Wnt/β-catenin-C-kit axis may play a role in adenoid cystic carcinoma prognostication

Adenoid cystic carcinoma (ACC) is one of the most common malignant salivary gland tumors. ACC is composed of myoepithelial and epithelial neoplastic cells which grow slowly and have a tendency for neural invasion. The long term prognosis is still relatively poor. Although several gene abnormalities, such as fusions involving MYB or MYBL1 oncogenes and the transcription factor gene NFIB, and overexpression of KIT have been reported in ACC, their precise functions in the pathogenesis of ACC remain unclear. We recently demonstrated that the elevated expression of Semaphorin 3A (SEMA3A), specifically expressed in myoepithelial neoplastic cells, might function as a novel oncogene-related molecule to enhance cell proliferation through activated AKT signaling in 9/10 (90%) ACC cases. In the current study, the patient with ACC whose tumor was negative for SEMA3A in the previous study, revisited our hospital with late metastasis of ACC to the cervical lymph node eight years after surgical resection of the primary tumor. We characterized this recurrent ACC, and compared it with the primary ACC using immunohistochemical methods. In the recurrent ACC, the duct lining epithelial cells, not myoepithelial neoplastic cells, showed an elevated Ki-67 index and increased cell membrane expression of C-kit, along with the expression of phosphorylated ERK. Late metastasis ACC specimens were not positive for β-catenin and lymphocyte enhancer binding factor 1 (LEF1), which were detected in the nuclei of perineural infiltrating cells in primary ACC cells. In addition, experiments with the GSK-3 inhibitor revealed that β-catenin pathway suppressed not only KIT expression but also proliferation of ACC cells. Moreover, stem cell factor (SCF; also known as KIT ligand, KITL) induced ERK activation in ACC cells. These results suggest that inactivation of Wnt/β-catenin signaling may promote C-kit-ERK signaling and cell proliferation of in metastatic ACC.

RANKL neutralisation prevents osteoclast activation in a human in vitro ameloblastoma-bone model

Ameloblastoma is a benign, locally invasive epithelial odontogenic neoplasm of the jaw. Treatment of choice is jaw resection, often resulting in significant morbidity. The aim of this study was to recapitulate ameloblastoma in a completely humanised 3D disease model containing ameloblastoma cells, osteoblasts and activated osteoclasts to investigate the RANKL pathway within the ameloblastoma stromal environment and its response to the RANKL antibody denosumab. In vitro bone was engineered by culturing human osteoblasts (hOB) in a biomimetic, dense collagen type I matrix, resulting in extensive mineral deposits by day 21 forming alizarin red positive bone like nodules throughout the 3D model. Activated TRAP + human osteoclasts were confirmed through the differentiation of human CD14+ monocytes after 10 days within the model. Lastly, the ameloblastoma cell lines AM-1 and AM-3 were incorporated into the 3D model. RANKL release was validated through TACE/ADAM17 activation chemically or through hOB co-culture. Denosumab treatment resulted in decreased osteoclast activation in the presence of hOB and ameloblastoma cells. These findings stress the importance of accurately modelling tumour and stromal populations as a preclinical testing platform.

RAF1-MEK/ERK pathway-dependent ARL4C expression promotes ameloblastoma cell proliferation and osteoclast formation

Ameloblastoma is an odontogenic neoplasm characterized by slow intraosseous growth with progressive jaw resorption. Recent reports have revealed that ameloblastoma harbours an oncogenic BRAFV600E mutation with mitogen-activated protein kinase (MAPK) pathway activation and described cases of ameloblastoma harbouring a BRAFV600E mutation in which patients were successfully treated with a BRAF inhibitor. Therefore, the MAPK pathway may be involved in the development of ameloblastoma; however, the precise mechanism by which it induces ameloblastoma is unclear. The expression of ADP-ribosylation factor (ARF)-like 4c (ARL4C), induced by a combination of the EGF-MAPK pathway and Wnt/β-catenin signalling, has been shown to induce epithelial morphogenesis. It was also reported that the overexpression of ARL4C, due to alterations in the EGF/RAS-MAPK pathway and Wnt/β-catenin signalling, promotes tumourigenesis. However, the roles of ARL4C in ameloblastoma are unknown. We investigated the involvement of ARL4C in the development of ameloblastoma. In immunohistochemical analyses of tissue specimens obtained from 38 ameloblastoma patients, ARL4C was hardly detected in non-tumour regions but tumours frequently showed strong expression of ARL4C, along with the expression of both BRAFV600E and RAF1 (also known as C-RAF). Loss-of-function experiments using inhibitors or siRNAs revealed that ARL4C elevation depended on the RAF1-MEK/ERK pathway in ameloblastoma cells. It was also shown that the RAF1-ARL4C and BRAFV600E-MEK/ERK pathways promoted cell proliferation independently. ARL4C-depleted tumour cells (generated by knockdown or knockout) exhibited decreased proliferation and migration capabilities. Finally, when ameloblastoma cells were co-cultured with mouse bone marrow cells and primary osteoblasts, ameloblastoma cells induced osteoclast formation. ARL4C elevation in ameloblastoma further promoted its formation capabilities through the increased RANKL expression of mouse bone marrow cells and/or primary osteoblasts. These results suggest that the RAF1-MEK/ERK-ARL4C axis, which may function in cooperation with the BRAFV600E-MEK/ERK pathway, promotes ameloblastoma development. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

Comparative transcriptional profiling of canine acanthomatous ameloblastoma and homology with human ameloblastoma

Ameloblastomas are odontogenic tumors that are rare in people but have a relatively high prevalence in dogs. Because canine acanthomatous ameloblastomas (CAA) have clinicopathologic and molecular features in common with human ameloblastomas (AM), spontaneous CAA can serve as a useful translational model of disease. However, the molecular basis of CAA and how it compares to AM are incompletely understood. In this study, we compared the global genomic expression profile of CAA with AM and evaluated its dental origin by using a bulk RNA-seq approach. For these studies, healthy gingiva and canine oral squamous cell carcinoma served as controls. We found that aberrant RAS signaling, and activation of the epithelial-to-mesenchymal transition cellular program are involved in the pathogenesis of CAA, and that CAA is enriched with genes known to be upregulated in AM including those expressed during the early stages of tooth development, suggesting a high level of molecular homology. These results support the model that domestic dogs with spontaneous CAA have potential for pre-clinical assessment of targeted therapeutic modalities against AM.

