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This Article Full Text Full Text (PDF) Supplemental Data All Versions of this Article: fj.06-7716comv1 21/14/4121    most recent Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Lopez, C. I. Articles by Mayorga, L. S. PubMed PubMed Citation Articles by Lopez, C. I. Articles by Mayorga, L. S.

Membrane-permeant Rab3A triggers acrosomal exocytosis in living human sperm

Laboratorio de Biología Celular y Molecular, Instituto de Histología y Embriología (IHEM-CONICET), Facultad de Ciencias Médicas, Universidad Nacional de Cuyo, Mendoza, Argentina

¹Correspondence: Casilla de Correo 56, 5500 Mendoza, Argentina. E-mail: lmayorga{at}fcm.uncu.edu.ar

The acrosome reaction is a regulated Ca²⁺-dependent secretion event required for sperm-egg interaction. Previous studies indicate that the process requires Rab3-dependent tethering of membranes, SNARE complex assembly, and Ca²⁺-mediated activation of synaptotagmin. Sperm are transcriptionally and translationally inactive; hence, most studies of the exocytosis mechanism are limited to membrane-permeant reagents. The effect of proteins involved in exocytosis has been assessed only in permeabilized cells. Polyarginine peptides are a powerful tool for delivering macromolecules to cells. Most reports indicate that membrane translocation of arginine-containing proteins requires endocytosis; therefore, this strategy might not be useful in sperm. However, our results indicate that GST and Rab3A, when fused with an arginine-rich peptide, were able to translocate into sperm. Moreover, membrane-permeant Rab3A initiated exocytosis when prenylated and activated with GTP. We show here that a key event after the cytoplasmic Ca²⁺ increase caused by progesterone is the activation of Rab3A. When active Rab3A is introduced into sperm, Ca²⁺ in the extracellular medium and in the cytoplasm is dispensable. However, a Ca²⁺ efflux from inside the acrosome is still required to achieve exocytosis. In conclusion, arginine-containing proteins can penetrate the sperm plasma membrane and thus are valuable tools to study sperm physiology in intact cells.—Lopez, C. I., Belmonte, S. A., De Blas, G. A., Mayorga, L. S. Membrane-permeant Rab3A triggers acrosomal exocytosis in living human sperm.

Key Words: membrane-permeant proteins • arginine-rich peptides • Rab3A • acrosome reaction