observations suggest these defects are due to cis RA-induced inhibition of cranial neural crest cell migration. Using day-10 mouse embryos cultured for 48 hours in Waymouth's medium containing 50% fetal calf serum, we observed that cis RA at 2 X 10(-5) M produced a high percentage of embryos with limb defects and median cleft lip. Our results demonstrate that labeled cis RA enters the tissues of the embryo both in vivo and in vitro. Cis RA inhibited proliferation of the frontonasal mesenchyme cells in primary culture with 31% inhibition occurring at 2 X 10(-5) M cis RA.     

A lineage specific enhancer drives Otx2 expression in teleost organizer tissues

In mouse Otx2 plays essential roles in anterior-posterior axis formation and head development in anterior visceral endoderm and anterior mesendoderm. The Otx2 expression in these sites is regulated by VE and CM enhancers at the 5' proximal to the translation start site, and we proposed that these enhancers would have been established in ancestral sarcoptergians after divergence from actinopterigians for the use of Otx2 as the head organizer gene (Kurokawa et al., 2010). This would make doubtful an earlier proposal of ours that a 1.1 kb fragment located at +14.4 to +15.5 kb 3' (3'En) of fugu Otx2a gene harbors enhancers phylogenetically and functionally homologous to mouse VE and CM enhancers (Kimura-Yoshida et al., 2007). In the present study, we demonstrate that fugu Otx2a is not expressed in the dorsal margin of blastoderm, shield and early anterior mesendoderm, and that the fugu Otx2a 3'En do not exhibit activities at these sites of fugu embryos. We conclude that the fugu Otx2a 3'En does not harbor an organizer enhancer, but encodes an enhancer for the expression in later anterior mesendodermal tissues. Instead, in fugu embryos Otx2b is expressed in the dorsal margin of blastoderm at blastula stage and shield at 50% epiboly, and this expression is directed by an enhancer, 5'En, located at -1000 to -800 bp, which is uniquely conserved among teleost Otx2b orthologues.     

Craniofacial and central nervous system malformations induced by triamcinolone acetonide in nonhuman primates: II. Craniofacial pathogenesis

This study further defines the craniofacial malformations induced by triamcinolone acetonide in the rhesus monkey. Ten timed-mated pregnant rhesus monkeys (Macaca mulatta) received intramuscular injections of 10 mg/kg TAC on days 23, 25, 27, 29, and 31 of gestation. Results of previous experiments with rhesus and bonnet monkeys and baboons indicated that specific craniofacial and brain malformations could be induced with TAC during this period of pregnancy (Hendrickx et al., '80). Stage-matched TAC-treated and control embryos (stages 17-18 and 22) and age-matched TAC-treated and control fetuses (50, 60, and 70 days gestation) were removed by hysterotomy. Stage 17-18 TAC embryos appeared grossly normal but histologic evaluation revealed a shortened anlage of the posterior cranial base. Stage 22 TAC embryos and all TAC fetuses exhibited craniofacial dysmorphia and encephalocele. The developing sphenoid was the earliest affected and most severely malformed bone. Its defects included reduced anterioposterior and transverse dimensions, reduced orbitosphenoid and alisphenoid, abnormal pituitary fossa, and reduced dorsum and tuberculum sellae. In addition, shortening of the posterior cranial base and decreased cranial base angle was a consistent finding in the treated embryos and fetuses. Decreased ossification and remodeling in the facial bones and abnormal position due to the malformed sphenoid occurred.     

5' LTR complete nucleotide sequence of Chinese hamster intracisternal A-particle.

Retrovirus like sequences homologous to mouse IAP are present in Chinese hamster genome (Lueders K.K. and Kuff, E.L., 1981, 1983, Servenay et al., 1990). Murine IAP long terminal repeats (LTRs) can function as effective promoters in different cell types (Horowitz M. et al., 1984, Howe, C.C. et al., 1986). Thus CHO IAP sequences could act as retrotransposons in the cellular genome, and in this way affect the expression of other genes at the target sites. We had sequenced previously a Chinese hamster IAP genomic region corresponding mainly to the gag gene and including 57 nucleotides of U5 5' LTR (Servenay et al., 1988). In this paper, we present the 5' LTR complete nucleotide sequence of the Chinese hamster IAP element and its comparison with those of mouse and Syrian hamster.     

