Bmpr1a signaling plays critical roles in palatal shelf growth and palatal bone formation

Cleft palate, including submucous cleft palate, is among the most common birth defects in humans. While overt cleft palate results from defects in growth or fusion of the developing palatal shelves, submucous cleft palate is characterized by defects in palatal bones. In this report, we show that the Bmpr1a gene, encoding a type I receptor for bone morphogenetic proteins (Bmp), is preferentially expressed in the primary palate and anterior secondary palate during palatal outgrowth. Following palatal fusion, Bmpr1a mRNA expression was upregulated in the condensed mesenchyme progenitors of palatal bone. Tissue-specific inactivation of Bmpr1a in the developing palatal mesenchyme in mice caused reduced cell proliferation in the primary and anterior secondary palate, resulting in partial cleft of the anterior palate at birth. Expression of Msx1 and Fgf10 was downregulated in the anterior palate mesenchyme and expression of Shh was downregulated in the anterior palatal epithelium in the Bmpr1a conditional mutant embryos, indicating that Bmp signaling regulates mesenchymal-epithelial interactions during palatal outgrowth. In addition, formation of the palatal processes of the maxilla was blocked while formation of the palatal processes of the palatine was significantly delayed, resulting in submucous cleft of the hard palate in the mutant mice. Our data indicate that Bmp signaling plays critical roles in the regulation of palatal mesenchyme condensation and osteoblast differentiation during palatal bone formation.     

Morphologic diversity of the minor salivary glands of the rat: fertile ground for studies in gene function and proteomics

In this article the locations and histologic and ultrastructural features of all of the minor salivary glands of the rat are presented; similarities and differences among them are highlighted. These glands are almost as diverse morphologically as the major salivary glands of the rat. The acini of von Ebner's glands are serous; those of the anterior and posterior buccal glands and minor sublingual glands are mucous; and those of the glossopalatal, palatal, and Weber's glands are mucous with serous demilunes. The anterior buccal, minor sublingual and von Ebner's glands have striated and stratified columnar ducts, while only the minor sublingual and von Ebner's glands have intercalated ducts. The glossopalatal, palatal, posterior buccal and Weber's glands have none of these ducts; the tubulo-acini drain abruptly into short terminal ducts composed of stratified squamous epithelium. All of the mucous acini react with an antibody to a mucin (Muc19) of the rat major sublingual gland, but in some of the glands the reaction varies in intensity among the acinar cells. Ultrastructurally, the mucous secretory granules of the anterior buccal, glossopalatal, palatal and Weber's glands are biphasic, while those of the minor sublingual and posterior buccal glands are monophasic. Although there is a considerable body of literature concerning the development, innervation, physiology and proteomics of von Ebner's glands, investigation of the other minor salivary glands of the rat ranges from modest to nearly nonexistent.     

Morphologic diversity of the minor salivary glands of the rat: fertile ground for studies in gene function and proteomics

In this article the locations and histologic and ultrastructural features of all of the minor salivary glands of the rat are presented; similarities and differences among them are highlighted. These glands are almost as diverse morphologically as the major salivary glands of the rat. The acini of von Ebner's glands are serous; those of the anterior and posterior buccal glands and minor sublingual glands are mucous; and those of the glossopalatal, palatal, and Weber's glands are mucous with serous demilunes. The anterior buccal, minor sublingual and von Ebner's glands have striated and stratified columnar ducts, while only the minor sublingual and von Ebner's glands have intercalated ducts. The glossopalatal, palatal, posterior buccal and Weber's glands have none of these ducts; the tubulo-acini drain abruptly into short terminal ducts composed of stratified squamous epithelium. All of the mucous acini react with an antibody to a mucin (Muc19) of the rat major sublingual gland, but in some of the glands the reaction varies in intensity among the acinar cells. Ultrastructurally, the mucous secretory granules of the anterior buccal, glossopalatal, palatal and Weber's glands are biphasic, while those of the minor sublingual and posterior buccal glands are monophasic. Although there is a considerable body of literature concerning the development, innervation, physiology and proteomics of von Ebner's glands, investigation of the other minor salivary glands of the rat ranges from modest to nearly nonexistent.     

