Immunohistochemistry of myoepithelial cells during development of the rat salivary glands

Specific localization of fibroblasts at the intercalated duct in the major salivary glands of rats

OBJECTIVES

Immunohistochemical methods were employed to investigate the morphological heterogeneity and localization of fibroblasts associated with the function of major salivary glands in rats.

METHODS

Histochemical and electron microscopic observations were made in rat parotid, submandibular, and sublingual glands and pancreas. Fibroblasts were immunostained using their specific marker, 47 kDa heat shock protein (Hsp47).

RESULTS

Hsp47-immunopositive fibroblasts within the intralobular connective tissue exhibited a notably smaller size compared with the interlobular connective tissue. They were loosely distributed throughout the connective tissue. However, fibroblasts with elongated long processes were explicitly identified at the intercalated ducts in parotid, sublingual, and submandibular glands. Fibroblastic bodies and processes were tightly approximated with the basement membrane of the duct. Electron microscopy confirmed these findings, revealing a thin layer consisting of collagen fibers was found between the fibroblasts and the basement membrane. Double staining of Hsp47 and α-smooth muscle actin (αSMA) in parotid glands indicating that Hsp47-positive fibroblasts enveloped both the duct and αSMA-positive myoepithelial cells. Additionally, They projected long and thin processes longitudinally at the straight portion or circularly at the bifurcated portion of the duct. The three-dimensional reconstruction showed a frame-like structure of fibroblasts surrounding the intercalated duct with longitudinal myoepithelial cells. However, such specific localization of fibroblasts was not detected in the exocrine pancreas lacking myoepithelium.

CONCLUSIONS

Small fibroblasts with long processes connecting or overwrapping each other and thin collagen layers surround the intercalated ducts in rat major salivary glands, presumably contributing to protecting the ducts from salivary flow and myoepithelial contraction.

Study of morphological structure in human fetus Wharton's duct opening area

OBJECTIVES

Not many morphological studies have been reported regarding the human salivary main duct, especially those based on observations of the fetal salivary main duct at various developmental stages. The relationships between fetal structural development and its function, functional disorders and diseases certainly have clinical significance.

METHODS

In this study, we conducted a morphological observation of seven 5-9 month old human fetal sublingual caruncula, the common opening between the submandibular (Wharton's) duct and the sublingual (Bartholin's) duct. After seven specimens were removed and paraffin sections were prepared, HE and EVG staining were used for histological study of structural differences in the various developmental stages. Furthermore, anti-α-SMA staining was used to observe the distribution of the smooth muscle inside of the Wharton's duct wall.

RESULTS

An abundance of elastic fibers were observed in the duct walls of both five and nine month old specimens with EVG staining. The smooth muscle fibers of five month old fetus were immature and were starting to distribute throughout the duct wall, whereas nine month old fetus' smooth muscle fibers were further developed and composed in layers.

CONCLUSION

In this study, we confirmed that the Wharton's duct wall structure of nine month old fetuses was close to its adult structural formation, while the inner structure consisted of an ample distribution of elastic fibers and smooth muscle fibers. Based on the distribution pattern of the smooth muscle, we speculate that the Wharton's duct's opening area does not possess a sphincter-like function in the regulation of salivary flow.

Plasticity of endometrial epithelial and stromal cells-A new approach towards the pathogenesis of equine endometrosis

Equine endometrosis, a frequent cause of subfertility, is characterized by periglandular fibrosis, and no treatment exists. Endometrial biopsies not only contain diseased glands, but also contain healthy glands and stroma. Myoepithelial (ME) and myofibroblastic (MF) markers are calponin, smooth muscle actin (SMA), desmin and glial fibrillary acidic protein (GFAP). Epithelial vimentin expression indicates epithelial to mesenchymal transition (EMT). The aim of this immunohistochemical study was to investigate whether biopsies with endometrosis express MF and ME markers and vimentin. Compared to healthy areas, significantly higher percentages of endometrotic glands were lined by calponin- and vimentin-positive epithelial cells, whereas periglandular fibrosis contained significantly higher percentages of stromal cells positive for vimentin, desmin and SMA and significantly less calponin-positive stromal cells. The rare GFAP expression was restricted to endometrotic glands. Of these, the most frequent features of endometrotic glands were higher percentages of SMA- and vimentin-positive stromal cells and the prominent epithelial calponin staining that occurred in 100%, 93% and 95% of examined biopsies. Results indicate plasticity of equine endometrial epithelial and stromal cells. Particularly, endometrotic glands show evidence for ME differentiation and EMT. The different expression of MF markers between stromal cells from healthy and endometrotic areas suggests functional differences. The characteristic changes in the expression of SMA, vimentin and calponin between endometrotic glands and healthy areas can be helpful to confirm early stages of endometrosis. The characterization of cellular differentiation may help to decipher the pathogenesis of endometrosis and could lead to therapeutic strategies.

