Early Development of Hearing in Zebrafish

The zebrafish ( Danio rerio ) has become a valuable vertebrate model for human hearing and balance disorders because it combines powerful genetics, excellent embryology, and exceptional in vivo visualization in one organism. In this study, we investigated auditory function of zebrafish at early developmental stages using the microphonic potential method. This is the first study to report ontogeny of response of hair cells in any fish during the first week post fertilization. The right ear of each zebrafish embedded in agarose was linearly stimulated with a glass probe that was driven by a calibrated piezoelectric actuator. Using beveled micropipettes filled with standard fish saline, extracellular microphonic potentials were recorded from hair cells in the inner ear of zebrafish embryos or larvae in response to 20, 50, 100, and 200-Hz stimulation. Saccular hair cells expressing green fluorescent protein of the transgenic zebrafish from 2 to 7 days post fertilization (dpf) were visualized and quantified using confocal microscopy. The otic vesicles’ areas, otoliths’ areas, and saccular hair cell count and density increased linearly with age and standard body length. Microphonic responses increased monotonically with stimulus intensity, stimulus frequency, and age of zebrafish. Microphonic threshold at 200 Hz gradually decreased with zebrafish age. The increases in microphonic response and sensitivity correlate with the increases in number and density of hair cells in the saccule. These results enhance our knowledge of early development of auditory function in zebrafish and provide the control data that can be used to evaluate hearing of young zebrafish morphants or mutants

The Generation of Zebrafish Mariner

ABSTRACT Targeted genome editing mediated by clustered, regularly interspaced, short palindromic repeat (CRISPR)/CRISPR‐associated nuclease 9 (Cas9) technology has emerged as a powerful tool for gene function studies and has great potential for gene therapy. Although CRISPR/Cas9 has been widely used in many research fields, only a few successful zebrafish models have been established using this technology in hearing research. In this study, we successfully created zebrafish mariner mutants by targeting the motor head domain of Myo7aa using CRISPR/Cas9. The CRISPR/Cas9‐generated mutants showed unbalanced swimming behavior and disorganized sterocilia of inner ear hair cells, which resemble the phenotype of the zebrafish mariner mutants. In addition, we found that CRISPR/Cas9‐generated mutants have reduced number of stereociliary bundles of inner ear hair cells and have significant hearing loss. Furthermore, phenotypic analysis was performed on F0 larvae within the first week post fertilization, which dramatically shortens data collection period. Therefore, results of this study showed that CRISPR/Cas9 is a quick and effective method to generate zebrafish mutants as a model for studying human genetic deafness. Anat Rec, 303:556–562, 2020. © 2019 American Association for Anatom

Hearing Assessment in Zebrafish During the First Week Postfertilization

The zebrafish (Danio rerio) is a valuable vertebrate model for human hearing disorders because of many advantages in genetics, embryology, and in vivo visualization. In this study, we investigated auditory function of zebrafish during the first week postfertilization using microphonic potential recording. Extracellular microphonic potentials were recorded from hair cells in the inner ear of wild-type AB and transgenic Et(krt4:GFP)(sqet4) zebrafish at 3, 5, and 7 days postfertilization in response to 20, 50, 100, 200, 300, and 400-Hz acoustic stimulation. We found that microphonic threshold significantly decreased with age in zebrafish. However, there was no significant difference of microphonic responses between wild-type and transgenic zebrafish, indicating that the transgenic zebrafish have normal hearing like wild-type zebrafish. In addition, we observed that microphonic threshold did not change with the recording electrode location. Furthermore, microphonic threshold increased significantly at all tested stimulus frequencies after displacement of the saccular otolith but only increased at low frequencies after displacement of the utricular otolith, showing that the saccule rather than the utricle plays the major role in larval zebrafish hearing. These results enhance our knowledge of early development of auditory function in zebrafish and the factors affecting hearing assessment with microphonic potential recording