Focal adenomatoid hyperplasia of salivary glands. A differential diagnostic problem in fine needle aspiration biopsy

Adenomatoid hyperplasia of minor salivary glands is an idiopathic lesion usually involving the palate and mimicking a primary salivary gland neoplasm. In particular, the lesions may resemble low-grade mucoepidermoid tumors clinically and by fine needle aspiration (FNA) cytology. An illustrative case is presented, and the nature of this unusual entity is reviewed. Its importance in the differential diagnosis of FNA biopsies of minor salivary gland lesions is also discussed.     

Inhibitory effect of corticoids on the proliferative pattern in mouse palatal processes.

The formation of the secondary palate in mice is accompanied by intensive mitotic activity, which is mainly concentrated at the medial edges of the palatal processes. In control H-Velaz randombred fetuses the mitotic activity culminated approximately 24 h before palatal-shelf horizontalization, so that the period of intensive cell proliferation coincided with the period when cleft palate could be induced by cortisone administration. Effects of teratogenic doses of corticoids, injected directly into amniotic sac of embryos on day 13 (0.3 mg hydrocortisone) or im to pregnant females on day 12 (7.5 mg cortisone acetate), on the proliferative peak in palatal processes were studied using intraamniotic injection of colchicine. Counts of colchicine-blocked mitoses in histological serial sections revealed both a significant decrease in overall mitotic density and a posterior shift of the proliferative peak in the palatal processes of fetuses treated with doses of corticoids producing cleft palate.     

A clinical analysis of nine new pediatric and adolescent cases of benign minor salivary gland neoplasms and a review of the literature

ABSTRACT: INTRODUCTION: Minor salivary gland neoplasms of epithelial origin are rare in children and adolescents and most are not well documented, except for a few small series and case reports. This study represents a retrospective clinical analysis of nine cases of benign epithelial salivary gland neoplasms accessioned over a 35-year period at the Louisiana State University School of Dentistry and combines the data with well-documented cases from the English-language literature. METHODS: A retrospective clinical analysis of nine cases of benign epithelial salivary gland neoplasms was performed over a 35-year period at the Louisiana State University School of Dentistry and combined with data of well-documented cases from the English-language literature. RESULTS: The nine benign salivary gland neoplasms in patients aged 19 months to 18 years accounted for 2.3% of the Louisiana State University School of Dentistry accessioned salivary gland tumors. These nine cases comprised eight pleomorphic adenomas and one cystadenoma. There were 40 cases in the literature, of which 34 were pleomorphic adenomas. Combining the data for the 42 pleomorphic adenomas resulted in a mean age of 12 years with a 2.8:1 female predilection. The hard palate and/or soft palate were the most common site (69.1%). The average duration and size was 2.1 years and 2.4cm, respectively. Bone involvement occurred in seven cases. Wide local excision was the treatment most often employed. Cases followed for two years or more had a recurrence rate of 13.0%. The remaining seven neoplasms in the combined data comprised myoepithelioma, cystadenoma and sialadenoma papilliferum. CONCLUSIONS: A relatively long duration (2 years) of a submucosal mass in a minor salivary gland-bearing area with or without bone involvement occurring in a child or adolescent should raise the question of a possible salivary gland neoplasm. A pleomorphic adenoma is the most common benign salivary gland neoplasm in the first and second decade of life. Complete surgical excision affords the best chance of preventing recurrence for pleomorphic adenomas. The recurrence rate of pleomorphic adenomas with two or more years follow-up is 13.0%. Other types of minor salivary gland neoplasms are exceedingly rare and therefore data is sparse, precluding any valid conclusions.     

The effect of hypervitaminosis A on rat palatal development.

Retinoic acid or retinyl acetate was administered to pregnant rats in doses sufficient to induce a 90% incidence of cleft palate. In another study, a delay in the reorientation of the palatal shelves was observed to be longer with the more potent teratogen, retinoic acid. On day 16 of gestation, 24 hours after final dosage with vitamin A, the synthesis of DNA and protein was studied in fetal carcass, mandible, and palate, and that of sulfated mucopolysaccharides (S-MPS) and glycoproteins (GP) in fetal head, mandible, and palate. Increases in DNA synthesis in fetal palate and in GP synthesis in fetal palate were found; thus, the mechanism of action of vitamin A in inducing cleft palates in rats may be caused by interference with the normal biochemical synthetic pattern of the palatal shelves.     