Morphological Changes of Myoepithelial Cells in the Rat Submandibular Gland Following the Application of Surgical Stimuli

Myoepithelial cells (MECs) exist on the basal surface of acini in major exocrine glands, include myofilaments and various constructive proteins, and share characteristics with smooth muscle and epithelial cells. MECs project several ramified processes to invest acini, and possibly contract to compress acini to support the secretion by the glandular cells. However, the functional roles of MECs in salivary secretion are still unclear. We investigated morphological changes in immunostained MECs using the anti-α-smooth muscle actin (αSMA) antibody in operated or non-operated contralateral (NC) submandibular glands after partial or total resection. Furthermore, we investigated and discuss other salivary glands of rats. MECs in the parotid, sublingual and submandibular gland of adult rats exhibited different shapes and localizations. After surgery, in both operated and NC glands, the number of MECs and αSMA-immunopositive areas increased significantly. Three-dimensional analysis using a confocal laser-scanning microscope revealed that substantial and significant enhancement became evident in the number, length, and thickness of MEC-processes covering acini of the operated and NC submandibular glands. The preset findings indicate that MECs alter the morphology of their processes in operated and NC glands after surgery of the partial or total resection. It is suggested that MECs promote salivary secretion using elongated, thickened, and more ramified processes.

Characterization of the myoepithelial cells in the major salivary glands of the fruit bat Artibeus jamaicensis

Bats constitute one of the most numerous mammalian species. Bats have a wide range of dietary habits and include carnivorous, haematophagous, insectivorous, frugivorous and nectivorous species. The salivary glands of these species have been of particular research interest due to their structural variability among chiropterans with different types of diets. Myoepithelial cells (MECs), which support and facilitate the expulsion of saliva from the secretory portions of salivary glands, are very important for their function; however, this cell type has not been extensively studied in the salivary glands of bats. In this study, we characterized the MECs in the major salivary glands of the fruit bat Artibeus jamaicensis. Herein, we describe the morphology of the parotid, submandibular and sublingual glands of A. jamaicensis at the light- and electro-microscopic level and the distribution of MECs in these glands, as defined by their expression of smooth-muscle markers such as α-smooth muscle actin (SMAα) and desmin, and of epithelial cell markers, such as KRT14. We found that the anatomical locations of the major salivary glands in this bat species are similar to those of humans, except that the bat sublingual gland appears to be unique, extending to join the contralateral homologous gland. Morphologically, the parotid gland has the characteristics of a mixed-secretory gland, whereas the submandibular and sublingual glands were identified as mucous-secretory glands. MECs positive for SMAα, KRT14 and desmin were found in all of the structural components of the three glands, except in their excretory ducts. Desmin is expressed at a lower level in the parotid gland than in the other glands. Our results suggest that the major salivary glands of A. jamaicensis, although anatomically and structurally similar to those of humans, play different physiological roles that can be attributed to the dietary habits of this species.

Immunohistochemical localization of keratin 5 in the submandibular gland in adult and postnatal developing mice