Ultra-frequent HRAS p.Q61R somatic mutation in canine acanthomatous ameloblastoma reveals pathogenic similarities with human ameloblastoma

Ameloblastoma is a locally aggressive odontogenic tumour that occurs in humans and dogs. Most ameloblastomas (AM) in humans harbour mutually-exclusive driving mutations in BRAF, HRAS, KRAS, NRAS or FGFR2 that activate MAPK signalling, and in SMO that activates Hedgehog signalling. The remarkable clinical and histological similarities between canine acanthomatous ameloblastoma (CAA) and AM suggest they may harbour similar driving mutations. In this study, aimed at characterizing the mutational status of SMO, BRAF, HRAS, KRAS, NRAS and FGFR2 in CAA, we used RNA sequencing, Sanger sequencing and restriction fragment length polymorphism assays to demonstrate that 94% of CAA (n = 16) harbour a somatic HRAS p.Q61R mutation. The similarities in MAPK-activating mutational profiles between CAA and AM implicate conserved molecular mechanisms of tumorigenesis, thus, qualifying the dog as a potentially useful model of disease. Given the relevance of RAS mutations in the pathogenesis of odontogenic tumours and other types of cancer, the results of this study are of comparative, translational, and veterinary value.

The Mutational Profile of Unicystic Ameloblastoma

BRAF V600E is the most common mutation in conventional ameloblastoma (AM) of the mandible. In contrast, maxillary AMs appear to harbor more frequently RAS, FGFR2, or SMO mutations. Unicystic ameloblastoma (UAM) is considered a less aggressive variant of ameloblastoma, amenable to more conservative treatment, and classified as a distinct entity. The aim of this study was to characterize the mutation profile of UAM ( n = 39) and to compare it to conventional AM ( n = 39). The associations between mutation status and recurrence probability were also analyzed. In the mandible, 94% of UAMs (29/31, including 8/8 luminal, 6/8 intraluminal, and 15/15 mural subtypes) and 74% of AMs (28/38) revealed BRAF V600E mutations. Among the BRAF wild-type cases, 1 UAM showed a missense SMO mutation (p.L412F), whereas 2 NRAS (p.Q61R), 2 HRAS (p.Q61R), and 2 FGFR2 (p.C383R) activating mutations were identified in AM. Of the 3 maxillary UAMs, only 1 revealed a BRAF V600E mutation. Taken together, our findings demonstrate high frequency of activating BRAF V600E mutations in both UAM and AM of the mandible. In maxillary UAMs, the BRAF V600E mutation prevalence appears to be lower as was shown for AM previously. It could therefore be argued that UAM and AM are part of the spectrum of the same disease. AMs without BRAF V600E mutations were associated with an increased rate of local recurrence ( P = 0.0003), which might indicate that routine mutation testing also has an impact on prognosis.

Treatment with soluble activin type IIB-receptor improves bone mass and strength in a mouse model of Duchenne muscular dystrophy

BACKGROUND

Inhibition of activin/myostatin pathway has emerged as a novel approach to increase muscle mass and bone strength. Duchenne muscular dystrophy (DMD) is a neuromuscular disorder that leads to progressive muscle degeneration and also high incidence of fractures. The aim of our study was to test whether inhibition of activin receptor IIB ligands with or without exercise could improve bone strength in the mdx mouse model for DMD.

METHODS

Thirty-two mdx mice were divided to running and non-running groups and to receive either PBS control or soluble activin type IIB-receptor (ActRIIB-Fc) once weekly for 7 weeks.

RESULTS

Treatment of mdx mice with ActRIIB-Fc resulted in significantly increased body and muscle weights in both sedentary and exercising mice. Femoral μCT analysis showed increased bone volume and trabecular number (BV/TV +80%, Tb.N +70%, P < 0.05) in both ActRIIB-Fc treated groups. Running also resulted in increased bone volume and trabecular number in PBS-treated mice. However, there was no significant difference in trabecular bone structure or volumetric bone mineral density between the ActRIIB-Fc and ActRIIB-Fc-R indicating that running did not further improve bone structure in ActRIIB-Fc-treated mice. ActRIIB-Fc increased bone mass also in vertebrae (BV/TV +20%, Tb.N +30%, P < 0.05) but the effects were more modest. The number of osteoclasts was decreased in histological analysis and the expression of several osteoblast marker genes was increased in ActRIIB-Fc treated mice suggesting decreased bone resorption and increased bone formation in these mice. Increased bone mass in femurs translated into enhanced bone strength in biomechanical testing as the maximum force and stiffness were significantly elevated in ActRIIB-Fc-treated mice.

CONCLUSIONS

Our results indicate that treatment of mdx mice with the soluble ActRIIB-Fc results in a robust increase in bone mass, without any additive effect by voluntary running. Thus ActRIIB-Fc could be an attractive option in the treatment of musculoskeletal disorders.

Genetic Changes in Sporadic Keratocystic Odontogenic Tumors (Odontogenic Keratocysts)

Little is known about the genetic background of keratocystic odontogenic tumors (KCOT, odontogenic keratocysts). Our aim was to characterize genomic aberrations in sporadic KCOT using cDNA-expression arrays and array-comparative genomic hybridization. For cDNA-expression arrays, 10 KCOT specimens and 20 fetal tooth germs were studied. Quantitative real-time reverse-transcription/polymerase chain-reaction and immunohistochemical studies were also undertaken. Several genes were over-expressed in 12q13, including cytokeratin 6B ( KRT6B) (≈ 10-fold), epidermal growth factor receptor ERBB3 (~ 4.7-fold), and glioma-associated oncogene homologue 1 ( GLI1) (~ 5- to 12-fold). One amplicon (~ 0.7 Mega base pairs [Mbp]), covering several genes involved in the regulation of cell growth, was found in 12q13.2. Deletions were found in 3q13.1, 5p14.3, and 7q31.3, including the cell-adhesion-related gene cadherin 18 ( CDH18) and leukocyte cell adhesion molecule ( ALCAM, MEMD). Over-expressed and amplified genes in 12q13, also reported in several other tumors and cell lines, may contribute to the persistent growth characteristics of KCOT.

Early dental epithelial transcription factors distinguish ameloblastoma from keratocystic odontogenic tumor

The aim of the study was to characterize the molecular relationship between ameloblastoma and keratocystic odontogenic tumor (KCOT) by means of a genome-wide expression analysis. Total RNA from 27 fresh tumor samples of 15 solid/multicystic intraosseous ameloblastomas and 12 sporadic KCOTs was hybridized on Affymetrix whole genome arrays. Hierarchical clustering separated ameloblastomas and KCOTs into 2 distinct groups. The gene set enrichment analysis based on 303 dental genes showed a similar separation of ameloblastomas and KCOTs. Early dental epithelial markers PITX2, MSX2, DLX2, RUNX1, and ISL1 were differentially overexpressed in ameloblastoma, indicating its dental identity. Also, PTHLH, a hormone involved in tooth eruption and invasive growth, was one of the most differentially upregulated genes in ameloblastoma. The most differentially overexpressed genes in KCOT were squamous epithelial differentiation markers SPRR1A, KRTDAP, and KRT4, as well as DSG1, a component of desmosomal cell-cell junctions. Additonally, the epithelial stem cell marker SOX2 was significantly upregulated in KCOT when compared with ameloblastoma. Taken together, the gene expression profile of ameloblastoma reflects differentiation from dental lamina toward the cap/bell stage of tooth development, as indicated by dental epithelium-specific transcription factors. In contrast, gene expression of KCOT indicates differentiation toward keratinocytes.

