Membrane-permeant Rab3A triggers acrosomal exocytosis in living human sperm.

LOPEZ, CI; BELMONTE, SA; DE BLAS, GA; MAYORGA, LS

FASEB JOURNAL

FEDERATION AMER SOC EXP BIOL

Año: 2007 vol. 21 p. 4121 - 4130

0892-6638

The acrosome reaction is a regulated Ca2+-dependent secretion event required forsperm-egg interaction. Previous studies indicate that the process requires Rab3-dependent tethering of membranes, SNARE complex assembly and Ca2+-mediatedactivation of synaptotagmin. Sperm are transcriptionally and translationally inactive;hence most studies on the exocytosis mechanism are limited to membrane-permeantreagents. The effect of proteins involved in exocytosis has only been assessed inpermeabilized cells. Poly-arginine peptides are a powerful tool for deliveringmacromolecules to cells. Most reports indicate that membrane translocation of argininecontainingproteins requires endocytosis; therefore this strategy might not be useful insperm. However, our results indicate that GST and Rab3A when fused with an argininerichpeptide were able to translocate into sperm. Moreover, membrane-permeant Rab3Ainitiated exocytosis when prenylated and activated with GTP. We show here that a keyevent after the cytoplasmic Ca2+ increase caused by progesterone is the activation ofRab3A. When active Rab3A is introduced into sperm, Ca2+ in the extracellular mediumand in the cytoplasm is dispensable. However, a Ca2+ efflux from inside the acrosome isstill required to achieve exocytosis. In conclusion, arginine-containing proteins canpenetrate the sperm plasma membrane and are thus valuable tools to study spermphysiology in intact cells.