title: A heterozygous mutation disrupting the SPAG16 gene results in biochemical instability of central apparatus components of the human sperm axoneme.
abstract: The SPAG16 gene encodes two major transcripts, one for the 71-kDa SPAG16L, which is the orthologue of the Chlamydomonas rheinhardtii central apparatus protein PF20, and a smaller transcript, which codes for the 35-kDa SPAG16S nuclear protein that represents the C-terminus (exons 11-16) of SPAG16L. We have previously reported that a targeted mutation in exon 11 of the Spag16 gene impairs spermatogenesis and prevents transmission of the mutant allele in chimeric mice. In the present report, we describe a heterozygous mutation in exon 13 of the SPAG16 gene, which causes a frame shift and premature stop codon, affording the opportunity to compare mutations with similar impacts on SPAG16L and SPAG16S for male reproductive function in mice and men. We studied two male heterozygotes for the SPAG16 mutation, both of which were fertile. Freezing-boiling of isolated sperm from both affected males resulted in the loss of the SPAG16L protein, SPAG6, another central apparatus protein that interacts with SPAG16L, and the 28-kDa fragment of SPAG17, which associates with SPAG6. These proteins were also lost after freezing-boiling cycles of sperm extracts from mice that were heterozygous for an inactivating mutation (exons 2 and 3) in Spag16. Our findings suggest that a heterozygous mutation that affects both SPAG16L and SPAG16S does not cause male infertility in man, but is associated with reduced stability of the interacting proteins of the central apparatus in response to a thermal challenge, a phenotype shared by the sperm of mice heterozygous for a mutation that affects SPAG16L.
authors: Department of Obstetrics & Gynecology, Virginia Commonwealth University, Richmond, Virginia 23298, USA. zzhang4@vcu.edu
authors: Zhibing
authors: Z
authors: Zhang
authors: Maimoona A
authors: MA
authors: Zariwala
authors: Maha M
authors: MM
authors: Mahadevan
authors: Pedro
authors: P
authors: Caballero-Campo
authors: Xuening
authors: X
authors: Shen
authors: Estelle
authors: E
authors: Escudier
authors: Bénédicte
authors: B
authors: Duriez
authors: Anne-Marie
authors: AM
authors: Bridoux
authors: Margaret
authors: M
authors: Leigh
authors: George L
authors: GL
authors: Gerton
authors: Marcus
authors: M
authors: Kennedy
authors: Serge
authors: S
authors: Amselem
authors: Michael R
authors: MR
authors: Knowles
authors: Jerome F
authors: JF
authors: Strauss
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D054468:Axoneme / Q000378:metabolism* / Q000648:ultrastructure; D004252:DNA Mutational Analysis; D006579:Heterozygote; D006801:Humans; D008297:Male; D051379:Mice; D008868:Microtubule Proteins / Q000378:metabolism; D008869:Microtubule-Associated Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009154:Mutation; D013081:Sperm Motility / Q000235:genetics; D013094:Spermatozoa / Q000378:metabolism / Q000648:ultrastructure*
chemical_list: D008868:Microtubule Proteins; D008869:Microtubule-Associated Proteins; C450619:SPAG16 protein, human; C400106:SPAG6 protein, human