A novel homozygous mutation in DNAJB13-a gene associated with the sperm axoneme-leads to teratozoospermia.

PURPOSE: To evaluate the unknown genetic causes of teratozoospermia, and determine the pathogenicity of candidate variants. METHODS: A primary infertile patient and his family members were recruited in the West China Second University Hospital of Sichuan University. Whole-exome sequencing was performed to identify causative genes in a man with teratozoospermia. Immunofluorescence staining and western blotting were applied to assess the pathogenicity of the identified variant. Intracytoplasmic sperm injection (ICSI) was used to assist fertilization for the patient with teratozoospermia. RESULTS: We performed whole-exome sequencing (WES) and detected a novel homozygous frameshift mutation of c.335_336del [p.E112Vfs*3] in DNAJB13 on a primary infertile male patient. Intriguingly, we identified abnormal sperm morphology in this patient, with recurrent respiratory infections and chronic cough. Furthermore, we confirmed that this mutation resulted in negative effects on DNAJB13 expression in the spermatozoa of the affected individual, causing ultrastructural defects in his sperm. Remarkably, our staining revealed that DNAJB13 was expressed in the cytoplasm of primary germ cells and in the flagella of spermatids during spermiogenesis in humans and mice. Finally, we are the first group to report a favorable prognosis using ICSI for a patient carrying this DNAJB13 mutation. CONCLUSION: Our study revealed a novel homozygous frameshift mutation of c.335_336del [p.E112Vfs*3] in DNAJB13 involved in teratozoospermia phenotype. Our study greatly expands the spectrum of limited DNAJB13 mutations, and is expected to provide a better understanding of genetic counseling diagnoses and subsequent treatment of male infertility.

[Expression of Dnajb13 and its involvement in the apoptosis of spermatogenic cells in the testis of the mouse with cryptorchidism].

OBJECTIVE: To study the mRNA and protein expressions of Dnajb13 and its localization in the testis of the mouse with cryptorchidism and its association with the apoptosis of spermatogenic cells. METHODS: The localization of Dnajb13 in the spermatogenic cells of 8-week-old mice was detected by immunohistochemistry. The model of unilateral cryptorchidism was surgically established in the mice and verified by TUNEL, flow cytometry and morphological observation. The apoptosis of the spermatogenic cells was analyzed and the mRNA and protein expressions of Dnajb13 in both cryptorchid and healthy testes were determined by quantitative polymerase chain reaction (qPCR), Western blot and immunohistochemistry at 1, 2, 3, 4, 5, 6, 9 and 15 days after modeling. RESULTS: Immunohistochemistry showed that Dnajb13 was localized in the elongated spermatids at steps 9－16 of spermiogenesis in the testis tissue of the healthy mice. TUNEL and flow cytometry manifested that the round spermatids at step 1 and primary spermatocytes in miosis were most sensitive to elevated temperature. After modeling, apoptosis was first observed in the round spermatids at steps 1－8, which were decreased from 17.09% to 6.52% (P < 0.05), then in the spermatids during metamorphosis at steps 9－16, and then in the primary spermatocytes. At 3 days after surgery, the expression of Dnajb13 mRNA in the cryptorchid testis was 1.6 times higher than that in the healthy one (P < 0.05) and decreased at 4 days, 1.2 times that of the normal. The expression of the Dnajb13 protein exhibited no significant change at 1－3 days, but a 0.68-fold reduction at 4 days (P < 0.05) and a 0.4-fold reduction at 9 days. Immunohistochemical staining revealed the expression of the Dnajb13 protein in the apoptotic multinucleated giant cells at 6 days. CONCLUSIONS: Dnajb13 is localized in the spermatids during metamorphosis and in the tails of mature sperm in adult mice, involved in sperm metamorphosis and sperm flagellum formation, and expressed in apoptotic multinucleated giant cells in the cryptorchid testis, which may be associated with the apoptosis of round spermatids at stages Ⅵ－Ⅷ.

Mechanistic insights into acephalic spermatozoa syndrome-associated mutations in the human SUN5 gene.