Clear cell carcinoma arising from pleomorphic adenoma of a minor salivary gland: Report of a case with fine needle aspiration, histologic and immunohistochemical findings

BACKGROUND: Malignant changes in pleomorphic adenoma (PA) of the salivary gland (carcinoma ex pleomorphic adenoma) are not common. Clear cell carcinoma is a rare form of salivary gland tumor and involves mostly minor salivary glands, especially those of the palate. Only 3 cases of clear cell carcinoma arising in PA have been reported, 2 in submandibular glands and 1 in a minor salivary gland of the palate. CASE : A 53-year-old man presented with an enlarged mass on the left side of the palate. He had a history of palate mass about 30 years earlier; it was excised and reported as PA. Since then the tumor had recurred twice in the same place; it had been excised and was diagnosed as PA again. A few years later the mass showed rapid growth over a few months. Fine needle aspiration of the mass showed epithelial clusters with bland nuclear features and myxohyaline material typical of PA. Also noted were large and small papillary, trabecular and well-circumscribed clusters of neoplastic cells with a moderate amount offoamy, vacuolated cytoplasm with distinct borders. Glandlike and acinar structures with hyaline globule material resembling cannonballs were also noted. The cytology was suspicious for malignancy. Incisional biopsy was reported as PA. Due to the suspicion of malignancy, the whole mass was excised up to the floor of the orbit. The final diagnosis was clear cell carcinoma expleomorphic adenoma. CONCLUSION: Due to nonspecific cytologic findings in clear cell carcinoma and a mixture of elements of PA in this case, we did not consider clear cell carcinoma as the malignant component.     

Incidence of cleft palate fistula: an institutional experience with two-stage palatal repair.

The purpose of this study was to determine the incidence of cleft palatal fistula in a series of nonsyndromic children treated at the authors' institution. This retrospective analysis of 103 patients with cleft palate treated by five surgeons between 1982 and 1995 includes 60 boys and 33 girls, whose median age was 18.4 months at the time of surgery. The median length of follow-up was 4.9 years after primary palatoplasty. Cleft palatal fistula was defined as a failure of healing or a breakdown in the primary surgical repair of the palate. Intentionally unrepaired fistulas of the primary and secondary palate were excluded. Extent of clefting was described according to the Veau classification. Statistical examination of multiple variables was performed using contingency table analysis, multivariate logistic regression, and the Wilcoxon rank sum test. The incidence of cleft palatal fistula in this series was 8.7 percent. All of these fistulas were clinically significant. The rate of fistula recurrence was 33 percent. The incidence of cleft palatal fistula when compared by Veau classification was statistically significant, with nine fistulas occurring in patients with Veau 3 and 4 clefts and no fistulas occurring in patients with Veau 1 and 2 clefts (p = 0.0441). No significant differences between patients with and without fistulas were identified with respect to operating surgeon, patient sex, patient age at palatoplasty, type of palatoplasty, and use of presurgical orthopedics or palatal expansion. All three recurrent fistulas occurred in the anterior palate, two in patients with Veau class 3 clefts and one in a patient with a Veau class 4 cleft. The low rate of clinically significant fistula was attributed to early delayed primary closure, with smaller secondary clefts allowing repair with a minimum of dissection and disruption of vascularity.     

Strain differences between C57BL/6 and SWV mice in time of palate closure and induction of palatal slit and cleft palate

Palatal slit, which occurs spontaneously in C57BL/6 (C57BL) mice, is increased in frequency among C57BL fetuses from dams treated with triamcinolone acetonide, but is not induced in SWV fetuses. On the other hand, C57BL is more resistant than SWV to cleft palate induction by triamcinolone. Using these C57BL and SWV mice, the relation of palate stage and chronological age was examined from 1 P.M. on day 14 to 9 A.M. on day 16 in untreated embryos, and the condition of the palate after triamcinolone treatment on day 12 was examined at 9 A.M. on day 16. In untreated embryos, horizontalization and fusion of the palatal shelves occurred earlier in C57BL than in SWV embryos, but fusion of the primary palate with the secondary palate occurred later. After triamcinolone treatment, the development of the palate was delayed in both C57BL and SWV embryos. These results suggest that the times of normal palate closure are related to the differences between C57BL and SWV mice in their susceptibilities to palatal slit and cleft palate induction and that triamcinolone produces palatal slit and cleft palate by delaying palate closure.     

