Mouse embryonic palatal mesenchymal cells maintain stemness through the PTEN-Akt-mTOR autophagic pathway

BACKGROUND

Both genetic and environmental factors are implicated in the pathogenesis of cleft palate. However, the molecular and cellular mechanisms that regulate the development of palatal shelves, which are composed of mesenchymal cells, have not yet been fully elucidated. This study aimed to determine the stemness and multilineage differentiation potential of mouse embryonic palatal mesenchyme (MEPM) cells in palatal shelves and to explore the underlying regulatory mechanism associated with cleft palate formation.

METHODS

Palatal shelves excised from mice models were cultured in vitro to ascertain whether MEPM are stem cells through immunofluorescence and flow cytometry. The osteogenic, adipogenic, and chondrogenic differentiation potential of MEPM cells were also determined to characterize MEPM stemness. In addition, the role of the PTEN-Akt-mTOR autophagic pathway was investigated using quantitative RT-PCR, Western blotting, and transmission electron microscopy.

RESULTS

MEPM cells in culture exhibited cell surface marker expression profiles similar to that of mouse bone marrow stem cells and exhibited positive staining for vimentin (mesodermal marker), nestin (ectodermal marker), PDGFRα, Efnb1, Osr2, and Meox2 (MEPM cells markers). In addition, exposure to PDGFA stimulated chemotaxis of MEPM cells. MEPM cells exhibited stronger potential for osteogenic differentiation as compared to that for adipogenic and chondrogenic differentiation. Undifferentiated MEPM cells displayed a high concentration of autophagosomes, which disappeared after differentiation (at passage four), indicating the involvement of PTEN-Akt-mTOR signaling.

CONCLUSIONS

Our findings suggest that MEPM cells are ectomesenchymal stem cells with a strong osteogenic differentiation potential and that maintenance of their stemness via PTEN/AKT/mTOR autophagic signaling prevents cleft palate development.

Candida albicans-Cell Interactions Activate Innate Immune Defense in Human Palate Epithelial Primary Cells via Nitric Oxide (NO) and β-Defensin 2 (hBD-2)

The presence of Candida albicans in the biofilm underlying the dental prosthesis is related to denture stomatitis (DS), an inflammatory reaction of the oral mucosa. The oral epithelium, a component of the innate immune response, has the ability to react to fungal invasion. In this study, we evaluated the in vitro effect of viable C. albicans on the apoptosis, nitric oxide (NO) production, and β-defensin 2 (hBD-2) expression and production of human palate epithelial cells (HPECs). We further determined whether or not these effects were correlated with fungal invasion of epithelial cells. Interaction between HPEC primary culture and C. albicans was obtained through either direct or indirect cell–cell contact with a supernatant from a hyphal fungus. We found that the hyphae supernatants were sufficient to induce slight HPEC apoptosis, which occurred prior to the activation of the specific mechanisms of epithelial defense. The epithelial defense responses were found to occur via NO and antimicrobial peptide hBD-2 production only during direct contact between C. albicans and HPECs and coincided with the fungus’s intraepithelial invasion. However, although the hBD-2 levels remained constant in the HPEC supernatants over time, the NO release and hBD-2 gene expression were reduced at a later time (10 h), indicating that the epithelial defense capacity against the fungal invasion was not maintained in later phases. This aspect of the immune response was associated with increased epithelial invasion and apoptosis maintenance.

Embryonic Midfacial Palatal Organ Culture Methods in Developmental Toxicology

The morphogenesis of the secondary palate provides an interesting model for many of the processes involved in embryonic development. A number of in vitro models have been used to study craniofacial development, including whole embryo culture, palatal mesenchymal and micromass cell cultures, and Trowell-like palatal cultures in which dissected palates are cultured individually or as pairs in contact on a support above medium. This chapter presents a detailed protocol for the culture of maxillary midfacial tissues, including the palatal shelves, in suspension culture. This method involves isolation of the midfacial tissues (maxillary arch and palatal shelves) and suspension of the tissues in medium in flasks. On a rocker in an incubator, the palatal shelves elevate, grow, make contact, and fuse in a time span analogous to that occurring in the intact embryo in utero.

Constitutive activation of hedgehog signaling adversely affects epithelial cell fate during palatal fusion

Cleft palate is one of the most common craniofacial congenital defects in humans. It is associated with multiple genetic and environmental risk factors, including mutations in the genes encoding signaling molecules in the sonic hedgehog (Shh) pathway, which are risk factors for cleft palate in both humans and mice. However, the function of Shh signaling in the palatal epithelium during palatal fusion remains largely unknown. Although components of the Shh pathway are localized in the palatal epithelium, specific inhibition of Shh signaling in palatal epithelium does not affect palatogenesis. We therefore utilized a hedgehog (Hh) signaling gain-of-function mouse model, K14-Cre;R26SmoM2, to uncover the role of Shh signaling in the palatal epithelium during palatal fusion. In this study, we discovered that constitutive activation of Hh signaling in the palatal epithelium results in submucous cleft palate and persistence of the medial edge epithelium (MEE). Further investigation revealed that precise downregulation of Shh signaling is required at a specific time point in the MEE during palatal fusion. Upregulation of Hh signaling in the palatal epithelium maintains the proliferation of MEE cells. This may be due to a dysfunctional p63/Irf6 regulatory loop. The resistance of MEE cells to apoptosis is likely conferred by enhancement of a cell adhesion network through the maintenance of p63 expression. Collectively, our data illustrate that persistent Hh signaling in the palatal epithelium contributes to the etiology and pathogenesis of submucous cleft palate through its interaction with a p63/Irf6-dependent biological regulatory loop and through a p63-induced cell adhesion network.

Inactivation of Fgfr2 gene in mouse secondary palate mesenchymal cells leads to cleft palate

Numerous studies have been conducted to understand the molecular mechanisms controlling mammalian secondary palate development such as growth, reorientation and fusion. However, little is known about the signaling factors regulating palate initiation. Mouse fibroblast growth factor (FGF) receptor 2 gene (Fgfr2) is expressed on E11.5 in the palate outgrowth within the maxillary process, in a region that is responsible for palate cell specification and shelf initiation. Fgfr2 continues to express in palate on E12.5 and E13.5 in both epithelial and mesenchymal cells, and inactivation of Fgfr2 expression in mesenchymal cells using floxed Fgfr2 allele and Osr2-Cre leads to cleft palate at various stages including reorientation, horizontal growth and fusion. Notably, some mutant embryos displayed no sign of palate shelf formation suggesting that FGF receptor 2 mediated FGF signaling may play an important role in palate initiation.

Development of a multilayered palate substitute in rabbits: a histochemical ex vivo and in vivo analysis

Current tissue engineering technology focuses on developing simple tissues, whereas multilayered structures comprising several tissue types have rarely been described. We developed a highly biomimetic multilayered palate substitute with bone and oral mucosa tissues using rabbit cells and biomaterials subjected to nanotechnological techniques based on plastic compression. This novel palate substitute was autologously grafted in vivo, and histological and histochemical analyses were used to evaluate biointegration, cell function, and cell differentiation in the multilayered palate substitute. The three-dimensional structure of the multilayered palate substitute was histologically similar to control tissues, but the ex vivo level of cell and tissue differentiation were low as determined by the absence of epithelial differentiation although cytokeratins 4 and 13 were expressed. In vivo grafting was associated with greater cell differentiation, epithelial stratification, and maturation, but the expression of cytokeratins 4, 13, 5, and 19 at did not reach control tissue levels. Histochemical analysis of the oral mucosa stroma and bone detected weak signals for proteoglycans, elastic and collagen fibers, mineralization deposits and osteocalcin in the multilayered palate substitute cultured ex vivo. However, in vivo grafting was able to induce cell and tissue differentiation, although the expression levels of these components were always significantly lower than those found in controls, except for collagen in the bone layer. These results suggest that generation of a full-thickness multilayered palate substitute is achievable and that tissues become partially differentiated upon in vivo grafting.

