Pancreatic beta-cells express hepcidin, an iron-uptake regulatory peptide.

Body iron is involved in various vital functions. Its uptake in the intestine is regulated by hepcidin, a bioactive peptide originally identified in plasma and urine and subsequently in the liver. In the present study, we provide evidence at the transcriptional and translational levels that hepcidin is also expressed in the pancreas of rat and man.

Secretory granules of hypophyseal and pancreatic endocrine cells contain proteins of the neuronal postsynaptic density.

The PDZ domain-containing protein Shank is a master scaffolding protein of the neuronal postsynaptic density and directly or indirectly links neurotransmitter receptors and cell adhesion molecules to the actin-based cytoskeleton. ProSAP/Shank proteins have recently also been detected in several non-neuronal cells in which they are mostly concentrated in the apical subplasmalemmal cytoplasm. In contrast, we have previously reported a more widespread cytoplasmic immunostaining pattern for the ProSAP1/Shank2 protein in endocrine cells at the light-microscopic level.

Expression of postsynaptic density proteins of the ProSAP/Shank family in the thymus.

PSD95-DLG-ZO1 domain-containing proteins of the ProSAP/Shank family are major scaffolding proteins of the neuronal postsynaptic density which play a pivotal role in the linkage of membrane receptors to downstream signal effectors and the actin-based cytoskeleton. Recently, ProSAP1/Shank2 has also been localized in various non-neuronal cells where it may fulfill similar functions as in neurons. We now complement these data by the study of ProSAP/Shank expression at the mRNA and protein level in a primary lymphoid organ, i.

The clathrin interacting protein Clint/epsinR in rat testicular germ cells.

The plasma membrane and the trans-Golgi network (TGN) are major intracellular sites for clathrin-mediated membrane budding. Only recently has the clathrin interacting protein Clint/epsinR/enthoprotin been identified, which is thought to be involved in clathrin-dependent membrane budding from the TGN. Using immunocytochemistry, we now report the presence of Clint in the Golgi region of spermatocytes and spermatids of the rat testis.

Association of Caldendrin splice isoforms with secretory vesicles in neurohypophyseal axons and the pituitary.

Caldendrin is a neuronal calcium-binding protein, which is highly enriched in the postsynaptic density fraction and exhibits a prominent somato-dendritic distribution in brain. Two additional splice variants derive from the caldendrin gene, which have unrelated N-termini and were previously only detected in the retina. We now show that these isoforms are present in neurohypophyseal axons and on secretory granules of endocrine cells.

Brain synaptic junctional proteins at the acrosome of rat testicular germ cells.

Proteins of the presynaptic exocytic machinery have been found associated with the acrosome of male germ cells, suggesting that the sperm acrosome reaction and neurotransmission at chemical synapses may share some common mechanisms. To substantiate this hypothesis, we studied the expression and ultrastructural localization of prominent pre- and postsynaptic protein components in rat testis. The presynaptic membrane trafficking proteins SV2 and complexin, the vesicular amino acid transporters VGLUT and VIAAT, the postsynaptic scaffolding protein ProSAP/Shank, and the postsynaptic calcium-sensor protein caldendrin, could be identified in germ line cells.

Uteroglobin promoter-targeted c-MYC expression in transgenic mice cause hyperplasia of Clara cells and malignant transformation of T-lymphoblasts and tubular epithelial cells.

To investigate the influence of the proto-oncogene c-MYC on tumor development in different epithelial tissues which secrete Clara Cell Secretory Protein (uteroglobin, UG), transgenic mouse lines were established expressing the human c-MYC proto-oncogene under the control of the rabbit UG-promoter. These mice expressed the c-MYC transgene in Clara cells and other UG expressing tissues like uterus and prostate. In the bronchioalveolar epithelium of the lung hyperplasias developed originating from Clara cells.

The cortactin-binding postsynaptic density protein proSAP1 in non-neuronal cells.

Proline-rich synapse-associated protein-1 (ProSAP1) is a neuronal PDZ domain-containing protein that has recently been identified as an essential element of the postsynaptic density. Via its interaction with the actin-binding protein cortactin and its integrative function in the organization of neurotransmitter receptors, ProSAP1 is believed to be involved in the linkage of the postsynaptic signaling machinery to the actin-based cytoskeleton, and may play a role in the cytoskeletal rearrangements that underlie synaptic plasticity. As a result of our ongoing studies on the distribution and function of this novel PDZ domain protein, we now report that the expression of ProSAP1 is restricted neither to neurons and interneuronal junctions nor to the nervous system.

Evidence for microvesicular storage and release of glycine in rodent pinealocytes.