No sexual dimorphism in human prenatal metacarpal ratios

BACKGROUND

Ratios of digit lengths are studied intensively as markers of prenatal sex hormone levels.

AIM

Study sexual dimorphism in ratios of metacarpals, which received less attention.

METHODS

We studied six metacarpal ratios in deceased human fetuses of ages 10 to 42weeks.

RESULTS AND CONCLUSION

We found no indication of a sexual dimorphism at this early stage of development.

When right differs from left: human limb directional asymmetry emerges during very early development

The often observed directional asymmetry (DA) in human limb bones may have a genetic/developmental basis and/or could emerge from different mechanical loadings across sides due to handedness. Because behavioural lateralization in itself has a genetic basis, it has been suggested that DA in limbs could develop prenatally as a pre-adaptation to adult life. However, the presence of consistent differences in the size of left and right limb bones in early development is understudied. We study asymmetry in limb bones during early development (10-20 weeks of gestation) in a sample of 178 aborted foetuses. Statistically significant DA was found in several upper and lower limb bones, where the right-hand side was consistently larger than the left. We argue that this pattern is probably the consequence of developmental processes related to internal asymmetric positioning of organs.

High frequency of BRAF V600E mutations in ameloblastoma

Ameloblastoma is a benign but locally infiltrative odontogenic neoplasm. Although ameloblastomas rarely metastasise, recurrences together with radical surgery often result in facial deformity and significant morbidity. Development of non-invasive therapies has been precluded by a lack of understanding of the molecular background of ameloblastoma pathogenesis. When addressing the role of ERBB receptors as potential new targets for ameloblastoma, we discovered significant EGFR over-expression in clinical samples using real-time RT-PCR, but observed variable sensitivity of novel primary ameloblastoma cells to EGFR-targeted drugs in vitro. In the quest for mutations downstream of EGFR that could explain this apparent discrepancy, Sanger sequencing revealed an oncogenic BRAF V600E mutation in the cell line resistant to EGFR inhibition. Further analysis of the clinical samples by Sanger sequencing and BRAF V600E-specific immunohistochemistry demonstrated a high frequency of BRAF V600E mutations (15 of 24 samples, 63%). These data provide novel insight into the poorly understood molecular pathogenesis of ameloblastoma and offer a rationale to test drugs targeting EGFR or mutant BRAF as novel therapies for ameloblastoma.

Cephalometric assessment of human fetal head specimens

BACKGROUND

Past investigations of prenatal craniofacial growth have largely relied on histological sections. Few studies have taken measurements on three-dimensional representations (3D reconstruction, 3D CT, postmortem) or varying depth levels (ultrasound), and we know of no craniofacial growth studies done on cleared-and-stained specimens of whole fetal heads.

MATERIALS AND METHODS

This study comprised 14 human fetal head specimens cleared and stained with alizarin red and alcian blue. They had been stored in glycerol and represented weeks 8-12 of gestation, with crown-rump lengths ranging from 23-145 mm. These specimens were cephalometrically analyzed in norma frontalis and norma lateralis, which notably included the opportunity for side-to-side comparison.

RESULTS

As the cranial membrane bones progressively approached each other, the orbits, maxilla, and mandible gradually grew wider. Likewise, the sagittal dimensions of the maxilla and mandible increased continuously and synchronically. We noted side-to-side differences ranging from 2-5 mm. Another notable finding concerned the inclination of the maxilla relative to the cranial base, which increased more on the right than on the left side.

CONCLUSION

This is the first investigation presenting side-to-side comparative measurements of human fetal head specimens. Such measurements are essential in the quest toward validating the findings of other imaging techniques such as CT or MRI and-most importantly-intrauterine sonography.

Sox2 marks epithelial competence to generate teeth in mammals and reptiles

Tooth renewal is initiated from epithelium associated with existing teeth. The development of new teeth requires dental epithelial cells that have competence for tooth formation, but specific marker genes for these cells have not been identified. Here, we analyzed expression patterns of the transcription factor Sox2 in two different modes of successional tooth formation: tooth replacement and serial addition of primary teeth. We observed specific Sox2 expression in the dental lamina that gives rise to successional teeth in mammals with one round of tooth replacement as well as in reptiles with continuous tooth replacement. Sox2 was also expressed in the dental lamina during serial addition of mammalian molars, and genetic lineage tracing indicated that Sox2(+) cells of the first molar give rise to the epithelial cell lineages of the second and third molars. Moreover, conditional deletion of Sox2 resulted in hyperplastic epithelium in the forming posterior molars. Our results indicate that the Sox2(+) dental epithelium has competence for successional tooth formation and that Sox2 regulates the progenitor state of dental epithelial cells. The findings imply that the function of Sox2 has been conserved during evolution and that tooth replacement and serial addition of primary teeth represent variations of the same developmental process. The expression patterns of Sox2 support the hypothesis that dormant capacity for continuous tooth renewal exists in mammals.

Critical role for αvβ6 integrin in enamel biomineralization

Tooth enamel has the highest degree of biomineralization of all vertebrate hard tissues. During the secretory stage of enamel formation, ameloblasts deposit an extracellular matrix that is in direct contact with ameloblast plasma membrane. Although it is known that integrins mediate cell-matrix adhesion and regulate cell signaling in most cell types, the receptors that regulate ameloblast adhesion and matrix production are not well characterized. Thus, we hypothesized that αvβ6 integrin is expressed in ameloblasts where it regulates biomineralization of enamel. Human and mouse ameloblasts were found to express both β6 integrin mRNA and protein. The maxillary incisors of Itgb6−/− mice lacked yellow pigment and their mandibular incisors appeared chalky and rounded. Molars of Itgb6−/− mice showed signs of reduced mineralization and severe attrition. The mineral-to-protein ratio in the incisors was significantly reduced in Itgb6−/− enamel, mimicking hypomineralized amelogenesis imperfecta. Interestingly, amelogenin-rich extracellular matrix abnormally accumulated between the ameloblast layer of Itgb6−/− mouse incisors and the forming enamel surface, and also between ameloblasts. This accumulation was related to increased synthesis of amelogenin, rather than to reduced removal of the matrix proteins. This was confirmed in cultured ameloblast-like cells, which did not use αvβ6 integrin as an endocytosis receptor for amelogenins, although it participated in cell adhesion on this matrix indirectly via endogenously produced matrix proteins. In summary, integrin αvβ6 is expressed by ameloblasts and it plays a crucial role in regulating amelogenin deposition/turnover and subsequent enamel biomineralization.

