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      Isoform-Specific Exocytotic Protein mRNA Expression in Hypothalamic Magnocellular Neurons: Regulation after Osmotic Challenge

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          Exocytosis is regulated by proteins which interact to promote docking and fusion of secretory granules with the plasma membrane. We have used in situ hybridization to study the mRNA expression for vesicle- associated membrane protein (VAMP) isoforms VAMP-1 and VAMP-2, synaptosomal- associated protein of 25-kDa (SNAP-25) isoforms SNAP-25a and SNAP-25b, mammalian homologue of unc-18 (munc-18) and Hrs-2 in neurosecretory neurons of the magnocellular paraventricular (PVN) and supraoptic (SON) nuclei of normal and osmotically challenged animals. In PVN and SON neurons of normal animals, strong labeling was demonstrated for VAMP-2 and SNAP-25a mRNA, whereas VAMP-1 or SNAP-25b mRNA could not be detected. Salt-loading (2% NaCl as drinking water), an animal model which increases the expression and secretion of hormones from hypothalamic magnocellular neurons, resulted in significantly increased mRNA levels for VAMP-2 (36%, 28%), munc-18 (74%, 68%) and SNAP-25a (59%, 77%) in the PVN and SON, respectively. There was no significant increase in Hrs-2 mRNA levels in the PVN, whereas a significant increase (22%) was observed in the SON. In the posterior pituitary, immunohistochemistry showed a marked decrease in numbers and intensity of vasopressin-immunoreactive (-IR) nerve endings after salt-loading. There were no obvious changes in numbers or intensity of VAMP-2-, munc-18-, Hrs-2- or SNAP-25-IR fibers. Large varicosities containing VAMP-2- and Hrs-2 immunocreactivity were seen in salt-loaded animals. The results show isoform-specific mRNA expression in neurosecretory neurons and an increased mRNA expression of proteins participating in the molecular regulation of exocytosis during an experimental situation characterized by increased secretion.

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          Most cited references 8

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          Marine barite as a monitor of seawater strontium isotope composition

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            A fusion protein required for vesicle-mediated transport in both mammalian cells and yeast.

            A protein sensitive to N-ethylmaleimide catalyses the fusion of transport vesicles with Golgi cisternae in a mammalian cell-free system. By cloning and sequencing its gene from Chinese hamster ovary cells and by use of in vitro assays, we show that this fusion protein is equivalent to the SEC18 gene product of the yeast Saccharomyces cerevisiae, known to be essential for vesicle-mediated transport from the endoplasmic reticulum to the Golgi apparatus. The mechanism of vesicular fusion is thus highly conserved, both between species and at different stages of transport.
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              SNAP family of NSF attachment proteins includes a brain-specific isoform.

              The soluble NSF attachment proteins (SNAPs) enable N-ethyl-maleimide-sensitive fusion protein (NSF) to bind to target membranes. Here we report the cloning and sequencing of complementary DNAs encoding alpha-, beta- and gamma-SNAPs. Two of these proteins, alpha and gamma, are found in a wide range of tissues, and act synergistically in intra-Golgi transport. The third, beta, is a brain-specific isoform of alpha-SNAP. Thus, NSF and SNAPs appear to be general components of the intracellular membrane fusion apparatus, and their action at specific sites of fusion must be controlled by SNAP receptors particular to the membranes being fused, as described in the accompanying article.

                Author and article information

                S. Karger AG
                December 1999
                24 December 1999
                : 70
                : 6
                : 392-401
                aDepartment of Neuroscience, Karolinska Institutet, Stockholm, Sweden and bDepartment of Neurobiology and Anatomy, University of Texas Medical School, Houston, Tex., USA
                54501 Neuroendocrinology 1999;70:392–401
                © 1999 S. Karger AG, Basel

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                Page count
                Figures: 5, References: 40, Pages: 10
                Regulation of Hypothalamic Neurons


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