Keratin 5 (K5) is a marker of basal progenitor cells in the epithelia of a number of organs. During prenatal development of the submandibular gland (SMG) in mice, K5(+) progenitor cells in the developing epithelia play important roles in its organogenesis. Although K5(+) cells are also present in the adult mouse SMG and may function in tissue regeneration, their histological localization has not yet investigated in detail. In the present study, we examined the immunohistochemical localization of K5 in the SMG in adult and postnatal developing mice. At birth, K5 immunoreactivity was detected in the entire duct system, in which it was localized in the basal cells of a double-layered epithelium, but was not detected in the terminal tubule or myoepithelial cells. At postnatal weeks 1-3, with the development of intercalated ducts (ID), striated ducts (SD), and excretory ducts (ED), K5-immunoreactive basal cells were gradually restricted to the ED and the proximal double-layered portions of the ID connecting to the SD. At the same time, K5 immunoreactivity appeared in myoepithelial cells, in which its positive ratio gradually increased. In adults, K5 immunoreactivity was localized to most myoepithelial cells, most basal cells in the ED, and a small number of ID cells at the boundary between the ID and SD in the female SMG or between the ID and granular convoluted tubules in the male SMG. These results suggest that K5 is a marker of differentiated myoepithelial cells and duct progenitor cells in the mouse SMG.

Stem Cell-Soluble Signals Enhance Multilumen Formation in SMG Cell Clusters

Saliva plays a major role in maintaining oral health. Patients with salivary hypofunction exhibit difficulty in chewing and swallowing foods, tooth decay, periodontal disease, and microbial infections. At this time, treatments for hyposalivation are limited to medications (e.g., muscarinic receptor agonists: pilocarpine and cevimeline) that induce saliva secretion from residual acinar cells as well as artificial salivary substitutes. Therefore, advancement of restorative treatments is necessary to improve the quality of life in these patients. Our previous studies indicated that salivary cells are able to form polarized 3-dimensional structures when grown on growth factor-reduced Matrigel. This basement membrane is rich in laminin-III (L1), which plays a critical role in salivary gland formation. Mitotically inactive feeder layers have been used previously to support the growth of many different cell types, as they provide factors necessary for cell growth and organization. The goal of this study was to improve salivary gland cell differentiation in primary cultures by using a combination of L1 and a feeder layer of human hair follicle-derived mesenchymal stem cells (hHF-MSCs). Our results indicated that the direct contact of mouse submandibular (mSMG) cell clusters and hHF-MSCs was not required for mSMG cells to form acinar and ductal structures. However, the hHF-MSC conditioned medium enhanced cell organization and multilumen formation, indicating that soluble signals secreted by hHF-MSCs play a role in promoting these features.

Spontaneous poorly differentiated carcinoma with cells positive for vimentin in a salivary gland of a young rat

Spontaneous salivary gland tumors in rats are rare. The authors report a poorly differentiated carcinoma of a submandibular gland in a ten-week-old rat that was positive for vimentin. Microscopically, the neoplastic cells showed a diffuse growth pattern in most areas of the tumor mass and a nestlike structure in a part of the peripheral area. Immunohistochemically, the cells were positive for keratin and vimentin but not for alpha-smooth muscle actin. Ultrastructurally, desmosome-like structures were observed. Based on these findings, the tumor was diagnosed as a poorly differentiated carcinoma. The origin of the neoplastic cells would be either acinar or ductal cells. This suggests that acinar or ductal cells have the potential to transform into vimentin-expressing cells.

Changes in the number and distribution of myoepithelial cells in the rat parotid gland during postnatal development

The mature rat parotid gland shows hardly any cell bodies of myoepithelial cells around the acini, only a few cell processes being visible. However, in the early postnatal period, the rat parotid gland shows many myoepithelial cell bodies around the acini, including the intercalated ducts. In order to clarify the reason for the disappearance of myoepithelial cells from the area around the acinus during postnatal development, changes in the number and distribution of myoepithelial cells in the rat parotid gland were examined histochemically and chronologically, with particular reference to cell proliferation and cell death. From day 7 to day 14, many myoepithelial cells showing a positive reaction with anti-actin antiserum were found around the acini and intercalated ducts, but thereafter the number of such cells decreased gradually, particularly around the acini, and had almost disappeared after day 35. BrdU/PCNA-positive myoepithelial cells surrounding the acini were easily detected on day 14, but disappeared by day 21, whereas BrdU/PCNA-positive acinar cells remained numerous even after day 21. TUNEL/ISEL staining showed no positive myoepithelial cells throughout the observation period. Transmission electron microscopy also demonstrated no myoepithelial cells with chromatin condensation characteristic of apoptosis through the observation period. These findings suggest that the main reason for the disappearance of myoepithelial cells from the area around the acinus during postnatal development is the large difference between the number of myoepithelial cells and that of acinar cells, because the acinar cells retain their proliferative activity even after myoepithelial cells have become quiescent.