Experimental induction of palate shelf elevation in glutamate decarboxylase 67-deficient mice with cleft palate due to vertically oriented palatal shelf

BACKGROUND: Gamma-aminobutyric acid is an inhibitory neurotransmitter, synthesized by two isoforms of glutamate decarboxylase (GAD), GAD65 and -67. Unexpectedly, inactivation of GAD67 induces cleft palate in mice. Reduction of spontaneous tongue movement resulting from decreased motor nerve activity has been related to the development of cleft palate in GAD67(-/-) fetuses. In the present study, development of cleft palate was examined histologically and manipulated with culture of the maxilla and partial resection of fetal tongue. METHODS: GAD67(-/-) mice and their littermates were used. Histological examination and immunohistochemistry were performed conventionally. Organ culture of the maxilla was carried out as reported previously. Fetuses were maintained alive under anesthesia and tips of their tongues were resected. RESULTS: Elevation of palatal shelves, the second step of palate formation, was not observed in GAD67(-/-) mice. In wild-type mice, GAD67 and gamma-aminobutyric acid were not expressed in the palatal shelves, except in the medial edge epithelium. During 2 days of culture of maxillae dissected from E13.5-E14.0 GAD67(-/-) fetuses, elevation and fusion of the palatal shelves were induced. When E13.5-15.5 mutant fetuses underwent partial tongue resection, the palatal shelves became elevated within 30 min. CONCLUSIONS: These results suggest that the potential for palate formation is maintained in the palatal shelves of GAD67(-/-) fetuses, but it is obstructed by other, probably neural, factors, resulting in cleft palate.     

Dose-response relations of palatal slit, cleft palate, and fetal mortality in mice treated with a glucocorticoid

C57BL/6 (C57BL) and SWV mice were treated subcutaneously with triamcinolone acetonide in a single dose of 1.0-7.0 mg/kg on day 12 of pregnancy, and the palate of their fetuses was examined at term. In C57BL mice palatal slit occurred spontaneously and its frequency increased with increasing doses of triamcinolone. However, this defect was not seen in SWV fetuses, even when dams were treated with the doses that induced cleft palate. The frequency of cleft palate increased in both C57BL and SWV as the dose of triamcinolone increased. Fetal mortality increased in SWV, but not in C57BL, with increasing doses of triamcinolone. Dose-response relations were analyzed by the log-probit transformation method. In C57BL mice, the slope of the dose-response curve of palatal slit was significantly different from that of cleft palate. In contrast, the dose-response curves of cleft palate were similar in both C57BL and SWV; the median effective dose was significantly greater in C57BL than in SWV. The mechanism of induced palatal slit appears to be different from that of induced cleft palate; the mechanism of cleft palate induction may be the same in both C57BL and SWV. The slope of the dose-response curve of fetal mortality in SWV mice was different from that of cleft palate; the mechanisms underlying the resorption and cleft palate responses must be different.     

Palatal thickening and facial form in Paranthropus: Examination of alternative developmental models

Paranthropus is distinctive among hominoids in its possession of a greatly thickened hard palate. Although traditionally considered a structural adaptation to counter high-magnitude masticatory stress, alternative developmental models are equally viable. Three models of palatal thickening were evaluated in this study. A mechanical model interprets palatal thickening as a compensatory response to increased instability of the midpalatal suture effected by an anterior placement of the masseteric muscle mass. This model predicts that palatal thickness is correlated with the length of the palate posterior to the masseteric tubercle. Two non-mechanical models consider the thickness of the hard palate to be structurally related to and therefore correlated with either 1) the degree to which the premaxilla overlaps the hard palate in the subnasal region or 2) the height of the posterior facial skeleton. The correlation of craniofacial variables was assessed intraspecifically in ontogenetic series of great ape and human crania. Tests of correlation were performed for each comparison using both residuals calculated from reduced major axis regression of the variable of interest against a measure of cranial size and shape ratios. A significant correlation of palatal thickness with posterior facial height in Pan suggests that the unusually thick hard palate of Paranthropus is directly related to the increased posterior facial height characteristic of this taxon. Further evaluation suggests that extreme palatal thickening in these specimens occurred by virtue of their possession of a nasal septum morphology in which the vomer extends onto the superior nasal surface of the premaxilla. Such a morphology would have constrained the palatal nasal lamina to maintain the approximate level of the premaxillary nasal lamina throughout the growth process thereby promoting palatal thickening. Am J Phys Anthropol 103:375–392, 1997. © 1997 Wiley-Liss, Inc.     

