Avaliação da morfologia palatina de indivíduos adultos, por meio de tomografia computadorizada de feixe cônico / Evaluation of palatal morphology in adults using cone beam computed tomography

O objetivo deste estudo foi averiguar por meio de tomografia computadorizada de feixe cônico (TCFC) se parâmetros da morfologia palatina podem influenciar a espessura do tecido ósseo e mucoso do palato duro de indivíduos adultos. A amostra consistiu em 82 exames tomográficos (31 homens, 51 mulheres) de pacientes adultos com dentição completa e sem tratamento ortodôntico prévio. A reconstrução multiplanar dos cortes tomográficos, orientação e medições foram realizadas com o software CS 3D Imaging. Foi mensurado o comprimento do palato, a altura palatina, a largura entre os caninos e primeiros molares superiores. A espessura de tecido ósseo (ETO) e a espessura de tecido mucoso para o (ETM) do palato duro foram mensuradas no sentido anteroposterior, a partir do forame incisivo a 4, 8, 12, 16, 20 e 24 mm, enquanto que no sentido mediolateral, foi realizada ao nível da sutura palatina mediana, 3 e 6 mm bilateralmente, totalizando em 60 mensurações por imagem tomográfica (30 para o ETO e 30paro o ETM). Para análise estatística, foram utilizados os testes de regressão linear univariada e multivariada. O nível de significância adotado para este estudo foi de 5%. O comprimento do palato influenciou a ETO na região anterior do palato. A altura palatina exerceu influencia na ETM da região anterior paramediana a 6 mm da sutura palatina mediana. A largura entre caninos exerceu influência na ETO da região posterior do palato e na ETM da região anterior da sutura e na região paramediana a 6 mm da sutura palatina mediana. A largura entre molares exerceu influencia na ETO da região paramediana a 3 mm da sutura palatina e na ETM de todo o palato O sexo teve influência apenas na ETO. Conclui-se que os parâmetros da morfologia apresentaram influência, com significância estatística, na espessura de tecido ósseo e mucoso do palato duro. No entanto, essa influência tem pouca relevância clínica. Faz-se necessário o uso de TCFC durante o planejamento da inserção de mini-implantes no palato ósseo, pois os parâmetros morfológicos não são preditores confiáveis da espessura de tecido ósseo e mucoso. (AU)

The aim of this study was to investigate using cone beam computed tomography (CBCT) whether parameters of palatal morphology can influence the thickness of bone and mucosa tissue of the hard palate of adults. The sample consisted of 82 CT scans of adult patients with complete dentition and no previous orthodontic treatment. The multiplanar reconstruction of the tomographic slices, orientation and measurements were performed with CS 3D Imaging software. The palate length, palatal height, width between the canines and first molars were measured. The palate bone thickness (PBT) and palate soft thickness (PST) of the hard palate were measured in the anteroposterior direction, from the incisive foramen at 4, 8, 12, 16, 20 and 24 mm, in the mediolateral direction, it was performed at the level of the midpalatal suture, 3 and 6 mm bilaterally. Totaling 60 measurements per tomographic image (30 for the PBT and 30 for the PST). For statistical analysis, univariate and multivariate linear regression tests were used. The significance level adopted for this study was 5%. The palate length influenced the PBT in the anterior region of the palate. Palatal height had an influence on the PST of the anterior paramedian region at 6 mm from the midpalatal suture. The width between canines had an influence on the PBT of the posterior palatal region and on the PST of the anterior palatal suture region and on the paramedian region at 6 mm from the midpalatal suture. The width between molars had an influence on the PBT of the paramedian region at 3 mm from the midpalatal suture and on the PST of the entire palate. Thus, it can be concluded that the morphology parameters had an influence with statistical significance on the thickness of bone and mucosa tissue of the hard palate, however, this influence has little clinical relevance. It is necessary to use CBCT when planning the insertion of mini-implants in the bony palate because morphological parameters are not reliable predictors of bone and mucosa tissue thickness. (AU)

Comparative gross and scanning electron microscopical study of the oropharyngeal roof of young and adult domestic pigeons (Columba livia domestica).