Analysis of cervical ribs in a series of human fetuses

In humans, an increasing body of evidence has linked the frequency of cervical ribs to stillbirths, other malformations and early childhood cancers. However, the frequency of cervical ribs in a putatively healthy fetal population is not sufficiently known to assess the actual medical risks of these prenatal findings. We therefore analyzed the presence of skeletal anomalies in a series of 199 electively aborted fetuses, which were whole-mount stained with alizarin red specific for skeletal tissues. Results show that approximately 40% of the fetuses had cervical ribs, even though external congenital abnormalities such as craniofacial and limb defects were absent. A literature overview indicates that the observed frequency of cervical ribs is comparable to results previously obtained for deceased fetuses with no or minor congenital anomalies, and higher than expected for healthy fetuses. This unexpected result can probably in part be explained by a higher detection rate of small cervical ribs when using alizarin red staining instead of radiographs. Additionally, studies in the literature suggest that the size of a cervical rib may indicate the severity of abnormalities, but this possibility requires further research. Anomalies of the axial skeleton are known to be caused by a disturbance of early development, which alters Hox gene expression, but in this study the origin of the stress could not be verified as maternal medical data were not available. The co-occurrence of rudimentary or absent 12th ribs in 23.6% of the cases with cervical ribs indicates that in approximately 8% of the fetuses a homeotic shift occurred over a larger part of the vertebral column. This suggests that the expression of multiple Hox genes may have been affected in these fetuses. Together, the high incidence of cervical ribs and also their co-occurrence with rudimentary or absent 12th ribs suggests that there may have been a disturbance of early development such that the studied fetuses are probably not informative about the general population. Future studies determining the frequency of cervical ribs in a more healthy fetal population are therefore needed to evaluate their potential as an indicator of medical risks.

Compound heterozygous desmoplakin mutations result in a phenotype with a combination of myocardial, skin, hair, and enamel abnormalities

Desmoplakin (DP) anchors the intermediate filament cytoskeleton to the desmosomal cadherins and thereby confers structural stability to tissues. In this study, we present a patient with extensive mucocutaneous blisters, epidermolytic palmoplantar keratoderma, nail dystrophy, enamel dysplasia, and sparse woolly hair. The patient died at the age of 14 years from undiagnosed cardiomyopathy. The skin showed hyperplasia and acantholysis in the mid- and lower epidermal layers, whereas the heart showed extensive fibrosis and fibrofatty replacement in both ventricles. Immunofluorescence microscopy showed a reduction in the C-terminal domain of DP in the skin and oral mucosa. Sequencing of the DP gene showed undescribed mutations in the maternal and paternal alleles. Both mutations affected exon 24 encoding the C-terminal domain. The paternal mutation, c.6310delA, leads to a premature stop codon. The maternal mutation, c.7964 C to A, results in a substitution of an aspartic acid for a conserved alanine residue at amino acid 2655 (A2655D). Structural modeling indicated that this mutation changes the electrostatic potential of the mutated region of DP, possibly altering functions that depend on intermolecular interactions. To conclude, we describe a combination of DP mutation phenotypes affecting the skin, heart, hair, and teeth. This patient case emphasizes the importance of heart examination of patients with desmosomal genodermatoses.

Regeneration of bone and periodontal ligament induced by recombinant amelogenin after periodontitis

Regeneration of mineralized tissues affected by chronic diseases comprises a major scientific and clinical challenge. Periodontitis, one such prevalent disease, involves destruction of the tooth-supporting tissues, alveolar bone, periodontal-ligament and cementum, often leading to tooth loss. In 1997, it became clear that, in addition to their function in enamel formation, the hydrophobic ectodermal enamel matrix proteins (EMPs) play a role in the regeneration of these periodontal tissues. The epithelial EMPs are a heterogeneous mixture of polypeptides encoded by several genes. It was not clear, however, which of these many EMPs induces the regeneration and what mechanisms are involved. Here we show that a single recombinant human amelogenin protein (rHAM⁺), induced in vivo regeneration of all tooth-supporting tissues after creation of experimental periodontitis in a dog model. To further understand the regeneration process, amelogenin expression was detected in normal and regenerating cells of the alveolar bone (osteocytes, osteoblasts and osteoclasts), periodontal ligament, cementum and in bone marrow stromal cells. Amelogenin expression was highest in areas of high bone turnover and activity. Further studies showed that during the first 2 weeks after application, rHAM⁺ induced, directly or indirectly, significant recruitment of mesenchymal progenitor cells, which later differentiated to form the regenerated periodontal tissues. The ability of a single protein to bring about regeneration of all periodontal tissues, in the correct spatio-temporal order, through recruitment of mesenchymal progenitor cells, could pave the way for development of new therapeutic devices for treatment of periodontal, bone and ligament diseases based on rHAM⁺.

The seven-year outcome of an early orthodontic treatment strategy

The benefits of early orthodontic treatment are continuously discussed, but studies are few. We examined whether definite need for orthodontic treatment could be eliminated in public health care by systematically focusing on early intervention. One age cohort living in a rural Finnish municipality (N = 85) was regularly followed from ages 8 to 15 years, and persons with malocclusions were treated according to a pre-planned protocol. Treatment need was assessed according to the Dental Health Component (DHC) of the Index of Orthodontic Treatment Need, and treatment outcome by the Peer Assessment Rating Index (PAR). Fifty-two percent of the cohort received treatment, and definite treatment need decreased from 33% to 9%. In the treated group, the mean PAR score reduction was 63%, and 51% showed more than 70% improvement. The results suggest that an early treatment strategy may considerably reduce the need for orthodontic treatment in public health care with limited specialist resources.

