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Remodeling of the plasma membrane in preparation for sperm-egg recognition: roles of acrosomal proteins.

Tanphaichitr N, Kongmanas K, Kruevaisayawan H, Saewu A, Sugeng C, Fernandes J, Souda P, Angel JB, Faull KF, Aitken RJ, Whitelegge J, Hardy D, Berger T, Baker M - Asian J. Androl. (2015 Jul-Aug)

Bottom Line: The molecular mechanisms of this process have been studied for the past six decades with the results obtained being both interesting and confusing.Immunoprecipitation indicates that ZAN interacts with other acrosomal proteins, proacrosin/acrosin and sp32 (ACRBP), also present in the HMW complexes.Immunodetection of ZAN and proacrosin/acrosin on spermatozoa further indicates that both proteins traffic to the sperm head surface during capacitation where the sperm acrosomal matrix is still intact, and therefore they are likely involved in the initial sperm-ZP binding step.

View Article: PubMed Central - PubMed

Affiliation: Chronic Disease Program, Ottawa Hospital Research Institute, Ottawa; Department of Obstetrics and Gynaecology, University of Ottawa; Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ontario, Canada, .

ABSTRACT
The interaction of sperm with the egg's extracellular matrix, the zona pellucida (ZP) is the first step of the union between male and female gametes. The molecular mechanisms of this process have been studied for the past six decades with the results obtained being both interesting and confusing. In this article, we describe our recent work, which attempts to address two lines of questions from previous studies. First, because there are numerous ZP binding proteins reported by various researchers, how do these proteins act together in sperm-ZP interaction? Second, why do a number of acrosomal proteins have ZP affinity? Are they involved mainly in the initial sperm-ZP binding or rather in anchoring acrosome reacting/reacted spermatozoa to the ZP? Our studies reveal that a number of ZP binding proteins and chaperones, extracted from the anterior sperm head plasma membrane, coexist as high molecular weight (HMW) complexes, and that these complexes in capacitated spermatozoa have preferential ability to bind to the ZP. Zonadhesin (ZAN), known as an acrosomal protein with ZP affinity, is one of these proteins in the HMW complexes. Immunoprecipitation indicates that ZAN interacts with other acrosomal proteins, proacrosin/acrosin and sp32 (ACRBP), also present in the HMW complexes. Immunodetection of ZAN and proacrosin/acrosin on spermatozoa further indicates that both proteins traffic to the sperm head surface during capacitation where the sperm acrosomal matrix is still intact, and therefore they are likely involved in the initial sperm-ZP binding step.

No MeSH data available.


Related in: MedlinePlus

Proposed model of the involvement of acrosomal proteins in sperm–ZP interaction. During capacitation, a fraction of acrosomal proteins with ZP affinity traffics to the anterior sperm head surface as part of the initiation of acrosomal exocytosis. This endows the ability of Cap sperm to start binding to the ZP. Acrosomal exocytosis continues on the ZP with dispersion of the acrosomal matrix. The same acrosomal proteins in the matrix then contribute to the anchoring of acrosome reacting sperm to the ZP. Key: PM: plasma membrane; OAM: outer acrosomal membrane; IAM: inner acrosomal membrane; ZP: zona pellucida.
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Figure 4: Proposed model of the involvement of acrosomal proteins in sperm–ZP interaction. During capacitation, a fraction of acrosomal proteins with ZP affinity traffics to the anterior sperm head surface as part of the initiation of acrosomal exocytosis. This endows the ability of Cap sperm to start binding to the ZP. Acrosomal exocytosis continues on the ZP with dispersion of the acrosomal matrix. The same acrosomal proteins in the matrix then contribute to the anchoring of acrosome reacting sperm to the ZP. Key: PM: plasma membrane; OAM: outer acrosomal membrane; IAM: inner acrosomal membrane; ZP: zona pellucida.