The present study aims to compare the morphology of the oropharyngeal roof of young and adult domestic pigeon (Columba livia domestica) by gross observation, morphometric measurements, and scanning electron microscopy (SEM). The oropharyngeal roof was divided into the palate and pharyngeal roof. The palate was narrow triangular in shape and concave along its length. It could be divided into a rostral part contained three longitudinal palatine ridges and a caudal part contained the choanal slit. The choanal slit consisted of narrow rostral and wide caudal parts. The edges of the narrow part were encircled by small caudomedially directed papillae. On the contrary, the edges of the wide part of slit were free from papillae. By SEM, the palatal mucosa in young pigeon showed primordia of small papillae which increased in number and size forming a longitudinal row of papillae parallel to the edges of the rostral narrow part of slit in adult pigeon. The surface of the pharyngeal roof appeared smooth in young pigeon, while in adult pigeon, it showed dome-shaped elevations. The infundibular cleft had smooth edges. The caudal part of the pharyngeal roof formed an elevated transverse mucosal fold on which a transverse row of conical-shaped papillae was present. In conclusion, our results documented the presence of some differences between the oropharyngeal roof of young and adult pigeon, which suggest a high degree of functional adaptation in adult pigeon to their diet compared to young pigeon. Such adaptations might increase the efficiency of food prehension in adult pigeon. The present study compared the morphology of the oropharyngeal roof of young and adult domestic pigeon by gross observation, morphometry, and scanning electron microscopy. The morphometrical data showed higher values in adult pigeon compared to young pigeon. The palatal mucosa and the pharyngeal roof of adult pigeon showed papillae and elevations that were not present in young pigeon. Our results suggest a high degree of functional adaptation in adult pigeon to their diet compared to young pigeon. Such adaptations might increase the efficiency of food prehension in adult pigeon.

Activation of sonic hedgehog signaling by a Smoothened agonist restores congenital defects in mouse models of endocrine-cerebro-osteodysplasia syndrome.

BACKGROUND: Endocrine-cerebro-osteodysplasia (ECO) syndrome is a genetic disorder associated with congenital defects of the endocrine, cerebral, and skeletal systems in humans. ECO syndrome is caused by mutations of the intestinal cell kinase (ICK) gene, which encodes a mitogen-activated protein (MAP) kinase-related kinase that plays a critical role in controlling the length of primary cilia. Lack of ICK function disrupts transduction of sonic hedgehog (SHH) signaling, which is important for development and homeostasis in humans and mice. Craniofacial structure abnormalities, such as cleft palate, are one of the most common defects observed in ECO syndrome patients, but the role of ICK in palatal development has not been studied. METHODS: Using Ick-mutant mice, we investigated the mechanisms by which ICK function loss causes cleft palate and examined pharmacological rescue of the congenital defects. FINDINGS: SHH signaling was compromised with abnormally elongated primary cilia in the developing palate of Ick-mutant mice. Cell proliferation was significantly decreased, resulting in failure of palatal outgrowth, although palatal adhesion and fusion occurred normally. We thus attempted to rescue the congenital palatal defects of Ick mutants by pharmacological activation of SHH signaling. Treatment of Ick-mutant mice with an agonist for Smoothened (SAG) rescued several congenital defects, including cleft palate. INTERPRETATIONS: The recovery of congenital defects by pharmacological intervention in the mouse models for ECO syndrome highlights prenatal SHH signaling modulation as a potential therapeutic measure to overcome congenital defects of ciliopathies.

Developmental Morphology of the Palatine Glands in Rats: An Electron Microscope Study.

