INSTITUTO DE HISTOLOGIA Y EMBRIOLOGIA DE MENDOZA DR. MARIO H. BURGOS
Unidad Ejecutora - UE
capítulos de libros
TOMES CLAUDIA NORA
Molecular mechanisms of exocytosis
Landes Bioscience/Eurekah.com and Springer Science+Business Media
Lugar: Austin, Texas, and New York, New York, USA; Año: 2007; p. 117 - 147
Sexual reproduction to perpetuate a given species occurs through fertilization, during which a diploid zygote is formed to produce a genetically distinct individual. To this end, the haploid sperm and haploid egg must collide to allow entry of the sperm head delivering the male chromatin into the egg cytoplasm. Both the male and female gametes undergo regulated exocytosis - termed the acrosome reaction and the cortical reaction respectively - at different times during their encounter. The success of fertilization depends on these exocytoses. Exocytosis of the sperms single vesicle the acrosome - is a synchronized, all-or-nothing process that happens only once in the life of the cell and shares the basic fusion molecules with neuronal, endocrine, and all the other cells covered in this book. Acrosomal exocytosis (AE) depends on both Rab3 activation and neurotoxin-sensitive SNAREs; it also requires the efflux of calcium from inside the acrosome. Convergence of Rab- and toxin-sensitive SNARE-dependent pathways is a hallmark of AE that makes it an attractive mammalian model to study the different phases of the membrane fusion cascade. Furthermore, because nature has endowed sperm with a cellular specialization that gives them a single, irreversible chance to fertilize an egg, AE is more straightforward to dissect compared to fusion in other cell types, where the same substances are secreted again and again, requiring the membranes and fusion machinery to recycle multiple times. The presence of secretory granules in the egg and the sperm highlights the essential nature of regulated exocytosis for the continued existence of multicellular species. Identifying and understanding the role and timing of the players involved are important for manipulating fertilization, either to enhance it or block it. The benefits of this knowledge are, however, not restricted to the reproduction field, but could be extended to more complex membrane fusion scenarios.