title: CD55 in rat male reproductive tissue: differential expression in testis and expression of a unique truncated isoform on spermatozoa.
abstract: CD55 is a key regulator of complement activation, expressed on most tissues and cells in man and other mammals. In the rat, alternative splicing in the gene encoding CD55 yields GPI-anchored (GPI-CD55) and transmembrane (TM-CD55) forms. Published Northern blot analysis indicated that while GPI-CD55 was broadly expressed, TM-CD55 was primarily expressed in the testis, although the precise site of expression was not identified. To clarify the distribution of CD55 isoforms in rat reproductive tissues, we first performed immunohistochemistry and Western blot analysis with an anti-rat CD55 mAb that recognized all reported CD55 isoforms, and a polyclonal immunoglobulin specific for TM-CD55. CD55 was absent in testis prior to puberty. Post-puberty, CD55 was expressed at high levels on all spermiogenic cells from step 6 spermatid onward, and on mature spermatozoa focussed on the acrosome, but was absent from support cells and early progenitors. Enzymatic digestion revealed that GPI-CD55 was predominant in testis and spermatozoa. Staining for TM-CD55 with specific immunoglobulin confirmed its absence from mature sperm and expression on spermatids only between steps 11 and 14 of development. GPI-CD55 on spermatozoa was of lower molecular weight than that in testis and other tissues; sequencing from spermatozoal mRNA identified a unique isoform of GPI-CD55 missing short consensus repeat 4. The predominant acrosome expression and presence of a unique, truncated isoform of CD55 on spermatozoa provides further support for the hypothesis that the acrosome is a highly specialized region in which closely regulated complement activation may contribute to reproductive function.
authors.affiliation: Complement Biology Group, Department of Medical Biochemistry and Immunology, School of Medicine, Cardiff University, Heath Park, Cardiff CF14 4XN, UK.
authors.forename: Masashi
authors.initials: M
authors.lastname: Mizuno
authors.forename: Rossen M
authors.initials: RM
authors.lastname: Donev
authors.forename: Claire L
authors.initials: CL
authors.lastname: Harris
authors.forename: B Paul
authors.initials: BP
authors.lastname: Morgan
mesh_terms: D000177:Acrosome / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D000595:Amino Acid Sequence; D000818:Animals; D018958:CD55 Antigens / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D003165:Complement System Proteins / Q000378:metabolism; D005260:Female; D008297:Male; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D020033:Protein Isoforms / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017384:Sequence Deletion; D013091:Spermatogenesis / Q000235:genetics; D013094:Spermatozoa / Q000737:chemistry / Q000254:growth & development* / Q000276:immunology; D013737:Testis / Q000737:chemistry / Q000254:growth & development* / Q000276:immunology; D014018:Tissue Distribution
chemical_list: D018958:CD55 Antigens; D020033:Protein Isoforms; D012333:RNA, Messenger; D003165:Complement System Proteins