Although minor salivary glands play a significant functional role in the oral cavity, their developmental morphology and cell differentiation has been scarcely studied. This study aimed to describe the development of rat palatine glands with regard to the ultrastructural morphology of the secretory cells and surrounding myoepithelial cells (MECs). Palatine glands from rats at embryonic ages (E) 18 and 20 days, and postnatal days (PN) 0, 3, 7, 10, 13, 21, 30, 42, and 60 were fixed and prepared for morphological analysis and immunocytochemical labeling of alpha-smooth muscle actin (α-SMA). At E18, epithelial cords were observed extending from the palatal epithelium and showed negative reactivity to α-SMA. After luminization at E20, the cells of immature acini accumulated secretory granules of various densities: electron-dense, electron-lucent and some empty-appearing granules. MECs were poorly differentiated at E20 and exhibited only slight α-SMA expression. At birth, mucous and serous cells were typically located around a common lumen. Thereafter, serous cells began to move to the periphery to form demilunes by PN7. The mucous secretory granules of intermediate electron density became predominant around PN13. At PN21, these granules were dramatically reduced in number and most of the acini in adults contained acinar cells with numerous electron-lucent granules, and a few serous demilune cells with electron-dense granules. After birth, MECs progressively accumulated actin microfilaments until prominent α-SMA expressing MECs invested the acini and the proximal part of the intercalated ducts in the adult. Anat Rec, 301:1820-1833, 2018. © 2018 Wiley Periodicals, Inc.

New insights into the cellular makeup and progenitor potential of palatal connective tissues.

The present study investigated the regenerative potential of connective tissues harvested from two palatal areas widely used as donor sites for muco-gingival surgical approaches. Connective tissue grafts (CTGs) were obtained by de-epithelialisation of a free gingival graft (deCTG) and by a split flap approach from a previous donor site (reCTG). Two types of mesenchymal stem cell (MSCs) were isolated and were named de-epithelialised MSCs (deMSCs) and re-entry MSCs (reMSCs). The cells were characterised and cellular functionality was investigated. CTGs were evaluated using immunohistochemical and ultrastructural approaches. No significant differences were observed regarding the frequency of colony-forming unit- fibroblasts, migration potential, and population doubling time between the two cell lines (p > 0.05). Both cell lines showed positivity for CD105, CD73, CD90, and CD44 and negative expression for CD34/45, CD14, CD79a, and HLA-DR. MSCs from both cell lines successfully differentiated into osteogenic, adipogenic, and chondrogenic lineages. Cells expressing antigens characteristic of CD34+ stromal cells (CD34+, αSMA-, CD31-) were traced in both CTGs. Ultrastructural analysis highlighted the presence of putative progenitors, namely fibroblasts,-in the pericapillary regions and in remote regions of the lamina propria- and pericytes-surrounding the capillaries. This study provides supplementary arguments for the use of CTG grafts in clinical practice due to the presence of putative progenitor cell. However, results were inconclusive regarding clinical decision-making to determine optimal harvesting area. Prior harvesting in the donor area did not appear to alter the regenerative capabilities of the connective tissue.

Morphological Characteristics of the Oropharyngeal Cavity (Tongue, Palate and Laryngeal Entrance) in the Eurasian Coot (Fulica atra, Linnaeus, 1758).

The present study represents the first definitive anatomical description of the oropharyngeal cavity of the coot Fulica atra. For this purpose, the organs of six birds were prepared to examine grossly and by SEM and stereomicroscope. The oval lingual apex had multiple overlapping branched acicular processes on its anterior and lateral border. The lingual apex and body had multiple caudally directed filiform-like papillae. By stereomicroscopy, the lingual root had a characteristic appearance and consisted of four parts. The openings of the anterior glands were present on the dorsal lingual surface of the body, while the projected papillae with wide openings of the posterior glands were present on the dorsal surface of lingual root. There was a row of caudally directed pharyngeal papillae at the caudal border of the laryngeal mound. Grossly, the pharyngeal papillae arrangement took a W-shape, while by stereomicroscopy was observed to be heart shape. The palate was divided into two regions: a small rostral non-papillary and a large caudal papillary region, but the rostral region was characterized by the presence of three longitudinal ridges. The papillary crest had two paramedian longitudinal papillary rows, which continued caudally until the beginning of the third median row. The freely distributed papillae took a caudolateral direction, while the papillae encircling the rostral part of choanal cleft took a caudomedial direction. There was a transverse papillary row between the two parts of choanal cleft. There was a transverse papillary row between the caudal border of the infundibular cleft and oesophagus.