Inhibitors of choline uptake and metabolism cause developmental abnormalities in neurulating mouse embryos.

BACKGROUND: Choline is an essential nutrient in methylation, acetylcholine and phospholipid biosynthesis, and in cell signaling. The demand by an embryo or fetus for choline may place a pregnant woman and, subsequently, the developing conceptus at risk for choline deficiency. METHODS: To determine whether a disruption in choline uptake and metabolism results in developmental abnormalities, early somite staged mouse embryos were exposed in vitro to either an inhibitor of choline uptake and metabolism, 2-dimethylaminoethanol (DMAE), or an inhibitor of phosphatidylcholine synthesis, 1-O-octadecyl-2-O-methyl-rac-glycero-3-phosphocholine (ET-18-OCH(3)). Cell death following inhibitor exposure was investigated with LysoTracker Red and histology. RESULTS: Embryos exposed to 250-750 microM DMAE for 26 hr developed craniofacial hypoplasia and open neural tube defects in the forebrain, midbrain, and hindbrain regions. Embryos exposed to 125-275 microM ET-18-OCH(3) exhibited similar defects or expansion of the brain vesicles. ET-18-OCH(3)-affected embryos also had a distended neural tube at the posterior neuropore. Embryonic growth was reduced in embryos treated with either DMAE (375, 500, and 750 microM) or ET-18-OCH(3) (200 and 275 microM). Whole mount staining with LysoTracker Red and histological sections showed increased areas of cell death in embryos treated with 275 microM ET-18-OCH(3) for 6 hr, but there was no evidence of cell death in DMAE-exposed embryos. CONCLUSIONS: Inhibition of choline uptake and metabolism during neurulation results in growth retardation and developmental defects that affect the neural tube and face.     

Serotonin produces a configurational change of cultured smooth muscle cells that is associated with elevation of intracellular cAMP.

Early passaged bovine pulmonary artery smooth muscle cells (SMC) respond to serotonin (5-HT) by developing a reversible change in configuration. (Lee et al. J. Cell. Physiol. 138:145, 1989). This configurational change does not occur in pulmonary artery endothelial cells (EC) subjected to 5-HT and is adenosine triphosphate (ATP) dependent, lost with passage of SMC, and inhibited by various agents that block high-affinity 5-HT uptake. We now report a second configurational change (also dendritic formation) of SMC produced by 5-HT only in the presence of isobutylmethylxanthine (IBMX), an inhibitor of phosphodiesterase. This configurational change was also ATP dependent, but unlike the first response, (Lee et al., 1989), it occurred in both first and later passaged SMC and was not inhibited by blockade of 5-HT uptake. Also, unlike the response with 5-HT alone that failed to elevate cAMP, this one was associated with a large elevation of cAMP (eight fold above control values), similar to the response to the beta-agonist isoproterenol, plus IBMX. The second response was not blocked by a variety of 5-HT receptor antagonists but was reproduced by (+/-)-8-hydroxy-DPAT HBr (8-OH-DPAT), a reputed 5-HT1A agonist. The response was not dependent upon Ca2+ and was blocked by 1-2 mM n-phenylanthranilic acid or anthracene-9-carboxylic acid, electrically conductive Cl- channel inhibitors. Hence, 5-HT in the presence of IBMX causes a marked elevation of cAMP of SMC and this elevation in cAMP likely results in a cellular configurational change through a Cl- channel-dependent mechanism similar to that we previously described for EC in the presence of beta-adrenergic agonist stimulation (Ueda et al. Circ. Res. 66:951, 1990). EC do not show a similar response to 5-HT possibly because cAMP is not adequately elevated, even in the presence of IBMX, to enhance Cl- channel activity. We propose that our observations indicate the presence of two sites of action of 5-HT on the smooth muscle cell, one intracellularly and another at a cell surface receptor.     

The role of the visceral yolk sac in hyperglycemia-induced embryopathies in mouse embryos in vitro.

