Male Infertility, Impaired Sperm Motility, and Hydrocephalus in Mice Deficient in Sperm-Associated Antigen 6

Abstract

Gene targeting was used to create mice lacking sperm-associated antigen 6 (Spag6), the murine orthologue of Chlamydomonas PF16, an axonemal protein containing eight armadillo repeats predicted to be important for flagellar motility and stability of the axoneme central apparatus. Within 8 weeks of birth, approximately 50% of Spag6-deficient animals died with hydrocephalus. Spag6-deficient males surviving to maturity were infertile. Their sperm had marked motility defects and was morphologically abnormal with frequent loss of the sperm head and disorganization of flagellar structures, including loss of the central pair of microtubules and disorganization of the outer dense fibers and fibrous sheath. We conclude that Spag6 is essential for sperm flagellar motility and that it is important for the maintenance of the structural integrity of mature sperm. The occurrence of hydrocephalus in the mutant mice also implicates Spag6 in the motility of ependymal cilia.Fertilization is the process whereby sperm and eggs interact reciprocally to begin development. To initiate fertilization, mammalian sperm cells rely on the propulsive forces generated by their flagella to reach the site of fertilization in the oviduct and to penetrate the investments of the egg (8). All flagella contain an axoneme composed of structural elements and motor proteins that work in a coordinated and regulated fashion to produce wave forms that produce progressive movement (3,4,6,8,15,21). The axoneme consists of a central pair of microtubules (central apparatus) surrounded by nine doublets of microtubules with the associated force-generating dynein arms. The basic axonemal structure among cilia and flagella is conserved across species, and much of our understanding of the structure and function of the axoneme has been derived from the study of model organisms. Genetic studies on the green alga, Chlamydomonas, have revealed the importance of several genes for flagellar assembly, stability of specific axonemal structures, and motility (2-6, 15, 21). Inactivation of PF16, one of these Chlamydomonas genes, results in flagellar paralysis (2,20,21). Moreover, when the flagella from the pf16 mutant are demembranated to produce axonemes, the C1 microtubule is destabilized and C1-associated polypeptides are lost. We cloned the human and murine orthologues of PF16, named sperm-associated antigen 6 (Spag6), and found that the amino acid sequences of the mammalian and algal proteins were highly conserved, including the eight armadillo repeats required for the assembly of PF16 onto the C1 microtubule and for flagellar function (11,16,20,21). To determine if Spag6 plays a critical role in the function of the mammalian axoneme, we inactivated mouse Spag6. Males lacking Spag6 were infertile because their sperm had striking motility defects and were frequently decapitated and had disorganized flagellar structures. Approximately 50% of nullizygous males and females have enlarged heads and smaller bodies and die prematurely with hydrocephalus, presumably reflecting a...

An intronic insertion in KPL2 results in aberrant splicing and causes the immotile short-tail sperm defect in the pig

“…Mutations in pf16 (spag6) and pf20 have also been shown to affect spermatogenesis in the mouse, where spag6 interacts with pf20. Mutated spag6 is known to cause infertility and truncated flagella (28,29). These gene products have been localized to the central pair complex and are only expressed in the testis.…”

Deletion of the Parkin coregulated gene causes male sterility in the quaking viable mouse mutant

“…Structural and functional conservation of flagellar components between protozoa and mammals has been described. For instance, mice lacking Sperm antigen 6, the mammalian homologue of the Chlamydomonas axonemal protein PF16, are sterile due to sperm flagellar abnormalities (28). Ultrastructural localization of Pacrg in the developing sperm as well as additional biochemical analyses will be needed to confirm its function(s) in spermiogenesis.…”

Axonemal protofilament ribbons, DM10 domains, and the link to juvenile myoclonic epilepsy

“…Several studies have linked defects in ependymal ciliary motility with formation of hydrocephalus. For example, mutations in the Mdnah5 axonemal outer arm dynein heavy chain [Ibanez-Tallon et al, 2004], the sperm-associated antigen Spag6, which is related to the Chlamydomonas central pair microtubule complex protein PF16 [Smith and Lefebvre, 1996;Sapiro et al, 2002], and Polaris/Tg737 [Taulman et al, 2001], a component of the intraflagellar transport machinery [Pazour et al, 2000], all result in this phenotype; the dynein heavy chain mutant also exhibited stenosis of the cerebral aqueduct during the later stages of brain development [Ibanez-Tallon et al, 2004]. In addition, two rodent models for hydrocephalus (the WIC-Hyd rat and SUMS/ NP mouse) have ciliary defects although the mutated genes are not currently known [Bruni et al, 1988;Torikata et al, 1991].…”