Otoferlin as a multirole Ca2+ signaling protein: from inner ear synapses to cancer pathways

Transcriptomics and phenotypic analysis of OTOF gene knockdown in zebrafish mediated by CRISPR/Cas9

Deafness is a common genetic disorder, where mutations,in the OTOF gene can disrupt the normal functionof the Otoferlin protein, leading to impaired neurotransmitter release in the inner ear and subsequent deafness. Despite the complexity of the pathogenic mechanism,it is not fully understood. Zebrafish are an excellent model for studying genetically-induced deafness,but there have been no previous reports on the pathogenesis of OTOF in zebrafish.This study successfully established a zebrafish model with mutated OTOF genes using CRISPR/Cas9 gene editing technology to investigate the molecular basis of OTOF-induced deafness. Compared to AB wild type zebrafish, those with low otof expression showed injury and apoptosis of hair cells in the posterior lateral neuromasts along with significant increase in the number of macrophages and apoptotic cells in this region. Additionally, these mutants exhibited a reduction in body length. To further elucidate differences at 5dpf (days post-fertilization) between mutant and wild type zebrafish embryos, RNA-seq analysis was conducted to examine differentially expressed genes (DEGs).A total of 334 up-regulated DEGs and 111 down-regulated DEGs were identified in mutants compared to wild types.KEGG and GO enrichment analyses were performed on these DEGs to identify key signaling pathways and hub DEGs. The findings revealedan increased expression of several genes involved in the HSP70 oxidative stress system, suggesting that OTOF may protect cochlear hair cell from apoptosis induced by oxidative stress through regulation of MAPK signal and HSP70 expression.In summary, the establishment of a zebrafish model with OTOF knockout provides a valuable tool for investigating the function of Otoferlin and understanding the role of the OTOF gene in deafness. These potential molecular insights offer significant contributions towards understanding the pathogenesis of deafness experimental models and serves as a foundation for comprehending the involvement of the OTOF gene.

Auditory Neuropathy Caused by a Structural Variation in the OTOF Gene, Identified Using Oxford Nanopore Adaptive Sampling

BACKGROUND/OBJECTIVES

The OTOF gene is reported to be the causative gene for non-syndromic recessive sensorineural hearing loss and auditory neuropathy spectrum disorder. About 300 variants have been reported, but there have been no reports to date on copy gain variants.

METHODS

We identified a copy gain variant in the OTOF gene through short-read next-generation sequencing analysis from one patient with auditory neuropathy. We also performed long-read next-generation sequencing analysis using the Oxford Nanopore Technologies adaptive sampling procedure.

RESULTS

The four-year-old male carried a duplication of chr2: 26,477,852 to 26,483,106 (a 5254-base duplication including exon 14 to exon 18 of the OTOF gene NM_001287489) and a c.5385C>A single nucleotide variant. We also confirmed that these two variants were located in the trans configuration based on haplotype phasing results using the long-read next-generation sequencing data.

CONCLUSIONS

This is the first report of an auditory neuropathy patient with a large duplication variant in the OTOF gene. The identified variants were novel, but based on the clinical phenotype of the patient, these variants seem to be the genetic cause of this patient's phenotype. Oxford Nanopore Technologies adaptive sampling is a powerful tool for the analysis of structural variants (particularly for determining the breakpoint and direction) and haplotype phasing.

A free intravesicular C-terminal of otoferlin is essential for synaptic vesicle docking and fusion at auditory inner hair cell ribbon synapses

Our understanding of how otoferlin, the major calcium sensor in inner hair cells (IHCs) synaptic transmission, contributes to the overall dynamics of synaptic vesicle (SV) trafficking remains limited. To address this question, we generated a knock-in mouse model expressing an otoferlin-GFP protein, where GFP was fused to its C-terminal transmembrane domain. Similar to the wild type protein, the GFP-tagged otoferlin showed normal expression and was associated with IHC SV. Surprisingly, while the heterozygote Otof+/GFP mice exhibited a normal hearing function, homozygote OtofGFP/GFP mice were profoundly deaf attributed to severe reduction in SV exocytosis. Fluorescence recovery after photobleaching revealed a markedly increased mobile fraction of the otof-GFP-associated SV in Otof GFP/GFP IHCs. Correspondingly, 3D-electron tomographic of the ribbon synapses indicated a reduced density of SV attached to the ribbon active zone. Collectively, these results indicate that otoferlin requires a free intravesicular C-terminal end for normal SV docking and fusion.

Review and research gap identification in genetics causes of syndromic and nonsyndromic hearing loss in Saudi Arabia

Congenital hearing loss is one of the most common sensory disabilities worldwide. The genetic causes of hearing loss account for 50% of hearing loss. Genetic causes of hearing loss can be classified as nonsyndromic hearing loss (NSHL) or syndromic hearing loss (SHL). NSHL is defined as a partial or complete hearing loss without additional phenotypes; however, SHL, known as hearing loss, is associated with other phenotypes. Both types follow a simple Mendelian inheritance fashion. Several studies have been conducted to uncover the genetic factors contributing to NSHL and SHL in Saudi patients. However, these studies have encountered certain limitations. This review assesses and discusses the genetic factors underpinning NSHL and SHL globally, with a specific emphasis on the Saudi Arabian context. It also explores the prevalence of the most observed genetic causes of NSHL and SHL in Saudi Arabia. It also sheds light on areas where further research is needed to fully understand the genetic foundations of hearing loss in the Saudi population. This review identifies several gaps in research in NSHL and SHL and provides insights into potential research to be conducted.

Validation of RNA Extraction Methods and Suitable Reference Genes for Gene Expression Studies in Developing Fetal Human Inner Ear Tissue

A comprehensive gene expression investigation requires high-quality RNA extraction, in sufficient amounts for real-time quantitative polymerase chain reaction and next-generation sequencing. In this work, we compared different RNA extraction methods and evaluated different reference genes for gene expression studies in the fetal human inner ear. We compared the RNA extracted from formalin-fixed paraffin-embedded tissue with fresh tissue stored at -80 °C in RNAlater solution and validated the expression stability of 12 reference genes (from gestational week 11 to 19). The RNA from fresh tissue in RNAlater resulted in higher amounts and a better quality of RNA than that from the paraffin-embedded tissue. The reference gene evaluation exhibited four stably expressed reference genes (B2M, HPRT1, GAPDH and GUSB). The selected reference genes were then used to examine the effect on the expression outcome of target genes (OTOF and TECTA), which are known to be regulated during inner ear development. The selected reference genes displayed no differences in the expression profile of OTOF and TECTA, which was confirmed by immunostaining. The results underline the importance of the choice of the RNA extraction method and reference genes used in gene expression studies.