A Comprehensive Study of Palate Development in Miniature Pig.

Palate development is an important morphogenetic event in facial development, including the fusion of the lateral and medial nasal portions of the frontonasal process and maxilla. Derailments of any of these events may result in cleft palate, the most frequent congenital craniofacial abnormality. Recent research has shown that the microanatomy of the miniature pig oral maxillofacial region is quite similar to that of humans, and the use of miniature pigs as a large animal model for dental and orofacial research is increasing. Little information is available, however, about the development of the miniature pig palate. Here, using histological and ultrastructural methods, we describe the developmental stages of the palate in miniature pigs. Sections from E26, E30, E35, E40, E45, and E50 embryos were stained with hematoxylin-eosin, and selected specimens were also processed for electron microscopy. The development of the miniature pig palate can be divided into four stages: growth of the bilateral palatal shelves alongside the tongue at E30; elevation of the horizontal position above the tongue at E35; establishment of bilateral shelf contact at the midline from E35-50; and a final fusion step at E50, similar to the mouse and human. The histological characteristics of the miniature pig palate at different developmental stages were synchronously verified at the ultrastructural level. Our study provides a piece of first-hand data regarding palate morphological organogenesis in the miniature pig and a foundation for further research with this model to explore mechanisms of cleft palate development. Anat Rec, 300:1409-1419, 2017. © 2017 Wiley Periodicals, Inc.

Development of a contemporary animal model of Candida albicans-associated denture stomatitis using a novel intraoral denture system.

Denture stomatitis (DS) is a fungal infection characterized by inflammation of the oral mucosa in direct contact with the denture and affects up to 50% of denture wearers. Despite the prevalence, very little is known about the role of fungal or host factors that contribute to pathogenesis. Recently, we developed a novel intraoral denture system for rodent research. This denture system consists of custom-fitted fixed and removable parts to allow repeated sampling and longitudinal studies. The purpose of this study was to use this denture system to develop a clinically relevant animal model of DS. To establish DS, rats were inoculated with pelleted Candida albicans, which resulted in sustained colonization of the denture and palate for 8 weeks postinoculation. Biofilm formation on the denture was observed by week 4 and on the palate by week 6 postinoculation. Rats were monitored for clinical signs of disease by assigning a clinical score after macroscopic examination of the palate tissue according to Newton's method. By week 4 postinoculation, the majority of inoculated rats with dentures exhibited a clinical score of 1 (pinpoint erythema). By week 6 and week 8 postinoculation, increasing percentages of rats exhibited a clinical score of 2 (diffuse erythema/edema). Histological analysis of palate tissue demonstrated progressively increasing inflammatory cell recruitment throughout the time course of the infection. Palatal biofilm formation was commensurate with development of palatal erythema, which suggests a role for biofilm in the inflammatory response.

Ultrastructure and distribution of the taste buds in the buccal cavity in relation to the food and feeding habit of a herbivorous fish: Oreochromis niloticus.