Response of Merkel cells in the palatal rugae to the continuous mechanical stimulation by palatal plate

The aim of the present study was to investigate the responses of Merkel cells that are numerous in the palatine rugae, due to the continuous mechanical stimulation exerted by the palatal plate. Forty golden hamsters were used in this experiment. The palatal plate was made of adhesive resin and it was set on the palate of the animal. To exert a continuous pressure, a 0.8 mm elevation on the internal surface of the palatal plate was created at the middle portion of the fourth palatine ruga. Thereafter, the number of Merkel cells in the mucosa was calculated by immunohistochemical observation. Morphological changes of Merkel cells were examined by electron microscopy. There was significant difference among the control and any of the treated groups on the number of CK20 positive Merkel cells (p < 0.05) and that numbers were decreased at the sites where continuous mechanical stimulation was exerted. Degeneration of the cytoplasm mitochondria and nerve endings, and a decrease in both the number of neurosecretory granules and cytoplasmic processes were observed. Furthermore, the presence of nuclear chromatin aggregation and fragmentation was recognized. The continuous mechanical stimulation by the palatal plate affected the responses of Merkel cells and nerve endings, thus inducing a decrease in the number of Merkel cells. A portion of these changes was also associated with the expression of apoptosis.     

Fine needle aspiration cytology of minor salivary gland tumours of the palate

Fine needle aspiration cytology of minor salivary gland tumours of the palate This retrospective study was carried out to review aspirates from minor salivary gland tumours of the palate and to assess the problems encountered in their diagnosis, especially the cytological diagnosis of newer entities such as polymorphous low grade adenocarcinoma (PLGA). Fifty-five cases of palatal salivary gland tumours aspirated over a period of 16 years were reviewed. Histology was available in 26 cases. Pleomorphic adenoma (27 cases) was the most common benign cytodiagnosis. Eleven aspirates were malignant tumours of which eight cases were adenoid cystic carcinoma and three cases were mucoepidermoid carcinoma. Seven cases were diagnosed on fine needle aspiration as suggestive of PLGA. However histological confirmation was available in only one of these cases. Concordance between the initial and revised typings of the tumours was seen in only 28 cases (54%) in the present study. Initially 18 of the 51 tumours (35.3%) could not be typed; and after review, only three could not be typed. Three cases of oncocytoma could be diagnosed on review only. Palatal salivary gland tumours, although relatively uncommon, are difficult to diagnose cytologically. This is more so in cases of newer entities such as PLGA, as their cytological diagnosis is still not well characterized.     

Effect of intraamniotic vitamin A on palatal closure of fetal rats

On day 15 of gestation, intraamniotic vitamin A in a dose of 150 IU was administered to the fetal rats to examine its effect on palatal closure. Fetuses subjected to only amniocentesis acted as control for the study. The fetuses were recovered on day 19, 20 and 21, respectively. Vitamin A resulted in poor development of palatine shelves. There was no clear demarcation of the base and the free margins of the shelves were either rounded or blunted with poor attempt towards closure. In the vitamin A group, the incidence of cleft palate were similar in all three days while there was a gradual decline with increasing gestational age in the amniocentesis group. The results suggest that unlike amniocentesis, in vitamin A treated fetuses, there was no attempt towards a delayed closure of the palate.     

