Expression and Function of Complexin 1 in Mammalian Sperm Acrosomal Exocytosis
Zhao, Longmei
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Permalink
https://hdl.handle.net/2142/83590
Description
Title
Expression and Function of Complexin 1 in Mammalian Sperm Acrosomal Exocytosis
Author(s)
Zhao, Longmei
Issue Date
2005
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
Membrane-bound vesicle fusion is important for a wide variety of cellular events including exocytosis. Exocytosis is regulated by the SNARE complex, whose core includes three proteins. Complexins 1 and 2 are highly related cytosolic proteins that bind tightly to the assembled SNARE complex and promote neuronal exocytosis. Studies of complexin 1 and 2 deficient mice suggest that they serve redundant functions in cells expressing both complexins. Like somatic cells, sperm undergo regulated exocytosis but the sperm vesicle, known as the acrosome, is a single large vesicle whose release has different characteristics than neuronal exocytosis. Upon adhesion to the mammalian egg extracellular matrix, the sperm acrosome is released to allow penetration of the egg coat. How vesicle fusion occurs at multiple points in this single large vesicle is unclear. Here we show by RT-PCR and Western blots that complexin 1 and 2 are expressed in testis and sperm. Both proteins are found in the acrosomal region of mature sperm and are released during acrosomal exocytosis (acrosome reaction). Although complexin 1 deficient sperm acrosome react in response to calcium ionophore, they did not acrosome react in response to soluble egg coat proteins. Sperm from complexin 1 deficient mice have reduced fertilizing ability, as assessed by in vitro fertilization and artificial insemination. Sperm from complexin 1 deficient mice are normal morphologically with only minor differences in motility. Furthermore, sperm from complexin 1 deficient animals capacitate normally and are able to bind to the egg coat. The major defect in complexin 1 deficient sperm was in the acrosome reaction because if the egg coat was removed, fertilization proceeded normally. In GST pulldown assays, complexins 1 and 2 bind to SNARE complex proteins extracted from sperm. Therefore, complexin 1 regulates vesicle fusion in two related but morphologically distinct secretory processes. Sperm are unusual because they express both complexins 1 and 2 but have a unique requirement for complexin 1.
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