Synaptotagmin VIII is localized to the mouse sperm head and may function in acrosomal exocytosis.
The acrosome is a large secretory granule that undergoes exocytosis when receptors on the sperm surface bind ligands in the egg extracellular matrix. Acrosomal exocytosis resembles stimulated secretion in neurons in that it is triggered by a rise in intracellular Ca(2+). Synaptotagmins (Syt) comprise proteins thought to transduce this Ca(2+) signal to the fusion machinery. In this study, we showed that Syt VIII is present in spermatogenic cDNA libraries. Antiserum raised against a Syt VIII-specific peptide, which recognizes Syt VIII but does not cross-react with other Syt isoforms, labeled a single prominent band on Western immunoblots of mouse sperm homogenate. Syt VIII was restricted to the sperm membrane fraction enriched in markers associated with the mouse sperm head. Fluorescent immunocytochemistry on intact mouse sperm showed that Syt VIII is localized to the acrosomal crescent and is lost upon acrosome reaction. Moreover, the amount of Syt VIII remaining with the sperm decreased proportionately with the extent of acrosome-reacted sperm. Thus, Syt VIII is a candidate for the Ca(2+) sensor that regulates acrosomal exocytosis in mammalian sperm.
Hutt
Darren M
DM
Department of Cellular and Molecular Medicine, Ottawa Health Research Institute, University of Ottawa, Ottawa, Ontario K1Y 4E9, Canada.
Cardullo
Richard A
RA
Baltz
Jay M
JM
Ngsee
Johnny K
JK
D000177:Acrosome / Q000187:drug effects / Q000502:physiology*; D020101:Acrosome Reaction / Q000187:drug effects / Q000502:physiology*; D000818:Animals; D015139:Blotting, Southern; D000001:Calcimycin / Q000494:pharmacology; D002135:Calcium-Binding Proteins; D004926:Escherichia coli / Q000378:metabolism; D005089:Exocytosis / Q000187:drug effects / Q000502:physiology*; D007150:Immunohistochemistry; D007536:Isomerism; D008297:Male; D008562:Membrane Glycoproteins / Q000096:biosynthesis / Q000378:metabolism*; D051379:Mice; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics; D011994:Recombinant Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013077:Sperm Head / Q000378:metabolism*; D050857:Synaptotagmins
D002135:Calcium-Binding Proteins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D012333:RNA, Messenger; D011994:Recombinant Proteins; C494306:Syt8 protein, mouse; D050857:Synaptotagmins; D000001:Calcimycin