Cellular and Molecular Mechanisms of Palatogenesis

Palatogenesis involves the initiation, growth, morphogenesis, and fusion of the primary and secondary palatal shelves from initially separate facial prominences during embryogenesis to form the intact palate separating the oral cavity from the nostrils. The palatal shelves consist mainly of cranial neural crest-derived mesenchymal cells covered by a simple embryonic epithelium. The growth and patterning of the palatal shelves are controlled by reciprocal epithelial-mesenchymal interactions regulated by multiple signaling pathways and transcription factors. During palatal shelf outgrowth, the embryonic epithelium develops a "teflon" coat consisting of a single, continuous layer of periderm cells that prevents the facial prominences and palatal shelves from forming aberrant interepithelial adhesions. Palatal fusion involves not only spatiotemporally regulated disruption of the periderm but also dynamic cellular and molecular processes that result in adhesion and intercalation of the palatal medial edge epithelia to form an intershelf epithelial seam, and subsequent dissolution of the epithelial seam to form the intact roof of the oral cavity. The complexity of regulation of these morphogenetic processes is reflected by the common occurrence of cleft palate in humans. This review will summarize major recent advances and discuss major remaining gaps in the understanding of cellular and molecular mechanisms controlling palatogenesis.

Chemical composition modulates the adverse effects of particles on the mucociliary epithelium

OBJECTIVE

We compared the adverse effects of two types of real ambient particles; i.e., total suspended particles from an electrostatic precipitator of a steel mill and fine air particles from an urban ambient particulate matter of 2.5 µm, on mucociliary clearance.

METHOD

Mucociliary function was quantified by mucociliary transport, ciliary beating frequency and the amount of acid and neutral mucous in epithelial cells through morphometry of frog palate preparations. The palates were immersed in one of the following solutions: total suspended particles (0.1 mg/mL), particulate matter 2.5 µm 0.1 mg/mL (PM0.1) or 3.0 mg/mL (PM3.0) and amphibian Ringer's solution (control). Particle chemical compositions were determined by X-ray fluorescence and gas chromatography/mass spectrometry.

RESULTS

Exposure to total suspended particles and PM3.0 decreased mucociliary transport. Ciliary beating frequency was diminished by total suspended particles at all times during exposure, while particulate matter of 2.5 µm did not elicit changes. Particulate matter of 2.5 µm reduced epithelial mucous and epithelium thickness, while total suspended particles behaved similarly to the control group. Total suspended particles exhibited a predominance of Fe and no organic compounds, while the particulate matter 2.5 µm contained predominant amounts of S, Fe, Si and, to a lesser extent, Cu, Ni, V, Zn and organic compounds.

CONCLUSION

Our results showed that different compositions of particles induced different airway epithelial responses, emphasizing that knowledge of their individual characteristics may help to establish policies aimed at controlling air pollution.

Altered FGF Signaling Pathways Impair Cell Proliferation and Elevation of Palate Shelves

In palatogenesis, palatal shelves are patterned along the mediolateral axis as well as the anteroposterior axis before the onset of palatal fusion. Fgf10 specifically expressed in lateral mesenchyme of palate maintains Shh transcription in lateral epithelium, while Fgf7 activated in medial mesenchyme by Dlx5, suppressed the expansion of Shh expression to medial epithelium. How FGF signaling pathways regulate the cell behaviors of developing palate remains elusive. In our study, we found that when Fgf8 is ectopically expressed in the embryonic palatal mesenchyme, the elevation of palatal shelves is impaired and the posterior palatal shelves are enlarged, especially in the medial side. The palatal deformity results from the drastic increase of cell proliferation in posterior mesenchyme and decrease of cell proliferation in epithelium. The expression of mesenchymal Fgf10 and epithelial Shh in the lateral palate, as well as the Dlx5 and Fgf7 transcription in the medial mesenchyme are all interrupted, indicating that the epithelial-mesenchymal interactions during palatogenesis are disrupted by the ectopic activation of mesenchymal Fgf8. Besides the altered Fgf7, Fgf10, Dlx5 and Shh expression pattern, the reduced Osr2 expression domain in the lateral mesenchyme also suggests an impaired mediolateral patterning of posterior palate. Moreover, the ectopic Fgf8 expression up-regulates pJak1 throughout the palatal mesenchyme and pErk in the medial mesenchyme, but down-regulates pJak2 in the epithelium, suggesting that during normal palatogenesis, the medial mesenchymal cell proliferation is stimulated by FGF/Erk pathway, while the epithelial cell proliferation is maintained through FGF/Jak2 pathway.

[Effect of BMP-2 treatment on the morphology and proliferation of human embryonic palatal derived mesenchymal preosteoblast cells]

In dental implantation missing tooth or teeth are replaced by artificial root. To reduce the time required for the integration newest trends are the enhancement of bone formation around the implant by bioactive molecules, growth factors. Such a molecule is bone morphogenetic protein-2 (BMP-2) accepted by US Food and Drug Administration (FDA). In these kind of applications effect of BMP-2 is tested in vitro on appropriate cell lines. One of these cell lines is the osteoblast like human embrionic palatal mesenchymal cell line (HEPM). In our experiments the effect of BMP-2 homodimer treatment was investigated on the differentiation of HEPM cells to osteoblasts reflected by changes in morphology, and proliferation after a short, 3 days BMP-2 treatment. Results showed that after three days BMP-2 treatment facilitates cell attachment on a concentration dependent manner however changes in cell morphology and proliferation could not be observed. Continuing the BMP-2 treatment inhibitory effect was measured in cell proliferation, which may refer to cell differentiation.

Tracing CD34+ Stromal Fibroblasts in Palatal Mucosa and Periodontal Granulation Tissue as a Possible Cell Reservoir for Periodontal Regeneration

The aim of the present research was to trace CD34+ stromal fibroblastic cells (CD34+ SFCs) in the palatal connective tissue harvested for muco-gingival surgical procedures and in granulation tissues from periodontal pockets using immunohistochemical and transmission electron microscopy. Immunohistochemical analysis targeted the presence of three antigens: CD31, α-smooth muscle actin (α-SMA), and CD34. In the palate, CD31 staining revealed a colored inner ring of the vessels representing the endothelium, α-SMA+ was located in the medial layer of the vasculature, and CD34 was intensely expressed by endothelial cells and artery adventitial cells (considered to be CD34+ SFCs). Granulation tissue showed the same pattern for CD31+ and α-SMA, but a different staining pattern for CD34. Ultrastructural examination of the palatal tissue highlighted perivascular cells with fibroblast-like characteristics and pericytes in close spatial relationship to endothelial cells. The ultrastructural evaluation of granulation tissue sections confirmed the presence of neovasculature and the inflammatory nature of this tissue. The present study traced the presence of CD34+ SFCs and of pericytes in the palatal connective tissue thus highlighting once more its intrinsic regenerative capabilities. The clinical and systemic factors triggering mobilization and influencing the fate of local CD34+SCFs and other progenitors are issues to be further investigated.

Emdogain-regulated gene expression in palatal fibroblasts requires TGF-βRI kinase signaling

Genome-wide microarrays have suggested that Emdogain regulates TGF-β target genes in gingival and palatal fibroblasts. However, definitive support for this contention and the extent to which TGF-β signaling contributes to the effects of Emdogain has remained elusive. We therefore studied the role of the TGF-β receptor I (TGF-βRI) kinase to mediate the effect of Emdogain on palatal fibroblasts. Palatal fibroblasts were exposed to Emdogain with and without the inhibitor for TGF-βRI kinase, SB431542. Emdogain caused 39 coding genes to be differentially expressed in palatal fibroblasts by microarray analysis (p<0.05; >10-fold). Importantly, in the presence of the TGF-βRI kinase inhibitor SB431542, Emdogain failed to cause any significant changes in gene expression. Consistent with this mechanism, three independent TGF-βRI kinase inhibitors and a TGF-β neutralizing antibody abrogated the increased expression of IL-11, a selected Emdogain target gene. The MAPK inhibitors SB203580 and U0126 lowered the impact of Emdogain on IL-11 expression. The data support that TGF-βRI kinase activity is necessary to mediate the effects of Emdogain on gene expression in vitro.

