Alternative titles; symbols
HGNC Approved Gene Symbol: DNAH8
Cytogenetic location: 6p21.2 Genomic coordinates (GRCh38): 6:38,715,311-39,030,792 (from NCBI)
| Location | Phenotype |
Phenotype MIM number |
Inheritance |
Phenotype mapping key |
|---|---|---|---|---|
| 6p21.2 | Spermatogenic failure 46 | 619095 | Autosomal recessive | 3 |
Dyneins are microtubule-associated motor protein complexes composed of several heavy, light, and intermediate chains. Dynein heavy chains (DHCs) are responsible for force production and ATPase activity and contain a highly conserved catalytic domain with 4 P-loop consensus motifs involved in nucleotide binding. Two major classes of dyneins, axonemal and cytoplasmic, have been identified. Axonemal dyneins, found in cilia and flagella, are components of the outer and inner dynein arms attached to the peripheral microtubule doublets. DNAH8 is an outer arm axonemal DHC (Chapelin et al., 1997; Neesen et al., 1997).
By PCR of mouse and human testis cDNA with degenerate primers based on the sequences surrounding the P1-loop region, Neesen et al. (1997) isolated partial cDNAs encoding several DHCs. Sequence analysis revealed that mouse Dhc9 and human DHC9 (DNAH8) are putative outer arm axonemal DHCs and are homologous to rat DLP8.
By quantitative RT-PCR of outer dynein arm (ODA) heavy-chain genes in adult human tissues, Whitfield et al. (2019) observed that DNAH8 and DNAH17 (610063) were clearly expressed in the testis and less abundant in the lung, whereas DNAH5 (603335), DNAH9 (603330), and DNAH11 (603339) were the most abundant heavy chains detected in the lung. Analysis of available quantitative single-cell RNA sequencing datasets from human adult testis demonstrated DNAH8 and DNAH17 expression in germ cells from the early spermatocyte to late spermatid stages, but not in the somatic cells. DNAH9 was also detected in the germ cells, but with a shorter window of expression, from the late spermatocyte to early spermatid stages, whereas expression levels of DNAH5 and DNAH11 were very low in both the somatic and germ cell lineages of the testis.
By RT-PCR assays, Liu et al. (2020) observed that mouse Dnah8 is predominantly expressed in the testis. Dnah8 mRNA expression in testis began at 14 days after birth, corresponding to the pachytene stage.
Using RT-PCR, Yang et al. (2020) detected abundant Dnah8 mRNA expression in adult mouse testis but not in lung. Dnah8 was initially expressed in testis at postnatal day 14 (P14), continued to increase until P28, and then maintained a stable expression level. Immunofluorescence staining showed strong Dnah8 signals in the cytoplasm of spermatogonia and round sperm in stages 1 to 8, and in the flagella of elongated spermatids in stages 11 to 16. The authors concluded that DNAH8 plays a crucial role in sperm tail formation.
By genomic sequence analysis, Pazour et al. (2006) mapped the DNAH8 gene to chromosome 6p21.
Whitfield et al. (2019) analyzed the presence and location of all ODA heavy-chain proteins in airway epithelial cells (AECs) and spermatozoa from control individuals. Immunoblot analysis demonstrated the presence of DNAH8 and DNAH17 in sperm cells but not in AECs, whereas DNAH5, DNAH9, and DNAH11 were detected only in AECs. Immunofluorescence confirmed the results, showing DNAH5 along the full length of the cilia in AECs, whereas DNAH9 and DNAH11 were restricted to the distal and proximal part of the cilia, respectively. Neither DNAH8 nor DNAH17 were detected in cilia from AECs. In contrast, in spermatozoa from control individuals, only DNAH8 and DNAH17 could be detected along the sperm flagellum, with the exception of the terminal piece, which lacks a complete axonemal structure. The authors concluded that sperm cells harbor a set of ODA heavy chains consisting of DNAH8 and DNAH17, whereas respiratory ciliated cells have a distinct set involving DNAH5, DNAH9, and DNAH11.
