title: Spatiotemporal association of DNAJB13 with the annulus during mouse sperm flagellum development.
abstract: BACKGROUND
  The sperm annulus is a septin-based fibrous ring structure connecting the midpiece and the principal piece of the mammalian sperm flagellum. Although ultrastructural abnormalities and functional importance of the annulus have been addressed in Sept4-null mutant mice and a subset of human patients with asthenospermia syndrome, little is known about how the structure is assembled and positioned to the midpiece-principal piece junction during mammalian sperm flagellum development.
  
  
  RESULTS
  By performing immunofluorescence and biochemical approaches with antibodies against DNAJB13 and an annulus constituent SEPT4, we report here a spatiotemporal association of DNAJB13 with sperm annulus during mouse sperm flagellum development. DNAJB13 co-localized with SEPT4 to the annulus, and both were first able to be detected in step 9 spermatids. As spermiogenesis proceeded, the annular DNAJB13 immunosignal increased until the annulus reached the midpiece-principal piece junction, and then gradually disappeared from it in late spermiogenesis. In contrast, the SEPT4 immunosignal was relatively unaltered, and still present on annulus of mature spermatozoa. In Sept4-null mouse spermatids lacking the annulus structure, the annulus-like DNAJB13 immunosignal was still able to be detected, albeit weaker, at the neck region of the flagella. In vitro DNAJB13 was co-localized and interacted with SEPT4 directly.
  
  
  CONCLUSIONS
  The direct interaction of DNAJB13 with SEPT4 in vitro and its spatiotemporal association with the annulus during sperm flagellum development, and even its annulus-like appearance in the annulus-deficient spermatids, suggest that DNAJB13 may be involved in assembling the annulus structure and positioning it towards the midpiece-principal piece junction.
authors.affiliation: Department of Cell and Molecular Biology, Karolinska Institutet, SE-171 77 Stockholm, Sweden. Jikui.Guan@ki.se
authors.forename: Jikui
authors.initials: J
authors.lastname: Guan
authors.forename: Makoto
authors.initials: M
authors.lastname: Kinoshita
authors.forename: Li
authors.initials: L
authors.lastname: Yuan
mesh_terms: D000818:Animals; D051017:Apoptosis Regulatory Proteins; D003598:Cytoskeletal Proteins / Q000235:genetics / Q000378:metabolism*; D005260:Female; D020558:GTP Phosphohydrolases / Q000235:genetics / Q000378:metabolism*; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D050956:HSP40 Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D015151:Immunoblotting; D047468:Immunoprecipitation; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D018832:Molecular Chaperones; D011485:Protein Binding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D058112:Septins; D013082:Sperm Tail / Q000378:metabolism*; D013087:Spermatids / Q000166:cytology / Q000378:metabolism; D013091:Spermatogenesis; D013997:Time Factors; D014162:Transfection
chemical_list: D051017:Apoptosis Regulatory Proteins; D003598:Cytoskeletal Proteins; C531170:DNAJB13 protein, mouse; D050956:HSP40 Heat-Shock Proteins; D018832:Molecular Chaperones; D011993:Recombinant Fusion Proteins; D049452:Green Fluorescent Proteins; D020558:GTP Phosphohydrolases; C115474:Sept4 protein, mouse; D058112:Septins