Mentions: While pig APM vesicles comprise a number of ZP binding proteins and chaperones, only some of these proteins interact with each other to form HMW complexes. ZAN, SED1, proacrosin/acrosin, ACRBP, SP10 and ZPBP1 are the set of proteins in HMW complexes, which are known to be relevant in sperm–ZP binding, whereas TCP-1 subunits are chaperones found in these complexes. HMW complexes from Cap sperm have significantly higher capacity to bind to pig ZP3 glycoproteins (sperm receptors), and this is partly because of the higher amounts of both of these protein constituents, compared with HMW complexes of Noncap sperm. As ZAN, proacrosin/acrosin, ACRBP, ZPBP1 and SP10 are known to be acrosomal proteins, we performed studies with the first three of these to determine whether they are targeted to the sperm head surface during capacitation. Our results revealing that a fraction of ZAN and proacrosin/acrosin indeed traffics to the sperm head surface during capacitation is in accordance with the recent finding in the mouse system that acrosomal exocytosis initiates during sperm migration through the cumulus cell layers: that is, prior to the spermatozoon encountering the ZP. It remains to be seen whether the timing of the inception of acrosomal exocytosis is the same in the pig. Nonetheless, the results suggest that ZAN, proacrosin/acrosin and perhaps also other acrosomal proteins (yet to be identified) that have been trafficked to the sperm head surface are involved in the initial interaction between Cap sperm and the ZP (while the sperm acrosomal matrix still remains relatively intact; see our model in Figure 4). The remainder of these acrosomal proteins in the acrosome would then participate in the subsequent interaction of acrosome reacting spermatozoa with the ZP. Moreover, if these proteins move to the inner acrosomal membrane following the completion of acrosomal exocytosis, they might also participate in adhering acrosome-reacted sperm to the ZP. Given that the transport of ZAN to the sperm head surface has also been documented in mouse spermatozoa,65 the event may be used as a bioindex of sperm capacitation and we have research in progress to determine whether this movement occurs in human spermatozoa. Regardless, this phenomenon should be confirmed in oviductal spermatozoa Cap in vivo, to validate its biological relevance.


Remodeling of the plasma membrane in preparation for sperm-egg recognition: roles of acrosomal proteins.

Tanphaichitr N, Kongmanas K, Kruevaisayawan H, Saewu A, Sugeng C, Fernandes J, Souda P, Angel JB, Faull KF, Aitken RJ, Whitelegge J, Hardy D, Berger T, Baker M - Asian J. Androl. (2015 Jul-Aug)

Proposed model of the involvement of acrosomal proteins in sperm–ZP interaction. During capacitation, a fraction of acrosomal proteins with ZP affinity traffics to the anterior sperm head surface as part of the initiation of acrosomal exocytosis. This endows the ability of Cap sperm to start binding to the ZP. Acrosomal exocytosis continues on the ZP with dispersion of the acrosomal matrix. The same acrosomal proteins in the matrix then contribute to the anchoring of acrosome reacting sperm to the ZP. Key: PM: plasma membrane; OAM: outer acrosomal membrane; IAM: inner acrosomal membrane; ZP: zona pellucida.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4492047&req=5