The adverse developmental effects of hyperglycemia to rodent embryos have been shown using whole embryo culture. Although, a mechanism by which hyperglycemia-induced effects occur is unknown, recent work has focused on the visceral yolk sac as a potential target tissue. Therefore, we have evaluated the developmental effects of hyperglycemia in early head fold stage mouse embryos in vitro and assessed the histiotrophic function of the visceral yolk sac. As has been previously shown in rodents, hyperglycemia produced neural tube closure defects in a concentration dependent manner at 33, 50, and 67 mM glucose using a 44 h exposure period. However, exposure times between 6 and 12 h were sufficient to alter embryonic development when the glucose concentration was 50 or 67 mM. In contrast, early somite stage embryos (4-6 somite stage) appear to be less sensitive to dysmorphogenesis and a 48 h exposure to 67 mM glucose but not 33 or 50 mM also produced neural tube defects. Hyperglycemia (67 mM) did not alter the uptake of 35S-methionine and 35S-cysteine-labeled hemoglobin (35S-Hb) in the visceral yolk sac (VYS) in early headfold staged embryos. However, the accumulation of 35S in the embryo was reduced by 16-18% at glucose concentrations of 50 or 67 mM during the last 12 h of a 44 h exposure period. No effect on VYS uptake or embryonic accumulation of 35S-labeled products was observed at shorter exposure periods (12-24 and 24-36 h).(ABSTRACT TRUNCATED AT 250 WORDS)     

Alterations in craniofacial growth induced by isotretinoin (13-cis-retinoic acid) in mouse whole embryo and primary mesenchymal cell culture

Recent evidence has demonstrated that 13-cis-retinoic acid (13-cis-RA, or isotretinoin) is responsible for various craniofacial malformations in the rodent and human embryo. Our studies have been directed toward understanding this effect using mouse whole embryo and primary cell cultures. In whole embryo culture, 13-cis-RA caused significant overall embryonic growth retardation, especially in the primary and secondary palatal processes. In embryos explanted on day 10 of gestation and exposed for 24 or 48 hr, the mesenchyme beneath the epithelium of the nasal and maxillary processes contained pyknotic nuclei as well as a dramatically reduced number of nuclei incorporating 3H-thymidine. The secondary palatal processes and the roof of the oral-nasal cavity had fewer mesenchymal cells than control embryos. The incorporation of 3H-thymidine into TCA-insoluble macromolecules was 30% less in the retinoid-treated heads. In primary cell cultures from day-12 mouse secondary palatal mesenchyme, subsequent cell growth was decreased at concentrations of 13-cis-RA greater than 1 X 10(-5) M. After a 40-hr treatment period, labeling indices in retinoid-treated cells were significantly lower than control values (25% compared with 40%). Retinoic acid also caused a significant, concentration-dependent decrease in 3H-thymidine incorporation. The inhibitory effect of 13-cis-RA on proliferation of oral-nasal mesenchymal cells appears to be related to the production of craniofacial malformations.     

Maternal methionine supplementation promotes the remediation of axial defects in Axd mouse neural tube mutants.

The Axd (axial defects) mouse model system (Essien et al., Teratology 42:183-194, '90) is characterized by a dominant mutation which causes posterior open neural tube defects (NTD) and a variety of tail anomalies (curly tails, or CT). Repeated backcrosses to BALB/cByJ mice have resulted in a 50% increase in Axd penetrance among neonates of heterozygous matings and loss of a correlation with maternal tail phenotype. Analysis of D12-D18 embryos from Axd/+ x Axd/+ matings indicates that soft tissues can superficially heal over some lesions from open NTD and that some curly tails can straighten (macroscopically) as gestation proceeds. Similarly, in embryos of Axd/+ x BALB crosses, there is remediation of approximately 33% of the tail flexion defects by birth. Numerous studies show that maternal nutritional status can affect the development of the neural tube and related axial structures. One nutrient of special interest is methionine, which is required for neurulation in cultured rat embryos (Coelho et al., J. Nutr. 119:1716, '89). Thus, the major question addressed by this study was whether supplemental methionine administered to Axd/+ dams crossed to Axd/+ males would alter the prenatal expression of the gene. When given IP (70 mg/kg) on D8 and D9, methionine resulted in a 41% reduction (from 29% to 17%) in the incidence of NTD in D 14 embryos (P less than 0.01).     

