The B1-immunoreactive proteins of the perinatal submandibular gland: similarity to the major parotid gland protein, RPSP

The B1-immunoreactive proteins of type III cells of the perinatal rat submandibular gland are immunologically cross-reactive with proteins of both the sublingual and parotid glands; in particular, protein SMG-A appears similar to a major parotid protein. We isolated SMG-A and the parotid protein (known as M1 or leucine-rich protein), prepared polyclonal antibodies to them, and compared their biochemical properties and immunological reactivities. They were identical in their molecular weight on SDS-PAGE (23.5 kDa), tenacious binding to Affi-gel Blue, isoelectric point (pH 4.53), and proteolysis to a 14 kDa peptide: Antibodies to SMG-A showed reactivity with protein SMG-C, a product of the neonatal type I cells, as well as with proteins SMG-B1 and SMG-B2, contrasted with the absence of reactivity of anti-M1 IgG with these proteins. Anti-M1 reacted with the "parotid secretory protein" (PSP) of the mouse, and M1 appears to be the homologue, in the rat, of mouse PSP.

A novel peptide-producing cell in Xenopus: multinucleated gastric mucosal cell strikingly similar to the granular gland of the skin

We have characterized a novel peptide-containing cell within the gastric mucosa of Xenopus laevis. The cell is a spherical, multinucleated syncytial structure containing a cytoplasmic space filled with dense rice-shaped granules, and is strikingly similar in morphology to the well-studied granular gland of the amphibian skin. Immunohistochemical and immunogold methods were used to demonstrate that several peptides previously isolated from the granular glands of the skin, including the antimicrobial peptides magainin and PGLa (a peptide with amino-terminal glycine and carboxy-terminal leucinamide), are also stored in granules present in these enteric cells. These data demonstrate that this enteric peptide-producing cell is strikingly similar both morphologically and biochemically to the granular gland, previously considered a highly specialized structure of the amphibian integument. This novel gastric mucosal cell, which we have designated a "granular multinucleated cell," is distinct in its morphology and its diversity of stored peptide products from other well-characterized peptide-containing cells in the vertebrate gastrointestinal tract.

A neonatal secretory protein associated with secretion granule membranes in developing rat salivary glands

In the perinatal submandibular gland, the secretion granules of Type I cells contain protein C (89 KD) and those of Type III cells have Bl-immunoreactive proteins (Bl-IP, 23.5-27.5 KD). In this report we used immunocytochemistry at the light and electron microscopic levels to describe the developmental distribution and localization of protein D (175 KD), which is secreted by both Type I and Type III cells. At its first appearance in Type I cells at 18 days and in Type III cells at 19 days post conception, protein D immunoreactivity (D-IR) is associated with secretion granule membranes; this is more pronounced in Type I than in Type III cells. In early postnatal life the label remains membrane associated, but as Type III cells differentiate into seromucous acinar cells, the lower level of label present in these cells is found in the granule content. Label is found associated with the membrane in secretion granules of Type I cells as long as these cells are identifiable in acini, and subsequent to this similarly labeled cells are seen in intercalated ducts. In the sublingual gland (SLG), D-IR is membrane associated in secretion granules of serous demilune cells, and is present in the secretion granule content in mucous acinar cells. D-IR is also found in the lingual serous (von Ebner's) glands, lacrimal gland, and tracheal glands, primarily in the ducts, where it is localized in the content of secretion granules.

Decrease in insulin-containing secretory granules and mitochondrial gene expression in mouse pancreatic islets maintained in culture following streptozotocin exposure

We have previously described a preferential reduction in the secretory response to nutrient secretagogues in pancreatic mouse islets maintained in culture after in vitro exposure to streptozotocin (SZ). This reduction was associated with an impaired substrate metabolism at the mitochondrial level. To further clarify this issue, mouse pancreatic islets were exposed in vitro to 2.2 mM SZ for 30 min. At 4 h after SZ treatment ultrastructural changes were apparent in the endoplasmic reticulum and Golgi areas of the B-cells. However, 2 and 6 days following SZ exposure the B-cells appeared well preserved, except for a marked decrease in the number of insulin-containing secretory granules. A morphometric analysis of the B-cells 6 days after SZ exposure showed a normal B-cell size and a normal volume fraction of B-cell mitochondria. However, there was a decrease in total islet size and a 13% decrease in the volume fraction of B-cells in the islets. These mouse islets exhibited a decreased content of the mitochondrial DNA-encoded cytochrome b mRNA, as evaluated by dot-blot analysis. As a whole, the data obtained indicate that SZ treatment does not induce a decrease in the number of mitochondria or long-lasting ultrastructural damage to this organelle. However, there is a clear decrease in the cytochrome b mRNA, suggesting that SZ can induce damage to the mitochondrial DNA.

