H2A.Bbd: an X-chromosome-encoded histone involved in mammalian spermiogenesis |
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| Authors: | Toyotaka Ishibashi Andra Li José M Eirín-López Ming Zhao Kristal Missiaen D Wade Abbott Marvin Meistrich Michael J Hendzel Juan Ausió |
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| Institution: | 1.Department of Biochemistry and Microbiology, University of Victoria, Victoria, BC V8W 3P6, Canada, 2.CHROMEVOL-XENOMAR Group, Departamento de Biología Celular y Molecular, Universidade da Coruña, A Coruña, Spain, 3.Department of Experimental Radiation Oncology, University of Texas, M.D. Anderson Cancer Center, Houston, TX, USA and 4.Department of Oncology, Faculty of Medicine, University of Alberta, Edmonton T6G 1Z2, Canada |
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| Abstract: | Despite the identification of H2A.Bbd as a new vertebrate-specific replacement histone variant several years ago, and despite the many in vitro structural characterizations using reconstituted chromatin complexes consisting of this variant, the existence of H2A.Bbd in the cell and its location has remained elusive. Here, we report that the native form of this variant is present in highly advanced spermiogenic fractions of mammalian testis at the time when histones are highly acetylated and being replaced by protamines. It is also present in the nucleosomal chromatin fraction of mature human sperm. The ectopically expressed non-tagged version of the protein is associated with micrococcal nuclease-refractory insoluble fractions of chromatin and in mouse (20T1/2) cell line, H2A.Bbd is enriched at the periphery of chromocenters. The exceedingly rapid evolution of this unique X-chromosome-linked histone variant is shared with other reproductive proteins including those associated with chromatin in the mature sperm (protamines) of many vertebrates. This common rate of evolution provides further support for the functional and structural involvement of this protein in male gametogenesis in mammals. |
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