Prompted by previous studies suggesting a regulatory role for the inhibitory amino acid gamma-aminobutyric acid (GABA) within the mammalian pineal gland, we carried out a study of rat and gerbil pineal organs to elucidate whether there is evidence for a vesicular storage and release of GABA and/or glycine. Immunohistochemistry revealed the presence of the vesicular inhibitory amino acid transporter in pinealocytes. Moreover, we found that, in addition to glutamate and aspartate, cultured pinealocytes also released glycine upon stimulation by depolarizing concentrations of KCl, whereas the content of GABA in the culture medium did not exceed the detection limit either under control conditions or following KCl application.

Expression of synaptic vesicle trafficking proteins in the developing rat pineal gland.

Adult mammalian pinealocytes contain several synaptic membrane proteins that are probably involved in the regulation of targeting and exocytosis of synaptic-like microvesicles (SLMVs). Immunohistochemical techniques have now demonstrated the spatiotemporal expression pattern of some of these proteins during rat pineal ontogenesis. Various synaptic vesicle trafficking proteins are detectable in proliferating epithelial cells of the pineal anlage even at embryonic day 17.

Immunohistochemical study of the glutamate transporter proteins GLT-1 and GLAST in rat and gerbil pineal gland.

Several investigations performed during this decade have led to the hypothesis that small secretory vesicles of pinealocytes (generally referred to as synaptic-like microvesicles, SLMVs) are components of a system for intercellular paracrine communication between pineal cells, which shares many features with the process of synaptic neurotransmission. According to a recent study, one parallel that can be drawn to synaptic signal transduction seems to be the presence of pineal re-uptake systems for messenger molecules released from SLMVs, i.e.

Interstitial glial cells of the gerbil pineal gland display immunoreactivity for the metabotropic glutamate receptors mGluR2/3 and mGluR5.

Recent studies have strengthened the hypothesis that neuroactive amino acids such as L-glutamate play an important role in the physiology of the mammalian pineal gland. In particular, there is now considerable evidence that L-glutamate is liberated from electron-lucent microvesicles of pinealocytes for a paracrine modulation of melatonin synthesis and release which may at least partially be mediated by the metabotropic glutamate receptor mGluR3. In order to expand our incomplete knowledge of possible pineal target cells and signal transduction mechanisms which are involved in glutamate-dependent intercellular communication, we have performed an immunohistochemical study of the gerbil pineal gland with antibodies directed against the metabotropic glutamate receptors mGluR2/3 and mGluR5.

Immunoreactivity for multiple GABA transporters (GAT-1, GAT-2, GAT-3) in the gerbil pineal gland.

In order to further elucidate the role of gamma-aminobutyric acid (GABA) within the mammalian pineal gland, an immunocytochemical study was performed aimed at providing information on the occurrence and localization of the plasma-lemmal GABA transporters GAT-1-3 in the gerbil pineal organ. Whereas all three transporter subtypes were regularly present in this endocrine tissue, their cellular distribution differed. The analysis of serial semi-thin sections showed that pinealocytes as well as interstitial glial cells contain immunocytochemically detectable amounts of GAT proteins, indicating that both pineal parenchymal cell types participate in GABA reuptake.

Synaptic-like microvesicles in mammalian pinealocytes.

The recent deciphering of the protein composition of the synaptic vesicle membrane has led to the unexpected identification of a compartment of electron-lucent microvesicles in neuroendocrine cells which resemble neuronal synaptic vesicles in terms of molecular structure and function. These vesicles are generally referred to as synaptic-like microvesicles (SLMVs) and have been most intensively studied in pancreatic beta-cells, chromaffin cells of the adrenal medulla, and pinealocytes of the pineal gland. This chapter focuses on the present knowledge of SLMVs as now well-established constituents of mammalian pinealocytes.

Munc-18-1 and cysteine string protein (csp) in pinealocytes of the gerbil pineal gland.

Mammalian pinealocytes contain several synaptic membrane proteins which probably play a role in the targeting and exocytosis of secretory vesicles, in particular of synaptic-like microvesicles (SLMVs). The latter are considered as the endocrine equivalent of neuronal synaptic vesicles. By means of immunocytochemical techniques and immunoblot analyses, we now show that two further key components of the molecular apparatus regulating neurotransmitter release are present in the gerbil pineal gland, i.

Developmental pattern of cell type-specific calretinin immunoreactivity in the postnatal gerbil pineal gland.

The postnatal development of immunoreactivity for the neuronal calcium-binding protein calretinin in the pineal gland of the Mongolian gerbil was investigated using immunostaining of serial semithin sections. Calretinin-positive pineal cells could readily be visualized from the day of birth (P0) onwards and coexpressed the intermediate filament (IF) protein vimentin. During the first half of the first postnatal week, many of the calretinin-/vimentin-positive cells were also immunopositive for synaptophysin and neuron-specific enolase (NSE) and thus corresponded to pinealocytes.