Regulation of the epithelial adhesion molecule CEACAM1 is important for palate formation

Cleft palate results from a mixture of genetic and environmental factors and occurs when the bilateral palatal shelves fail to fuse. The objective of this study was to search for new genes involved in mouse palate formation. Gene expression of murine embryonic palatal tissue was analyzed at various developmental stages before, during, and after palate fusion using GeneChip® microarrays. Ceacam1 was one of the highly up-regulated genes during palate formation, and this was confirmed by quantitative real-time PCR. Immunohistochemical staining showed that CEACAM1 was present in prefusion palatal epithelium and was degraded during fusion. To investigate the developmental role of CEACAM1, function-blocking antibody was added to embryonic mouse palate in organ culture. Palatal fusion was inhibited by this function-blocking antibody. To investigate the subsequent developmental role of CEACAM1, we characterized Ceacam1-deficient (Ceacam1^−/−) mice. Epithelial cells persisted abnormally at the midline of the embryonic palate even on day E16.0, and palatal fusion was delayed in Ceacam1^−/− mice. TGFβ3 expression, apoptosis, and cell proliferation in palatal epithelium were not affected in the palate of Ceacam1^−/−mice. However, CEACAM1 expression was retained in the remaining MEE of TGFβ-deficient mice. These results suggest that CEACAM1 has roles in the initiation of palatal fusion via epithelial cell adhesion.

In vitro characterization of multipotent mesenchymal stromal cells isolated from palatal subepithelial tissue grafts

The aim of this study was to analyze whether the mesenchymal stromal cells (MSCs) isolated from palatal tissue grafts harvested in order to cover gingival recessions have the basic characteristics of stem cells. The palatal tissue cells were processed using a special culture medium that stimulated the development of only undifferentiated cellular lines. Cells at passage 4 were evaluated by flow cytometry to examine the expression of specific surface markers and were tested for multilineage differentiation capacity. These cells collected at passage 4 were also investigated for the capacity to cluster into embryoid body aggregates. Palatal MSCs displayed positive staining for the mesenchymal markers CD29, CD73, CD105, CD 49e, and CD44, but did not express hematopoietic markers CD34/45. The palatal MSCs successfully differentiated into osteogenic, adipogenic, and chondrogenic lineages. When seeded in special conditions, palatal MSCs propagated into unattached spheres resembling embryoid body aggregates consisting both of differentiated and undifferentiated cells as revealed at the ultrastructural evaluation. It is concluded that the isolated palatal MSCs fulfilled the basic criteria defining the stem cells. This new source of stem cells characterized here for the first time opens new perspectives on possible applications in basic research and in regenerative medicine.

[Establishment of palatal organ culture in vitro]

OBJECTIVE

The purpose of this study was to establish a palatal organ culture method and to investigate the palatogenesis in vitro.

METHODS

20 pregnant 14-day mice were killed, embryos were separated ascetically, and palatal shelves were dissected and placed on a modified Trowell's system. All explants were cultured 24 h and 48 h respectively. Finally, all explants were embedded and stained by Hematoxylin and Eosin.

RESULTS

All explants grew healthy. After incubation for 24 h, medial edge epithelium maintained, whereas after 48 h, medial edge epithelium disappeared, bilateral mesenchymal cells contacted, palates fused.

CONCLUSION

This method provides an effective way for investigating the etiology of cleft palate in vitro.

Ephrin reverse signaling controls palate fusion via a PI3 kinase-dependent mechanism

Secondary palate fusion requires adhesion and epithelial-to-mesenchymal transition (EMT) of the epithelial layers on opposing palatal shelves. This EMT requires transforming growth factor β3 (TGFβ3), and its failure results in cleft palate. Ephrins, and their receptors, the Ephs, are responsible for migration, adhesion, and midline closure events throughout development. Ephrins can also act as signal-transducing receptors in these processes, with the Ephs serving as ligands (termed "reverse" signaling). We found that activation of ephrin reverse signaling in chicken palates induced fusion in the absence of TGFβ3, and that PI3K inhibition abrogated this effect. Further, blockage of reverse signaling inhibited TGFβ3-induced fusion in the chicken and natural fusion in the mouse. Thus, ephrin reverse signaling is necessary and sufficient to induce palate fusion independent of TGFβ3. These data describe both a novel role for ephrins in palate morphogenesis, and a previously unknown mechanism of ephrin signaling.

Hand2 is required in the epithelium for palatogenesis in mice

The basic helix-loop-helix (bHLH) transcription factor Hand2 has been implicated in the development of multiple organs, including craniofacial organs. Mice carrying Hand2 hypomorphic alleles (Hand2(LoxP/-)) display a cleft palate phenotype. A specific deletion of the Hand2 branchial arch-specific enhancer also leads to a hypoplastic mandible and cleft palate formation in mice. However, the underlying mechanism of Hand2 regulation of palate development remains unknown. Here we show that Hand2 is expressed in both the epithelium and mesenchyme of the developing palate. While mesenchymal specific inactivation of Hand2 has no impact on palate development, epithelial specific deletion of Hand2 creates a cleft palate phenotype. Hand2 appears to exert distinct roles in the anterior and posterior palate. In the anterior palate of Hand2(LoxP/-) mice, premature death of periderm cells and a down-regulation of Shh are observed in the medial edge epithelium (MEE), accompanied by a decreased level of cell proliferation in the palatal mesenchyme. In the posterior palate, a lower dose of Hand2 causes aberrant periderm cell death on the surface of the epithelium, triggering abnormal fusion between the palatal shelf and mandible and preventing palatal shelf elevation. We further demonstrate that BMP activities are essential for the expression of Hand2 in the palate. We conclude that Hand2 is an intrinsic regulator in the epithelium and is required for palate development.

TGFbeta3 inhibits E-cadherin gene expression in palate medial-edge epithelial cells through a Smad2-Smad4-LEF1 transcription complex

Dissociation of medial-edge epithelium (MEE) during palate development is essential for mediating correct craniofacial morphogenesis. This phenomenon is initiated by TGFbeta3 upon adherence of opposing palatal shelves, because loss of E-cadherin causes the MEE seam to break into small epithelial islands. To investigate the molecular mechanisms that cause this E-cadherin loss, we isolated and cultured murine embryonic primary MEE cells from adhered or non-adhered palates. Here, we provide the first evidence that lymphoid enhancer factor 1 (LEF1), when functionally activated by phosphorylated Smad2 (Smad2-P) and Smad4 (rather than beta-catenin), binds with the promoter of the E-cadherin gene to repress its transcription in response to TGFbeta3 signaling. Furthermore, we found that TGFbeta3 signaling stimulates epithelial-mesenchymal transformation (EMT) and cell migration in these cells. LEF1 and Smad4 were found to be necessary for up-regulation of the mesenchymal markers vimentin and fibronectin, independently of beta-catenin. We proved that TGFbeta3 signaling induces EMT in MEE cells by forming activated transcription complexes of Smad2-P, Smad4 and LEF1 that directly inhibit E-cadherin gene expression.

Downregulated gene expression in human palate fibroblasts after cyclosporin A treatment

BACKGROUND

Cyclosporin A is a powerful immunosuppressive drug with considerable impact on transplants and is able to modify extracellular matrix (ECM) composition. It has recently been demonstrated that cyclosporin A stimulates the production of the cytokine family. Cytokines such as interleukin, transforming growth factor beta(1), and bone morphogenetic protein induce the deposition of glycosaminoglycans (GAGs), proteoglycans, and collagen fibers in the connective ECM. ECM composition is very important for normal tissue development and function. In this work, we examine the effects caused by cyclosporin A on cultures of normal human palate fibroblasts in order to evaluate interleukin, transforming growth factor beta II, and bone morphogenetic protein II membrane receptor induction and extracellular GAG changes such as hyaluronic acid, heparin sulfate, and chondroitin sulfate.

