Synaptotagmin I and IV define distinct populations of neuronal transport vesicles

Authors

  • Frédérique Berton,

    1. INSERM U 464, Institut Fédératif Jean Roche, Université de la Méditerranée, Faculté de Médecine, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
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  • Véronique Cornet,

    1. INSERM U 464, Institut Fédératif Jean Roche, Université de la Méditerranée, Faculté de Médecine, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
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  • Cécile Iborra,

    1. INSERM U 464, Institut Fédératif Jean Roche, Université de la Méditerranée, Faculté de Médecine, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
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  • Juan Garrido,

    1. INSERM U 464, Institut Fédératif Jean Roche, Université de la Méditerranée, Faculté de Médecine, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
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  • Bénédicte Dargent,

    1. INSERM U 464, Institut Fédératif Jean Roche, Université de la Méditerranée, Faculté de Médecine, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
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  • Mitsunori Fukuda,

    1. Developmental Neurobiology Laboratory, Brain Science Institute, The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako, Saitama, 351-0198 Japan
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  • Michael Seagar,

    1. INSERM U 464, Institut Fédératif Jean Roche, Université de la Méditerranée, Faculté de Médecine, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
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  • Béatrice Marquèze

    1. INSERM U 464, Institut Fédératif Jean Roche, Université de la Méditerranée, Faculté de Médecine, Boulevard Pierre Dramard, 13916 Marseille Cedex 20, France
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: Dr B. Marquèze, as above.
E-mail: marqueze@jean-roche.univ-mrs.fr

Abstract

Mammalian synaptotagmins constitute a multigene family of at least 11 membrane proteins. We have characterized synaptotagmin IV using antibodies directed against the C2A domain of the protein. Antibodies reacted specifically with a protein band that migrated as a 41–44 kDa doublet. Synaptotagmin IV expression was regulated throughout development. A strong decrease in the amount detected by Western blotting occurred between postnatal day 5 and adulthood, in agreement with studies on the expression of synaptotagmin IV transcripts. In subcellular fractionation, synaptotagmin IV was not detected in the synaptic vesicle-enriched fraction. Immunofluorescence microscopy was concordant with this finding. In 6-day-old rat cerebellum and cultured hippocampal neurons the subcellular distribution of synaptotagmin IV was clearly different from that of synaptotagmin I. Synaptotagmin IV displayed a punctate non-polarized distribution on neuronal extensions, whereas synaptotagmin I staining was essentially synaptic. Synaptotagmin IV staining was also observed in the soma in strong perinuclear fluorescent puncta superimposed on that of Golgi/TGN markers. Furthermore, synaptotagmin IV was seen in the proximal part of the growth cone domain and not in the microfilament-rich region which includes filopodia. Co-localizations with the adhesion molecules vinculin and zyxin at the proximal part of growth cones were observed. Synaptotagmin IV may thus be involved in the regulation of specific membrane-trafficking pathways during brain development.

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