Accumulation and localization of two adult acinar cell secretory proteins during development of the rat submandibular gland

The seromucous acinar cells of the adult rat submandibular gland secrete a characteristic mucin glycoprotein and a family of unusual glutamine/glutamic acid-rich proteins (GRP). Monoclonal antibodies to the mucin and GRP localized in a very few Type III cells in glands of newborn and 1 day-old rats, using light and electron microscopic immunocytochemistry. Both mucin and GRP reactivities were present in the polymorphic Type IIIP granules during the 1st postnatal week. By 9 days after birth, the granules contained both mucin and GRP and were mucous-like in appearance. At earlier stages, however, cells containing only GRP or mucin could be found, indicating that the initiation of GRP and mucin biosynthesis may not be coordinately regulated. No reactivity was seen in the neonatal Type I cells or in duct cells at any age. Northern and Western blot analysis showed GRP mRNA and protein levels to be barely detectable at birth, with marked increases during the first 2 postnatal weeks. In contrast, Western blots of B1-immunoreactive proteins (B1-IP) showed levels highest in the 1st week and markedly decreased in the adult. Immunocytochemical colocalization, using gold particles of different sizes, showed that the B1-IP, mucin, and GRP colocalized in the granules. These results strengthen the hypothesis that the adult acinar cells develop from the neonatal Type III cells. No evidence was obtained for the involvement of Type I cells in the pathway of acinar cell development.

Endothelin as an autocrine factor in the regulation of parathyroid cells

Endothelin, originally purified from porcine aortic endothelial cells, is widely distributed in tissues and is recognized as a product of epithelial cells, glial cells, and neurons in addition to endothelial cells. We found evidence by mRNA content and immunoreactivity that this peptide is synthesized in rat parathyroid epithelial cells (PT-r cells) and bovine parathyroid chief cells. The peptide synthesized by PT-r cells comigrated with synthetic endothelin 1 in reverse-phase HPLC and was diluted out in radioimmunoassay in parallel with the synthetic peptide. Bovine parathyroid endothelial cells (BPE-1 cells) did not express this peptide. Preproendothelin 1 mRNA expression by PT-r cells and endothelin 1 peptide production were regulated by calcium. Shifts in extracellular calcium either from high to low concentrations or vice versa elicited similar evanescent increases in expression of mRNA with a peak at 1 h. Synthesis of the peptide seems to be controlled by mRNA expression, and peptide in the medium appears to be continuously degraded or taken up by cells because its concentration in the medium showed a time course similar to that of mRNA expression. PT-r cells also bear a single class of receptors highly specific for endothelin 1, suggesting an autocrine regulation by endothelin 1 of the parathyroid. The facile regulation of endothelin concentrations in the medium by shifts in extracellular calcium concentration and possible autocrine regulation by endothelin 1 suggest that this peptide may mediate, at least in part, effects of calcium on the parathyroid system.

Magainin-like immunoreactivity in human submandibular and labial salivary glands

Magainins, antimicrobial peptides secreted by granular glands of frog skin, may be related to the high resistance to infections of this epithelial surface. The oral mucosa of healthy individuals is another tissue in which infection is not frequent, probably owing to the activity of potent salivary and mucosal defense mechanisms. To investigate if magainin-like factors are a component of these oral defense mechanisms, human and animal minor (mucosal) and major salivary glands were examined by immunohistochemistry, using a polyclonal rabbit anti-magainin antibody. Cryostat sections of (para) formaldehyde-fixed tissues were incubated with the antibody and then stained with fluorescein-complexed anti-rabbit IgG. Specific staining was observed in the apical portion of the cytoplasm of ductal epithelial cells of human submandibular and labial salivary glands. Diffuse staining was present in submandibular acinar cells. Bovine, rat, hamster, and mouse tissues were unreactive. The presence of magainin-like substances in human salivary gland duct cells is consistent with reports of the occurrence of other biologically active substances in salivary gland ducts.