Serotonin localization and its functional significance during mouse preimplantation embryo development

Serotonin is a neurotransmitter functioning also as a hormone and growth factor. To further investigate the biological role of serotonin during embryo development, we analysed serotonin localization as well as the expression of specific serotonin 5-HT1D receptor mRNA in mouse oocytes and preimplantation embryos. The functional significance of serotonin during the preimplantation period was examined by studying the effects of serotonin on mouse embryo development. Embryo exposure to serotonin (1 microM) highly significantly reduced the mean cell number, whereas lower concentrations of serotonin (0.1 microM and 0.01 microM) had no significant effects on embryo cell numbers. In all serotonin-treated groups a significant increase in the number of embryos with apoptotic and secondary necrotic nuclei was observed. Expression of serotonin 5-HT1D receptor mRNA in mouse oocytes and preimplantation embryos was confirmed by in situ hybridization showing a clearly distinct punctate signal. Immunocytochemistry results revealed the localization of serotonin in oocytes and embryos to the blastocyst stage as diffuse punctate cytoplasmic labelling. It appears that endogenous and/or exogenous serotonin in preimplantation embryos could be involved in complex autocrine/paracrine regulations of embryo development and embryo-maternal interactions.     

Biochemical basis for D,L,-beta-hydroxybutyrate-induced teratogenesis

Previous investigations have demonstrated that a potential mechanism for D,L,-beta-hydroxybutyrate (BOHB)-induced teratogenesis in neurulating mouse embryos (5-6 somite stage) after 24 hours of exposure in vitro is mediated by an inhibition of the pentose phosphate pathway (PPP) (Hunter, et al. '87). Employing conceptuses of an earlier stage (2-3 somite stage), the biochemistry of BOHB-induced abnormalities was examined further by exposing embryos to 32 mM BOHB for 24 hour and comparing results with controls with respect to the rate of metabolism via the PPP, de novo pyrimidine biosynthesis (PB), and BOHB utilization. Moreover, the capability of these BOHB-exposed embryos to recover from such an insult was also assessed by transferring them to fresh control medium and allowing them to grow for an additional 36 hours. Both controls and BOHB-exposed embryos showed a progressive increase in rate of BOHB utilization between days 9 and 11.5 of gestation in vitro. Exposure to ketone body produced a 100% rate of neural tube defects and a 25.2% decrease in total embryonic protein content. In contrast to results obtained at the 5-6 somite stage, no inhibition of the PPP in whole conceptuses, embryos, or visceral yolk sacs was observed in the group exposed to BOHB at the 2-3 somite stage. Furthermore, a 7.5 mM D-ribose supplement, an intermediate in the PPP, was unable to rescue the younger embryos from BOHB-induced abnormalities and growth retardation. On the other hand, BOHB produced a 34.3% decrease in pyrimidine biosynthesis in the 2-3 somite embryos, but not in the visceral yolk sac. In addition, embryos recovered biochemically after being transferred to control medium, demonstrating a 25.5% overshoot in pyrimidine biosynthesis. Therefore, the mechanism of BOHB-induced teratogenesis appears to differ depending on the stage of embryonic development at the time of initial exposure.     

Retinoic acid inhibits migration of cranial neural crest cells in the cultured mouse embryo

Clinical observations have demonstrated that isotretinoin (13-cis-retinoic acid; cis-RA) is a human teratogen causing primarily heart and craniofacial malformations. Isotretinoin exposure to the early postimplantation mouse embryo in culture results in specific defects in craniofacial development that may be due to an interference in the early migration of cranial neural crest (CNC) cells [Goulding and Pratt, 1986]. The present study was designed to test this hypothesis by examining the migration of these cells in whole embryo culture. Day 8 CD-1 mouse embryos were cultured for 6-48 hr in the presence or absence of cis-RA at 2 X 10(-6) to 2 X 10(-5) M. Embryos either were fixed for light microscopy using Nichols' method for localization of CNC cells or were processed for scanning and transmission electron microscopy. At the light microscopic level, CNC cells in the mid-brain region of control embryos had migrated to the region of the first and second visceral arches after 6 hr in culture. Cis-RA interfered with this migration; CNC cells in treated embryos either did not leave the neuroepithelium (NE) or were aggregated near the NE. Autoradiographic studies indicated that cis-RA did not affect the overall viability or DNA synthesis of the CNC cells. However, at the TEM level, there was a dramatic increase in the number of cellular blebs in the CNC cells. Our results demonstrate a direct effect of 13-cis-RA on the CNC cells and suggest that this effect is due to alterations in the cell surface.     

