Maintenance of cell-type-specific cytoskeletal character in epithelial cells out of epithelial context: cytokeratins and other cytoskeletal proteins in the rests of Malassez of the periodontal ligament

The ameliorating role of epithelial cell rests of Malassez in the alleviation of experimentally-induced periodontitis in rats

OBJECTIVE

The present study aimed to investigate the effect of experimentally-induced periodontitis on epithelial cell rests of Malassez (ERM) distribution and its subsequent role in regenerating periodontal ligament (PDL).

DESIGN

The study included 60 rats, aged seven months, randomly and equally divided into two groups: Group I, the control group, and Group II, the experimental group, in which ligature-periodontitis was induced. Ten rats from each group were euthanized at 1, 2, and 4 weeks. For ERM detection, specimens were processed for histological and immunohistochemical examination of cytokeratin-14. Additionally, specimens were prepared for the transmission electron microscope.

RESULTS

Group I demonstrated well-organized PDL fibers with few ERM clumps close to the cervical root portion. In contrast, one week after periodontitis induction, Group II showed marked degeneration, a damaged cluster of ERM cells, narrowing of the PDL space, and early signs of PDL hyalinization. After two weeks, a disorganized PDL was observed with the detection of small ERM clumps enclosing very few cells. After four weeks, PDL fibers were reorganized, and ERM clusters increased significantly. Notably, ERM cells were positive for CK14 in all groups.

CONCLUSION

Early-stage ERM may be affected by periodontitis. However, ERM is capable of recovering its putative role in PDL maintenance.

Localized juvenile spongiotic gingival hyperplasia: Microscopic variations and proposed change to nomenclature

OBJECTIVES

Localized juvenile spongiotic gingival hyperplasia (LJSGH) is a recently described entity with distinct manifestations. Herein we report a comprehensive histopathologic study of 21 lesions and a literature review. Additionally, we propose a new term that we consider more appropriate.

STUDY DESIGN

LJSGH cases were retrieved and their clinicopathologic characteristics were assessed. A review of all pertinent literature was also conducted.

RESULTS

Eighteen patients with LJSGH (21 biopsied lesions) were identified. Microscopically, surface morphology was classified into exophytic/papillary, flat, and micropapillary (8, 7, and 6 lesions, respectively). Cases with parakeratinization (n = 9), no prominent spongiosis (n = 5), or epithelial atrophy (n = 4) were recorded. Increased vascularity, mixed inflammation with exocytosis, and cytokeratin-19 positivity were uniformly observed. Less frequent findings included pseudoepitheliomatous hyperplasia (n = 8), bacterial colonies (n = 5), acantholysis (n = 3), and dystrophic calcifications (n = 2). The literature review disclosed 201 patients with a mean age of 14.8 years (range, 3-72; 13.6% affecting adults), similar sex distribution (103:98, female:male), and predominance of the anterior maxilla (≈ 80%). Eighteen cases were multifocal (≈ 10%).

CONCLUSIONS

Our data suggest that the terminology could be modified, because LJSGH may be multifocal, affect older individuals, or exhibit epithelial atrophy, and the entity's odontogenic origin (as highlighted by the histopathologic and immunohistochemical findings) needs to be emphasized.

Transcriptome analysis of ankylosed primary molars with infraocclusion

Primary molar ankylosis with infraocclusion can retard dental arch development and cause dental asymmetry. Despite its widespread prevalence, little is known about its molecular etiology and pathogenesis. To address this, RNA sequencing was used to generate transcriptomes of furcal bone from infraoccluded (n = 7) and non-infraoccluded (n = 9) primary second molars, all without succeeding biscuspids. Of the 18 529 expressed genes, 432 (2.3%) genes were differentially expressed between the two groups (false discovery rate < 0.05). Hierarchical clustering and principal component analysis showed clear separation in gene expression between infraoccluded and non-infraoccluded samples. Pathway analyses indicated that molar ankylosis is associated with the expression of genes consistent with the cellular inflammatory response and epithelial cell turnover. Independent validation using six expressed genes by immunohistochemical analysis demonstrated that the corresponding proteins are strongly expressed in the developing molar tooth germ, in particular the dental follicle and inner enamel epithelium. The descendants of these structures include the periodontal ligament, cementum, bone and epithelial rests of Malassez; tissues that are central to the ankylotic process. We therefore propose that ankylosis involves an increased inflammatory response associated with disruptions to the developmental remnants of the dental follicle and epithelial rests of Malassez.