Localization of neonatal secretory proteins in different cell types of the rat submandibular gland from embryogenesis to adulthood

In the neonatal rat submandibular gland, Type III cells contain a group of related proteins that we call the B1-immunoreactive proteins (B1-IP; 23.5, 26, and 27.5 kDa). Type I cells lack these, but synthesize a different protein, Protein C (89 kDa). With maturation of the gland, these neonatal cell types are no longer seen in the seromucous acini, which are no longer reactive for the B1-IP. Here, we report the ultrastructural immunocytochemical localization of the B1-IP and Protein C over the course of development. From their first appearance in the embryo, the B1-IP and Protein C are present in different cells which become morphologically typical Type I and III cells prior to birth. At all stages, Type I cells have strong Protein C labeling and no B1 labeling. By 3 days postpartum, ultrastructurally atypical Type III cells are seen (Type IIIP); these label for the B1-IP, but also show labeling with antibody to Protein C. In the next week, as mucous cells appear in the acini, these show both B1-IP and C labeling; the B1 marker is lost by 30 days postpartum, but adult mucous acinar cells continue to show Protein C reactivity. In view of the appearance of Protein C reactivity in neonatal Type IIIP and then in mucous cells, and the presence of B1 reactivity in early but not mature mucous cells, we suggest that Type III cells differentiate into mucous cells and that Type IIIP cells are intermediates in this transformation. We see no evidence for the differentiation of either Type III or mucous cells from Type I cells, although our data cannot rule out this possibility. In adult glands, cells with B1 labeling are seen in intercalated ducts. Cells that appear to be Type I cells are also present in these ducts and label for Protein C. Double labeling for B1-IP and Protein C demonstrated that the two markers were exclusively present in different cells within intercalated ducts. This is of considerable interest, as intercalated ducts have been reported to be the stem cell population for normal and trauma-induced cellular replacement.

Light and electron microscopic immunolocalization of rat submandibular gland mucin glycoprotein and glutamine/glutamic acid-rich proteins

We studied the subcellular localization of two major secretory products of adult rat submandibular gland (RSMG), blood group A-reactive mucin glycoprotein and glutamine/glutamic acid-rich protein (GRP), by light and electron microscopic immunocytochemistry. The structure of the major neutral oligosaccharide of the mucin was shown to be: GalNAc alpha 1,3(Fuc alpha 1,2)Gal beta 1,3GalNAc. A mouse monoclonal antibody (1F9) with specificity for blood group A determinants was prepared against the mucin. The antibody recognized a single band of approximately 114 KD on Western blots of RSMG extract. A previously characterized monoclonal antibody (59) against GRP (Mirels et al.: J Biol Chem 262: 7289, 1987) reacted with a doublet of 45-50 KD on Western blots of extraparotid saliva. Immunofluorescence and immunoperoxidase staining of cryostat sections of RSMG with anti-mucin antibodies and anti-GRP antibodies revealed reactivity in acinar cells of the gland. No specific labeling was seen in duct cells of RSMG or in mucous acinar cells of the adjacent sublingual gland. Post-embedding immunogold labeling of thin sections of glutaraldehyde-fixed RSMG with anti-mucin showed strong labeling of the Golgi apparatus and secretory granules of acinar cells. Gold particles were seen mainly over electron-lucent areas of the granules. No labeling occurred over the endoplasmic reticulum. The labeling pattern with the anti-GRP antibodies was similar, except that both electron-dense and -lucent areas of the granules were labeled, and the endoplasmic reticulum was reactive. Double labeling with two different sizes of gold particles showed that both mucin and GRP co-localized in the same granules. Pre-absorption of the antibodies with their respective antigens eliminated immunolabeling of the acinar cells. These antibodies will be useful in studies of cell differentiation in RSMG and of synthesis, processing, and packaging of RSMG secretory products.

Lack of acute effects of methotrexate on rat parotid salivary gland function

Like other cytotoxic drugs, methotrexate (MTX) produces adverse reactions in oral tissues. Parotid gland function was examined, in vivo and in vitro, 18 h after MTX administration (15 mg/kg, i.p.). No salivary effects could be detected consistently. In addition, the integrity of the oral mucosa remained intact. Thus, at this dose, MTX does not exert an acute cytotoxic effect either on a rapidly replicating oral tissue like the mucosa, or on tissue with a slow turnover rate like the parotid.

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.

[Characteristics of the absorption surface of the intestinal epithelium of Alouatta caraya]

Electron microscopy of the absorption surface of the jejunal epithelium of the howler monkey Alouatta caraya showed the presence of core filaments implanted at the level of the terminal web in the microvilli. These microvilli are 5 to 7 mum long and up to 5 mum thick, their extraordinary development is attributed to a conditioned adaptation of the species to its feeding habits and nature of absorption.