Developmental pattern of cell type-specific calretinin immunoreactivity in the postnatal gerbil pineal gland.

The postnatal development of immunoreactivity for the neuronal calcium-binding protein calretinin in the pineal gland of the Mongolian gerbil was investigated using immunostaining of serial semithin sections. Calretinin-positive pineal cells could readily be visualized from the day of birth (P0) onwards and coexpressed the intermediate filament (IF) protein vimentin. During the first half of the first postnatal week, many of the calretinin-/vimentin-positive cells were also immunopositive for synaptophysin and neuron-specific enolase (NSE) and thus corresponded to pinealocytes.

Rodent pancreatic islet cells contain the calcium-binding proteins calcineurin and calretinin.

Calcium is known to be of critical importance for hormone secretion in the insulin-producing B-cells of the endocrine, pancreas. Calcium-mediated intracellular signal transduction and the regulation of the concentration of free calcium in B-cells probably involve calcium-binding proteins. In the present study, we have investigated the expression of the calcium/calmodulin-dependent phosphatase, calcineurin, and the EF-hand calcium-binding protein, calretinin, in pancreata of hamsters, gerbils, and rats by immunocytochemistry.

Expression of synaptic membrane proteins in gerbil pinealocytes in primary culture.

Pinealocytes of various mammalian species contain abundant synaptic-like microvesicles (SLMVs) which are considered the endocrine equivalent of neuronal synaptic vesicles. Although the pinealocytes may thus be a suitable cellular model for experimental in vitro studies of SLMVs, nothing is known about the presence of SLMVs in isolated pinealocytes maintained under tissue culture conditions. In the present investigation, we prepared dissociated primary cultures of gerbil pinealocytes to study the expression and distribution of protein components of synaptic vesicles/SLMVs and the presynaptic plasmalemma in pinealocytes kept in vitro.

Rat and gerbil pinealocytes contain the synaptosomal-associated protein 25 (SNAP-25).

It has recently been established that the neuroendocrine pinealocytes of mammals contain several synaptic membrane proteins that are involved in the regulation of vesicle trafficking in the nerve terminal. In the present study, we have conducted immunoblot and immunocytochemical analyses to demonstrate that another key component of the presynaptic plasmalemma, i.e.

Synaptotagmin I, synaptobrevin II, and syntaxin I are coexpressed in rat and gerbil pinealocytes.

Recent studies have shown that mammalian pinealocytes contain a compartment of synaptic-like microvesicles that may serve secretory functions; however, knowledge of the molecular composition of these microvesicles is still incomplete. Therefore, we have analyzed rat and gerbil pineal glands for the presence of synaptotagmin I, synaptobrevin I and II, syntaxin I, and synaptoporin (synaptophysin II) by immunoblot analyses and immunostaining of serial semithin sections. These proteins, which are components of the synaptic vesicle membrane or presynaptic plasmalemma, are thought to be essential for synaptic vesicle trafficking and exocytosis.

Differential immunocytochemical localization of calretinin in the pineal gland of three mammalian species.

Calcium plays an important role for signal transduction in the mammalian pineal organ. The regulation of the intracellular concentration of free calcium probably involves calcium-binding proteins of the calmodulin superfamily. In the present study, we have investigated the expression of calretinin, one member of this superfamily, in the pineal organ of hamsters, gerbils and guinea-pigs by means of immunochemical and immunocytochemical analyses with a calretinin-specific antiserum.

Differential distribution of synaptotagmin I and rab3 in the anterior pituitary of four mammalian species.

In the anterior pituitary of rat, gerbil, hamster and guinea pig, the presence and cellular distribution of the synaptic vesicle-associated proteins synaptotagmin I and rab3 were analyzed by immunoblotting and by immunocytochemical staining of serial semithin sections. Our results show that rab3 proteins are ubiquitously expressed in all endocrine cell types of both the anterior and intermediate lobe. In many cells, rab3 immunoreactivity was concentrated beneath the plasmalemma.

Bronchiolar nonciliated secretory (Clara) cells: source of guanylin in the mammalian lung.

The peptide guanylin, which has recently been isolated from the intestine, is involved in the regulation of fluid secretion in the intestinal epithelium by activation of guanylate cyclase C, the putative guanylin receptor. Since the latter protein is also expressed in airway epithelia, we investigated the lung of three mammalian species for the presence and cellular localization of guanylin by immunoblot (Western blot) analyses and light and electron microscopical immunocytochemistry. In Western blots of bovine, guinea pig, and rat lung extracts, three different guanylin antisera directed against the midportion and against the C terminus of the precursor molecule identified a peptide band corresponding to the apparent molecular mass of guanylin.