METHODS

Palate fibroblasts were maintained for 24 h in serum-free 199 medium containing 5 microg/mL (3)H glucosamine hydrochloride. After this time, TGF II and BMP II receptors were determined by microarray analysis and GAG classes by the biochemical method.

RESULTS

The results show that TGFbeta(1) II and BMP II membrane receptors are significantly inhibited in cyclosporin A-treated cultures as compared to controls, whereas IL-1R2 membrane receptors are stimulated. The behavior of total intra- and extracellular GAGs is significantly increased in cyclosporin A-treated cultures, whereas the ratio between non-sulfated/sulfated GAGs decreases (p <or=0.01) vis-à-vis controls.

CONCLUSIONS

Because they form a highly complicated macromolecular network in the ECM, which provides an indication of cell function and gene expression and modulates growth factor activities, GAG changes are related to modification of ECM functions. Our data show that cyclosporin A causes biochemical changes to ECM through alterations in cytokines and respective membrane receptor linkages.

Mechanisms of palatal epithelial seam disintegration by transforming growth factor (TGF) beta3

TGFbeta3 signaling initiates and completes sequential phases of cellular differentiation that is required for complete disintegration of the palatal medial edge seam, that progresses between 14 and 17 embryonic days in the murine system, which is necessary in establishing confluence of the palatal stroma. Understanding the cellular mechanism of palatal MES disintegration in response to TGFbeta3 signaling will result in new approaches to defining the causes of cleft palate and other facial clefts that may result from failure of seam disintegration. We have isolated MES primary cells to study the details of MES disintegration mechanism by TGFbeta3 during palate development using several biochemical and genetic approaches. Our results demonstrate a novel mechanism of MES disintegration where MES, independently yet sequentially, undergoes cell cycle arrest, cell migration and apoptosis to generate immaculate palatal confluency during palatogenesis in response to robust TGFbeta3 signaling. The results contribute to a missing fundamental element to our base knowledge of the diverse roles of TGFbeta3 in functional and morphological changes that MES undergo during palatal seam disintegration. We believe that our findings will lead to more effective treatment of facial clefting.

Microarray analysis of gene expression during epithelial-mesenchymal transformation

One of the most fundamental biological processes in development, as well as a primary mechanism for tumor metastasis, is epithelial-mesenchymal transformation (EMT). To gain a greater understanding of this transition, we have obtained a genomic profile of the critical stages before and during this rapid change in morphology in the developing mouse palate. By isolating the medial edge epithelium of each palatal shelf, we were able to obtain pure gene expression data without contamination from surrounding mesenchymal cells. Our results support the important role of the TGF-beta/Smad signal transduction pathway in the stimulation of EMT by means of up-regulation of the EMT-inducing gene, LEF-1. We document changes in gene expression profiles during palatal adherence and subsequent transformation of the medial edge epithelial seam that suggests a high number of LEF-1 target genes promote cellular transformation to mesenchyme. These include genes involved in cell adhesion, polarity, cytoskeletal dynamics, migration, and intracellular signaling. This knowledge of the changes in gene expression levels during palatogenesis should lead to a better understanding of the mechanisms of EMT.

Amniotic fluid induces rapid epithelialization in the experimentally ruptured fetal mouse palate--implications for fetal wound healing

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.

Effect of local antimicrobial agents on excisional palatal wound healing: a clinical and histomorphometric study in rats

AIM

To assess the effect of topically applied antimicrobial agents on palatal excisional wound in rats.

MATERIALS AND METHODS

Excisional wounds, 5 mm in diameter, were made in the centre of the palate of 125 Wistar male rats. In four experimental groups, chlorhexidine digluconate (CHX) 0.12% solution, 1% CHX gel, phenolic compounds solution (Listerine), amine/stannous fluoride solution (Meridol) and saline solution as a control group were applied daily for 1 min. The wound area was measured photographically and the epithelialization rate was determined histologically at 3, 7, 14 and 21 days post-surgery.

RESULTS

The mean wound area and mean distance between the epithelial margins decreased significantly with time (p<0.001) in experimental and control groups, with the greatest wound area reduction and rate of epithelialization on day 14. A significantly superior rate of wound epithelialization (p=0.03) was presented following use of 1% CHX gel and Listerine and a comparatively inferior one when the Meridol solution was applied.

CONCLUSIONS

Each tested antimicrobial agent when applied on an excisional wound with epithelial and connective tissue deficiency did not have a negative effect on the rate of wound closure. The best results were achieved with 1%CHX gel and Listerine.

Substance P and acetylcholine are co-localized in the pathway mediating mucociliary activity in Rana pipiens

Mucociliary activity is an important clearance mechanism in the respiratory system of air breathing vertebrates. Substance P (SP) and acetylcholine play a key role in the stimulation of the mucociliary transport in the frog palate. In this study, retrograde neuronal tracing was combined with immunocytochemistry for SP and choline acetyl transferase (ChAT) in the trigeminal ganglion and for neurokinin-1 receptor (NK1R) in the palate of Rana pipiens. The cells of origin of the palatine nerve were identified in the trigeminal ganglion using the retrograde tracer Fluorogold (FG). Optimal labeling of FG cells in the trigeminal ganglion was obtained at 96 h of exposure. Immunoflorescent shows that SP and acetylcholine are co-localized in 92% of the cells labeled with FG in the trigeminal ganglion. NK1 receptors were found in the membrane of epithelial and goblet cells of the palate. Ultrastructural study of the palate showed axonal-like endings with vesicles in connection with epithelial and goblet cells. These results further support the concerted action of both neurotransmitters in the regulation of mucociliary activity in the frog palate.

Development of an engineering autologous palatal mucosa-like tissue for potential clinical applications

The goal of this study was to optimize key processes in recreating functional and viable palatal mucosa-like tissue that would be easy to handle and would promote wound healing. Normal human gingival fibroblasts and epithelial cells and a clinically useful biomaterial, CollaTape, were used. Structural and ultrastructural analyses showed that the gingival fibroblasts and epithelial cells adhered to the biomaterial and proliferated. Following a 6-day culture, using 10(5) fibroblasts and 10(6) epithelial cells, a well-organized palatal mucosa-like tissue was engineered. The engineered epithelium displayed various layers, including a stratum corneum, and contained cytokeratin 16-positive cells located in the supra-basal layer. This palatal mucosa-like engineered tissue was designed to meet a variety of surgical needs. The biodegradable collagen membrane (CollaTape) contributed to the flexibility of the engineered tissue. This engineered innovative tissue may contribute to the reconstruction of oral soft-tissue defects secondary to trauma, congenital defects, and acquired diseases.

Modulation of cell proliferation during palatogenesis by the interplay between Tbx3 and Bmp4

During secondary palate development, two shelves are elevated to a horizontal position above the tongue through a process involving many cellular mechanisms, including proliferation. In particular, the expression patterns of Tbx3 and Bmp4, which are colocalized at embryonic day 13.5 (E13.5) and have unique expression patterns in specific regions at E14.5, have been investigated in early mouse palatogenesis. Tbx3 expression is reported to be associated with Bmp4 signaling during the process of organogenesis in other areas, such as limb development. However, the function of Tbx3 and the relationship between Tbx3 and Bmp4 in palate development have not been determined. We have examined the gene expression pattern and cell proliferation in order to understand the mutual interactions and function of Tbx3 and Bmp4. An electroporation method was used to investigate the altered pattern of these genes after their over-expression in organ cultures. NOGGIN protein-soaked beads were also implanted into the cultured palate to determine the function of Bmp4 in palatogenesis. After electroporation and NOGGIN bead implantation, the number of PCNA-positive cells was counted. The results showed that Tbx3 and Bmp4 strongly up- and down-regulated each other in order to control the proliferation of the palatal shelf. Thus, Tbx3 expression is induced by Bmp4 in the mesenchyme of the anterior palatal shelves, whereas mesenchymal expression of Tbx3 down-regulates Bmp4 expression in the mesenchyme of the palate. The harmonization between Tbx3 and Bmp4 therefore controls cell proliferation to regulate secondary palate development.

