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Loss of alpha3beta1 integrin function results in an altered differentiation program in the mouse submandibular gland.

Mammalian submandibular gland (SMG) development leads to the establishment of highly organized secretory acinar and nonsecretory ductal epithelial cells. The ability of maturing salivary epithelial cells to attain their differentiated state has been shown to depend, in part, on interactions between extracellular matrix (ECM) proteins and their integrin receptors. In a search for key regulators of salivary cell lineage, we have studied alpha3beta1 integrin, a receptor for the basement membrane protein laminin, by characterizing embryonic day 18 (E18) SMGs isolated from mice carrying a targeted mutation in the alpha3 integrin gene. Transmission electron microscopy studies showed that the mutant SMGs exhibited an aberrant differentiation phenotype with defects in the apical-basal polarity axis and in the basement membrane. Based on immunohistochemistry and Western blot analyses, the alpha3beta1-deficient SMGs had altered expression and/or localization of several ECM and adhesive molecules, including laminin beta1, fibronectin, alpha5 integrin, and E-cadherin. These changes correlated with alterations in the activation state of Ras-extracellular signal-regulated kinase (ERK), as well as the expression and/or localization of Cdc42 and RhoA, two Rho GTPases that regulate the organization of the actin cytoskeleton. We conclude that alpha3beta1 is required for normal salivary cell differentiation and that its absence affects multiple components of adhesive complexes and their associated signalling pathways.

Actins↗

Effects of 4,4'-diisothiocyano-2,2'-stilbene disulphonic acid and amiloride on salivary secretion by isolated, perfused rat submandibular glands.

Isolated submandibular glands of adult rats were perfused through the arterial system with oxygenated, HCO3-containing or HCO3-free physiological salt solutions. Secretion of saliva was then induced with acetylcholine (10(-6) M) in the absence or presence of the ion-transport inhibitors 4,4'-diisothiocyano-2,2'-stilbene disulphonic acid (DIDS), furosemide or amiloride. In HCO3-containing perfusates, 10(-4) M DIDS enhanced the initial secretory response (maximum rate of flow increased 18 per cent), but reduced the overall volume of saliva secreted in a 60-min period by 47 per cent. Furosemide (10(-3) M) alone reduced the volume of saliva by 73 per cent and, in combination with 10(-4) M DIDS, by 82 per cent. Amiloride (10(-3) M) caused a 68 per cent reduction in salivary volumes. Replacement of perfusate HCO3 with HEPES did not affect acetylcholine-induced secretion but enhanced the effects of the transport inhibitors, so that total volume of secretion was reduced 94 per cent by furosemide, 55 per cent by DIDS and 80 per cent by amiloride. In HCO3-containing perfusates, DIDS caused a 30-50 per cent increase in salivary Na+ and residual anion (Na + K - Cl) concentrations but amiloride induced a marked increase in salivary Na+ and Cl- concentrations and a decrease in salivary K+ concentrations. Furosemide caused a marked decrease in salivary Cl- concentrations and a marked increase in residual anions. These effects were similar but of smaller magnitude in HCO3-free, HEPES-containing perfusates.(ABSTRACT TRUNCATED AT 250 WORDS)

4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid↗

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.

Animals↗

Expression of the epidermal growth factor gene in mouse lachrymal gland: comparison with that in the submandibular gland and kidney.

Expression of the epidermal growth factor (EGF) gene in mouse lachrymal gland was studied. The lachrymal gland of adult male and female mice contained immunoreactive EGF at a concentration of 0.013 +/- 0.002 (S.E.M.) and 0.014 +/- 0.003 ng/mg wet tissue respectively. Northern blot analysis of RNA from the lachrymal gland revealed the presence of 4.1-4.3 kb preproEGF mRNA, which was smaller in size than the 4.7-4.8 kb preproEGF mRNA in the submandibular gland and kidney. There was no sex difference in the mRNA level in the lachrymal gland, whereas the mRNA levels in the submandibular gland and kidney of adult male mice were 42-fold higher and twofold lower respectively than those of female animals. Administration of testosterone propionate or L-thyroxine to female mice increased submandibular gland levels of preproEGF mRNA by 35-fold or 12-fold respectively, but caused no change in lachrymal gland levels of preproEGF mRNA. The level of mRNA in the kidney was decreased by administration of androgen to one-third of that in control animals. The mRNA in the lachrymal gland was detected as early as 2 weeks of age and thereafter it remained at a constant level throughout adulthood, while that in the submandibular gland increased greatly during the pubertal stage. These results indicate differential hormonal and developmental regulation of EGF gene expression in the lachrymal gland, submandibular gland and kidney.

