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Spetex‐1: A new component in the middle piece of flagellum in rodent spermatozoa

Spetex‐1 has recently been isolated by differential display and screening of cDNA library. It encodes a protein of 556 amino acid residues possessing coiled‐coil motifs. In the rat seminiferous tubules (ST), Spetex‐1 was expressed in the cytoplasm of elongating spermatids. To examine the subcellular distribution of Spetex‐1 in mature spermatozoa, we performed biochemical and immunocytochemical approaches. We found that Spetex‐1 that was synthesized in the cytoplasm of elongating spermatids was subsequently integrated as a middle piece component into spermatozoa during spermiogenesis. After integration, the majority of Spetex‐1 in spermatozoa could be extracted by 6M urea under reduced condition but not released by the treatment of 1% Triton X‐100. Immunoelectron microscopy demonstrated that Spetex‐1 seemed to locate at the inner side of outer dense fibers (ODFs) in the middle piece or the narrow space between ODFs and axoneme. Spetex‐1 might be involved in the stability of the structural complexity comprising axoneme and ODFs in the middle piece of sperm flagellum. Mol. Reprod. Dev. © 2005 Wiley‐Liss, Inc.