Analysis of cell migration, transdifferentiation and apoptosis during mouse secondary palate fusion

Malformations in secondary palate fusion will lead to cleft palate, a common human birth defect. Palate fusion involves the formation and subsequent degeneration of the medial edge epithelial seam. The cellular mechanisms underlying seam degeneration have been a major focus in the study of palatogenesis. Three mechanisms have been proposed for seam degeneration: lateral migration of medial edge epithelial cells; epithelial-mesenchymal trans-differentiation; and apoptosis of medial edge epithelial cells. However, there is still a great deal of controversy over these proposed mechanisms. In this study, we established a [Rosa26<-->C57BL/6] chimeric culture system, in which a Rosa26-originated ;blue' palatal shelf was paired with a C57BL/6-derived ;white' palatal shelf. Using this organ culture system, we observed the migration of medial edge epithelial cells to the nasal side, but not to the oral side. We also observed an anteroposterior migration of medial edge epithelial cells, which may play an important role in posterior palate fusion. To examine epithelial-mesenchymal transdifferentiation during palate fusion, we bred a cytokeratin 14-Cre transgenic line into the R26R background. In situ hybridization showed that the Cre transgene is expressed exclusively in the epithelium. However, beta-galactosidase staining gave extensive signals in the palatal mesenchymal region during and after palate fusion, demonstrating the occurrence of an epithelial-mesenchymal transdifferentiation mechanism during palate fusion. Finally, we showed that Apaf1 mutant mouse embryos are able to complete palate fusion without DNA fragmentation-mediated programmed cell death, indicating that this is not essential for palate fusion in vivo.

Cell autonomous requirement for Tgfbr2 in the disappearance of medial edge epithelium during palatal fusion

Palatal fusion is a complex, multi-step developmental process; the consequence of failure in this process is cleft palate, one of the most common birth defects in humans. Previous studies have shown that regression of the medial edge epithelium (MEE) upon palatal fusion is required for this process, and TGF-beta signaling plays an important role in regulating palatal fusion. However, the fate of the MEE and the mechanisms underlying its disappearance are still unclear. By using the Cre/lox system, we are able to label the MEE genetically and to ablate Tgfbr2 specifically in the palatal epithelial cells. Our results indicate that epithelial-mesenchymal transformation does not occur in the regression of MEE cells. Ablation of Tgfbr2 in the palatal epithelial cells causes soft palate cleft, submucosal cleft and failure of the primary palate to fuse with the secondary palate. Whereas wild-type MEE cells disappear, the mutant MEE cells continue to proliferate and form cysts and epithelial bridges in the midline of the palate. Our study provides for the first time an animal model for soft palate cleft and submucous cleft. At the molecular level, Tgfb3 and Irf6 have similar expression patterns in the MEE. Mutations in IRF6 disrupt orofacial development and cause cleft palate in humans. We show here that Irf6 expression is downregulated in the MEE of the Tgfbr2 mutant. As a recent study shows that heterozygous mutations in TGFBR1 or TGFBR2 cause multiple human congenital malformations, including soft palate cleft, we propose that TGF-beta mediated Irf6 expression plays an important, cell-autonomous role in regulating the fate of MEE cells during palatogenesis in both mice and humans.

A histological study on the prenatal development of the palatal rugae in the white rat

This study was designed to investigate the prenatal development of the palatal rugae in the White Rat and to discuss the possible role played by the developing rugae in palatal shelf elevation. Extraction of embryos from twenty pregnant female rats was carried out in the 12th, 13th, 14th, 15th and 16th day of pregnancy. Four embryos from each age were decapitated and their heads were fixed and processed. Serial coronal and sagittal sections were made and stained with haematoxylin and eosin and with Mallory's trichrome stains. The results of the present study revealed that in the 12th day rat embryo the lateral and medial surfaces of the vertical palatine processes were covered with epithelium of uniform thickness but there was marked epithelial thickening at the junction between the lateral surface of the palatine process and the maxillary process with increased condensation in the subjacent mesenchyme. In the 13th day, the thickened epithelium was invaginated into the underlying mesenchyme to form a well-marked groove. In the 14th day, the anterior set of palatal rugae started to appear on the future oral surface of the vertical palatine process as three vertically arranged areas of epithelial thickenings. In the 15th day, the palatine processes became horizontal and the anterior set of rugae became apparent in coronal and sagittal sections. In the 16th day, the anterior set of rugae became well developed and their thickened epithelium became invaded by the subjacent mesenchyme. The posterior set of rugae started to appear as localized epithelial thickenings. It was concluded that the anterior set of rugae is developed prior to shelf elevation while the posterior set is developed only after palatal shelf elevation. The rugae may act as struts which help in keeping the palatine shelves horizontal when they have been elevated.

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.

[Separation and culture of mouse embryonic palatal mesenchymal cells in vitro]

OBJECTIVE

To modify the operation of dissecting embryonic palatal shelves and purify the mouse embryonic palatal mesenchymal (EPM) cells in primary culture.

METHODS

The embryonic palatal shelves were dissected using a surgical microscope by modified operation. Then the embryonic palatal shelves were incubated with Dispase and the isolated EPM cells were cultured. Immunofluorescence technique was used to identify the characteristics of cells.

RESULTS

Embryonic palatal shelves could be dissected accurately and easily with a modified operation. The purified EPM cells contained scarcely epithelial cells. EPM cells were anti-HNK-1, S-100, vimentin positive and anti-CK negative.

CONCLUSION

A modified method for dissecting embryonic palatal shelves and purifying the EPM cells of primary culture was established.

Apoptosis Induced by atRA in MEPM Cells Is Mediated through Activation of Caspase and RAR

We have previously demonstrated that all-trans retinoic (atRA) induced growth inhibition and apoptosis in mouse embryonic palate mesenchymal cells (MEPM). In the present study, we investigated the molecular mechanisms of atRA-induced apoptosis and its putative action pathway. atRA-induced apoptosis is associated with activation of the initiator caspase-9 and the effector caspase-3, but not of the effector caspase-8. A broad caspase inhibitor (z-VAD-fmk), caspase-9 inhibitor z-LEHD-fmk and caspase-3 inhibitor (z-DEVD-fmk) blocked atRA-induced DNA fragmentation and sub-G1 fraction, but not caspase-8 inhibitor z-IETD-fmk. We further showed that atRA dose-dependently promoted mRNA expression of retinoic acid receptor beta (RAR-beta) and gamma. A weaker increase in RAR-alpha mRNA was seen only at the highest concentration of atRA (5 muM). The pan RAR antagonist, BMS493, completely abrogated atRA-induced DNA fragmentation, Sub-G1 fraction, and caspase-3 activation. Taken together, these findings show that caspase-mediated induction of apoptosis by atRA is an RAR-dependent signaling pathway.

Electrospun protein fibers as matrices for tissue engineering

Electrospinning has recently emerged as a leading technique for generating biomimetic scaffolds made of synthetic and natural polymers for tissue engineering applications. In this study, we compared collagen, gelatin (denatured collagen), solubilized alpha-elastin, and, as a first, recombinant human tropoelastin as biopolymeric materials for fabricating tissue engineered scaffolds by electrospinning. In extending previous studies, we optimized the shape and size (diameter or width) of the ensuing electrospun fibers by varying important parameters of the electrospinning process, such as solute concentration and delivery rate of the polymers. Our results indicate that the average diameter of gelatin and collagen fibers could be scaled down to 200-500 nm without any beads, while the alpha-elastin and tropoelastin fibers were several microns in width. Importantly, and contrary to any hitherto reported structures of electrospun polymers, fibers composed of alpha-elastin, especially tropoelastin, exhibited "quasi-elastic" wave-like patterns at increased solution delivery rates. The periodicity of these wave-like tropoelastin fibers was partly affected by the delivery rate. Atomic force microscopy was utilized to profile the topography of individual electrospun fibers and microtensile testing was performed to measure their mechanical properties. Cell culture studies confirmed that the electrospun engineered protein scaffolds support attachment and growth of human embryonic palatal mesenchymal (HEPM) cells.

