Basonuclin is a zinc finger protein that was thought to be restricted to keratinocytes of stratified squamous epithelia. In epidermis, basonuclin is associated with the nuclei of mitotically active basal cells but not in terminally differentiating keratinocytes. We report here the isolation of a novel form of basonuclin, which we show is also expressed in stratified epithelia. Most unexpectedly, we find both forms in testis, where a surprising localization pattern was uncovered. While basonuclin RNA expression occurs in mitotically active germ cells, protein was not detected until the meiotic stage, where basonuclin localized to the appendage of the distal centriole of spermatocytes and spermatids. Near the end of spermiogenesis, basonuclin also accumulated in the acrosome and mitochondrial sheath surrounding the flagellum. Intriguingly, a perfect six– amino acid residue mitochondrial targeting sequence (Komiya, T., N. Hachiya, M. Sakaguchi, T. Omura, and K. Mihara. 1994. J. Biol. Chem. 269:30893–30897; Shore, G.C., H.M. McBride, D.G. Millar, N.A. Steenaart, and M. Nguyen. 1995. Eur. J. Biochem. 227: 9–18; McBride, H.M., I.S. Goping, and G.C. Shore. 1996. J. Cell. Biol. 134:307–313) is present in basonuclin 1a but not in the 1b form. Moreover, three distinct affinity-purified peptide antibodies gave this unusual pattern of basonuclin antibody staining, which was confirmed by cell fractionation studies. Our findings suggest a unique role for basonuclin in centrosomes within the developing spermatid, and a role for one of the protein forms in germ cell mitochondrial function. Its localization with the acrosome suggests that it may also perform a special function during or shortly after fertilization.
An Unexpected Localization of Basonuclin in the Centrosome, Mitochondria, and Acrosome of Developing Spermatids
1. Abbreviations used in this paper: BSN, basonuclin; DAPI, 4,6-diamidino-2-phenylindole.
Z.-H. Yang was supported by a grant from the National Institutes of Health (AR31737), and Dr. I. Gallicano was a postdoctoral fellow supported by a training grant awarded to the University of Chicago from the National Cancer Institute. Dr. E. Fuchs is an Investigator of the Howard Hughes Medical Institute.
Address all correspondence to Elaine Fuchs, Howard Hughes Medical Institute, Department of Molecular Genetics and Cell Biology, The University of Chicago, 5841 S. Maryland Avenue, Room N314, Chicago, IL 60637. Tel.: (773) 702–1347. Fax: (773) 702-0141.
Zhao-hui Yang, G. Ian Gallicano, Qian-Chun Yu, Elaine Fuchs; An Unexpected Localization of Basonuclin in the Centrosome, Mitochondria, and Acrosome of Developing Spermatids. J Cell Biol 5 May 1997; 137 (3): 657–669. doi: https://doi.org/10.1083/jcb.137.3.657
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