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Characterization of an A-kinase anchor protein in equine spermatozoa and examination of the effect of semen cooling and cryopreservation on the binding of that protein to the regulatory subunit of protein kinase-A

Regina M. O. TurnerCenter for Animal Transgenesis and Germ Cell Research, Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348-1692.

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Raul Casas-DolzCenter for Animal Transgenesis and Germ Cell Research, Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348-1692.

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Karen L. SchlingmannCenter for Animal Transgenesis and Germ Cell Research, Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348-1692.

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Saima HameedCenter for Animal Transgenesis and Germ Cell Research, Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square, PA 19348-1692.

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Abstract

Objective—To determine whether a homologue of A-kinase anchor protein 4 (AKAP4) is present and functional as an AKAP in equine spermatozoa and examine the effect of semen cooling and cryopreservation on binding of equine AKAP4 to the regulatory (RII) subunit of protein kinase-A (PK-A).

Sample Population—Ejaculated semen collected from 2 fertile stallions, 3 bulls, and 3 humans.

Procedure—Identification of an equine homologue of AKAP4 was investigated via DNA sequencing. Protein was extracted from the spermatozoa of each species for immunoblot analysis to identify AKAP4 and its precursor protein, pro-AKAP4; immunofluorescence microscopy was used to localize those proteins in spermatozoa. Ligand overlay assays were used to determine whether the identified proteins bound to the RII subunit of PK-A and whether cooling or cryopreservation of spermatozoa affected that binding.

Results—The partial genomic sequence of AKAP4 was identified in equine spermatozoa, and immunoblot analysis confirmed that AKAP4 and pro-AKAP4 are present in equine spermatozoa. Via immunofluorescence microscopy, these proteins were localized to the spermatozoal principal piece. Results of ligand overlay assays indicated that equine AKAP4 and pro-AKAP4 bind to the RII subunit of PKA and are AKAPs; AKAP4-RII binding was not affected by cooling or cryopreservation of spermatozoa.

Conclusions and Clinical Relevance—Results suggest that equine AKAP4 anchors PK-A to the spermatozoal flagellum (where the kinase is likely to be required for the regulation of spermatozoal motility), but decreases in spermatozoal motility in cooled or cryopreserved semen are not associated with decreased binding of AKAP4 and PK-A. (Am J Vet Res 2005;66:1056–1064)

Abstract

Objective—To determine whether a homologue of A-kinase anchor protein 4 (AKAP4) is present and functional as an AKAP in equine spermatozoa and examine the effect of semen cooling and cryopreservation on binding of equine AKAP4 to the regulatory (RII) subunit of protein kinase-A (PK-A).

Sample Population—Ejaculated semen collected from 2 fertile stallions, 3 bulls, and 3 humans.

Procedure—Identification of an equine homologue of AKAP4 was investigated via DNA sequencing. Protein was extracted from the spermatozoa of each species for immunoblot analysis to identify AKAP4 and its precursor protein, pro-AKAP4; immunofluorescence microscopy was used to localize those proteins in spermatozoa. Ligand overlay assays were used to determine whether the identified proteins bound to the RII subunit of PK-A and whether cooling or cryopreservation of spermatozoa affected that binding.

Results—The partial genomic sequence of AKAP4 was identified in equine spermatozoa, and immunoblot analysis confirmed that AKAP4 and pro-AKAP4 are present in equine spermatozoa. Via immunofluorescence microscopy, these proteins were localized to the spermatozoal principal piece. Results of ligand overlay assays indicated that equine AKAP4 and pro-AKAP4 bind to the RII subunit of PKA and are AKAPs; AKAP4-RII binding was not affected by cooling or cryopreservation of spermatozoa.

Conclusions and Clinical Relevance—Results suggest that equine AKAP4 anchors PK-A to the spermatozoal flagellum (where the kinase is likely to be required for the regulation of spermatozoal motility), but decreases in spermatozoal motility in cooled or cryopreserved semen are not associated with decreased binding of AKAP4 and PK-A. (Am J Vet Res 2005;66:1056–1064)