The buccal cavity of an herbivorous fish Oreochromis niloticus was investigated by means of scanning electron microscopy. The buccal cavity distinguished into the roof and the floor. Three different types of taste buds (type I, II and III) are distributed in the buccal cavity. The proximal part of the buccal cavity bears relatively high epidermal papillae in which type I TBs was found. The middle region of the buccal cavity is mostly occupied by low epidermal papillae containing type II TBs. Type III TBs which are present within the metabranchial buccal cavity; never rise above the normal level of the epithelium. The different types of TBs are useful for ensuring full utilization of the gustatory ability of the fish. It is postulated that the TBs serve different functions: TBs type I and II may act as chemoreceptors and mechanoreceptors. TBs type III acts predominantly as a chemoreceptors. TBs of each type show two kinds of receptor villi within their receptor areas: tall villi and small villi. The surface of the lining epithelial cells shows a delicate microridge system. These structures protect against physical abrasion potentially caused during food maneuvering and swallowing. Furthermore, protection of the epithelium from abrasion is enhanced with goblet cells secretion.

Cooperation of two ADAMTS metalloproteases in closure of the mouse palate identifies a requirement for versican proteolysis in regulating palatal mesenchyme proliferation.

We have identified a role for two evolutionarily related, secreted metalloproteases of the ADAMTS family, ADAMTS20 and ADAMTS9, in palatogenesis. Adamts20 mutations cause the mouse white-spotting mutant belted (bt), whereas Adamts9 is essential for survival beyond 7.5 days gestation (E7.5). Functional overlap of Adamts9 with Adamts20 was identified using Adamts9(+/-);bt/bt mice, which have a fully penetrant cleft palate. Palate closure was delayed, although eventually completed, in both Adamts9(+/-);bt/+ and bt/bt mice, demonstrating cooperation of these genes. Adamts20 is expressed in palatal mesenchyme, whereas Adamts9 is expressed exclusively in palate microvascular endothelium. Palatal shelves isolated from Adamts9(+/-);bt/bt mice fused in culture, suggesting an intact epithelial TGFß3 signaling pathway. Cleft palate resulted from a temporally specific delay in palatal shelf elevation and growth towards the midline. Mesenchyme of Adamts9(+/-);bt/bt palatal shelves had reduced cell proliferation, a lower cell density and decreased processing of versican (VCAN), an extracellular matrix (ECM) proteoglycan and ADAMTS9/20 substrate, from E13.5 to E14.5. Vcan haploinsufficiency led to greater penetrance of cleft palate in bt mice, with a similar defect in palatal shelf extension as Adamts9(+/-);bt/bt mice. Cell density was normal in bt/bt;Vcan(hdf)(/+) mice, consistent with reduced total intact versican in ECM, but impaired proliferation persisted in palate mesenchyme, suggesting that ADAMTS-cleaved versican is required for cell proliferation. These findings support a model in which cooperative versican proteolysis by ADAMTS9 in vascular endothelium and by ADAMTS20 in palate mesenchyme drives palatal shelf sculpting and extension.

[Ultrastructural and element spectrometric analysis of distraction osteogenesis for reconstruction of cleft palate in rhesus macaque model].

OBJECTIVE: To study the ultrastructure and Ca/P element spectrometry of distraction osteogenesis (DO) for reconstruction of cleft palate (CP), so as to explore the osteogenesis and remodeling of new bone in situ. METHODS: 23 rhesus macaques were operated to establish animal models of CP. 2 monkeys didn't received DO as controls. The other 21 monkeys in experimental group underwent DO to correct both bony and soft tissue defects in palate. The distraction was performed at a rate of 0.8 mm/d, twice a day until the cleft was closed. After fixation for 1, 2, 4, 6, 8, 12, 24 weeks, every 3 animals were sacrificed to get the specimens at the distraction gap. The scanning electron microscopic study and Ca, P elements spectrometric analysis were adopted. There were also two unoperated animals as sham group. RESULTS: After fixation for 1-2 weeks, the distraction gap was full of collagen fibers oriented along vector of distraction. Few trabeculae was seen at the margin area. After fixation for 4-6 weeks, active osteogenesis was presented with new formed bone trabeculae and abundant cellular component. After fixation for 8-12 weeks, the new formed bone became mature and couldn't distinguish from the normal bone. 24 weeks later, the bone between the distraction gap had a similar structure to the normal bone. Elements spectrometric analysis results indicated that in early stage of osteogenesis, the P and S peaks were relatively high while the Ca peak was much lower. During the late stage, the S peak was obviously decreased, and Ca/P ratio increased to normal level as in the empty control group. CONCLUSIONS: The CP can be corrected by DO. The new bone between the distraction gap is formed and remodeled through intramembraneous osteogenesis.