By immunoprecipitation assays, Yang et al. (2020) confirmed interaction of DNAH17 and DNAH8 in mouse testis tissues and human spermatozoa.
Spermatogenic Failure 46
In 2 unrelated Chinese men and a Moroccan man who had infertility due to multiple morphologic abnormalities of the sperm flagella (SPGF46; 619095), Liu et al. (2020) identified homozygosity or compound heterozygosity for mutations in the DNAH8 gene (603337.0002-603337.0006). Immunostaining revealed near-absence of DNAH8 in patient flagella, and mutant spermatozoa also showed marked reduction of DNAH17 (610063), required for accurate localization of DNAH8.
In a 30-year-old infertile Chinese man, Yang et al. (2020) identified homozygosity for a 2-bp deletion in the DNAH8 gene (603337.0007). The authors noted that the patient presented with no chronic disease associated with the respiratory system, and no clinical signs of primary ciliary dyskinesia were observed in the patient by computed tomography scan.
Associations Pending Confirmation
For discussion of a possible association between primary ciliary dyskinesia (see 244400) and variation in the DNAH8 gene, see 603337.0001.
Samant et al. (2005) stated that mouse t haplotypes (t) are closely related variant homologs of a 40-Mb region, the t complex, at the proximal end of chromosome 17 that share 4 nonoverlapping inversions relative to the wildtype homolog. Heterozygosity for t in male mice results in distorted transmission (TRD) of the t-bearing chromosome 17 homolog to offspring, whereas homozygosity for t causes male sterility. The Ca(2+)-dependent sperm tail curvature phenotypes 'fishhook,' where high levels of sperm exhibit sharp bends in the midpiece, and 'curlicue,' where motile sperm exhibit chronic negative curving of the tail, are linked to t-associated TRD and sterility traits, respectively. Dnahc8 is located within an inversion in the t complex and has 17 missense mutations in its t allele. Using Western blot analysis, Samant et al. (2005) showed that only the Dnahc8 isoform carrying a unique N-terminal extension and full-length C terminus accumulated to equivalent steady state levels in testis and sperm of both wildtype and t/t male mice. Sequence analysis revealed numerous Dnahc8 mRNAs coding for the complete N-terminal extension with different 5-prime UTRs. Immunofluorescence analysis showed that the Dnahc8 isoform with the N-terminal extension was confined to the principal piece of the cauda epididymal sperm flagellum in testis of both +/+ and t/t mice. Comparative computational analyses identified 3 of the 17 Dnahc8 t-allele mutations as primary candidates for Dnahc8 dysfunction in mice, supporting a role for Dnahc8 in manifestation of the curlicue phenotype. However, the overall results of the study suggested that Dnahc8 is not the cause of accelerated manifestation of the fishhook phenotype.
Liu et al. (2020) generated Dnah8 -/- mice and observed diminished sperm movement compared to heterozygous mice. Hematoxylin and eosin (H&E) staining showed significantly higher rates of abnormal flagella in the knockout mice, including absent, short, coiled, bent, and/or irregularly shaped flagella, which the authors noted recapitulated the phenotype observed in MMAF-affected men with biallelic DNAH8 variants (see MOLECULAR GENETICS). Transmission electron microscopy revealed disorganized microtubules and outer dense fibers in the sperm flagella of knockout mice. H&E staining of the testes of Dnah8 knockout mice showed normal round spermatids but no elongated tails in stage VII to VIII seminiferous tubules. Periodic acid-Schiff staining of the cauda epididymis from Dnah8 knockout male mice showed fewer sperm heads than those from heterozygotes. The Dnah8 -/- male mice failed to produce any offspring over 2 months of breeding, whereas heterozygous mutated males routinely produced offspring. However, pups were successfully obtained by intracytoplasmic sperm injection using sperm from Dnah8 knockout male mice.
This variant is classified as a variant of unknown significance because its contribution to primary ciliary dyskinesia (see 244400) has not been confirmed.
