Tpx-1 is a component of the outer dense fibers and acrosome of rat spermatozoa

Previously we reported the cloning of a member of the cysteine-rich secreto ry protein family, tpx-1, from a testis expression library using an outer d ense fiber (ODF)-specific antiserum. Using immunohistochemical and immunoel ectron microscopic techniques and Western blotting of purified sperm tail c omponents, we have determined that tpx-1 exists as 25 and 27 kDa proteins i n two components of rat spermatid: the ODFs and the acrosome. Tpx-1 mRNA is first expressed in the late pachytene spermatocytes, but the production of these tpx-1 proteins is translationally delayed for 4-5 days before being incorporated into the developing sperm acrosome, surrounding the elongating and condensing spermatid nucleus. Concurrent with sperm head formation, tp x-1 protein was incorporated into the developing sperm tail, and specifical ly the ODFs. The tpx-1 protein was seen within structures resembling granul ated bodies in the cytoplasmic lobe of elongating spermatids and was incorp orated subsequently into the growing tail in a manner consistent with ODF d evelopment. In addition, tpx-1 protein was localized at the ultrastructural level of the connecting piece of the neck and longitudinal columns of the fibrous sheath, suggesting common protein components in these cytoskeletal structures. As such, tpx-1 may have functional significance in the processe s of sperm head development and tail function. (C) 2001 Wiley-Liss, Inc.