Alternative titles; symbols
HGNC Approved Gene Symbol: DNAAF2
Cytogenetic location: 14q21.3 Genomic coordinates (GRCh38): 14:49,625,174-49,635,244 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 14q21.3 | Ciliary dyskinesia, primary, 10 | 612518 | Autosomal recessive | 3 |
The DNAAF2 gene encodes a protein conserved in animals and ciliated unicellular organisms involved in preassembly of dynein arm complexes in species from algae to humans (Omran et al., 2008).
Omran et al. (2008) identified human KTU as the hypothetical protein C14ORF104 through searches of sequence databases. The full-length cDNA of 2,511 basepairs encodes an 837-amino acid protein; a shorter in-frame splice variant lacking exon 2 comprises 2,367 basepairs. RT-PCR analysis detected Ktu expression in medaka embryo and in nearly all organs of adult mice, with higher expression in mouse tissues with motile cilia and flagella such as brain and testis. Ktu localized to the cytoplasm but not the flagellum of sperm. In renal tubules Ktu localized to the apical cytoplasm around the gamma-tubulin (191135)-positive pericentriolar region, not in the cilia.
Using RT-PCR analysis, Cheong et al. (2019) showed that Dnaaf2 was expressed across different stages of mouse embryos and in various adult mouse tissues, including brain, kidney, liver, lung, ovary, oviduct, spleen, and testis.
Omran et al. (2008) determined that the KTU gene consists of 3 exons.
The DNAAF2 gene maps to chromosome 14q21.3 (Omran et al., 2008).
In biochemical and immunohistochemical studies, Omran et al. (2008) demonstrated that KTU is involved in preassembly of dynein arm complexes in the cytoplasm before intraflagellar transport loads them for the ciliary compartment. High resolution immunofluorescence microscopy of KTU mutant respiratory cells with specific monoclonal antibodies against dynein arm components demonstrated that loss of KTU resulted in combined outer and inner dynein arm defects. Omran et al. (2008) observed that mouse Ktu coprecipitated the intermediate chain DNAI2 (605483), which showed defective assembly in human and Chlamydomonas Ktu mutant cilia. In pull-down assays full-length and, more weakly, the N-terminal region of Ktu, but not the C-terminal region, could pull down DNAI2. MALDI-TOF spectrometry of immunoprecipitates from mouse testis showed that Ktu interacts with Hsp70 (140550).
Omran et al. (2008) screened probands from 112 primary ciliary dyskinesia families for the presence of a mutation in the KTU gene. In 2 consanguineous families (CILD10; 612518), Omran et al. (2008) identified homozygous loss-of-function mutations (612517.0001, 612517.0002). The parents were heterozygous for the detected mutations. Transmission electron microscopy of respiratory cilia and sperm tails identified abnormal axonemal dynein arms in all affected individuals.
Using targeted next-generation sequencing, Sun et al. (2020) identified 2 novel compound heterozygous mutations in exon 1 of the DNAAF2 gene (Y52X, 612517.0003 and S9X, 612517.0004) in a 40-year-old Han Chinese male with primary ciliary dyskinesia. The variants were validated using Sanger sequencing and were not found in 600 normal controls.
Omran et al. (2008) identified kintoun (KTU) in medaka mutants showing organ laterality defects due to altered ciliary motility. Mutant fish lacked directional liquid flow in Kupffer vesicle, an organ functionally equivalent to the mouse node in terms of left-right specification. Although the number and length of cilia in Kupffer vesicle seemed normal, their motility was completely lost. Ktu-null fish were viable but developed polycystic kidney disease, and male mutant fish had impaired sperm motility leading to reduced fertility. Ultrastructurally affected cilia and flagella showed partial or complete loss of outer and inner dynein arms. Omran et al. (2008) found a single nonsense mutation responsible for the phenotype in the medaka Ktu gene, which is homologous to Chlamydomonas Pf13. The authors reported that Ktu knockout mice exhibit a primary ciliary dyskinesia-like phenotype.
