Sperm-Associated Antigen–17 Gene Is Essential for Motile Cilia Function and Neonatal Survival

Abstract

Primary ciliary dyskinesia (PCD), resulting from defects in cilia assembly or motility, is caused by mutations in a number of genes encoding axonemal proteins. PCD phenotypes are variable, and include recurrent respiratory tract infections, bronchiectasis, hydrocephaly, situs inversus, and male infertility. We generated knockout mice for the sperm-associated antigen-17 (Spag17) gene, which encodes a central pair (CP) protein present in the axonemes of cells with "9 1 2" motile cilia or flagella. The targeting of Spag17 resulted in a severe phenotype characterized by immotile nasal and tracheal cilia, reduced clearance of nasal mucus, profound respiratory distress associated with lung fluid accumulation and disruption of the alveolar epithelium, cerebral ventricular expansion consistent with emerging hydrocephalus, failure to suckle, and neonatal demise within 12 hours of birth. Ultrastructural analysis revealed the loss of one CP microtubule in approximately one quarter of tracheal cilia axonemes, an absence of a C1 microtubule projection, and other less frequent CP structural abnormalities. SPAG6 and SPAG16 (CP proteins that interact with SPAG17) were increased in tracheal tissue from SPAG17-deficient mice. We conclude that Spag17 plays a critical role in the function and structure of motile cilia, and that neonatal lethality is likely explained by impaired airway mucociliary clearance.Keywords: primary ciliary dyskinesia; axoneme; central pair; Spag17; cilia Cilia are organelles that play key roles, including the determination of left-right asymmetry in the body; clearing mucus, particles, and fluid out of the airways; and facilitating the flow of cerebrospinal fluid (CSF) (1). Primary ciliary dyskinesia (PCD), which results from defects in the formation and function of cilia and flagella, is a relatively rare disorder affecting 1 in 16,000 individuals worldwide (2). The axoneme, the highly conserved cytoskeletal structure of motile cilia, has a "9 1 2" arrangement consisting of nine outer doublet microtubules surrounding a central microtubule pair. Motility is dependent upon proteins associated with the outer doublet microtubules, including dynein arms, radial spokes, and nexin links.The sliding of the outer doublet microtubules is modulated by the central pair (CP) apparatus (2-4). The two microtubules in the CP are structurally and biochemically dimorphic, and by convention receive separate designations (e.g., C1 and C2). At least 10 different polypeptides are uniquely associated with the C1 microtubule, and seven are unique to the C2 microtubule (3-6). This biochemical and structural asymmetry is believed to have functional significance with respect to the cilia or flagellar beat and waveform (7).The mammalian sperm-associated antigen-17 protein (SPAG17) is the orthologue of Chlamydomonas reinhardtii PF6 (8), a protein located on a projection from the C1 CP microtubule in green algae (9). The PF6 protein interacts with a number of other proteins, including calmodulin, and ultimately influences the radial s...

Mammalian axoneme central pair complex proteins: Broader roles revealed by gene knockout phenotypes

“…In contrast, a targeted mutation that deletes exon 2 and 3 of the Spag16 gene affects only SPAG16L expression. The resulting null mice show no evidence of primary ciliary dyskinesia phenotypes including hydrocephalus, or sinusitis, [Zhang et al, ], and display tracheal epithelial cells with motile cilia [Teves et al, ]. Males have normal spermatogenesis but are infertile due to severe sperm motility defects, even though the sperm have a normal axoneme ultrastructure [Zhang et al, ] (Table ).…”

Secreted Phosphoprotein 1 Is a Determinant of Lung Function Development in Mice

“…Noteworthy transcripts in these categories/pathways included forkhead box P2 (FOXP2) (57), midline 1 (MID1) (58), metal response element binding transcription factor 1 (MTF1) (59), SRY-box containing gene 9 (SOX9) (60), SOX5 (61), nuclear factor I/A (NFIA) (62), and spermassociated antigen 17 (SPAG17) (63). The GO/KEGG categories at P28 containing decreased transcripts (n = 1,161) in Spp1 (2/2) mouse lung were protein kinase activity, protein kinase cascade, cell-cell junction, and tight junction (Table 5).…”

A familial study of twins with severe asthenozoospermia identified a homozygous SPAG17 mutation by whole‐exome sequencing

“…17 Ultrastructural analysis of Spag17 knock-out mice revealed the loss of 1 central pair microtubule in cilia axonemes. 18 Although SPAG17 has been found to play an important role in sperm flagellar function, the association of SPAG17 with human male infertility remains unclear.…”