A missense mutation in DCDC2 causes human recessive deafness DFNB66, likely by interfering with sensory hair cell and supporting cell cilia length regulation

Hearing loss is the most common sensory deficit in humans. We show that a point mutation in DCDC2 (DCDC2a), a member of doublecortin domain-containing protein superfamily, causes non-syndromic recessive deafness DFNB66 in a Tunisian family. Using immunofluorescence on rat inner ear neuroepithelia, DCDC2a was found to localize to the kinocilia of sensory hair cells and the primary cilia of nonsensory supporting cells. DCDC2a fluorescence is distributed along the length of the kinocilium with increased density toward the tip. DCDC2a-GFP overexpression in non-polarized COS7 cells induces the formation of long microtubule-based cytosolic cables suggesting a role in microtubule formation and stabilization. Deafness mutant DCDC2a expression in hair cells and supporting cells causes cilium structural defects, such as cilium branching, and up to a 3-fold increase in length ratios. In zebrafish, the ortholog dcdc2b was found to be essential for hair cell development, survival and function. Our results reveal DCDC2a to be a deafness gene and a player in hair cell kinocilia and supporting cell primary cilia length regulation likely via its role in microtubule formation and stabilization

Educational Concerns About the Safety of Cataract Surgery During Residency: The E3CAPS Pedagogic Study

International audienceIntroductionCataract surgery is the most common surgical procedure performed in France. While the incidence of intraoperative complications affecting visual prognosis is extremely low, given the large number of patients operated on, the absolute number of patients affected by complications is quite high. Complication rates are significantly higher when ophthalmology residents (ORs) perform the surgery. Although lack of experience remains the main risk factor, sleep deprivation may adversely affect ORs' successful surgery rate. The value of the EyeSi and REG; surgical simulator in initial training has been demonstrated to increase cataract surgery safety through the transfer of surgical skills from the simulator to the operating room. However, there is no consensus regarding how much training is needed before the first-time ORs are allowed to operate. There is also no scientific evidence that sleep deprivation is associated with a decrease in surgical performance. Establishing a validated protocol for cataract surgery training using the EyeSi surgical simulator (referred to further as the EyeSi) and identifying risk factors for intraoperative complications related to sleep deprivation will improve cataract surgery safety and lead to the reorganization of our healthcare systems.Methods and Planned OutcomesThis multi-centre educational cohort study will include two distinct axes which will both aim to reduce the risks of cataract surgery. Enrollment will include 16 first-year ORs for Axis 1 and 25 experienced residents for Axis 2, all from the University Hospitals of Nantes, Tours, Angers and Rennes. Axis 1 will focus on investigating the learning curve of first-year ORs using the EyeSi, following the training program recommended by the "College des Ophtalmologistes Universitaires de France" in order to set up a future "licence to operate." Axis 2 will evaluate the impact of sleep deprivation on the surgical performance of experienced ORs using the EyeSi

FAM65B is a membrane-associated protein of hair cell stereocilia required for hearing

In a large consanguineous Turkish kindred with recessive nonsyndromic, prelingual, profound hearing loss, we identified in the gene FAM65B (MIM611410) a splice site mutation (c.102-1G>A) that perfectly cosegregates with the phenotype in the family. The mutation leads to exon skipping and deletion of 52-amino acid residues of a PX membrane localization domain. FAM65B is known to be involved in myotube formation and in regulation of cell adhesion, polarization, and migration. We show that wild-type Fam65b is expressed during embryonic and postnatal development stages in murine cochlea, and that the protein localizes to the plasma membranes of the stereocilia of inner and outer hair cells of the inner ear. The wild-type protein targets the plasma membrane, whereas the mutant protein accumulates in cytoplasmic inclusion bodies and does not reach the membrane. In zebrafish, knockdown of fam65b leads to significant reduction of numbers of saccular hair cells and neuromasts and to hearing loss. We conclude that FAM65B is a plasma membrane-associated protein of hair cell stereocilia that is essential for hearing

Spatiotemporal transitions in Pseudo-nitzschia species assemblages and domoic acid along the Alaska coast.