Mioepitelioma de glândula salivar menor: uma análise imunohistoquímica de quatro casos

INTRODUÇÃO E METODOLOGIA: Realizou-se um estudo imunohistoquímico em 4 casos de mioepiteliomas, visando traçar seu perfil quanto ao grau de diferenciação das células através dos anticorpos alfa-SMA, CK 14 e vimentina, bem como investigar o índice de proliferação celular pelo anti-PCNA, além de comparamos a imunorreatividade com o tecido glandular normal adjacente ao tumor. RESULTADOS: No tecido glandular normal as células mioepiteliais exibiram marcação para alfa-SMA e CK 14, enquanto que nas células ductais somente a presença da CK 14 foi verificada. Em todos os casos foi verificada positividade para CK 14 e vimentina, porém a CK 14 esteve presente somente em células epitelióides e fusiformes, enquanto que a vimentina mostrou-se positiva também nas células plasmocitóides. A alfa-SMA não foi detectada nas células neoplásicas. Imunopositividade para o PCNA foi observada em mais de 75% do componente celular dos tumores analisados, independente do tipo. CONCLUSÕES: Concluiu-se que não houve diferença na atividade proliferativa entre os tipos celulares presentes nos mioepiteliomas e, ainda, que os resultados deste estudo sugerem que as células constituintes desta neoplasia realmente representam células da linhagem mioepitelial, mas em diferentes estágios de diferenciação.

Myoepithelioma of minor salivary gland - An immunohistochemical analysis of four cases

Introduction and Methods

We performed an immunohistochemical study in four cases of myopitheliomas with objective to realize a profile in respect of differentiation grade by the monoclonal antibodies CK14, vimentin and alph-SMA, besides to investigate the cell proliferation by anti-PCNA, besides, we compare the immunoreactive with glandular normal tissue.

Results

In the glandular normal tissue the myoepithelials cells had shown expression for alpha-SMA and CK 14, while that in the ductals cells, only the presence of CK 14 was verified. All the cases was verified positivy for CK 14 and vimentin, however, CK 14 had been present only in epithelioid and fusiform cells, while that the vimentin revealed positive also in the cytoplasm of the plasmocytoid cells. alpha-SMA was not detected in the neoplasic cells. Immunopositivity for the PCNA was observed in more than 75% of the cellular component of the analyzed tumors, independent of the cellular type.

Conclusions

We concluded that it did not have difference in the proliferative activity among the cellular types presents in the myoepitheliomas and, still, the results of this study suggest that the constituent cells of this neoplasia one really represent cells of the mioepitelial ancestry, but in different stages of differentiation.

Localization of FGF-6 and FGFR-4 during prenatal and early postnatal development of the mouse sublingual gland

A number of fibroblast growth factors (FGFs) are involved in regulatory mechanisms of the salivary gland development. However, the role of FGF-6 unique in myogenic cells has not been elucidated in the developing sublingual gland. In the present study, temporo-spatial expression of FGF-6 and its receptor (FGFR)-4, in conjunction with some related histo-chemical properties, were investigated in the sublingual gland of the prenatal and early postnatal mice. The earliest expression of both FGF-6 and FGFR-4 was detected in immature acinar cells at gestational day 17 (GD17). The staining intensity increased gradually and some acinar cells showed a distinct staining at postnatal day 0 (PD0). The immunopositive cells had a relatively round profile and were assumed to be acinar cells. The positive staining decreased thereafter and disappeared completely by PD11. To confirm the identity of cells positive for FGF-6, double immunolabeling with anti-alphasmooth muscle actin (alphaSMA) and anti-FGF-6 antibodies was performed. The positive staining of alphaSMA, a marker of myoepithelial cells, was detected in the flattened cells surrounding the acini but not in the cells positive for FGF-6. The staining properties of secretory granules in acinar cells were also examined with periodic acid-Shiff (PAS) and alcian blue (AB). PAS-positive granules abundant in the late gestational stages (GD17 to PD0) began to be replaced with AB-positive mucous granules at early neonatal days (PD0-3), when the FGF-6/FGFR-4 expression was the strongest. These findings suggest that FGF-6/FGFR-4 might be involved in the changes of secretory granule content of acinar cells in the sublingual gland during the late gestational and early neonatal stages.

