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Localization and Physiological Regulation of the Exocytosis Protein SNAP‐25 in the Brain and Pituitary Gland of Xenopus laevis
Author(s) -
Sharon M. Kolk,
Robert E. Nordquist,
R. Tuinhof,
L. Gagliardini,
Brenda Thompson,
Alexander R. Cools,
Eric W. Roubos
Publication year - 2000
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1046/j.1365-2826.2000.00500.x
Subject(s) - biology , xenopus , immunocytochemistry , exocytosis , axon , colocalization , immunoelectron microscopy , microbiology and biotechnology , immunogold labelling , blot , medicine , endocrinology , anatomy , ultrastructure , biochemistry , immunohistochemistry , secretion , gene , immunology
In mammals, the synaptosomal‐associated protein of 25 kDa, SNAP‐25, is generally thought to play a role in synaptic exocytosis of neuronal messengers. Using a polyclonal antiserum against rat SNAP‐25, we have shown the presence of a SNAP‐25‐like protein in the brain of the South‐African clawed toad Xenopus laevis by Western blotting and immunocytochemistry. Xenopus SNAP‐25 is ubiquitously present throughout the brain, where its distribution in various identified neuronal perikarya and axon tracts is described. Western blot analysis and immunocytochemistry also demonstrated the presence of SNAP‐25 in the neural, intermediate and distal lobes of the pituitary gland. Intensity line plots of confocal laser scanning microscope images of isolated melanotropes indicated that SNAP‐25 is produced and processed in the rough endoplasmatic reticulum and Golgi apparatus, and is associated with the plasma membrane. Immunoelectron microscopy substantiated the idea that SNAP‐25 is present in the plasma membrane but also showed a close association of SNAP‐25 with the bounding membrane of peptide‐containing secretory granules in both the neurohemal axon terminals in the neural lobe and the endocrine melanotropes in the intermediate lobe. Quantitative Western blotting revealed that adapting Xenopus to a dark background has a clear stimulatory effect on the expression of SNAP‐25 in the neural lobe and in the melanotrope cells. This background light intensity‐dependent stimulation of SNAP‐25 expression was confirmed by the demonstration of increased immunofluorescence recorded by confocal laser scanning microscopy of individual melanotropes of black background‐adapted toads. On the basis of this study on Xenopus laevis , we conclude that SNAP‐25 (i) plays a substantial role in the secretion of a wide variety of neuronal messengers; (ii) functions in the central nervous system but also in neurohormonal and endocrine systems; (iii) acts at the plasma membrane but possibly also at the membrane of synaptic vesicles and peptide‐containing secretory granules; (iv) acts not only locally (as in synapses), but at various sites of the plasma membrane (as in the endocrine melanotrope cell); and (v) can be upregulated in its expression by physiological stimuli that increase the extent of the molecular machinery involved in exocytosis.