A Review of the Epithelial Cell Rests of Malassez on the Bicentennial of Their Description

The epithelial cell rests of Malassez (ERM) were first described in 1817, yet their significance has remained an enigma for more than 200 years. Given their embryological origins and persistence in adult periodontal tissue, recent research has investigated whether the ERM could be useful as stem cells to regenerate tissues lost as a consequence of periodontitis. The objective of this review is to describe results of studies that have vigorously investigated the functional capabilities of ERM, particularly with regard to periodontal ligament homeostasis and prevention of dentoalveolar ankylosis. The significance of the ERM relative to evolution of the dental attachment apparatus will be examined. The current status of use of ERM as stem cells for dental tissue engineering and in other applications will be reviewed.

Are Cementoblasts a Subpopulation of Osteoblasts or a Unique Phenotype?

Experimental studies have shown a great potential for periodontal regeneration. The limitations of periodontal regeneration largely depend on the regenerative potential at the root surface. Cellular intrinsic fiber cementum (CIFC), so-called bone-like tissue, may form instead of the desired acellular extrinsic fiber cementum (AEFC), and the interfacial tissue bonding may be weak. The periodontal ligament harbors progenitor cells that can differentiate into periodontal ligament fibroblasts, osteoblasts, and cementoblasts, but their precise location is unknown. It is also not known whether osteoblasts and cementoblasts arise from a common precursor cell line, or whether distinct precursor cell lines exist. Thus, there is limited knowledge about how cell diversity evolves in the space between the developing root and the alveolar bone. This review supports the hypothesis that AEFC is a unique tissue, while CIFC and bone share some similarities. Morphologically, functionally, and biochemically, however, CIFC is distinctly different from any bone type. There are several lines of evidence to propose that cementoblasts that produce both AEFC and CIFC are unique phenotypes that are unrelated to osteoblasts. Cementum attachment protein appears to be cementum-specific, and the expression of two proteoglycans, fibromodulin and lumican, appears to be stronger in CIFC than in bone. A theory is presented that may help explain how cell diversity evolves in the periodontal ligament. It proposes that Hertwig’s epithelial root sheath and cells derived from it play an essential role in the development and maintenance of the periodontium. The role of enamel matrix proteins in cementoblast and osteoblast differentiation and their potential use for tissue engineering are discussed.

Expression of cytokeratins in enamel organ, junctional epithelium and epithelial cell rests of Malassez

BACKGROUND AND OBJECTIVE

After tooth formation is complete, it is suggested that continuity exists between the epithelial cell rests of Malassez (ERM), reduced enamel epithelium (REE) and subsequently the junctional epithelium. However, the junctional epithelium was reported to differ from REE and ERM. The developmental relationships between and among them remain controversial. Therefore, in the present study we examined the expression of cytokeratins in the three types of epithelia to investigate the epithelial phenotypes.

MATERIAL AND METHODS

The maxillae of Wistar rats, 1, 2, 3 and 7 wk of age, were used, and the expression of CK14, CK17, CK19, CK10/CK13 and AE1/AE3 was detected using immunoperoxidase techniques.

RESULTS

There was negative staining for CK10/CK13 in all the epithelia. ERM stained strongly for AE1/AE3, CK14, CK17 and CK19. During the transformation of inner enamel epithelial (IEE) cells into reduced ameloblasts and subsequently into junctional epithelium, strong staining for CK14 was evident in IEE, REE and junctional epithelium, whereas the expression of AE1/AE3 and of CK19 were initially negative in IEE and then strong in REE and junctional epithelium, respectively. In particular, the expression of CK17 was strongly positive in ERM and REE, but was negative in IEE and junctional epithelium.