Ultramicroscopic examination of the ovine tonsillar epithelia.

As solid morphological knowledge of ovine tonsillar epithelia might contribute to a better understanding of the pathogenesis of several diseases including prion diseases, the epithelia of all tonsils of 7 one-year-old Texel sheep were examined using scanning and transmission electron microscopy. Major parts of the pharyngeal and tubal tonsils were covered by pseudostratified columnar ciliated epithelia that were interrupted by patches of epithelium containing cells with densely packed microfolds or microvilli, and cells with both microvilli and cilia. Smaller parts were covered by either flattened polygonal cells with densely packed microvilli or microfolds, squamous epithelial cells, or patches of reticular epithelium. The palatine and paraepiglottic tonsils were mainly lined by squamous epithelial cells with apical microplicae or short knobs. Additionally, regions of reticular epithelium containing epithelial cells with apical microvilli were seen. The lingual tonsil was uniformly covered by a keratinized squamous epithelium and devoid of microvillous cells and patches of reticular epithelium. The rostral half of the tonsil of the soft palate was lined by a pseudostratified columnar ciliated epithelium with characteristics of the pharyngeal and tubal tonsils. The epithelium of the caudal part resembled the epithelia of the palatine and paraepiglottic tonsils. Putative M cells, mainly characterized by apical microvilli or microfolds and a close association with lymphoid cells, seem manifestly present on the nasopharyngeal tonsils. The reticular epithelium of the palatine and paraepiglottic tonsils also harbor cells with small apical microvilli. The exact nature of these presumptive M cells should, however, be elucidated in functional studies.

Experimental study on protection of vitamin B6 on TCDD-induced palatal cleft formation in the mice.

BACKGROUND: 2, 3, 7, 8-Tetrachlorodibenzo-p-dioxin (TCDD) can cause a high percentage of cleft palate in fetuses when administered during organogenesis in certain strains of mice including the C57BL/6J. In this study, vitamin B(6) (B(6)) was tested for antiteratogenic effects on TCDD-induced cleft palate in fetal mice. METHODS: The pregnant C57BL/6J mice were dosed with 24 microg TCDD/kg and/or 5, 10, 20, and 40 mg B(6)/kg body weight on gestation day (GD) 10. The control group mice were dosed with 50 ml sesame oil/kg body weight on GD10. The mice were sacrificed on GD12.5, GD13.5, GD14.5, GD15.5, and GD17.5, respectively. The harvested embryos were examined to detect the incidence of cleft palate and the developing palatal shelves in a different phase were investigated morphologically and histologically among different groups. RESULTS: Total frequency of clefts is 55.56% in the TCDD group and 31.81% (5 mg), 44.44% (10 mg), 40.90% (20 mg), and 32.00% (40 mg) in the TCDD+ B(6) groups. There were no statistically significant differences among the TCDD and TCDD+ B(6) groups (p = 0.743 > 0.05). CONCLUSIONS: It was demonstrated in this study that B6 could not antagonize 2, 3, 7, 8-TCDD-indued cleft palate.

Morphological specializations of the buccal cavity in relation to the food and feeding habit of a carp Cirrhinus mrigala: a scanning electron microscopic investigation.