Transplantation of cultured salivary gland cells into an atrophic salivary gland

Patients with dry mouth have been treated with salivary substitutes and/or medications such as pilocarpine or cevimeline hydrochloride. These treatments temporarily relieve their symptoms and induce salivation from residual tissue. However, no treatment is available for the purpose of regenerating an atrophic gland. In this study, the feasibility of a cell transplantation therapy for the atrophic submandibular glands was investigated in rats. Further, the potential of cell differentiation into a useful phenotype was assessed by immunohistochemistry together with cell tracking with the fluorescent dye PKH 26. Rat submandibular glands were excised, and the salivary gland epithelial cells were cultured for 3 weeks with 3T3 cells as a feeder layer. Ductal ligation of the submandibular gland was employed to generate an atrophic gland. One week after the operation, the ligation was removed, and the cultured cells labeled with PKH 26 were injected into the atrophic submandibular glands. As a control, the cultured cells were also injected into normal submandibular glands. Two weeks after cell transplantation, the transplanted cells were detectable in both the experimental and control groups. The cells were clustered in the connective tissue between the lobules. Four weeks after transplantation, the labeled cells were detectable in the experimental group but not in the control group. In the atrophic glands, the scattered transplanted cells were observed over a broad area of the gland but localized mainly around the acini and ductal region. Immunostaining results showed a possible involvement of the transplanted cells in ductal regeneration, while neither myoepithelial nor acinar differentiations were observed within the 4 weeks since transplantation. This study demonstrated that cell transplantation to the salivary gland is feasible, and that the transplanted cells were selectively attracted to and remained in the damaged area without affecting normal tissue.

Transglutaminase 2 expression in the salivary myoepithelial cells of mouse embryo

Earlier a strong transient expression of transglutaminase 2 (TGase 2) localized at the anchoring sites of muscle bundles in human embryo was observed. In this study, we report a similar transient expression of the TGase 2 in the salivary myoepithelial cells of mouse embryo by immunohistochemistry, RNA in situ hybridisation, and RT-PCR. From 35 submandibular glands of mouse embryos and postnatal mice, a consistent expression of TGase 2 in the myoepithelial cells via a stage-specific manner was identified by mono-clonal antibody to TGase 2 immunostaining. A similar expression pattern of TGase 2 in the myoepithelial cells was also observed by RNA in situ hybridisation analysis. The expression of TGase 2 in the salivary epithelium and mesenchyme during the prenatal 14.5-15.5 days was found minimally diffusely spread and became intensely focalised in the myoepithelial cells of salivary acini and ducts during the prenatal 16.5-18.5 days but thereafter gradually decreased until postnatal 7 days and remained weak in postnatal 3 weeks. Such transient rise and fall expressions of TGase 2 were also found with the sequential amount of RT-PCR products during the same period. The alpha-smooth muscle actin (alpha-SMA) as a positive control in the myoepithelial cells of mouse submandibular glands was consistently expressed during the prenatal and postnatal period. These results of transient expression of TGase 2 in the myoepithelial cells coincided with the formation of the dendritic basket structure in the periphery of acini and ducts, suggest a possible catalytic role of transglutaminase in a newly formed cellular matrixes during the cytodifferentiating stage of mouse prenatal and neonatal submandibular glands.

Carbonic anhydrase VI in the mouse nasal gland

Western blotting analysis of mouse nasal tissue using a specific anti-mouse secreted carbonic anhydrase (CA VI) antibody has shown that CA VI is present in this tissue. A single immunoreactive band of 42 kD was observed, as has been found previously for salivary tissues. RT-PCR analysis has shown that nasal mucosa expressed CA VI mRNA. By immunohistochemistry (IHC), CA VI was observed in acinar cells, in duct contents of the anterior gland of the nasal septum, and in the lateral nasal gland. The Bowman's gland, the posterior gland of the nasal septum, and the maxillary sinus gland were negative. Immunoreactivity was also observed in the mucus covering the respiratory and olfactory mucosa and in the lumen of the nasolacrimal duct. In contrast, an anti-rat CA II antibody (that crossreacts with the mouse enzyme) stained only known CA II-positive cells and an occasional olfactory receptor neuron. These results indicate that CA VI is produced by the nasal gland and is secreted over the nasal mucosa. By reversible hydration of CO(2), CA VI is presumed to play a role in mucosal functions such as CO(2) sensation and acid-base balance. It may also play a role in olfactory function as a growth factor in maturation of the olfactory epithelial cells.