Epidemiologic analysis of prenatal exposure to cough medicines containing dextromethorphan: no evidence of human teratogenicity

BACKGROUND: In a recent experimental study on chick embryos, Andaloro et al. (1998, Pediatr. Res. 43:1-7) observed a relationship between neural crest/neural tube defects (NTDs) and prenatal exposure to dextromethorphan. These authors made an extrapolation of their results to the human embryo, indicating that this drug could produce NTDs in humans. Rosenquist (1999, Teratology 60:58-60) based on the results of the epidemiologic study performed by Ferencz et al. (1997, Perspect. Pediatr. Cardiol. 5:50-162), concluded that dextromethorphan could cause congenital heart defects in humans. Because this drug is an over-the-counter drug, the suggestion of those authors has led to great controversy and public concern about the possible teratogenic effect of this drug on the human embryo. METHODS: We present the results of a case-control study by using logistic regression analyses on the effect of prenatal exposure to drugs containing dextromethorphan only, or in combination with other drugs, on human development. We mostly analyzed dextromethorphan. The study was designed in part as hypothesis confirmation for NTDs and congenital heart defects and, in part, as hypotheses generation by testing the association with many other congenital defects. RESULTS: The results do not show a relation between the occurrence of NTDs and heart defects or other defects with exposure to drugs containing dextromethorphan. CONCLUSIONS: The usual use of dextromethorphan in cough medications during pregnancy does not increase the risk for congenital defects.     

Teratogenic effects of valproic acid and diphenylhydantoin on mouse embryos in culture

Teratogenic effects of the anticonvulsant drugs valproic acid (VPA) and diphenylhydantoin (DPH) on the development of mouse embryos during early organogenesis were studied using the whole embryo culture technique. Embryos with one to seven somites were exposed in vitro to 50-375 micrograms/ml VPA or 15-135 micrograms/ml DPH for up to 42 hours and compared to control embryos cultured in 80% rat serum without either drug. For both VPA- and DPH-treated embryos, a dose-dependent increase in the frequency of abnormal embryos and a decrease in viability were found. VPA and DPH produced a similar pattern of defects. Drug-induced anomalies included open neural tubes in the cranial regions, abnormal body curvature, craniofacial deformities, and yolk sac defects. Ultrastructural changes were noted in the neuroepithelium of exencephalic VPA-treated embryos. Growth and development were retarded in embryos exposed to greater than 35 micrograms/ml DPH or greater than 50 micrograms/ml VPA as indicated by the decrease in protein and DNA content and the reduction in somite number, crown-rump length, and yolk sac diameter. On a molar basis DPH was potentially more teratogenic than VPA, which correlates with the higher lipid solubility of DPH. With VPA, susceptibility to the drug depended on the developmental stage; e.g., at 150 micrograms/ml VPA the frequency of malformations was 70% in embryos with one to four somites as compared to 35% in embryos with five to seven somites.     

Sonic hedgehog is required for cardiac outflow tract and neural crest cell development

The Hedgehog signaling pathway is critical for a significant number of developmental patterning events. In this study, we focus on the defects in pharyngeal arch and cardiovascular patterning present in Sonic hedgehog (Shh) null mouse embryos. Our data indicate that, in the absence of Shh, there is general failure of the pharyngeal arch development leading to cardiac and craniofacial defects. The cardiac phenotype results from arch artery and outflow tract patterning defects, as well as abnormal development of migratory neural crest cells (NCCs). The constellation of cardiovascular defects resembles a severe form of the human birth defect syndrome tetralogy of Fallot with complete pulmonary artery atresia. Previous studies have demonstrated a role for Shh in NCC survival and proliferation at later stages of development. Our data suggest that SHH signaling does not act directly on NCCs as a survival factor, but rather acts to restrict the domains that NCCs can populate during early stages (e8.5-10.5) of cardiovascular and craniofacial development.