Squamous cell carcinomas arising from different types of oral epithelia differ in their tumor and patient characteristics and survival

A hypothesis that OSCCs originating from different types of oral epithelia may have different patient and tumor characteristics was evaluated in this retrospective analysis of 188 patients with primary OSCC treated at Turku University Central Hospital, Turku, Finland in 1988-1997. The tumors were categorized according to the type of oral epithelium from which they have originated: (1) specialized epithelium (dorsal tongue) (2) keratinized (masticatory) epithelium, (3) non-keratinized (lining) epithelium, and (4) tongue epithelium (epithelium on the lateral border of the tongue). The relevant clinical data, including age, sex, social status, and risk behavior of the patients and clinical presentation, histopathological grading, and treatment of the tumors, as well as the follow-up information, were collected from the patient charts of the hospital. In general, tumor and patient characteristics of OSCCs and survival rates were found to be in line with those of recent analyses reported from other industrialized countries. However, OSCCs in young patients (4.8%) seemed to be clinically at a lower stage and histologically more highly differentiated than those of the other patients. Eight out of 9 (89%) OSCCs in the young patients were located on the lateral tongue. The 5-year recurrence-free rates of the patients according to the epithelial origin of the tumors were as follows: masticatory epithelium 42%, lining epithelium 57%, and epithelium of the lateral border of the tongue 61%. In conclusion, the tumors originating from different types of oral epithelia may have distinct properties with regard to their clinical behavior and responsiveness to the different treatment modalities. It would seem to be meaningful to investigate the molecular characteristics of the different types of oral epithelium in order to elucidate possible differences in their susceptibility to malignant transformation.

Characterization of gene expression in major types of salivary gland carcinomas with epithelial differentiation

Gene expression profiles were studied in 13 cases of salivary gland carcinoma including mucoepidermoid carcinoma (MEC), acinic cell carcinoma (ACC), and salivary duct carcinoma (SDC) using a cDNA array. A total of 162 genes were deregulated. Only 5 genes were overexpressed in all carcinomas including fibronectin 1 (FN1), tissue metalloproteinase inhibitor 1 (TIMP1), biglycan (BGN), tenascin-C (HXB), and insulin-like growth factor binding protein 5 (IGFBP5), whereas 16 genes were underexpressed. The small number of similarly deregulated genes in these carcinoma entities suggests an extensive genetic variation between them. This result agrees with the great histopathological diversity of different entities of salivary gland carcinoma. Furthermore, diversity in gene expression between the carcinoma types was identified also by hierarchical clustering. Each carcinoma entity was clustered together but MEC, SDC, and ACC were separated from each other. Significance analysis of microarrays identified 27 genes expressed differently between the groups. In MEC, overexpressed genes included those of cell proliferation (IL-6 and SFN) and cell adhesion (SEMA3F and COL6A3), whereas many underexpressed genes were related to DNA modification (NTHL1 and RBBP4). Apoptosis-related genes CASP10 and MMP11 were overexpressed in SDC, in accordance with the typical tumor necrosis seen in this entity. An intermediate filament protein of basal epithelial cells, cytokeratin 14 (KRT14) was clearly differently expressed between the 3 types of carcinoma, and can be used as an aid in their differential diagnosis. The array results were validated by RT-PCR and immunohistochemistry.

Clinico-pathological conference 2002

INTRODUCTION

Six cases are reported, each presented at the 11th Biennial Congress of the International Association of Oral Pathologists as an instructive case for differential diagnosis on the basis of clinical, imaging or histological features.

CLINICAL PICTURE

Case diagnoses included a large, possibly intraosseous, myofibroma presenting with an oral mass; Langerhans cell histiocytosis with facial skin lesions; an intraosseous vascular hamartoma of the maxilla with worrying radiological features; an unusual mixed radiolucency of the jaw caused by cemento-ossifying fibroma; an osteosarcoma of the posterior mandible causing a well-defined radiolucency and an intraoral squamous cell carcinoma in a child.

Effects of snuff extract on epithelial growth and differentiation in vitro

Snuff is a locally irritative agent causing hyperkeratinization and hyperplasia of the oral epithelium. The aim of the study was to investigate the effects of snuff on epithelial cell growth and differentiation in vitro. Three-dimensional HaCaT cell cultures were grown for 6, 12, 14, and 18 days in the presence of 1% snuff extract. Ki-67, p53 and cytokeratins (Cks) 5, 13, 10, 19, 18, involucrin and filaggrin were studied by means of immunohistochemistry. Ki-67 indices were assessed, and the results analyzed statistically. Marked morphologic changes were seen with advanced culture time in the snuff group, probably as a result of increased toxic effects. Snuff exposure decreased the percentage of Ki-67 positive cells on days 6, 12, and 14, suggesting that snuff does not stimulate proliferation activity in this in vitro model. Cornification-related Ck 10 decreased after snuff exposure, indicating disturbances in the epithelial differentiation process.

CD44v6 in developing, dysplastic and malignant oral epithelia

The CD44v6 adhesion molecule has been linked to progression of various carcinomas, but its role in relation to oral-cancer development is not clear. The study was designed to determine whether CD44v6 levels were clinically significant in oral dysplasias. Twenty-nine oral dysplasias were immunostained with CD44v6 antibody on follow-up. Developing normal epithelia and adult normal epithelia and oral carcinomas were stained for comparison. Oral dysplasias and carcinomas exhibited heterogenous staining patterns. No statistically significant correlation between CD44v6 expression and outcome was found for dysplasia patients. The results show that in developing and healthy oral mucosa CD44v6 is associated with epithelium-specific differentiation but in dysplasias and carcinomas it mirrors disorderly epithelial maturation. The results also suggest that determination of CD44v6 levels is not helpful in judging the likely clinical behaviour of oral dysplasia.

Different mechanisms of syndecan-1 activation through a fibroblast-growth-factor-inducible response element (FiRE) in mucosal and cutaneous wounds

Syndecan-1 expression is enhanced in cutaneous and mucosal wounds. We have previously demonstrated that wounding-induced syndecan-1 expression in the skin occurs transcriptionally, through a fibroblast-growth-factor-inducible element (FiRE). Here, we show that FiRE is also activated in mucosal wounds. However, both the expression patterns and the activation mechanisms of FiRE are different from those in the skin. In the mucosa in vivo, the activation starts and ends earlier than in cutaneous wounds. FiRE is first detected at around 12 hours in keratinocytes, and the activation declines by the third day after wounding occurs. The activation is seen on the migrating sheet of epithelial mucosa, as in the case of cutaneous wounding. In contrast to the situation in vivo, organ-cultured mucosal wounds exhibit no FiRE activity, while organ-cultured cutaneous wounds show robust activity. Activation in mucosal wounds is enhanced, however, by the application of epidermal growth factor. This suggests that exogenous growth factor activity is required for activation of syndecan-1 in mucosal wounds but not in cutaneous wounds.

A case of multiple AOT-like jawbone lesions in a young patient--a new odontogenic entity?

We assessed the immunohistochemical profile of an unusual case of multiple similarly looking tumors in the jawbone of a young patient. Histologically, the tumors exhibited features of adenomatoid odontogenic tumor (AOT) and adenomatoid dentinoma but showed no resemblance to any other defined odontogenic tumor entities. They expressed high amounts of cytokeratin (CK) 8 and 14 together with some Vimentin. A small rim of peripheral cells showed CK 5, 17, and 19 reactivity. Also, these lesions expressed some bcl-2 as well as p53 and Ki67. Histologically and immunohistochemically, the unusual multiple lesions differed in details from a simultaneously examined group of 24 classical AOT cases, suggesting that they may represent a hitherto less well-defined odontogenic tumor entity.

