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Rab3A Triggers the Acrosome Reaction in Permeabilized Human Spermatozoa
Ist Teil von
Biology of reproduction, 2000-04, Vol.62 (4), p.1084-1089
Ort / Verlag
United States: Society for the Study of Reproduction
Erscheinungsjahr
2000
Link zum Volltext
Quelle
MEDLINE
Beschreibungen/Notizen
The acrosome reaction is a regulated exocytotic process leading to a massive fusion between the outer acrosomal membrane and
the cell membrane. In spite of the great amount of information available related to the acrosome reaction in several species,
there is a remarkable paucity about the role of monomeric guanosine triphosphatases (GTPases) of the Rab familyâwell-established
participants in exocytosis in other cell typesâin the acrosome reaction. Western blot and immunofluorescence analysis indicate
that Rab3A is present in human spermatozoa and localizes to the acrosomal region in the sperm head. One difficulty in studying
the role of proteins in intact cells is the fact that they are unable to cross the cell membrane. Therefore, we established
a working model of streptolysin O-permeabilized human spermatozoa. Permeabilized spermatozoa were able to respond in a regulated
way to different stimuli, such as G protein activators and calcium. An acrosomal reaction was also triggered by a Rab3A peptide
corresponding to the effector region. More important, recombinant Rab3A protein in the GTP-bound form caused acrosome exocytosis.
The same protein loaded with GDP or Rab11 in the GTP-bound form was inactive. Also, recombinant GDI (GDP dissociation inhibitor)âa
protein that releases Rab proteins from membraneâinhibited a GTPγS-stimulated acrosome reaction. Our results indicate that
1) permeabilized spermatozoa can be used to study the role of macromolecules in the acrosome reaction, 2) Rab3A is present
in human spermatozoa, and 3) Rab3A or another Rab3 isoform is involved in the exocytosis of the acrosomal granule in human
spermatozoa.