Occurrence of cleft palate, palatal slit, and fetal death in mice treated with a glucocorticoid: an embryo transfer experiment

SWV and C57BL/6 (C57BL) mice were treated subcutaneously with triamcinolone acetonide in a single dose of 2.5 mg/kg on day 12 of pregnancy (vaginal plug = day 0), and the palate of their fetuses was examined at term. Cleft palate was seen in some SWV and C57BL fetuses; its frequency was significantly higher in the former. Closer examination revealed palatal slit in some C57BL, but in no SWV fetuses. In addition, fetal mortality was significantly increased in SWV, but not in C57BL, exposed to triamcinolone. These strain differences in cleft palate, palatal slit, and fetal mortality were investigated by embryo transfer. The results showed that, in cleft palate induction, the effects of uterine environment were more important than those of fetal genotype. On the other hand, after transfer, palatal slit still occurred in C57BL but not in SWV fetuses; thus, in palatal slit occurrence, the fetal genotype played a more important role than the uterine environment. Accordingly, it is suggested that the nature of the participation of fetal genotype and uterine environment in palatal slit occurrence is different from that in cleft palate induction. In regard to fetal mortality, embryo transfer procedures influenced it in SWV dams and the effect of triamcinolone could not be detected after embryo transfer.     

Response of Merkel cells in the palatal rugae to the continuous mechanical stimulation by palatal plate

The aim of the present study was to investigate the responses of Merkel cells that are numerous in the palatine rugae, due to the continuous mechanical stimulation exerted by the palatal plate. Forty golden hamsters were used in this experiment. The palatal plate was made of adhesive resin and it was set on the palate of the animal. To exert a continuous pressure, a 0.8?mm elevation on the internal surface of the palatal plate was created at the middle portion of the fourth palatine ruga. Thereafter, the number of Merkel cells in the mucosa was calculated by immunohistochemical observation. Morphological changes of Merkel cells were examined by electron microscopy. There was significant difference among the control and any of the treated groups on the number of CK20 positive Merkel cells (p?<?0.05) and that numbers were decreased at the sites where continuous mechanical stimulation was exerted. Degeneration of the cytoplasm mitochondria and nerve endings, and a decrease in both the number of neurosecretory granules and cytoplasmic processes were observed. Furthermore, the presence of nuclear chromatin aggregation and fragmentation was recognized. The continuous mechanical stimulation by the palatal plate affected the responses of Merkel cells and nerve endings, thus inducing a decrease in the number of Merkel cells. A portion of these changes was also associated with the expression of apoptosis.     

Patterning of palatal rugae through sequential addition reveals an anterior/posterior boundary in palatal development

Background

The development of the secondary palate has been a main topic in craniofacial research, as its failure results in cleft palate, one of the most common birth defects in human. Nevertheless, palatal rugae (or rugae palatinae), which are transversal ridges developing on the secondary palate, received little attention. However, rugae could be useful as landmarks to monitor anterior/posterior (A/P) palatal growth, and they provide a simple model of mesenchymal-epithelial structures arranged in a serial pattern.

Results

We first determined in which order the nine mouse rugae appear during development. Our results revealed a reiterative process, which is coupled with A/P growth of palatal shelves, and by which rugae 3 to 7b are sequentially interposed, in the increasing distance between the second most anterior ruga, ruga 2, and the two most posterior rugae, rugae 8 and 9. We characterized the steps of ruga interposition in detail, showing that a new ruga forms from an active zone of high proliferation rate, next to the last formed ruga. Then, by analyzing the polymorphism of wild type and Eda^Ta mutant mice, we suggest that activation-inhibition mechanisms may be involved in positioning new rugae, like for other skin appendages. Finally, we show that the ruga in front of which new rugae form, i.e. ruga 8 in mouse, coincides with an A/P gene expression boundary in the palatal shelves (Shox2/Meox2-Tbx22). This coincidence is significant, since we also found it in hamster, despite differences in the adult ruga pattern of these two species.

Conclusion

We showed that palatal rugae are sequentially added to the growing palate, in an interposition process that appears to be dependent on activation-inhibition mechanisms and reveals a new developmental boundary in the growing palate. Further studies on rugae may help to shed light on both the development and evolution of structures arranged in regular patterns. Moreover, rugae will undoubtedly be powerful tools to further study the anteroposterior regionalization of the growing palate.