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1 June 2003 A-Kinase Anchoring Protein 4 Binding Proteins in the Fibrous Sheath of the Sperm Flagellum
Paula R. Brown, Kiyoshi Miki, Deborah B. Harper, Edward M. Eddy
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Abstract

The fibrous sheath is a unique cytoskeletal structure located in the principal piece of the sperm flagellum and is constructed of two longitudinal columns connected by closely spaced circumferential ribs. Cyclic AMP-dependent protein kinases are secured within specific cytoplasmic domains by A-kinase anchoring proteins (AKAPs), and the most abundant protein in the fibrous sheath is AKAP4. Several other fibrous sheath proteins have been identified, but how the fibrous sheath assembles is not understood. Yeast two-hybrid assays and deletion mutagenesis were used to identify AKAP4-binding proteins and to map the binding regions on AKAP4 and on the proteins identified. We found that AKAP4 binds AKAP3 and two novel spermatogenic cell-specific proteins, Fibrous Sheath Interacting Proteins 1 and 2 (FSIP1, FSIP2). Transcription of Akap4, Akap3, and Fsip1 begins in early spermatid development, whereas transcription of Fsip2 begins in late spermatocyte development. AKAP3 is synthesized in round spermatids and incorporated into the fibrous sheath concurrently with formation of the rib precursors. However, AKAP4 is synthesized and incorporated into the nascent fibrous sheath late in spermatid development. The AKAP4 precursor is processed in the flagellum and only the mature form of AKAP4 appears to bind AKAP3. These results suggest that AKAP3 is involved in organizing the basic structure of the fibrous sheath, whereas AKAP4 has a major role in completing fibrous sheath assembly.

Paula R. Brown, Kiyoshi Miki, Deborah B. Harper, and Edward M. Eddy "A-Kinase Anchoring Protein 4 Binding Proteins in the Fibrous Sheath of the Sperm Flagellum," Biology of Reproduction 68(6), 2241-2248, (1 June 2003). https://doi.org/10.1095/biolreprod.102.013466
Received: 26 November 2002; Accepted: 1 January 2003; Published: 1 June 2003
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