Prediction of cell type-specific gene modules: identification and initial characterization of a core set of smooth muscle-specific genes

Genes that are expressed in the same subset of cells potentially constitute a module regulated by shared cis-regulatory elements and a distinct set of transcription factors. Identifying such units is an important entry point to the molecular study of cell differentiation. We developed a general method to classify cell type-specific genes from expressed sequence tag (EST) data, and we optimized it for identification of smooth muscle cell (SMC)-specific genes. Expression profiles were derived from the quantitative distribution of EST data in mouse, and genes were classified based on their profile similarity to known reference genes, in this case smooth muscle myosin heavy chain. A large majority (>90%) of known SMC-specific genes were identified, together with novel candidates. Extensive experimental validation confirmed SMC-specific expression of candidates, for example, lipoma preferred partner (LPP) and a novel SMC-specific putative monoamine oxidase, SMAO. Our method performed considerably better than other computational methods in an objective cross validation comparison. The total number of SMC-specific genes is estimated to be approximately 50.

Immunocytochemistry of myoepithelial cells in the salivary glands

MECs are distributed on the basal aspect of the intercalated duct and acinus of human and rat salivary glands. However, they do not occur in the acinus of rat parotid glands, and sometimes occur in the striated duct of human salivary glands. MECs, as the name implies, have structural features of both epithelial and smooth muscle cells. They contract by autonomic nervous stimulation, and are thought to assist the secretion by compressing and/or reinforcing the underlying parenchyma. MECs can be best observed by immunocytochemistry. There are three types of immunocytochemical markers of MECs in salivary glands. The first type includes smooth muscle protein markers such as alpha-SMA, SMMHC, h-caldesmon and basic calponin, and these are expressed by MECs and the mesenchymal vasculature. The second type is expressed by MECs and the duct cells and includes keratins 14, 5 and 17, alpha 1 beta 1 integrin, and metallothionein. Vimentin is the third type and, in addition to MECs, is expressed by the mesenchymal cells and some duct cells. The same three types of markers are used for studying the developing gland. Development of MECs starts after the establishment of an extensively branched system of cellular cords each of which terminates as a spherical cell mass, a terminal bud. The pluripotent stem cell generates the acinar progenitor in the terminal bud and the ductal progenitor in the cellular cord. The acinar progenitor differentiates into MECs, acinar cells and intercalated duct cells, whereas the ductal progenitor differentiates into the striated and excretory duct cells. Both in the terminal bud and in the cellular cord, the immediate precursors of all types of the epithelial cells appear to express vimentin. The first identifiable MECs are seen at the periphery of the terminal bud or the immature acinus (the direct progeny of the terminal bud) as somewhat flattened cells with a single cilium projecting toward them. They express vimentin and later alpha-SMA and basic calponin. At the next developmental stage, MECs acquire cytoplasmic microfilaments and plasmalemmal caveolae but not as much as in the mature cell. They express SMMHC and, inconsistently, K14. This protein is consistently expressed in the mature cell. K14 is expressed by duct cells, and vimentin is expressed by both mesenchymal and epithelial cells. After development, the acinar progenitor and the ductal progenitor appear to reside in the acinus/intercalated duct and the larger ducts, respectively, and to contribute to the tissue homeostasis. Under unusual conditions such as massive parenchymal destruction, the acinar progenitor contributes to the maintenance of the larger ducts that result in the occurrence of striated ducts with MECs. The acinar progenitor is the origin of salivary gland tumors containing MECs. MECs in salivary gland tumors are best identified by immunocytochemistry for alpha-SMA. There are significant numbers of cells related to luminal tumor cells in the non-luminal tumor cells that have been believed to be neoplastic MECs.

