Adhesion Molecules-28

Advances and Experimental-3

Aging-9

Agricultural Biotechnology-37

Angiogenesis-29

Antisense-4

Apoptosis-49

Atherosclerosis-12

Autoimmunity-69

Bacterial Virulence-18

Bioinformatics-13

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Cancer Genetics-25

Cancer Metastasis-19

Cell Biology-16

Cell Cycle-34

Cell Metabolism-327

Channels and Transporters-79

Chaperones-11

Circadian Rhythms-13

Coagulation-14

Cytokines/Growth Factors-52

Development-223

DNA-56

DNA Surveillance and Repair-42

Drug Design-17

Endocrine-66

Evolution-33

Extracellular Matrix-30

Gastroenterology-52

Gene Expression-178

Gene Therapy-53

Heart-61

Heat Shock Proteins-19

Hematology-11

Immunology-93

Infectious Disease-71

Ischemia-Reperfusion-33

Leptin and Leptin Antagonists-1

Medical-20

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Prebiotic Evolution-2

Protein-12

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RNA-152

Signal Transduction-186

Stem Cells-80

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T-Cell Activation-12

Tissue Engineering-116

Transplant-51

Vaccines-82

Viruses-85

Chapter category: Cell Metabolism

Acrosomal Exocytosis

Chapter authors:
Claudia Nora Tomes

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 sperm’s 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.

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

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