Gene expression profiling of ameloblastoma and human tooth germ by means of a cDNA microarray

The molecular and genetic characteristics of ameloblastoma are still poorly understood. We analyzed gene expression in fresh-frozen ameloblastomas and human fetal tooth germs, using a cDNA microarray. Thirty-four genes exhibited significant changes in expression levels in the ameloblastoma. Eleven genes were overexpressed more than three-fold, and 23 genes were underexpressed to below 0.4 of the control level. The oncogene FOS was the most overexpressed gene (from eight- to 14-fold), followed by tumor-necrosis-factor-receptor 1 (TNFRSF1A). Genes for sonic hedgehog (SHH), TNF-receptor-associated-factor 3 (TRAF3), rhoGTP-ase-activating protein 4 (ARHGAP4), deleted in colorectal carcinoma (DCC), cadherins 12 and 13 (CDH12 and 13), teratocarcinoma-derived growth-factor-1 (TDGF1), and transforming growth-factor-beta1 (TGFB1) were underexpressed in all tumors. In selected genes, a comparison between cDNA microarray and real-time RT-PCR confirmed similar relative gene expression changes. The gene expression profile identifies candidate genes that may be involved in the origination of ameloblastoma and several genes previously unidentified in relation to human tooth development.

Cell proliferation and chromosomal changes in human ameloblastoma

Cell proliferation and chromosomal imbalances, important parameters in relation to tumor progression, were studied in ameloblastoma (n=20), a benign odontogenic tumor of locally recurrent nature. Immunocytochemical staining with MIB-1 antibody and comparative genomic hybridization (CGH) were performed on formalin-fixed paraffin-embedded ameloblastomas. The mean follow-up time was 12.4 years. An MIB-1-index was formed by counting 5000 tumor-cell nuclei in 10-15 randomly chosen high-power fields and calculating percentages of positively stained cells. CGH involved hybridization of FITC-dUTP-labeled tumor DNA with Texas-red-labeled normal DNA. Images were digitally analyzed. The MIB-1-index (range 0-2.51) was low for all tumors. No statistically significant correlation between MIB-1 index and tendency to recurrence was found. Chromosomal aberrations were detected in 2 of 17 cases. The results suggest that formation of an MIB-1 index is not helpful in assessing future clinical behavior of an ameloblastoma and that chromosomal imbalances are uncommon.

The human tuftelin gene: cloning and characterization

Tuftelin has been suggested to play an important role during the development and mineralization of enamel. We isolated the full-length human tuftelin cDNA using reverse transcription-polymerase chain reaction (RT-PCR) and rapid amplification of cDNA ends (5' RACE and 3' RACE) methods. Sequence analysis of the tuftelin cDNA revealed an open reading frame of 1170 bp encoding a 390 amino acid protein with a molecular mass of 44.3 kDa and an isoelectric point of 5.7. The human tuftelin protein shares 89 and 88% amino acid sequence identity with the bovine and mouse tuftelin, respectively. It contains a coiled-coil region, recently reported to be involved with tuftelin self-assembly and with the interaction of tuftelin with TIP39 (a novel tuftelin interacting protein). Detailed DNA analysis of the cloned genomic DNA revealed that the human tuftelin gene contains 13 exons and is larger than 26 kb. Two alternatively spliced tuftelin mRNA transcripts have now been identified in the human tooth bud, one lacking exon 2, and the other lacking exon 2 and exon 3. Primer extension analysis, corroborated by RT-PCR and DNA sequencing, revealed multiple transcription initiation sites. The cloned 1.6 kb promoter region contained several GC boxes and several transcription factor binding sites such as those for activator protein 1 and stimulatory protein 1. Our blast search of the human and mouse expressed sequence tag data bases, as well as our RT-PCR and DNA sequencing results, and a previous study using Northern blot analysis revealed that tuftelin cDNA sequences are also expressed in normal and cancerous non-mineralizing soft tissues, suggesting that tuftelin has a universal function. We have now identified and characterized different alternatively spliced mouse tuftelin mRNAs in several non-mineralizing tissues. These results provide an important baseline for future understanding of the biological role of tuftelin.

The role of effectors of the activin signalling pathway, activin receptors IIA and IIB, and Smad2, in patterning of tooth development

The gene for activin βA is expressed in the early odontogenic mesenchyme of all murine teeth but mutant mice show a patterning defect where incisors and mandibular molars fail to develop but maxillary molars develop normally. In order to understand why maxillary molar tooth development can proceed in the absence of activin, we have explored the role of mediators of activin signalling in tooth development. Analysis of tooth development in activin receptor II and Smad2 mutants shows that a similar tooth phenotype to activin βA mutants can be observed. In addition, we identify a novel downstream target of activin signalling, the Iroquois-related homeobox gene, Irx1, and show that its expression in activin βA mutant embryos is lost in all tooth germs, including the maxillary molars. These results strongly suggest that other transforming growth factor β molecules are not stimulating the activin signalling pathway in the absence of activin. This was confirmed by a non-genetic approach using exogenous soluble receptors to inhibit all activin signalling in tooth development, which reproduced the genetic phenotypes. Activin, thus, has an essential role in early development of incisor and mandibular molar teeth but this pathway is not required for development of maxillary molars.

Localization of growth differentiation factor-9 (GDF-9) mRNA and protein in rat ovaries and cDNA cloning of rat GDF-9 and its novel homolog GDF-9B

Although targeted gene disruption of GDF-9, an oocyte derived growth factor, leads to an arrest of folliculogenesis and causes infertility in female mice, little is known on the expression of GDF-9 protein in the ovary. We show that GDF-9 protein is expressed in rat oocytes during folliculogenesis from the early primary follicle stage onwards but the most intensive immunostaining was seen in primary and preantral follicles. Northern blot analyses of the ontogeny of GDF-9 gene expression in postnatal rat ovaries showed that the GDF-9 transcript levels are clearly increased on the second postnatal day concomitant with the appearance of primary follicles. Interestingly, Northern blot and in situ hybridization analyses indicate a similar expression pattern for GDF-9B, the rat ortholog of a mouse GDF-9 like factor for which we recently reported the partial amino acid sequence. The polypeptide sequences deduced from isolated ovarian cDNAs indicate that the rat GDF-9 prepropeptide is 440 amino acids (aa) in length and the putative mature peptide is 135 aa whereas rat GDF-9B is 391 aa long and the mature region is 125 aa. We conclude that (1) the GDF-9 protein is highly expressed in the oocytes of primary follicles of rat ovaries suggesting that it plays a role mainly in early folliculogenesis and that (2) the full-length polypeptide sequence of GDF-9B suggests that this novel TGF-beta family member is likely to be a secreted growth factor that may regulate folliculogenesis at similar developmental stages as GDF-9.