The buccal cavity of an herbivorous fish, Cirrhinus mrigala, was investigated by scanning electron microscopy to determine its surface ultrastructure. The buccal cavity shows significant adaptive modifications in relation to food and feeding ecology of the fish. The buccal cavity of the fish is of modest size and limited capacity, which is considered an adaptation with respect to the small-sized food items primarily consumed by the fish that could be accommodated in a small space. Modification of surface epithelial cells, on the upper jaw, into characteristic structures-the unculi-is considered an adaptation to browse or scrap, to grasp food materials, e.g., algal felts, and to protect the epithelial surface against abrasions, likely to occur during their characteristic feeding behavior. Differentiation of the highly specialized lamellar organ on the anterior region of the palate could be an adaptation playing a significant role in the selection, retention, and sorting out of palatable food particles from the unpalatable items ingested by the fish. The filamentous epithelial projections and the lingulate epithelial projections on the palatal organ in the posterior region of the palate are considered to serve a critical function in final selection, handling, maneuvering, and propelling the food particles toward the esophagus. The abundance of different categories of taste buds in the buccal cavity suggests that gustation is well developed and the fish is highly responsive in the evaluation and the selection of the preferred palatable food items. The secretions of mucous cells in the buccal cavity are associated with multiple functions-particle entrapment, lubrication of the buccal epithelium and food particles to assist smooth passage of food, and to protect the epithelium from possible abrasion. These morphological characteristics ensure efficient working of the buccal cavity in the assessment of the quality and palatability of ingested food, their retention and transport toward the esophagus. Such an adaptation may be essential in conducting the function most basic to the survival of the individuals and species-feeding.

Runx1 is involved in the fusion of the primary and the secondary palatal shelves.

Runx1 is expressed in medial edge epithelial (MEE) cells of the palatal shelf. Conditionally rescued Runx1(-/-) mice showed limited clefting in the anterior junction between the primary and the secondary palatal shelves, but not in the junction between the secondary palates. In wild type mice, the fusing epithelial surface exhibited a rounded cobblestone-like appearance, while such cellular prominence was less evident in the Runx1 mutants. We also found that Fgf18 was expressed in the mesenchyme underlying the MEE and that locally applied FGF18 induced ectopic Runx1 expression in the epithelium of the palatal explants, indicating that Runx1 was induced by mesenchymal Fgf18 signaling. On the other hand, unpaired palatal explant cultures revealed the presence of anterior-posterior (A-P) differences in the MEE fates and fusion mechanism. Interestingly, the location of anterior clefting in Runx1 mutants corresponded to the region with different MEE behavior. These data showed a novel function of Runx1 in morphological changes in the MEE cells in palatal fusion, which is, at least in part, regulated by the mesenchymal Fgf signaling via an epithelial-mesenchymal interaction.

Palatal seam disintegration: to die or not to die? that is no longer the question.

Formation of the medial epithelial seam (MES) by palatal shelf fusion is a crucial step of palate development. Complete disintegration of the MES is the final essential phase of palatal confluency with surrounding mesenchymal cells. In general, the mechanisms of palatal seam disintegration are not overwhelmingly complex, but given the large number of interacting constituents; their complicated circuitry involving feedforward, feedback, and crosstalk; and the fact that the kinetics of interaction matter, this otherwise simple mechanism can be quite difficult to interpret. As a result of this complexity, apparently simple but highly important questions remain unanswered. One such question pertains to the fate of the palatal seam. Such questions may be answered by detailed and extensive quantitative experimentation of basic biological studies (cellular, structural) and the newest molecular biological determinants (genetic/dye cell lineage, gene activity, kinase/enzyme activity), as well as animal model (knockouts, transgenic) approaches. System biology and cellular kinetics play a crucial role in cellular MES function; omissions of such critical contributors may lead to inaccurate understanding of the fate of MES. Excellent progress has been made relevant to elucidation of the mechanism(s) of palatal seam disintegration. Current understanding of palatal seam disintegration suggests epithelial-mesenchymal transition and/or programmed cell death as two most common mechanisms of MES disintegration. In this review, I discuss those two mechanisms and the differences between them.

Tgfb1 expressed in the Tgfb3 locus partially rescues the cleft palate phenotype of Tgfb3 null mutants.

