Molecular Interactions During Fertilization: Sperm -Egg Binding and Regulation of the Acrosome Reaction
Burkin, Heather Rheanne
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Permalink
https://hdl.handle.net/2142/83550
Description
Title
Molecular Interactions During Fertilization: Sperm -Egg Binding and Regulation of the Acrosome Reaction
Author(s)
Burkin, Heather Rheanne
Issue Date
2003
Doctoral Committee Chair(s)
Miller, David J.
Department of Study
Animal Sciences
Discipline
Animal Sciences
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Language
eng
Abstract
Fertilization requires a series of molecular interactions between the sperm and egg, but many of the molecules involved remain unknown. Experiments were performed to characterize and identify the primary sperm receptor for the porcine zona pellucida. Zona proteins were labeled with a fluorescent dye and incubated with live boar sperm. Zona proteins bound the anterior portion of the head, concentrated at the acrosomal ridge. Zona protein binding ability was acquired in the corpus of the epididymis, correlating with the developmental stage at which sperm become fertilization competent. A library of phage displaying peptides derived from boar testis was screened for candidate porcine zona pellucida receptors; however, a viable candidate receptor was not identified. The sperm acrosome reaction is an exocytotic event that is initiated when sperm bind to the zona and is required for zona penetration. During the acrosome reaction, the plasma membrane fuses with the outer acrosomal membrane and vesicle contents are released. Many of the molecules required for membrane fusion during the acrosome reaction remain enigmatic. Using neurotransmitter release as a model, molecules that might regulate membrane fusion were identified in sperm. Complexin is present in the acrosomal region and an antibody to complexin blocked the acrosome reaction, suggesting complexin may regulate membrane fusion during the acrosome reaction. Munc18, a molecule known to regulate membrane fusion in neurons, was detected in testis and localized to the XY body and the sperm acrosomal region. CASK is an adaptor protein that has been implicated in coupling neuronal cell adhesion to exocytosis, and might also be an important link between zona binding and membrane fusion during the acrosome reaction. CASK is expressed in testis; however, only smaller immunoreactive products were detected in mature sperm. Both full length CASK and smaller proteins were detected in the sperm acrosomal region, but not in other testicular cell types. Western analysis of epididymal sections indicated CASK might be proteolytically processed during epididymal maturation. Because sperm acquire the ability to bind zona proteins, acrosome react, and fertilize eggs during epididymal maturation, CASK processing may play a role in the acquisition of these functions.
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