Expression of laminin-5 in ameloblastomas and human fetal teeth

Extracellular matrix proteins have been shown to play important roles in the cell migration and differentiation in both normal and pathological conditions. In the present study, we used immunohistochemistry and in situ hybridization to determine the distribution of laminin-5 in ameloblastomas and developing human teeth. In ameloblastomas, the immunoreaction for the laminin-5 gamma2 chain was confined to the tumor cells of the peripheral area. The staining reaction was variable, being mostly weak and fragmented in the basement membrane structures surrounding the neoplastic islands. Some peripheral epithelial cells and some invading small ameloblastoma cell islands showed intense intracellular staining for the gamma2 chain. Tumor cells in the proliferating areas of ameloblastomas expressed gamma2 chain mRNA. The laminin-5 gamma2 chain was located beneath the dental lamina and in the outer, but not in the inner, enamel epithelium of the developing teeth. During the early hard tissue apposition stage, intense staining for the gamma2 chain was confined to ameloblasts, which also gave a strong signal for gamma2 chain mRNA. These results suggest that laminin-5 may contribute to the infiltrative and progressive growing potential of ameloblastomas. During human tooth development, however, laminin-5 may participate in the terminal differentiation of ameloblasts and in enamel matrix formation.

Activin and bone morphogenetic protein (BMP) signalling during tooth development

Activins and bone morphogenetic proteins (BMPs) belong to the transforming growth factor-beta (TGF-beta) superfamily of structurally related cytokines. Results of recent in vivo and in vitro studies suggest that activin A, several BMPs, and their cell surface receptors may participate in tooth development. In addition, follistatin an extracellular protein that may interact with activin and BMP signaling, appears to be involved. This review focuses on recent advances in relation to the roles of activin/BMP receptors, their ligands and extracellular modifiers during tooth development.

An open clinical trial of a new mouth-PUVA variant in the treatment of oral lichenoid lesions

OBJECTIVE

To investigate the feasibility of topical psoralen PUVA (sensitization in photosensitizing psoralen drug + UVA radiation) treatment of oral lichenoid lesions (OLL).

STUDY DESIGN

A total of 16 patients with OLL were treated using a 0.01% trioxsalen ointment and UVA doses in the 0.09 to 1.80 J/cm2 range. The average number of sessions was 8.7 and a mean cumulative irradiation dose was 4.25 J/cm2.

RESULTS

A marked-to-complete healing occurred in 3 to 16 (19%) patients immediately after therapy, in 4 of 14 (29%) after 3 months, and in 5 of 14 (38%) after 14 months, respectively. Of the 16 subjects with OLL, five were diagnosed as oral lichen planus (OLP) and 11 were classified as oral lichenoid reaction (OLR). Post-PUVA amelioration rate in patients with genuine OLP (4 of 5, 80%) was superior to that in patients with OLR (1 of 9, 11%).

CONCLUSION

Topical trioxsalen photosensitization can be used in mouth-PUVA treatment, and lichen planus is a main indication for this therapy.

The activin-binding protein follistatin is expressed in developing murine molar and induces odontoblast-like cell differentiation in vitro

It has recently been shown that mice deficient in activin-beta A subunits and follistatin exhibit major defects in dentition. To increase understanding of the roles played by these molecules during tooth development, we determined the temporospatial expression of activin-beta A subunit and follistatin messenger RNA and their corresponding proteins in developing murine molars (between day E 14 and 2 days after birth). The effects of recombinant human activin A and its binding protein follistatin on odontoblast differentiation were also studied in cultures of dental papillae (DP) isolated from the mandibular first molars of E-17-day mice. In situ hybridization indicated that transcripts for activin-beta A subunit were abundant in pre-odontoblasts at the tips of forming cusps prior to odontoblast terminal differentiation, and transcripts for follistatin in overlying inner enamel epithelial cells (pre-ameloblasts). Pre-odontoblasts were also weakly immunoreactive in relation to activin-beta A subunit, pre-ameloblasts in relation to follistatin. When follistatin was added at different concentrations to a DP culture model (2-14 nmol/DP) together with heparin at constant concentration, differentiation of odontoblast-like cells was induced, as evidenced by polarization and deposition of extracellular matrix in vitro, to extents depending on the follistatin concentration. In contrast, the addition of activin A (2 nmol/DP) had no effect on the differentiation parameters studied. These findings suggest that the activin-follistatin system regulates odontoblast differentiation during tooth development. In particular, we suggest that binding of endogenous activin A by follistatin may allow odontoblast terminal differentiation to occur.

Effect of snuff and smoking on tenascin expression in oral mucosa

We have shown, by using two monoclonal antibodies (143DB7 and 100EB2), that the expression of the extracellular matrix protein tenascin (Tn) is increased in the connective tissue of biopsies taken from snuff users' and tobacco smokers' oral mucosa. In normal oral mucosa Tn was seen to underlie the epithelium as a thin delicate band. The most increase in Tn reaction was observed in snuff users' mucosa while the immunoreaction in smokers' mucosa was less conspicuous. Often the most prominent Tn reaction took place in association with round cell inflammatory infiltration, indicating epithelial irritation. Tn has been shown to take part in epithelial-mesenchymal interactions during embryogenesis, wound healing and tumorigenesis. Here, a superficial epithelial irritant has been shown to cause conspicuous alterations not only in the epithelial cell layers but also in the underlying connective tissue by increasing its Tn content. As a result of our findings we suggest a further link for Tn in a dynamic epithelial-mesenchymal interplay by virtue of this marked connective tissue reaction in snuff users' and smokers' oral mucosa.

Effect of snuff on cytokeratin expression in oral vestibular sulcus epithelium

Differences in the expression of cytokeratins (CK) in specimens obtained from snuff-affected oral epithelium of the maxillary vestibular sulcus and clinically normal sulcular epithelium were studied by indirect immunofluorescence staining with a panel of monoclonal antibodies (MAbs). CK 14, a marker of stratified squamous epithelium was not seen expressed in 3/11 of the snuff user's specimens. Terminal differentiation markers, typical of cornified epithelia (CK 1, 9, 10 and 11), were detected suprabasally in the snuff user's keratosis but not in the normal control epithelium. The use of snuff seemed to change the CK staining pattern of the mucosa so that it resembles more that of a cornified type of epithelium. Simple epithelial-type CK were included in the study in order to establish the CK profile of the snuff-induced keratosis, for comparison with normal and dysplastic lesions. MAb to CK 7 and 19 showed reactivity in the basal cells and suprabasally whereas the monospecific MAb anti-CK 7 showed suprabasal staining both in the control and affected epithelia. By using MAbs, we found no immunoreactivity against CK 18 either in normal or affected epithelia, whereas we found suprabasal reaction (5/11) against CK 8 in the snuff user's epithelia. The two MAbs demonstrating the expression of CK 19, normally confined to the basal cells of the stratified squamous epithelium, showed variable patterns of expression both in basal cells and suprabasally in the snuff lesions. The results show that use of oral snuff causes some alterations in the CK expression pattern of the affected epithelium. Whether the alterations are indicative of a premalignant change is, however, uncertain. The results encourage further studies on the subject.