CONCLUSION

ERM are of odontogenic origin and junctional epithelium has an epithelial phenotype different from REE and ERM. This is the first report to demonstrate that CK17 can be used as a marker to distinguish junctional epithelium from ERM.

Oxytalan-positive peripheral ossifying fibromas express runt-related transcription factor 2, bone morphogenetic protein-2, and cementum attachment protein. An immunohistochemical study

BACKGROUND

The peripheral ossifying fibroma (POF) represents one of the most common lesions of the periodontal tissues that may originate from the gingival soft tissues, the periosteum, or the periodontal ligament.

AIM

To investigate the immunohistochemical expression of runt-related transcription factor 2 (Runx-2), bone morphogenetic protein-2 (BMP-2), and cementum attachment protein (CAP) in oxytalan-positive POF, to establish the use of POF as an in vivo model for the study of the periodontal ligament.

MATERIALS AND METHODS

Thirty tumors that presented clinical and histologic features of POF, as well as oxytalan fibers, were included in the study. Immunohistochemical expression of Runx-2, BMP-2, and CAP was evaluated by light microscopy.

RESULTS

Runx-2, BMP-2, and CAP were abundantly expressed by POFs; 22 of 30 tumors expressed positive staining for Runx-2, twenty-six tumors for BMP-2, and twenty-five tumors for CAP. The expression of Runx-2 was abundant in POFs where bone was histologically present (P = 0.04) and of BMP-2 in POFs where dystrophic calcifications were present (P = 0.03).

CONCLUSION

It is suggested that oxytalan-positive POFs, purportedly originating from the periodontal ligament, express molecules that are specific to bone and cementum (Runx-2, BMP-2), or cementum only (CAP). Thus, the cell populations present in the lesion belong to the mineralized-tissue-forming cell lineages, the cementoblastic or osteoblastic lineage.

Reactions of periodontal ligament epithelial cell clusters and OX6-immunopositive cells to experimental tooth movement and periodontitis

BACKGROUND AND OBJECTIVE

The aim of this study was to investigate reactions of periodontal ligament epithelial cell clusters and major histocompatibility complex class II (OX6)-immunopositive cells to simultaneously induced tooth movement and periodontitis employing Waldo's method.

MATERIAL AND METHODS

Elastic gums were inserted between the right upper first and second molars of rats. Animals were killed by intracardiac perfusion on days 1, 3, 7 and 14 after the experimental procedures, and maxillary molars were decalcified and processed for OCT compound. Cytokeratin and OX6 antibodies to detect epithelial and immunocompetent cells were used for double-fluorescence immunohistochemistry. Immunostained sections of rat upper molar regions were examined with a fluorescence microscope.

RESULTS

Large periodontal ligament epithelial cell clusters appeared and became contiguous with each other, and OX6-immunopositive cells surrounded the clusters over time in the periodontal ligament near the gum insertion site. In the periodontal ligament distant from the gum insertion site, epithelial cell clusters and OX6-immunopositive cells were scattered. After 14 d, thickened epithelium and elongated rete pegs were found close to large epithelial cell clusters in the periodontal ligament near the gum insertion site.

CONCLUSION

These findings suggest proliferation and/or aggregation of periodontal ligament epithelial cells, and interaction between OX6-immunopositive cells and the periodontal ligament epithelial cells, in response to tooth movement and periodontal inflammation. This method may be a useful experimental model to elucidate the relationship between rete pegs and periodontal ligament epithelial cell clusters in inflammatory conditions.