Acephalic spermatozoa syndrome has been reported for many decades; it is characterized by very few intact spermatozoa and tailless sperm heads in the semen and causes severe male infertility. The only gene in which mutations have been found to be associated with this syndrome encodes Sad1 and UNC84 domain-containing 5 (SUN5), a testis-specific nuclear envelope protein. The functional role of SUN5 has been well-studied in mouse models, but the molecular basis for the pathogenic effects of mutations in the human SUN5 gene remains elusive. Here, we report a new SUN5 mutation (c.475C→T; p.Arg159*), and explore the pathogenic effects of all known SUN5 mutations on acephalic spermatozoa syndrome. Using an artificial splicing system, we found that the intronic mutation affects the splicing of SUN5 mRNA, yielding a premature stop codon that results in a truncated SUN5 protein. We also found that SUN5 interacts with the coupling apparatus protein DnaJ heat shock protein family (Hsp40) member B13 (DNAJB13) during spermatogenesis, and the substitutions in the SUN5 SUN domain impair its interaction with DNAJB13. Furthermore, we observed that many SUN5 mutations affect the secondary structure of the protein and influence its folding and cellular localization. In summary, our findings indicate an interaction of SUN5 with DNAJB13 during spermatogenesis, provide mechanistic insights into the functional role of this interaction in sperm head-tail integration, and elucidate the molecular etiology of acephalic spermatozoa syndrome-associated SUN5 mutations.

Mutations in DNAJB13, Encoding an HSP40 Family Member, Cause Primary Ciliary Dyskinesia and Male Infertility.

Primary ciliary dyskinesia (PCD) is an autosomal-recessive disease due to functional or ultra-structural defects of motile cilia. Affected individuals display recurrent respiratory-tract infections; most males are infertile as a result of sperm flagellar dysfunction. The great majority of the PCD-associated genes identified so far encode either components of dynein arms (DAs), which are multiprotein-ATPase complexes essential for ciliary motility, or proteins involved in DA assembly. To identify the molecular basis of a PCD phenotype characterized by central complex (CC) defects but normal DA structure, a phenotype found in ∼15% of cases, we performed whole-exome sequencing in a male individual with PCD and unexplained CC defects. This analysis, combined with whole-genome SNP genotyping, identified a homozygous mutation in DNAJB13 (c.833T>G), a gene encoding a HSP40 co-chaperone whose ortholog in the flagellated alga Chlamydomonas localizes to the radial spokes. In vitro studies showed that this missense substitution (p.Met278Arg), which involves a highly conserved residue of several HSP40 family members, leads to protein instability and triggers proteasomal degradation, a result confirmed by the absence of endogenous DNAJB13 in cilia and sperm from this individual. Subsequent DNAJB13 analyses identified another homozygous mutation in a second family; the study of DNAJB13 transcripts obtained from airway cells showed that this mutation (c.68+1G>C) results in a splicing defect consistent with a loss-of-function mutation. Overall, this study, which establishes mutations in DNAJB13 as a cause of PCD, unveils the key role played by DNAJB13 in the proper formation and function of ciliary and flagellar axonemes in humans.

Missense mutation in DNAJB13 gene correlated with male fertility in asthenozoospermia.

BACKGROUND: The most common type of male infertility is asthenospermia. We cloned DnaJ heat shock protein family member B13 (Dnajb13/DNAJB13), a type II HSP40 family member that is highly expressed in the testis. DNAJB13 plays a crucial role in sperm flagellar function. OBJECTIVES: The aim of this study was to investigate whether a correlation exists between DNAJB13 and low sperm motility in infertile men. MATERIALS AND METHODS: In the present study, we performed a mutation screening of the DNAJB13 gene in 92 idiopathic asthenozoospermia patients and 200 men with normal fertility. Additionally, we used immunoelectron microscopy, co-immunoprecipitation, mass spectrometric detection, indirect immunofluorescence assay, transmission electron microscopy studies, isobaric tags for relative and absolute quantitation, and multiple reaction monitoring studies to analyze changes in DNAJB13 protein. RESULTS: A novel c.106T>C mutation of DNAJB13 was present in nearly 10% (9/92) of idiopathic asthenozoospermia patients and was absent in 200 fertile men. A computer-assisted sperm analyzer and transmission electron microscopy analysis using samples from 9 patients with DNAJB13 mutations demonstrated that most spermatozoa were immotile due to sperm tail defects. Multiple reaction monitoring results indicated that DNAJB13 protein levels were reduced after gene mutation. We achieved a pregnancy rate of 100% in 8 patients with DNAJB13 mutations using ICSI. DISCUSSION AND CONCLUSION: The DNAJB13 heterozygous variant may affect fertility. ICSI can help these patients with low fertility to father children.