In a patient, born of consanguineous parents, with primary ciliary dyskinesia, Watson et al. (2014) identified a homozygous c.1768C-T transition in the DNAH8 gene, resulting in an arg590-to-ter (R590X) substitution. The variant, which was found by a combination of autozygosity mapping, solution capture enrichment, and a novel variant-filtering interface, segregated with the disorder in the family. Functional studies of the variant were not performed, but Watson et al. (2014) noted that this gene, which encodes a known outer dynein arm heavy chain component, may play a role in ciliary function.
In a Chinese man (A051) with infertility due to multiple morphologic abnormalities of the flagella (SPGF46; 619095), Liu et al. (2020) identified compound heterozygosity for a c.11771C-T transition (c.11771C-T, NM_001206927.2) in the DNAH8 gene, resulting in a thr3924-to-met (T3924M) substitution, and a c.6689A-G transition, resulting in a lys2230-to-arg (K2230R) substitution, both involving highly conserved residues. His unaffected parents were each heterozygous for 1 of the mutations, neither of which was found in the 1000 Genomes database; however, the T3924M variant was present at low minor allele frequency (0.006729) in the gnomAD database. RT-PCR analysis of patient sperm showed significantly reduced levels of DNAH8 compared to control. Immunostaining revealed near-absence of DNAH8 in patient flagella, and mutant spermatozoa also showed marked reduction of DNAH17 (610063), required for accurate localization of DNAH8.
For discussion of the c.6689A-G transition (c.6689A-G, NM_001206927.2) in the DNAH8 gene, resulting in a lys2230-to-arg (K2230R) substitution, that was found in compound heterozygous state in a Chinese man (A051) with infertility due to multiple morphologic abnormalities of the flagella (SPGF46; 619095) by Liu et al. (2020), see 603337.0002.
In a Chinese man (X003) with infertility due to multiple morphologic abnormalities of the flagella (SPGF46; 619095), Liu et al. (2020) identified compound heterozygosity for a c.9427C-T transition (c.9427C-T, NM_001206927.2) in the DNAH8 gene, resulting in an arg3143-to-cys (R3143C) substitution, and a c.12721G-A transition, resulting in an ala4241-to-thr (A4241T) substitution, both involving highly conserved residues. His unaffected parents were each heterozygous for 1 of the mutations, neither of which was found in the 1000 Genomes database; however, both were present at low minor allele frequencies (0.0004677 and 0.0001187) in the gnomAD database. Immunostaining revealed near-absence of DNAH8 in patient flagella, and mutant spermatozoa also showed marked reduction of DNAH17 (610063), required for accurate localization of DNAH8.
For discussion of the c.12721G-A transition (c.12721G-A, NM_001206927.2) in the DNAH8 gene, resulting in an ala4241-to-thr (A4241T) substitution, that was found in compound heterozygous state in a Chinese man (X003) with infertility due to multiple morphologic abnormalities of the flagella (SPGF46; 619095) by Liu et al. (2020), see 603337.0004.
In a Moroccan man (F0300) with infertility due to multiple morphologic abnormalities of the flagella (SPGF46; 619095), Liu et al. (2020) identified homozygosity for a 7-bp deletion (c.6962_6968del, NM_001206927.2) in the DNAH8 gene, causing a frameshift predicted to result in a premature termination codon (His2321ProfsTer4). The mutation was not found in the 1000 Genomes or gnomAD databases. The proband reportedly had an infertile brother, but family members were unavailable for study. Immunostaining revealed near-absence of DNAH8 in patient flagella, and mutant spermatozoa also showed marked reduction of DNAH17 (610063), required for accurate localization of DNAH8.