Expression of basement membrane type IV collagen and type IV collagenases (MMP-2 and MMP-9) in human fetal teeth

Formation and degradation of dental basement membrane (BM) are important for tooth development. Data on the expression of genes for type IV collagen (the major structural component of the BM) and type IV collagenases [MMP-2 (72 kDa) and MMP-9 (92 kDa)], enzymes that degrade type IV collagen during human tooth development, are lacking. We studied expression of type IV collagen and the MMP-2 and MMP-9 in human fetal teeth (from the 13th to the 20th gestational weeks, covering cap stage through early hard tissue formation). During cap and bell stages, in situ hybridization located transcripts for alpha 1 type IV collagen chain in the fibroblasts surrounding the enamel organ. No alpha 1 type IV collagen chain mRNA was detected in tooth germ epithelium or dental papilla. However, type IV collagen immunoreactivity was observed in BM underlying the dental epithelium up to the appositional stage. Transcripts for MMP-2 were located mostly in the cells of the dental papilla and follicle. Transient expression of MMP-2 mRNA was observed in the inner enamel epithelium of late cap/early bell-stage teeth. During early apposition, a high level of MMP-2 was confined to secretory odontoblasts. Transcripts for MMP-9 were detected by the sensitive reverse-transcription polymerase chain reaction (RT-PCR) in developing teeth. Thus, in dental BM, alpha 1 type IV collagen chain may be of mesenchymal cell origin. Further, MMP-2 but not MMP-9 may participate in remodeling and degradation of BM during human tooth morphogenesis.

Stage-specific expression of decapentaplegic-Vg-related genes 2, 4, and 6 (bone morphogenetic proteins 2, 4, and 6) during human tooth morphogenesis

Members of the decapentaplegic-Vg-related (DVR) gene family are diffusible signaling molecules regulating inductive tissue interactions during vertebrate development. Expression of DVR/bone morphogenetic protein (BMP) 2, 4, and 6 was studied in human fetal teeth. Sequential morphogenetic stage-specific studies of DVR/BMP 2 and 4 mRNA expression by in situ hybridization revealed transcripts for DVR/BMP 4 during compaction of the dental mesenchyme. In contrast, DVR/BMP 2 mRNA appeared later during tooth development and was located in differentiated cells (odontoblasts). These results were confirmed by reverse-transcription polymerase chain reaction (RT-PCR), which detected DVR/BMP 2 and 4 mRNA in human tooth-germ samples. DVR/BMP 6 protein was distributed in the early dental epithelium and, later, in pre-odontoblasts and odontoblasts, where it remained during dentin formation. These results suggest that DVR/BMP 4 is involved in the early tooth morphogenesis. DVR/BMP 6 may, in particular, be implicated in epithelial-mesenchymal interactions controlling cytodifferentiation. DVR/BMP 2 and 6 may also be involved in odontoblast secretory function. The results suggest that members of the DVR gene family may play regulatory roles during human tooth development.

EGF receptor and its ligands, EGF and TGF-alpha, in developing and neoplastic human odontogenic tissues

Epidermal growth factor (EGF) and transforming growth factor-alpha (TGF-alpha) regulate cell proliferation and functional maturation through the EGF receptor (EGF-R). Their roles in human tooth development and odontogenic tumorigenesis have not been explored. We studied the expression of EGF, TGF-alpha and EGF-R in human fetal teeth (cap stage to early hard tissue formation) and various odontogenic tumors. EGF-R mRNA and immunoreactive cells were mostly located in odontogenic epithelium. EGF-R expression was subject to temporospatial variation at different stages of tooth development. EGF and TGF-alpha mRNAs were detected in fetal teeth only by the reverse transcription polymerase chain reaction (RT-PCR). However, EGF and TGF-alpha immunoreactive cells were demonstrated in epithelial elements of tooth germ, suggesting that the peptides partially originate from non-odontogenic sources. In odontogenic tumors, EGF-R mRNA and immunoreactivity were confined to neoplastic epithelium. Transcripts for TGF-alpha but not for EGF were detected in tumors of odontogenic epithelial, epithelial-ectomesenchymal and ectomesenchymal origins. It is concluded that regulation of EGF-R expression is developmentally regulated in human odontogenesis. Furthermore, the odontogenic epithelium is the main target tissue for both EGF and TGF-alpha during tooth development. TGF-alpha and its receptor may also be involved in odontogenic tumorigenesis.

Inhibin/activin subunit mRNA expression in human granulosa-luteal cells

We studied the expression of inhibin/activin subunit mRNAs in granulosa-luteal cells of preovulatory ovarian follicles obtained from women undergoing in vitro fertilization, and in corpus luteum tissue samples of early pregnancy. Northern analysis of granulosa-luteal cell and corpus luteum RNA with single-stranded cDNA or cRNA probes revealed an 1.6-kb mRNA for the alpha subunit and about 6.0-, 4.0-, 2.8-, and 1.7-kb transcripts for the beta A subunit. No clear hybridization signal for the beta B subunit could be detected. The relative expression levels of alpha and beta A subunit mRNAs were determined at 2-day intervals in granulosa-luteal cells cultured for 5 to 11 days. The levels of alpha subunit mRNAs declined steadily with increasing culture age, whereas those of beta A remained unchanged. Reverse transcription-polymerase chain reaction analysis with 35 amplification cycles confirmed the expression of alpha and beta A subunit mRNAs in cultured granulosa-luteal cells. The beta B transcripts were also weakly detectable by this sensitive assay. In situ hybridization of human early pregnancy corpus luteum revealed intense hybridization with the alpha cRNA probe and a weaker signal for the beta A subunit in the granulosa cell compartment. We conclude that: (1) the inhibin alpha and beta A subunits (and to a lesser extent beta B) are expressed in cultured human granulosa-luteal cells; (2) during extended culture periods the alpha/beta A mRNA expression ratio decreases; and that (3) the alpha and beta A subunit mRNA expression is observed in the granulosa cell compartment of early pregnancy corpora lutea.