title: Sak57, an acidic keratin initially present in the spermatid manchette before becoming a component of paraaxonemal structures of the developing tail.
abstract: We have previously reported that Sak57 (for Spermatogenic cell/Sperm-associated keratin of molecular mass 57 kDa) is an acidic keratin found in rat spermatocytes, spermatids, and sperm. Sak57 displays conserved amino acid sequences found in the 1A and 2A regions of the alpha-helical rod domain of keratins in human, rat, and mouse. We now report indirect immunofluorescence, confocal laser scanning microscopy and immunogold electron microscopy data showing that Sak57 is associated with the microtubular mantie of the manchette, a transient microtubular structure largely regarded as formed by tubulin and microtubule-associated proteins. The immunocytochemical localization of Sak57 was detected with a polyclonal antiserum to a multiple antigenic peptide (MAP) containing an amino acid sequence known to be present in the 2A region of the alpha-helical rod domain. During spermiogenic steps 8-12, Sak57 immunoreactive sites were restricted to microtubular mantie of the manchette which encircles the spermatid nucleus during shaping and chromatin condensation. At later stages (spermiogenic steps 12-14), Sak57 immunoreactive sites in the spermatid head region disappeared gradually as specific immunoreactivity appeared along the already assembled axoneme of the developing spermatid tail. Immunogold electron microscopy confirmed the presence of Sak57 immunoreactivity among microtubules of the manchette and on outer dense fibers and the longitudinal columns linking the ribs of the fibrous sheath. Mature spermatids (spermiogenic step 19) displayed tails with an immunofluorescent banding pattern contrasting with the lack of Sak57 immunoreactivity in the head region. Results from this study suggest that, during early spermiogenesis, a microtubular-Sak57 scaffolding is associated with the spermatid nucleus during shaping and chromatin condensation. During late spermiogenesis, the dispersion of the manchette coincides with the progressive visualization of Sak57 in the paraaxonemal outer dense fibers and longitudinal columns of the fibrous sheath in the developing spermatid tail.
authors.affiliation: Department of Cell Biology and Anatomical Sciences, City University of New York Medical School, New York 10031, USA.
authors.forename: L L
authors.initials: LL
authors.lastname: Tres
authors.forename: A L
authors.initials: AL
authors.lastname: Kierszenbaum
mesh_terms: D000818:Animals; D007633:Keratins / Q000378:metabolism*; D008297:Male; D008854:Microscopy, Electron; D008870:Microtubules / Q000378:metabolism* / Q000648:ultrastructure; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D013082:Sperm Tail / Q000378:metabolism* / Q000648:ultrastructure; D013087:Spermatids / Q000378:metabolism* / Q000648:ultrastructure
chemical_list: D007633:Keratins