Animals↗

A secretory protein restricted to type I cells in neonatal rat submandibular glands.

The perinatal submandibular gland of the rat contains an 89-kDa secretory protein (Protein C) that is released upon cholinergic stimulation. Polyclonal antibodies raised against Protein C show that this protein is localized in the Type I cells and is not found in typical Type III cells. However, morphological variants of Type III cells (Type IIIP) contain material that is cross-reactive with antibodies to Protein C. Cross-reactive components also are found in mucous cells of the neonatal sublingual glands, parotid and minor sublingual glands, and adult submandibular and sublingual glands. Immunoblots of electrophoretically separated proteins show a distinct Protein C band at 89 kDa only in neonatal submandibular glands; neonatal sublingual and minor sublingual glands show some diffuse reactivity over a range of mobilities encompassing that of Protein C. We propose that the cross-reactive components of mucous cells and Type IIIP cells are not Protein C, but different proteins associated with mucous differentiation, and that the Type IIIP cells of the neonatal submandibular gland are in transition from Type III to mature mucous cells.

Animals↗

Amiloride impairs the cholinergic regulation of potassium permeability in the human sweat gland but not in the rat submandibular gland.

Potassium permeability was monitored in human sweat glands and rat submandibular glands. Acetylcholine increased permeability in both tissues and the responses consisted of transient, calcium-independent and sustained, calcium-dependent components. Amiloride, a drug which inhibits Na(+)-H+ countertransport, impaired the regulation of potassium permeability in sweat glands but not in the submandibular gland. It is suggested that the stimulus-permeability coupling process in the sweat gland may be sensitive to the lowering of internal pH.

Acetylcholine↗

Morphological changes in collagen fiber during development of human fetal parotid and submandibular glands.

Parotid and submandibular glands from human fetuses (16, 20, 24, 28, 32 weeks of gestation) were examined under a scanning electron microscope. Changes were found in the arrangement of collagen fibers in the connective tissue surrounding the salivary gland. In particular, several layers around the salivary gland were formed by a collagen network structure. These structures, although in varied arrangements, were recognizable in each stage of fetal growth. They are thought to play the role of a "cushion" against pressure created by accumulation of granules because of the reflex activity of myoepithelial cells during secretion. These structural changes are related to the mechanical performance of granule formation in the salivary gland and secretion during the development of the fetus.

Collagen↗

Three-dimensional observation of blood vessels supplying the gland proper and capsule of the mouse submandibular gland.

Previous studies have shown that submandibular glands suffering interruption of the blood circulation from the main supplying artery have more surviving parenchymal cells in their peripheral portion than in their central portion. Although the reason for this difference between the peripheral and central portions has not yet been clarified, the existence of collateral circulation has been suspected. The present study was designed to examine whether or not the vessels binding the gland proper to the capsule provide such collateral circulation. Silicone rubber or methacrylate was injected into the main artery supplying the mouse submandibular gland, in which the gland proper is wrapped by a capsule similar to that of the human submandibular gland, and then the gland was observed by both stereoscopic and scanning electron microscopy. Three-dimensional observations showed no communicating vessels between the gland proper and the capsule. Therefore, it is suggested that the parenchymal cells surviving in the ischemic peripheral portion of the submandibular gland are nourished by permeation of tissue fluid contained in the capsule.

Animals↗

[The relationship of function and pathology of submandibular gland with sialolithiasis].

Submandibular glands with sialolithiasis are analysed histopathologically. The formation of the calculi of the submandibular glands may be related to the sialoadentitis and to the changes of saliva composition. Mineralization of the organic matrix may be one of the cause of calculus formation. By comparison of the glandular function with the pathology of the gland, it shows that the reduction of glandular function is associated with the severity of grandular inflammation. When function index is normal, grandular inflammation is in the Stage I or II, while it decreases or zero, grandular inflammation is in the Stage III or IV. Glandular function index may predict the severity of grandular inflammation.

Adult↗