Although TGF-beta isoforms (TGF-beta1-3) display very similar biochemical characteristics in vitro, it has been determined that they demonstrate different or even opposing effects in vivo. During embryogenesis, TGF-betas play important roles in several developmental processes. Tgfb3 is strongly expressed in the prefusion palatal epithelium, and mice lacking Tgfb3 display a cleft of the secondary palate. To test whether the effect of TGF-beta3 in palatogenesis is isoform-specific in vivo, we generated a knockin mouse by replacing the coding region of exon1 in the Tgfb3 gene with the full-length Tgfb1 cDNA, which resulted in the expression of Tgfb1 in the Tgfb3 expressing domain. The homozygote knockin mice display a complete fusion at the mid-portion of the secondary palate, while the most anterior and posterior regions fail to fuse appropriately indicating that in vivo replacement of TGF-beta3 with TGF-beta1 can only partially correct the epithelial fusion defect of Tgfb3 knockout embryos. Palatal shelves of Tgfb1 knockin homozygote mice adhere, intercalate, and form characteristic epithelial triangles. However, decreased apoptosis in the midline epithelium, slower breakdown of the basement membrane and a general delay in epithelial fusion were observed when compared to control littermates. These results demonstrate an isoform-specific role for TGF-beta3 in the palatal epithelium during palate formation, which cannot be fully substituted with TGF-beta1.

Involvement of apoptotic cell death and cell cycle perturbation in retinoic acid-induced cleft palate in mice.

Retinoic acid (RA), a metabolite of vitamin A, plays a key role in a variety of biological processes and is essential for normal embryonic development. On the other hand, exogenous RA could cause cleft palate in offspring when it is given to pregnant animals at either the early or late phases of palatogenesis, but the pathogenetic mechanism of cleft palate caused by excess RA remains not fully elucidated. The aim of the present study was to investigate the effects of excess of RA on early palatogenesis in mouse fetuses and analyze the teratogenic mechanism, especially at the stage prior to palatal shelf elevation. We gave all-trans RA (100 mg/kg) orally to E11.5 ICR pregnant mice and observed the changes occurring in the palatal shelves of their fetuses. It was found that apoptotic cell death increased not only in the epithelium of the palatal shelves but also in the tongue primordium, which might affect tongue withdrawal movement during palatogenesis and impair the horizontal elevation of palatal shelves. In addition, RA was found to prevent the G(1)/S progression of palatal mesenchymal cells through upregulation of p21(Cip1), leading to Rb hypophospholylation. Thus, RA appears to cause G(1) arrest in palatal mesenchymal cells in a similar manner as in various cancer and embryonic cells. It is likely that apoptotic cell death and cell cycle disruption are involved in cleft palate formation induced by RA.

Palatal fusion - where do the midline cells go? A review on cleft palate, a major human birth defect.

Formation of the palate, the organ that separates the oral cavity from the nasal cavity, is a developmental process characteristic to embryos of higher vertebrates. Failure in this process results in palatal cleft. During the final steps of palatogenesis, two palatal shelves outgrowing from the sides of the embryonic oronasal cavity elevate above the tongue, meet in the midline, and rapidly fuse together. Over the decades, multiple mechanisms have been proposed to explain how the superficial mucous membranes disappear from the contact line, thus allowing for normal midline mesenchymal confluence. A substantial body of experimental evidence exists for cell death, cell migration, epithelial-to-mesenchymal transdifferentiation (EMT), replacement through new tissue intercalation, and other mechanisms. However, the most recent use of gene recombination techniques in cell fate tracking disfavors the EMT concept, and suggests that apoptosis is the major fate of the midline cells during physiological palatal fusion. This article summarizes the benefits and drawbacks of histochemical and molecular tools used to determine the fates of cells within the palatal midline. Mechanisms of normal disintegration of the midline epithelial seam are reviewed together with pathologic processes that prevent this disintegration, thus causing cleft palate.