Figure 4: Proposed model of the involvement of acrosomal proteins in sperm–ZP interaction. During capacitation, a fraction of acrosomal proteins with ZP affinity traffics to the anterior sperm head surface as part of the initiation of acrosomal exocytosis. This endows the ability of Cap sperm to start binding to the ZP. Acrosomal exocytosis continues on the ZP with dispersion of the acrosomal matrix. The same acrosomal proteins in the matrix then contribute to the anchoring of acrosome reacting sperm to the ZP. Key: PM: plasma membrane; OAM: outer acrosomal membrane; IAM: inner acrosomal membrane; ZP: zona pellucida.
Mentions: While pig APM vesicles comprise a number of ZP binding proteins and chaperones, only some of these proteins interact with each other to form HMW complexes. ZAN, SED1, proacrosin/acrosin, ACRBP, SP10 and ZPBP1 are the set of proteins in HMW complexes, which are known to be relevant in sperm–ZP binding, whereas TCP-1 subunits are chaperones found in these complexes. HMW complexes from Cap sperm have significantly higher capacity to bind to pig ZP3 glycoproteins (sperm receptors), and this is partly because of the higher amounts of both of these protein constituents, compared with HMW complexes of Noncap sperm. As ZAN, proacrosin/acrosin, ACRBP, ZPBP1 and SP10 are known to be acrosomal proteins, we performed studies with the first three of these to determine whether they are targeted to the sperm head surface during capacitation. Our results revealing that a fraction of ZAN and proacrosin/acrosin indeed traffics to the sperm head surface during capacitation is in accordance with the recent finding in the mouse system that acrosomal exocytosis initiates during sperm migration through the cumulus cell layers: that is, prior to the spermatozoon encountering the ZP. It remains to be seen whether the timing of the inception of acrosomal exocytosis is the same in the pig. Nonetheless, the results suggest that ZAN, proacrosin/acrosin and perhaps also other acrosomal proteins (yet to be identified) that have been trafficked to the sperm head surface are involved in the initial interaction between Cap sperm and the ZP (while the sperm acrosomal matrix still remains relatively intact; see our model in Figure 4). The remainder of these acrosomal proteins in the acrosome would then participate in the subsequent interaction of acrosome reacting spermatozoa with the ZP. Moreover, if these proteins move to the inner acrosomal membrane following the completion of acrosomal exocytosis, they might also participate in adhering acrosome-reacted sperm to the ZP. Given that the transport of ZAN to the sperm head surface has also been documented in mouse spermatozoa,65 the event may be used as a bioindex of sperm capacitation and we have research in progress to determine whether this movement occurs in human spermatozoa. Regardless, this phenomenon should be confirmed in oviductal spermatozoa Cap in vivo, to validate its biological relevance.

Bottom Line: The molecular mechanisms of this process have been studied for the past six decades with the results obtained being both interesting and confusing.Immunoprecipitation indicates that ZAN interacts with other acrosomal proteins, proacrosin/acrosin and sp32 (ACRBP), also present in the HMW complexes.Immunodetection of ZAN and proacrosin/acrosin on spermatozoa further indicates that both proteins traffic to the sperm head surface during capacitation where the sperm acrosomal matrix is still intact, and therefore they are likely involved in the initial sperm-ZP binding step.

View Article: PubMed Central - PubMed

Affiliation: Chronic Disease Program, Ottawa Hospital Research Institute, Ottawa; Department of Obstetrics and Gynaecology, University of Ottawa; Department of Biochemistry, Microbiology and Immunology, University of Ottawa, Ontario, Canada, .

ABSTRACT
The interaction of sperm with the egg's extracellular matrix, the zona pellucida (ZP) is the first step of the union between male and female gametes. The molecular mechanisms of this process have been studied for the past six decades with the results obtained being both interesting and confusing. In this article, we describe our recent work, which attempts to address two lines of questions from previous studies. First, because there are numerous ZP binding proteins reported by various researchers, how do these proteins act together in sperm-ZP interaction? Second, why do a number of acrosomal proteins have ZP affinity? Are they involved mainly in the initial sperm-ZP binding or rather in anchoring acrosome reacting/reacted spermatozoa to the ZP? Our studies reveal that a number of ZP binding proteins and chaperones, extracted from the anterior sperm head plasma membrane, coexist as high molecular weight (HMW) complexes, and that these complexes in capacitated spermatozoa have preferential ability to bind to the ZP. Zonadhesin (ZAN), known as an acrosomal protein with ZP affinity, is one of these proteins in the HMW complexes. Immunoprecipitation indicates that ZAN interacts with other acrosomal proteins, proacrosin/acrosin and sp32 (ACRBP), also present in the HMW complexes. Immunodetection of ZAN and proacrosin/acrosin on spermatozoa further indicates that both proteins traffic to the sperm head surface during capacitation where the sperm acrosomal matrix is still intact, and therefore they are likely involved in the initial sperm-ZP binding step.

No MeSH data available.


Related in: MedlinePlus