Distribution of epithelial cells and their relationship to immunocompetent cells in rat molars: a confocal and transmission electron microscope study

This study sought to investigate the distribution of cytokeratin (CK)-immunopositive cells and their relationship to immunocompetent ED1- and OX6-immunopositive cells in rat periodontium by immunohistochemistry and electron microscopy. CK-immunopositive cells were generally distributed along the surface of the tooth root. They could also be found between root dentin and cementum, in the perivascular space, and close to or in the alveolar bone lacunae. ED1-immunopositive cells exhibited a compact shape with small processes and were widely distributed in the periodontium. Few sections demonstrated an intimate relationship between the CK- and ED1-immunopositive cells close to the cementum, in the perivascular space, and close to or in the alveolar bone. Numerous OX6-immunopositive cells with long branching processes were widely distributed in the periodontal ligament, surrounding and holding CK-immunopositive cells in the cell clusters, close to the cementum. Transmission electron microscopy revealed OX6-immunopositive cells that extended their cytoplasmic processes, which contained vesicles and occasionally lysosomes in between the epithelial cells. This study demonstrates the close relationship between the epithelial cells and the immunocompetent cells in a rat periodontium, indicating a functional interrelationship. It is possible that in a non-inflammatory periodontium, the epithelial cells act not independently, but through interaction with immunocompetent cells.

Odontogenic keratocysts arise from quiescent epithelial rests and are associated with deregulated hedgehog signaling in mice and humans

Odontogenic keratocysts in humans are aggressive, noninflammatory jaw cysts that may harbor PTCH1 mutations, leading to constitutive activity of the embryonic Hedgehog (Hh) signaling pathway. We show here that epithelial expression of the Hh transcriptional effector Gli2 is sufficient for highly penetrant keratocyst development in transgenic mice. Mouse and human keratocysts expressed similar markers, leading to tooth misalignment, bone remodeling, and craniofacial abnormalities. We detected Hh target gene expression in epithelial cells lining keratocysts from both species, implicating deregulated Hh signaling in their development. Most mouse keratocysts arose from rests of Malassez--quiescent, residual embryonic epithelial cells that remain embedded in the periodontal ligament surrounding mature teeth. In Gli2-expressing mice, these rests were stimulated to proliferate, stratify, and form a differentiated squamous epithelium. The frequent development of keratocysts in Gli2-expressing mice supports the idea that GLI transcription factor activity mediates pathological responses to deregulated Hh signaling in humans. Moreover, Gli2-mediated reactivation of quiescent epithelial rests to form keratocysts indicates that these cells retain the capacity to function as progenitor cells on activation by an appropriate developmental signal.

The epithelial cell rests of Malassez--a role in periodontal regeneration?

This article reviews general aspects about the epithelial cell rests of Malassez (ERM). The historical and general morphological features of the ERM are briefly described. The embryological derivation of the ERM is presented as an important consideration in understanding the events associated with their origin and possible functional roles within the periodontal ligament. The ultrastructural description of the ERM is also included to complement the morphological characteristics which distinguish these cells as the unique epithelial element of the periodontal ligament. The unique ability of these cells to synthesize and secrete a number of proteins usually associated with cells of mesenchymal origin, rather than ectodermal origin, is discussed in light of their role in cementum repair and regeneration. Such considerations lead to our hypothesis that one of the functional roles of the ERM may lie not only their role in maintaining and contributing to the normal periodontal cellular elements and function but also contributing, in a significant manner, to periodontal regeneration.

Production of osteopontin by cultured porcine epithelial cell rests of Malassez

BACKGROUND

The epithelial cell rests of Malassez (ERM) are derived from Hertwig's epithelial root sheath (HERS). During development the cells of HERS deposit a variety of molecules on the newly forming root surface. The possibility that ERM retain this potential after root development is completed and secrete bone or cementum-related proteins needs to be investigated. The purpose of this study was to determine the expression of the non-collagenous proteins osteopontin (OPN) and bone sialoprotein (BSP) by cells derived from the epithelial cell rests of porcine periodontium.

METHODS

ERM and fibroblasts were cultured from porcine periodontal ligament. The cells were identified and characterized using transmission electron microscopy, immunohistochemistry, western blot analysis of proteins, reverse transcription-polymerase chain reaction and ability to form mineralized nodules in culture. In particular the expression of the mineralized tissue-related proteins, BSP and OPN, was studied.