[Retinoic acid induced cell cycle arrest and apoptosis in mouse embryonic palatal mesenchymal cells]

OBJECTIVES

To investigate the effect of all-trans retinoic acid (atRA) on proliferation activity and cell cycle distribution in mouse embryonic palatal mesenchymal (MEPM) cells and the underlying molecular mechanisms.

METHODS

MEPM cells were prepared from palate shelves of mouse fetal on gestation day 13. Cell viability was determined by MTI assay. Cell cycle distribution and subdiploid population were analyzed by cytometry. The expression of cyclin D and E and phosphorylation of retinoblastoma protein was examined using Western-blot.

RESULTS

atRA remarkably inhibited the growth of MEPM cells in a dose-dependent manner. atRA also caused an increase in the proportion of cells in G0/G1 and a decrease in the proportion of cells in S phase. atRA inhibited expression of cyclins D and E at protein level. Furthermore, atRA treatment reduced phosphorylated Rb.

CONCLUSION

These data suggested that atRA had antiproliferative activity by modulating G1/S cell cycle regulators and by inhibition of Rb phosphorylation in MEPM cells, which might account for the pathogenesis of cleft palate induced by retinoic acid.

Anti-oxidants reduce the acute adverse effects of residual oil fly ash on the frog palate mucociliary epithelium

There is evidence indicating that oxidants play a pivotal role in determining air pollution-dependent lung injury. In the present study we explored the role of oxidants present in ambient particles in causing damage to the mucociliary epithelium. We explored the protective effects of pretreatment with three substances (n-propyl gallate, DL-alpha-tocopherol acetate, and EDTA) on the frog palate exposed to residual oil fly ash (ROFA). The parameters analyzed were mucociliary transport (MCT) and ciliary beating frequency (CBF) after 0, 10, 20, 30, 60, and 120 min of exposure. MCT was decreased significantly by ROFA (P < 0.001), with a significant interaction effect (P = 0.02) between the duration of exposure and treatment with antioxidants. The inhibitory effects on MCT of the substances tested were significantly different (P = 0.002); vitamin E was similar to control (Ringer) and different from all other groups. CBF showed no significant effect of duration of exposure (P = 0.465), but a significant interaction between duration of exposure and treatments was observed (P = 0.011). Significant differences were detected among treatments (P < 0.001), with ROFA and n-propyl gallate at concentrations of 50 microM presenting a short-lived increase in CBF, which was not observed in the remaining groups. The results showed that both MCT and CBF were affected within a short period (100 min) of exposure to ROFA and that the presence of antioxidant substances, such as vitamin E (4 mg/mL) and n-propyl gallate (300 microM), protected against the mucociliary impairment induced by ROFA on the frog palate.

Interaction between Smad 3 and Dishevelled in murine embryonic craniofacial mesenchymal cells

OBJECTIVES

To determine the in vivo interaction between Smad 3 and Dishevelled-1.

DESIGN

Cell culture transfection followed by immunoprecipitation with specific antibodies.

SETTING AND SAMPLE POPULATION

The Department of Molecular, Cellular, and Craniofacial Biology, Birth Defects Center, University of Louisville.

EXPERIMENTAL VARIABLE

Overexpression of myc-Smad 3.

OUTCOME MEASURE

Western blotting of anti-Dishevelled immunoprecipitates for Smad 3.

RESULTS

Smad 3 and Dishevelled isoforms-1, -2, and -3 all bind Smad 3 in glutathione-S-transferase (GST) pull-down assays and Smad 3 binds to Dishevelled-1 in vivo. Stimulation of the transforming growth factor beta (TGFbeta) pathway leads to increased binding of Smad 3 and Dishevelled-1 in vivo.

CONCLUSION

Smad 3 binds all three known isoforms of Dishevelled and binds Dishevelled 1 in vivo. TGFbeta signaling modulates the interaction between Smad 3 and Dishevelled-1.

FOXN1 is critical for onycholemmal terminal differentiation in nude (Foxn1) mice

Nude mice have a mutation in the transcription factor Foxn1(nu), resulting in downregulation of hair keratins. Although hair follicles develop normally, the hair fibers become structurally weak, curl, and break off at the surface. Nails in nude mice are deformed, based on alterations of the onychocyte differentiation process. Elemental microanalysis of the nail plate reveals marked decreases in sulfur concentrations in the nude mouse nail plates. Immunohistochemistry shows a lack of keratin 1 expression in terminally differentiating keratinocytes of the nail matrix. Instead, the typical differentiation process of the matrix is altered toward an epidermis-like differentiation pattern, comprising the production of filaggrin-containing keratohyalin granules in cells resembling those of the stratum granulosum, which are never observed in normally haired mice. The nail plate has diffuse basophilic stippling. It is thinner than normal, weak, and in most Foxn1(nu)/Foxn1(nu) mice breaks where it separates from the hyponychium. These studies indicate that the Foxn1(nu) mutated gene has effects beyond downregulating keratin expression, including changes in filaggrin expression, and is critical for normal onycholemmal differentiation. The nails of nude mice provide new insights into the molecular controls of onychocyte differentiation, and they offer a useful model to investigate the pathogenesis of nail hypergranulosis, a common feature in human nail diseases.

Secalonic acid D blocks embryonic palatal mesenchymal cell-cycle by altering the activity of CDK2 and the expression of p21 and cyclin E

BACKGROUND

The mycotoxin, secalonic acid D (SAD), a known animal and potential human cleft palate (CP)-inducing agent, is produced by Pencillium oxalicum in corn. SAD selectively inhibits proliferation of murine embryonic palatal mesenchymal (MEPM) cells leading to a reduction in cell numbers. These effects can explain the reduction in shelf size and the resulting CP seen in the offspring of SAD-exposed mice. Ability of SAD to inhibit proliferation as well as to block the progression of cells from G1- to S-phase of the cell-cycle were also shown in the human embryonic palatal mesenchymal (HEPM) cells suggesting the potential CP-inducing effect of SAD in human beings

METHODS

Gestation day (GD) 12 mouse embryos and HEPM cells were used to test the hypothesis that the cell-cycle block induced by SAD results from a disruption of stage-specific regulatory components both in vivo and in vitro. The effects of SAD on the activity of various cyclin dependent kinases (CDK) and on the levels of various positive (cyclins and CDK) and negative (CDK inhibitors p15, 16, 18, 19, 21, 27, 57) cell-cycle regulators were assessed by performing kinase assays and immunoblots, respectively.

RESULTS

In the murine embryonic palates, SAD specifically inhibited G1/S-phase-specific CDK2 activity, reduced the level of cyclin E and tended to increase the level of the CIP/kip CDK inhibitor, p21. In the HEPM cell cultures, exposure to IC50 of SAD significantly affected all of the above targets. In addition, a reduction in the levels/activity of CDK 4/6, a reduction in the levels of cyclins D1, D2, D3, E, A, and all INK4 family proteins, and an increase in the level of the CIP/kip CDK inhibitor, p57, were also seen.

CONCLUSIONS

These results suggest that the S-phase-specific cell-cycle proteins CDK2, cyclin E and possibly p21 are the common targets of SAD in murine palatal shelves in vivo and in human embryonic palatal mesenchymal cells in vitro and may be relevant to the pathogenesis of SAD-induced CP.