In a 30-year-old Chinese man with infertility due to multiple morphologic abnormalities of the flagella (SPGF46; 619095), Yang et al. (2020) identified homozygosity for a 2-bp deletion (c.378_379del) in the DNAH8 gene, causing a frameshift predicted to result in a premature termination codon (Lys127ArgfsTer5). His unaffected first-cousin parents were heterozygous for the mutation. Immunofluorescence staining of patient sperm showed almost no DNAH8 expression in the sperm tail compared to control, and Western blot detected no mutant DNAH8, consistent with degradation of the truncated protein. In addition, there was markedly reduced staining of DNAH17 (610063) in the tail of patient sperm.
Chapelin, C., Duriez, N., Magnino, F., Goossens, M., Escudier, E., Amselem, S. Isolation of several human axonemal dynein heavy chain genes: genomic structure of the catalytic site, phylogenetic analysis and chromosomal assignment. FEBS Lett. 412: 325-330, 1997. [PubMed: 9256245] [Full Text: https://doi.org/10.1016/s0014-5793(97)00800-4]
Liu, C., Miyata, H., Gao, Y., Sha, Y., Tang, S., Xu, Z., Whitfield, M., Patrat, C., Wu, H., Dulioust, E., Tian, S., Shimada, K., and 14 others. Bi-allelic DNAH8 variants lead to multiple morphological abnormalities of the sperm flagella and primary male infertility. Am. J. Hum. Genet. 107: 330-341, 2020. [PubMed: 32619401] [Full Text: https://doi.org/10.1016/j.ajhg.2020.06.004]
Neesen, J., Koehler, M. R., Kirschner, R., Steinlein, C., Kreutzberger, J., Engel, W., Schmid, M. Identification of dynein heavy chain genes expressed in human and mouse testis: chromosomal localization of an axonemal dynein gene. Gene 200: 193-202, 1997. [PubMed: 9373155] [Full Text: https://doi.org/10.1016/s0378-1119(97)00417-4]
Pazour, G. J., Agrin, N., Walker, B. L., Witman, G. B. Identification of predicted human outer dynein arm genes: candidates for primary ciliary dyskinesia genes. (Letter) J. Med. Genet. 43: 62-73, 2006. [PubMed: 15937072] [Full Text: https://doi.org/10.1136/jmg.2005.033001]
Samant, S. A., Ogunkua, O. O., Hui, L., Lu, J., Han, Y., Orth, J. M., Pilder, S. H. The mouse t complex distorter/sterility candidate, Dnahc8, expresses a gamma-type axonemal dynein heavy chain isoform confined to the principal piece of the sperm tail. Dev. Biol. 285: 57-69, 2005. [PubMed: 16054618] [Full Text: https://doi.org/10.1016/j.ydbio.2005.06.002]
Watson, C. M., Crinnion, L. A., Morgan, J. E., Harrison, S. M., Diggle, C. P., Adlard, J., Lindsay, H. A., Camm, N., Charlton, R., Sheridan, E., Bonthron, D. T., Taylor, G. R., Carr, I. M. Robust diagnostic genetic testing using solution capture enrichment and a novel variant-filtering interface. Hum. Mutat. 35: 434-441, 2014. [PubMed: 24307375] [Full Text: https://doi.org/10.1002/humu.22490]
Whitfield, M., Thomas, L., Bequignon, E., Schmitt, A., Stouvenel, L., Montanin, G., Tissier, S., Duquesnoy, P., Copin, B., Chantot, S., Dastot, F., Faucon, C., and 9 others. Mutations in DNAH17, encoding a sperm-specific axonemal outer dynein arm heavy chain, cause isolated male infertility due to asthenozoospermia. Am. J. Hum. Genet. 105: 198-212, 2019. [PubMed: 31178125] [Full Text: https://doi.org/10.1016/j.ajhg.2019.04.015]
Yang, Y., Jiang, C., Zhang, X., Liu, X., Li, J., Qiao, X., Liu, H., Shen, Y. Loss-of-function mutation in DNAH8 induces asthenoteratospermia associated with multiple morphological abnormalities of the sperm flagella. Clin. Genet. 98: 396-401, 2020. [PubMed: 32681648] [Full Text: https://doi.org/10.1111/cge.13815]