RESULTS

Cells from porcine periodontal ligaments were successfully cultured; separated and characterized as being of either an epithelial or fibroblastic phenotype. Although the ERM did not form mineralized nodules in culture, they did express a significant amount of mRNA for OPN.

CONCLUSION

The results from this study provide evidence that ERM express mRNA for at least one bone/cementum-related protein. Whether this function would be consistent with a role for ERM in tissue formation, inflammation and regeneration remains to be established.

Immunohistochemical localization of insulin-like growth factor-II and its binding protein-6 in human epithelial cells of Malassez

So-called epithelial rests of Malassez are derived from the Hertwig's root sheath and are located in the periodontal ligament, with still unknown functions. Different pathological conditions may lead to proliferation of these otherwise non-proliferative cell clusters. The insulin-like growth factor (IGF) system is an important growth factor system controlling proliferation and differentiation. In our study on Malassez cells from extracted human deciduous teeth, we investigated their structure by means of light and electron microscopy. Although they appeared as cellular clusters with a uniform epithelial phenotype, immunohistochemical analyses of components of the IGF system revealed an unique pattern: weak immunoreactivity could be seen for IGF-II while among all IGF binding proteins (IGFBPs) only IGFBP-6 and weakly IGFBP-4 were detectable in epithelial cells of Malassez. Since IGFBP-6 has a very high affinity for IGF-II and can inhibit its functions, we discuss that, in the normal periodontal ligament, autocrine IGFBP-6 may function as an antiproliferative molecule suppressing mitogenic effects of IGFs on Malassez cells.

Tight junctions and compositionally related junctional structures in mammalian stratified epithelia and cell cultures derived therefrom

The occurrence of extended tight junction (TJ) structures, including zonulae occludentes (ZO), and the spatial arrangement of TJ proteins in stratified mammalian epithelia has long been controversially discussed. Therefore, we have systematically examined the localization of TJ proteins in diverse stratified epithelial tissues (e.g., epidermis, heel pad, snout, gingiva, tongue, esophagus, exocervix, vagina, urothelium, cornea) of various species (human, bovine, rodents) as well as in human cell culture lines derived from stratified epithelia, by electron microscopy as well as by immunocytochemistry at both the light and the electron microscopic level, using antibodies to TJ proteins such as occludin, claudins 1 and 4, protein ZO-1, cingulin and symplekin. We have found an unexpected diversity of TJ-related structures of which only those showing colocalization with the most restricted transmembrane TJ marker protein, occludin, are presented here. While in epidermis and urothelium occludin is restricted to the uppermost living cell layer, TJ-related junctions are abundant in the upper third or even in the majority of the suprabasal cell layers in other stratified epithelia. Interfollicular epidermis contains, in the stratum granulosum, extended, probably continuous ZO-like structures which can also be traced at least through the Henle cell layer of hair follicles. Similar apical ZO-like structures have been seen in the upper living cell layers of all other stratified epithelia and cell cultures examined, but in most of them we have noticed, in addition, junctional regions showing relatively broad, ribbon-like membrane contacts which in cross-section often appear pentalaminar, with an electron-dense middle lamella ("lamellated TJs", coniunctiones laminosae). In suprabasal layers of several stratified epithelia we have further observed TJ protein-containing junctions of variable sizes which are characterized by a 10-30-nm dense lamina interposed between the two membranes ("sandwich junctions"; iuncturae structae). Moreover, we have often observed variously sized regions in which the intermembrane distance is rather regularly bridged by short rod-like elements ("cross-bridged cell walls"; parietes transtillati), often in close vicinity of TJ-related structures or desmosomes. The significance of these structures and their possible biological importance are discussed.