Regulation of cadherin junctions during mouse submandibular gland development

Submandibular gland (SMG) development involves branching morphogenesis of the salivary epithelium into the surrounding mesenchyme, accompanied by proliferation and differentiation of immature salivary cells along acinar and ductal cell lineages. During development, salivary cell sorting and cell-cell adhesion are likely to be directed by cadherin adhesion receptors. We show that two classic cadherins, N- and E-cadherin, participate in SMG development. Early in embryonic morphogenesis, both cadherins displayed diffuse staining with regionalized localization to cell-cell borders. At this stage, significant pools of N- and E-cadherins were Triton-soluble, suggesting that fractions of these molecules were not localized to stable junctional complexes associated with the actin cytoskeleton. With cytodifferentiation, cadherins became progressively Triton-insoluble, and this correlated with their organization at cell-cell interfaces. In the cytodifferentiated SMG, N-cadherin was absent, whereas E-cadherin remained at cell-cell interfaces. Early in morphogenesis, beta-catenin was also primarily Triton-soluble, and its association with the actin cytoskeleton and localization to the adherens junctions increased with cytodifferentiation. Greater recruitment of cadherins and beta-catenin to cell-cell borders was paralleled by changes in membrane association of two Rho GTPases, Cdc42 and RhoA. N-cadherin was detected only at early stages of postnatal development, whereas E-cadherin and beta-catenin became progressively Triton-insoluble during differentiation. Our results indicate that N-cadherin functions transiently in SMG development. On the other hand, E-cadherin and beta-catenin appear to play different roles during tissue organization and cytodifferentiation. In early morphogenesis, E-cadherin and beta-catenin are likely to participate in SMG remodeling, whereas during cytodifferentiation, they form stable cell-cell contacts, and may collaborate with Rho GTPases in the establishment and maintenance of salivary cell polarity.

Transient occurrence of 27 kDa heat-shock protein in the terminal tubule cells during postnatal development of the rat submandibular gland

It has been suggested that the 27 kDa heat-shock protein (Hsp27) plays a role at crucial cellular checkpoints for proliferation, apoptosis, and differentiation. We examined the immunolocalization of Hsp27 in the rat submandibular gland during postnatal development, wherein acinar cells proliferate and differentiate at earlier postnatal periods. At 2 weeks of age, weak Hsp27 immunoreactivity was distributed diffusely over all gland components. At 3 weeks, Hsp27 immunoreactivity disappeared in most parts of the acini and ducts, but was intensely accumulated in a small cell population located in the acinar center. This population was composed mostly of terminal tubule (TT) type I cells. At 4 weeks, the Hsp27-immunopositive cell population in the acinar center was composed primarily of immature (type II) acinar cells, partly of immature (granulated) intercalated duct (ID) cells, and occasionally of apoptotic cells. After 5 weeks, all acinar components became mature and were no longer immunoreactive for Hsp27. When acinar cell differentiation was accelerated by administration of isoproterenol to 3-week-old rats for 7 days, the number of Hsp27-positive cells was significantly lower than in the control gland at 4 weeks, confirming that Hsp27 expression is downregulated in mature acinar cells. These results suggest that at around 3-4 weeks in postnatal development, the centroacinar TT cells stop proliferating and begin to differentiate into acinar and ID cells, and occasionally undergo apoptosis. Hsp27 is transiently expressed in the centroacinar TT cells during this critical period, and thus may play a role in their differentiation into the immediate descendants.

Apoptosis and proliferation of myoepithelial cells in atrophic rat submandibular glands

This study was designed to determine whether apoptosis and proliferation of myoepithelial cells occur in atrophic rat submandibular glands. The excretory duct of the right submandibular gland was doubly ligated with metal clips. The atrophic right submandibular glands removed after 1-28 days of duct ligation were investigated using immunohistochemical double staining for actin as a marker for myoepithelial cells and proliferating cell nuclear antigen (PCNA) as a marker for proliferating cells, double staining for actin immunohistochemistry, nick end-labeling (TUNEL) as a marker for apoptotic cells, and transmission electron microscopy (TEM). A few PCNA- and no TUNEL-positive myoepithelial cells were found in the control submandibular glands taken from animals with no operation. In the experimental glands, PCNA-positive myoepithelial cells were common 2 and 3 days after duct ligation and then decreased in number. TUNEL-positive myoepithelial cells appeared at 2 days and were observed most frequently at 5 days. Apoptotic myoepithelial cells were also identified by TEM. These observations suggest that both apoptosis and proliferation of myoepithelial cells occur, especially in the early phase of atrophy, in the rat submandibular gland.