Programmed cell death is not a necessary prerequisite for fusion of the fetal mouse palate

It has been widely accepted that programmed cell death (PCD) is an essential event in palatogenesis and that its failure can result in cleft palate, one of the most common birth defects in the human. However, some conflicting results have been reported concerning the timing of cell death occurring in the fusing palate and therefore the role of PCD in palatal fusion is controversial. In order to clarify whether cell death is indispensable for mammalian palatogenesis, we cultivated the palates of day-13 mouse fetuses in vitro and prevented cell death by treating them with the inhibitors of caspases-1 and -3 or with aurintricarboxylic acid which inhibits the activity of caspase-activated DNase. Even when cell death was almost completely inhibited, palatal fusion took place successfully. Histological examination revealed that in the absence of apoptotic cell death, the medial edge epithelia of opposing palatal shelves adhered to each other and subsequently, the midline epithelial seam was disrupted and disappeared to bring about mesenchymal confluence across the palate. It seems that cell death is not a necessary prerequisite for palatal fusion but it may help to efficiently eliminate unnecessary cells which failed to migrate or differentiate properly.

Blood-brain barrier opened by stimulation of the parasympathetic sphenopalatine ganglion: a new method for macromolecule delivery to the brain

OBJECT

Drug delivery across the blood-brain barrier remains a significant challenge. Based on earlier findings, the authors hypothesized that parasympathetic innervation of the brain vasculature could be used to augment drug delivery to the brain.

METHODS

Using a craniotomy-cerebrospinal fluid superfusate paradigm in rats with an intravenous injection of tracer the authors demonstrated that stimulation of the postganglionic parasympathetic fibers of the sphenopalatine ganglion (SPG) increased the concentration of fluorescein isothiocyanate-dextran (4-250 kD) in the superfusate by two- to sixfold. A histological examination indicated the presence of dextran in the parenchyma. In another experiment the amount of Evans blue dye in the brain following SPG activation was similarly significantly elevated. The chemotherapeutic agents anti-HER2 monoclonal antibody and etoposide were also delivered to the brain and reached therapeutic concentrations. Brain homeostasis was not disturbed by this procedure; a measurement of nicotinamide adenine dinucleotide reduction did not show a decrease in the tissue metabolic state and brain water content did not increase significantly.

CONCLUSIONS

Sphenopalatine ganglion activation demonstrates a promising potential for clinical use in the delivery of small and large molecules to the brain.

Disruption of Fgf10/Fgfr2b-coordinated epithelial-mesenchymal interactions causes cleft palate

Classical research has suggested that early palate formation develops via epithelial-mesenchymal interactions, and in this study we reveal which signals control this process. Using Fgf10-/-, FGF receptor 2b-/- (Fgfr2b-/-), and Sonic hedgehog (Shh) mutant mice, which all exhibit cleft palate, we show that Shh is a downstream target of Fgf10/Fgfr2b signaling. Our results demonstrate that mesenchymal Fgf10 regulates the epithelial expression of Shh, which in turn signals back to the mesenchyme. This was confirmed by demonstrating that cell proliferation is decreased not only in the palatal epithelium but also in the mesenchyme of Fgfr2b-/- mice. These results reveal a new role for Fgf signaling in mammalian palate development. We show that coordinated epithelial-mesenchymal interactions are essential during the initial stages of palate development and require an Fgf-Shh signaling network.

Nasal capsular cartilage is required for rat transpalatal suture morphogenesis

In the cranial vault, suture morphogenesis occurs when the growing cranial bones approximate and overlap or abut one another. Patency of developing sutures is regulated by the underlying dura mater. Once cranial sutures form, bone growth proceeds from the sutures in response to growth signals from the rapidly expanding neurocranium. Facial sutures do not develop in contact with the dura mater. It was therefore hypothesized that facial suture morphogenesis and bone growth from facial sutures are regulated by tissues with an equivalent role to the dura mater. The present study was designed to test this hypothesis by characterizing the morphology and growth factor expression in developing transpalatal (TP) sutures and their surrounding tissues, and then assessing the role of the overlying nasal capsular (NC) cartilages in maintaining suture patency. TP sutures develop as overlapping sutures, similar to cranial coronal sutures, and expression of Tgf-betas in TP sutures was similar to their distribution in cranial coronal sutures. To establish whether NC cartilages play a role in regulating TP suture morphogenesis, fetal rat TP sutures were cultured with associated attached NC cartilages or with NC cartilages removed. Sutures cultured for upward of 5 days with intact NC cartilages remained patent and maintained their cellular and fibrous components. However, in the absence of NC cartilages, the cellular nature of the sutures was not maintained and they became progressively acellular, with bony bridging across the suture. This finding is similar to that for cranial vault sutures cultured in the absence of dura mater, indicating that NC cartilages play an equivalent role to dura mater in maintaining the patency of developing sutures. These studies indicate that tissue interactions likely regulate morphogenesis of all cranial and facial sutures.

Distributional changes of BrdU, PCNA, E2F1 and PAL31 molecules in developing murine palatal rugae

The distribution of cells incorporating bromodeoxyuridine (BrdU) and the expression of molecules involved in the control of cell proliferation (proliferating cell nuclear antigen [PCNA], a cellular factor in F9 teratocarcinoma cells that recognizes an adenovirus E1A inducible promoter 1 [E2F1] and proliferation-related acidic nuclear protein 31 [PAL31]) during morphogenesis of the murine palatine rugae (PR) was examined histochemically. Pattern formation of the PR rudiment was initiated with cell cycle related molecules in the epithelium of the primary palate. Cells which had incorporated BrdU were detected at the outer areas of the presumptive epithelial placode (EP) and the EP at 11.5-13.5 days post coitum (dpc) and the outer areas of the PR protrusion after 14.5 dpc. The number of PCNA-positive cells at the central area of the PR protrusion decreased after 16.5 dpc. E2F-positive cells were detected at the outer areas of the PR protrusion at 15.5 and 16.5 dpc. The number of PAL31-positive cells at the presumptive EP area and the already-formed EP area was decreased at 11.5-13.5 dpc. In two dimensional histological reconstructions, PAL31 expression approximately corresponded to the distribution of BrdU-positive cells at 11.5 and 13.5 dpc. EP placode formation might be regulated by spatiotemporal cell proliferation control involving the expression of the PAL31 molecule. Following EP formation, PR development and growth control involved the expression of E2F1 and PCNA molecules.

TGFbeta3 signaling activates transcription of the LEF1 gene to induce epithelial mesenchymal transformation during mouse palate development

Epithelial mesenchymal transformation (EMT) of the medial edge epithelial (MEE) seam creates palatal confluence. This work aims to elucidate the molecular mechanisms by which TGFβ₃ brings about palatal seam EMT. We collected mRNA for PCR analysis from individual transforming MEE cells by laser microdissection techniques and demonstrated that TGFβ₃ stimulates lymphoid-enhancing factor 1 (LEF1) mRNA synthesis in MEE cells. We show with antisense β-catenin oligonucleotides that up-regulated LEF1 is not activated by β-catenin in palate EMT. We ruled out other TGFβ₃ targets, such as RhoA and MEK1/2 pathways, and we present evidence using dominant-negative Smad4 and dominant-negative LEF1 showing that TGFβ₃ uses Smads both to up-regulate synthesis of LEF1 and to activate LEF1 transcription during induction of palatal EMT. When phospho-Smad2 and Smad4 are present in the nucleus, LEF1 is activated without β-catenin. Our paper is the first to show that the Smad2,4/LEF1 complex replaces β-catenin/LEF1 during activation of EMT in vivo by TGFβ₃.