Cytokeratin expression patterns in jaw cyst linings with metaplastic epithelium

BACKGROUND

Cytokeratin (CK) expression patterns have been studied in numerous intact and diseased oral tissues. However, CK expression in metaplastic squamous cells has not been explored in depth and the origin of metaplastic epithelial linings of the jaw cysts has not been sufficiently investigated.

METHODS

We examined CK expression in 46 postoperative maxillary cysts (POMCs) which were lined with pseudostratified columnar cells only, columnar and squamous cells, and squamous cells only, in 13, 30 and 3 cases, respectively.

RESULTS

The expression of CK8, CK13 and CK18 were observed in 39, 9 and all 43 of the columnar epithelial linings, respectively. Metaplastic squamous epithelia expressed more CK13, and less CK18 and CK8. Of the 33 metaplastic linings, 24 expressed CK8, 23 CK13 and 26 linings expressed CK18. The patterns of expression of CK13 and CK18 observed were CK18(+)-CK13(-) in 10 metaplastic linings, CK18(+)-CK13(+) in 16, and CK18(-)-CK13(+) in 7. The expression of CK13- and CK18-mRNA was generally correlated with level of protein expressed. CK18-mRNA expression was observed by in situ hybridization, not only in the 26 metaplastic linings which were positive for CK18 protein, but also in five of the seven metaplastic linings which did not express CK18 protein. In addition, RT-PCR revealed an expression of CK18-mRNA in all metaplastic squamous linings, although the expression level was weaker than that in the columnar epithelial linings. The CK13-mRNA was expressed inversely to the CK18-mRNA.

CONCLUSIONS

These results indicate that CK18-mRNA is preserved through metaplasia, although the protein expression decreased. Metaplastic squamous cells differentiate with a decrease of CK18 and an increase of CK13 expression.

Expression of cytokeratins (CKs) 8, 13 and 18 and their mRNA in epithelial linings of radicular cysts: implication for the same CK profiles as nasal columnar epithelium in squamous epithelial lining

OBJECTIVE

Our objective was to specify cytokeratin (CK) patterns in lining epithelia of radicular cysts which are sometime lined with ciliated columnar epithelia as seen in the nasal epithelia.

MATERIALS AND METHODS

We examined the CK expression in 52 radicular cysts obtained from 32 maxillary and 20 mandibular lesions and investigated CK-mRNA expression using in situ hybridization in 24 maxillary and 13 mandibular cysts and reverse transcription-polymerase chain reaction (RT-PCR) in 24 maxillary cysts.

RESULTS

Of the maxillary cysts, 20, 29 and 19 squamous epithelial linings were positive for CK8, CK13 and CK18, respectively; of the mandibular cysts, 10, 20 and 11 linings were positive for these CKs, respectively. The expression patterns of CK18(+)-CK13(-), CK18(+)-CK13(+) and CK18(-)-CK13(+) were observed in 3, 16 and 13 linings of the maxillary cysts and 0, 11 and 9 linings of the mandibular cysts, respectively. In situ hybridization revealed the expression of CK18-mRNA in 9 and 4 linings of 24 maxillary and 13 mandibular cysts examined, respectively. With RT-PCR, we explored that both CK18- and CK13-mRNA were expressed not only in the normal nasal and gingival epithelia but also in the examined maxillary cyst linings although their expression levels differed correlating with the difference in CK staining.

CONCLUSION

It is concluded that CK13- and CK18-mRNA are constitutively expressed in columnar and squamous epithelial cells, respectively, and that the variant CK expression patterns with CK18-mRNA expression in maxillary radicular cysts are indicative of the possibility of phenotypic transformation in the cyst linings.