Cheong et al. (2019) found that Dnaaf2 -/- embryos were delayed in development compared with controls and failed to develop beyond early organogenesis, likely due to accumulation and increase in apoptotic cells. Dnaaf2 -/- embryos also displayed multiple abnormalities, including left-right patterning defects. Further analysis showed that Dnnaaf2 did not interact directly with left-right signaling pathways, but that it was required for proper cilia function and nodal flow.
In 2 sibs with primary ciliary dyskinesia (CILD10; 612518) from a consanguineous family, Omran et al. (2008) identified homozygosity for a 16-basepair insertion (c.1214_1215insACGATACCTGCGTGGC, NM_018139.2) between nucleotides 1214 and 1215 of the KTU gene, resulting in a conversion of the glycine at position 406 to arginine followed by frameshift and premature termination (G406Rfs89X). Each parent was heterozygous for the detected mutation. The affected sibs showed no KTU protein detectable by Western blot analysis of cell lysates from respiratory cells. The affected girl had situs solitus and her brother had situs inversus totalis. Both children had chronic lung disease and suffered from birth from chronic otitis media and sinusitis.
In a child with primary ciliary dyskinesia (CILD10; 612518) from a consanguineous family, Omran et al. (2008) identified homozygosity for a C-to-A transversion at nucleotide 23 (c.23C-A, NM_018139.2) of the KTU gene resulting in a serine-to-termination substitution at codon 8 (S8X). Each parent was heterozygous for this mutation. No protein was detected by Western blot analysis of respiratory cell lysates from the affected individual. The proband had situs inversus totalis and had suffered from chronic otitis media and sinusitis as well as recurrent pneumonia since birth.
In a 40-year-old Han Chinese male with primary ciliary dyskinesia-10 (CILD10; 612518) including situs inversus, Sun et al. (2020) identified compound heterozygosity for mutations in the DNAAF2 gene: a C-to-A transversion at nucleotide 156 (c.156C-A, NM_001083908.1) resulting in a tyr52-to-ter (Y52X) substitution, and a S9X substitution (612517.0004). Each parent was heterozygous for one of the mutations. The mutations were identified by targeted next-generation sequencing and validated by Sanger sequencing, and were not detected in 600 normal controls. Both mutations occurred at highly conserved positions in exon 1. Immunofluorescence staining and Western blot analysis of patient spermatozoa showed absence of DNAAF2 expression. Immunostaining of patient respiratory epithelial cells using antibodies targeting various axonemal proteins showed only residual staining for DNAH5 (603335) in the proximal ciliary axoneme and complete absence of DNAH9 (603330) and DNALI1 (602135), proteins of the outer and inner dynein arms, respectively. In sperm tails of the proband, DNAH9 and DNALI1 were not detected, and DNAH5 was detected only weakly.
For discussion of a c.26C-A transversion (c.26C-A, NM_001083908.1) in the DNAAF2 gene that was found in compound heterozygous state in a man with primary ciliary dyskinesia-10 (CILD10; (612518) by Sun et al. (2020), see 612517.0003).
Cheong, A., Degani, R., Tremblay, K. D., Mager, J. A null allele of Dnaaf2 displays embryonic lethality and mimics human ciliary dyskinesia. Hum. Molec. Genet. 28: 2775-2784, 2019. [PubMed: 31107948] [Full Text: https://doi.org/10.1093/hmg/ddz106]
Omran, H., Kobayashi, D., Olbrich, H., Tsukahara, T., Loges, N. T., Hagiwara, H., Zhang, Q., Leblond, G., O'Toole, E., Hara, C., Mizuno, H., Kawano, H., and 11 others. Ktu/PF13 is required for cytoplasmic pre-assembly of axonemal dyneins. Nature 456: 611-616, 2008. [PubMed: 19052621] [Full Text: https://doi.org/10.1038/nature07471]
Sun, M., Zhang, Y., Yang, J., Wang, Y., Tan, H., Wang, H., Lei, T., Li, X., Zhang, X., Xiong, W., Dou, K., Ma, Y. Novel compound heterozygous DNAAF2 mutations cause primary ciliary dyskinesia in a Han Chinese family. J. Assist. Reprod. Genet. 37: 2159-2170, 2020. [PubMed: 32638265] [Full Text: https://doi.org/10.1007/s10815-020-01859-7]