Relevance of the palatal protein kinase A pathway to the pathogenesis of cleft palate by secalonic acid D in mice

Secalonic acid-D (SAD) is a teratogenic mycotoxin inducing cleft palate (CP) in the offspring of the exposed mice by reducing palatal shelf size secondary to reduced proliferation of the palatal mesenchymal (PM) cells. Co-administration of dimethylsulfoxide (DMSO) reversed the CP-inducing effect of SAD. Although SAD has been shown to affect both protein kinases A (PKA) and C (PKC) pathways, the relevance of each of these pathways to its CP induction is unknown. The present studies were designed to test the hypothesis that the protective effect of DMSO is mediated by its specific reversal of the effect(s) of SAD on one of these two pathways using ELISA-based activity assays, Western blot analysis, electrophoretic mobility shift assays (EMSA), and murine embryonic PM (MEPM) cell growth in culture. Within the PKA pathway, SAD inhibited the activity of the catalytic subunit of PKA and its migration into the nucleus, elevated phosphorylated cyclic AMP (cAMP) response element (CRE)-binding protein (pCREB) level, and reduced the binding of CREB to CRE. In the PKC pathway, SAD reduced the activity of PKC and the binding of transcription factors (TF) to 12-O-tetradecanoate-13 phorbol acetate-response element (TRE). SAD also inhibited MEPM cell growth and the expression of the CRE- and TRE-containing gene, proliferating cell nuclear antigen (PCNA). Reversal, by DMSO, of the effects of SAD on MEPM cell growth, on PCNA expression and on all components of the PKA, but not of PKC, pathway suggests that the perturbation of the PKA pathway by SAD is relevant to its induction of CP in mice.

Terminal differentiation of palatal medial edge epithelial cells in vitro is not necessarily dependent on palatal shelf contact and midline epithelial seam formation

During fusion of the mammalian secondary palate, it has been suggested that palatal medial edge epithelial (MEE) cells disappear by means of apoptosis, epithelial-mesenchymal transformation (EMT) and epithelial cell migration. However, it is widely believed that MEE cells never differentiate unless palatal shelves make contact and the midline epithelial seam is formed. In order to clarify the potential of MEE cells to differentiate, we cultured single (unpaired) palatal shelves of ICR mouse fetuses by using suspension and static culture methods with two kinds of gas-mixtures. We thereby found that MEE cells can disappear throughout the medial edge even without contact and adhesion to the opposing MEE in suspension culture with 95% O2/5% CO2. Careful examination of MEE cell behavior in the culture revealed that apoptosis, EMT, and epithelial cell migration all occurred at various stages of MEE cell disappearance, including the transient formation and disappearance of epithelial triangles and islets. In contrast, MEE cells showed poor differentiation in static culture in a CO2 incubator. Furthermore, mouse and human amniotic fluids were found to prevent MEE cell differentiation in the cultured single palatal shelf, although paired palatal shelves fused successfully even in the presence of amniotic fluid. We therefore conclude that terminal differentiation of MEE cells is not necessarily dependent on palatal shelf contact and midline epithelial seam formation, but such MEE cell differentiation appears to be prevented in utero by amniotic fluid unless palatal shelves make close contact and the midline epithelial seam is formed.

Death is the major fate of medial edge epithelial cells and the cause of basal lamina degradation during palatogenesis

During mammalian development, a pair of shelves fuses to form the secondary palate, a process that requires the adhesion of the medial edge epithelial tissue (MEE) of each shelf and the degeneration of the resulting medial epithelial seam (MES). It has been reported that epithelialmesenchymal transformation (EMT) occurs during shelf fusion and is considered a fundamental process for MES degeneration. We recently found that cell death is a necessary process for shelf fusion. These findings uncovered the relevance of cell death in MES degeneration; however, they do not discard the participation of other processes. In the present work, we focus on the evaluation of the processes that could contribute to palate shelf fusion. We tested EMT by traditional labeling of MEE cells with a dye, by infection of MEE with an adenovirus carrying the lacZ gene, and by fusing wild-type shelves with the ones from EGFP-expressing mouse embryos. Fate of MEE labeled cells was followed by culturing whole palates, or by a novel slice culture system that allows individual cells to be followed during the fusion process. Very few labeled cells were found in the mesenchyme compartment, and almost all were undergoing cell death. Inhibition of metalloproteinases prevented basal lamina degradation without affecting MES degeneration and MEE cell death. Remarkably, independently of shelf fusion,activation of cell death promoted the degradation of the basal lamina underlying the MEE (`cataptosis'). Finally, by specific labeling of periderm cells (i.e. the superficial cells that cover the basal epithelium), we observed that epithelial triangles at oral and nasal ends of the epithelial seam do not appear to result from MEE cell migration but rather from periderm cell migration. Inhibition of migration or removal of these periderm cells suggests that they have a transient function controlling MEE cell adhesion and survival, and ultimately die within the epithelial triangles. We conclude that MES degeneration occurs almost uniquely by cell death, and for the first time we show that this process can activate basal lamina degradation during a developmental process.

Intracellular dynamics of Smad-mediated TGFbeta signaling

The transforming growth factor-beta (TGFbeta) family represents a class of signaling molecules that plays a central role in morphogenesis, growth, and cell differentiation during normal embryonic development. Members of this growth factor family are particularly vital to development of the mammalian secondary palate where they regulate palate mesenchymal cell proliferation and extracellular matrix synthesis. Such regulation is particularly critical since perturbation of either cellular process results in a cleft of the palate. While the cellular and phenotypic effects of TGFbeta on embryonic craniofacial tissue have been extensively catalogued, the specific genes that function as downstream mediators of TGFbeta action in the embryo during palatal ontogenesis are poorly defined. Embryonic palatal tissue in vivo and murine embryonic palate mesenchymal (MEPM) cells in vitro secrete and respond to TGFbeta. In the current study, elements of the Smad component of the TGFbeta intracellular signaling system were identified and characterized in cells of the embryonic palate and functional activation of the Smad pathway by TGFbeta1, TGFbeta2, and TGFbeta3 was demonstrated. TGFbeta-initiated Smad signaling in cells of the embryonic palate was found to result in: (1) phosphorylation of Smad 2; (2) nuclear translocation of the Smads 2, 3, and 4 protein complex; (3) binding of Smads 3 and 4 to a consensus Smad binding element (SBE) oligonucleotide; (4) transactivation of transfected reporter constructs, containing TGFbeta-inducible Smad response elements; and (4) increased expression of gelatinases A and B (endogenous genes containing Smad response elements) whose expression is critical to matrix remodeling during palatal ontogenesis. Collectively, these data point to the presence of a functional Smad-mediated TGFbeta signaling system in cells of the developing murine palate.

Conditional inactivation of Tgfbr2 in cranial neural crest causes cleft palate and calvaria defects

Cleft palate and skull malformations represent some of the most frequent congenital birth defects in the human population. Previous studies have shown that TGFbeta signaling regulates the fate of the medial edge epithelium during palatal fusion and postnatal cranial suture closure during skull development. It is not understood, however, what the functional significance of TGFbeta signaling is in regulating the fate of cranial neural crest (CNC) cells during craniofacial development. We show that mice with Tgfbr2 conditional gene ablation in the CNC have complete cleft secondary palate, calvaria agenesis, and other skull defects with complete phenotype penetrance. Significantly, disruption of the TGFbeta signaling does not adversely affect CNC migration. Cleft palate in Tgfbr2 mutant mice results from a cell proliferation defect within the CNC-derived palatal mesenchyme. The midline epithelium of the mutant palatal shelf remains functionally competent to mediate palatal fusion once the palatal shelves are placed in close contact in vitro. Our data suggests that TGFbeta IIR plays a crucial, cell-autonomous role in regulating the fate of CNC cells during palatogenesis. During skull development, disruption of TGFbeta signaling in the CNC severely impairs cell proliferation in the dura mater, consequently resulting in calvaria agenesis. We provide in vivo evidence that TGFbeta signaling within the CNC-derived dura mater provides essential inductive instruction for both the CNC- and mesoderm-derived calvarial bone development. This study demonstrates that TGFbeta IIR plays an essential role in the development of the CNC and provides a model for the study of abnormal CNC development.