Identification of tuftelin- and amelogenin-interacting proteins using the yeast two-hybrid system

Biomineralization of enamel is a complex process that involves the eventual replacement of an extracellular protein matrix by hydroxyapatite crystallites. To date four different enamel matrix proteins have been identified; the amelogenins, tuftelin, enamelin and ameloblastin. Assembly of the enamel extracellular matrix from these component proteins is believed to be critical in producing a matrix competent to undergo mineral replacement. Enamel formation is a complex process and additional proteins are likely to have a role in the assembly of the extracellular matrix. In order to identify additional proteins involved in the assembly process, the yeast two-hybrid system developed by Fields and Song (1989) has been implemented. This system allows for the identification of unknown proteins that interact with proteins of interest. Typically a known protein is used as "bait" to screen a cDNA expression library of interest. In our studies, tuftelin or amelogenin have been used to screen a mouse tooth library produced from one day old pups. A library screening of six million clones with amelogenin as bait resulted in eleven positive clones all of which show high homology to the human leukocyte antigen-B (HLA-B) associated transcript (BAT) family of genes. A library screening of one million clones using tuftelin as the bait identified twenty-one tuftelin-interacting proteins. Ten of these proteins are either keratin K5 or keratin K6, four are constitutively expressed and the remaining seven are novel. Further characterization of the proteins shown to interact with amelogenin or tuftelin may shed additional light on this complex process of enamel matrix assembly.

Morphological variation in the tyrosine receptor kinase A-immunoreactive periodontal ligament epithelium of developing and mature rats

Tyrosine receptor kinase A (trkA) is the high-affinity receptor for nerve growth factor. It has been found in several non-neuronal cell types, indicating biological roles independent of neural function, as well as in the nervous system. An initial study demonstrated that an antibody to the full extracellular domain did not label periodontal ligament epithelium (PLE; also known as epithelial rests of Malassez), but that another antibody which recognises a truncated 41-kDa form of trkA did label PLE. Thus, truncated trkA-immunoreactive (-IR) PLE was further investigated here in developing molars of young rats, and in its mature form in adult rat molars, for its reaction to moderate or deep molar injuries, and for its appearance along the continuously erupting incisors of mature rats. In some of the adult rat molars we also analysed the association of nerve fibres with PLE using antibodies for p75 neurotrophin receptor or peripherin. Rat jaws were fixed with 4% formaldehyde and demineralised, and bound antibody was detected with avidin-biotin-peroxidase and diaminobenzidine or fluorescence procedures. Light microscopy showed great variation in the appearance of trkA-IR PLE and considerable morphological changes during the eruption of molars and incisors. By electron microscopy it was shown that trkA-IR was not uniformly distributed in PLE cells but rather was concentrated in the peripheral zones of each cell cluster. Tooth injury did not influence the form or occurrence of PLE unless there was specific destruction of a ligament region. Qualitative analyses of nerve fibres showed that they only rarely innervated PLE in adult rats, indicating that the truncated receptor has non-neuronal functions in this epithelium. These results suggest that neurotrophin growth factors, acting via truncated trkA receptors, affect the interactions between PLE cells and the periodontal ligament, with fewer PLE interactions with nerves. Furthermore, the expression of these receptors on PLE supports the possibility that these cells are active during tooth development and eruption rather than being merely passive remnants of the degenerating tooth sheath. The similar trkA-IR of PLE and junctional epithelium, as well as their structural association, suggests interactions between these two epithelia.

Delayed eruption of permanent teeth in hyperimmunoglobulinemia E recurrent infection syndrome

OBJECTIVE

To determine the incidence of abnormal tooth eruption in patients with hyperimmunoglobulinemia E (hyper-IgE) syndrome.

STUDY DESIGN

This study evaluated 34 individuals with hyper-IgE syndrome (age range, 2-40 years). A comprehensive dental history and a head and neck evaluation were performed on all patients. Dental age was assessed in patients younger than 17 years by 2 methods: (1) clinical assessment of tooth eruption and (2) a radiographic method. Relationships between the chronologic age, dental developmental age, and age at tooth eruption were determined. Other oral or dental anomalies were recorded.

RESULTS

Of patients older than 7 years, 75% reported problems with permanent tooth eruption, as evidenced by retained primary teeth or the need for elective extractions of primary teeth to allow eruption of permanent teeth. None of the patients experienced problems with eruption of primary teeth. Eruption of the first and second permanent molars also occurred on time. Dental maturity scores were established for 14 patients 17 years of age or younger. In each case, the difference between chronologic age and the estimated dental developmental age was less than 12 months; however, we found a significant discrepancy between the chronologic age and the mean age of tooth eruption in 80% of these patients when using a particular set of standardized values. Persistence of Hertwig's epithelial root sheath was observed on histologic examination. Chronic multifocal oral candidiasis was a consistent feature in patients with hyper-IgE recurrent infection syndrome. Other oral anomalies were also noted.

CONCLUSION

We confirmed that a disorder of tooth eruption is part of the hyper-IgE syndrome. This problem occurs because of delayed primary tooth exfoliation rather than a developmental delay in the formation of the permanent dentition. The persistence of Hertwig's epithelial root sheath is unusual and may be associated with the lack of resorption of the primary teeth. Dentists should be aware of this feature of hyper-IgE syndrome because timely intervention will allow normal eruption to occur.

Immunofluorescence detection of cadherins in mouse tooth germs during root development

The distribution of two cell-adhesion molecules, E- and P-cadherin, was studied in relation to morphological changes in Hertwig's epithelial root sheath Before root dentinogenesis had started, the root sheath expressed both cadherins. As dentinogenesis proceeded, the sheath fragmented and lost P-cadherin rapidly and E-cadherin slowly, whereas the intact sheath at the apical end continued to express both. These results suggest that the two cadherins play a part in root as well as in crown development, and indicate that the decrease in the amount of these molecules and the fragmentation of the epithelial root sheath are interrelated.

The structure of bovine periodontal ligament with special reference to the epithelial cell rests

The aim of this study was to determine the structure of the bovine periodontal ligament, with special reference to epithelial cell rests (ECR) and their cytokeratin content. Periodontal ligament was obtained from bovine molar teeth and studied at both the light microscopic and electron microscopic levels. Cytokeratin content was determined using immunohistochemistry against a number of cytokeratin antibodies and specificity tested against bovine and human oral mucosa. Collagen fibril diameters and the area of a fiber bundle occupied by collagen were determined using a digital planimeter with a digitizing tablet. The majority of periodontal fibroblasts possessed considerable quantities of roughened endoplasmic reticulum, indicating rapid synthesis and secretion of collagen, but no intracellular collagen profiles were present. Endothelial cells showed Weibel-Palade bodies. Collagen fibril diameters showed a unimodal distribution with a mean collagen fibril diameter of 55.3 nm. The mean percentage area of the extracellular matrix occupied by collagen was 42%. Structurally, ECR were unusual in exhibiting large numbers of microvilli and conspicuous amounts of cytokeratin filaments. Bovine ECR showed a positive reaction to the pancytokeratin MNF116 (which reacts with the cytokeratins 5, 6, 8, 17, and probably 19), to PCK-26 (which reacts with the type II cytokeratins 1, 5, 6, and 8) and to cytokeratin 13. There was no reaction for cytokeratins 1, 4, 10, 11 and 18. Structurally, bovine periodontal ligament showed features common to other species. However, ECR in terms of both structure and cytokeratin content showed features indicative of important species differences which may have relevance when considering the etiology of radicular cysts.

Identification of K1/K10 and K5/K14 keratin pairs in human melanoma cell lines

Keratin expression in cultured malignant melanoma cells has been studied only rarely. Moreover, no studies have reported of universality of keratin expression in human malignant melanoma cells. In this study, therefore, we analyzed keratin expression in eight cell lines. Using a low-salt aqueous solution without high salt and Triton X-100, as a washing buffer for keratin extraction, followed by two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) and immunological analysis, we demonstrated keratin expression in all eight human malignant melanoma cell lines. The keratin polypeptide expressions common to all melanoma cells were K1, K5, K10 and K14. In addition, K8, K13, K17 and K18, respectively, were detected in individual cells. A measure of keratin expression universality in malignant melanoma cells may have implications regarding their invasive and metastatic behaviors, co-expressed with vimentin.