The toxic diatom genus Pseudo-nitzschia is distributed from equatorial to polar regions and is comprised of >57 species, some capable of producing the neurotoxin domoic acid (DA). In the Pacific Arctic Region spanning the Bering, Chukchi, and Beaufort seas, DA is recognized as an emerging human and ecosystem health threat, yet little is known about the composition and distribution of Pseudo-nitzschia species in these waters. This investigation characterized Pseudo-nitzschia assemblages in samples collected in 2018 during summer (August) and fall (October-November) surveys as part of the Distributed Biological Observatory and Arctic Observing Network, encompassing a broad geographic range (57.8° to 73.0°N, -138.9° to -169.9°W) and spanning temperature (-1.79 to 11.7°C) and salinity (22.9 to 32.9) gradients associated with distinct water masses. Species were identified using a genus-specific Automated Ribosomal Intergenic Spacer Analysis (ARISA). Seventeen amplicons were observed; seven corresponded to temperate, sub-polar, or polar Pseudo-nitzschia species based on parallel sequencing efforts (P. arctica, P. delicatissima, P. granii, P. obtusa, P. pungens, and two genotypes of P. seriata), and one represented Fragilariopsis oceanica. During summer, particulate DA (pDA; 4.0 to 130.0 ng L-1) was observed in the Bering Strait and Chukchi Sea where P. obtusa was prevalent. In fall, pDA (3.3 to 111.8 ng L-1) occurred along the Beaufort Sea shelf coincident with one P. seriata genotype, and south of the Bering Strait in association with the other P. seriata genotype. Taxa were correlated with latitude, longitude, temperature, salinity, pDA, and/or chlorophyll a, and each had a distinct distribution pattern. The observation of DA in association with different species, seasons, geographic regions, and water masses underscores the significant risk of Amnesic Shellfish Poisoning (ASP) and DA-poisoning in Alaska waters

Learning curves of novice residents on cataract surgery simulator: the E3CAPS pedagogic study

International audienceIntroduction: Training novice ophthalmology residents on the EyeSi® simulator increases cataract surgery safety. However, there is no consensus regarding how much training residents should perform before their first time on patients. We evaluated the French national training program through the analysis of the learning curves of novice residents.Methods: This prospective multicentric pedagogic study was conducted with French novice residents. Each resident completed the recommended four two-hour training sessions and performed a standardized assessment simulating standard cataract surgery before the first session (A0), at the end of the first (A1), second (A2), third (A3) and fourth (A4) sessions. For each surgical step of each attempt, the following data were collected: score, odometer, completion time, posterior capsular rupture and cumulative energy delivered (ultrasounds) during phacoemulsification. A performance threshold was set at a score of 80/100 for each surgical step, 400/500 for the overall procedure. Only descriptive statistics were employed.Results: Sixteen newly nominated ophthalmology residents were included. Median score progressively increased from 95 [IQR 53; 147]) at A0 to 425 [IQR 411; 451] at A4. Despite a significant progression, the \"emulsification\" step had the lowest A4 scores 86 [IQR 60; 94] without reduction in completion time, odometer or ultrasounds delivered. The rate of posterior capsular rupture decreased linearly from 75% at A0 to 13% at A4 during \"emulsification\" and from 69 to 0% during \"irrigation and aspiration\". At A4, only 25% [8; 53] of residents had > 80 at each step and only 75% [47; 92] had > 400/500 overall.Conclusion: A training program consisting of four two-hour sessions on the EyeSi simulator over four consecutive days effectively enhances the surgical skills of novice ophthalmology residents. Undergoing more training sessions may improve scores and decrease the incidence of surgical complications, particularly at the emulsification step of cataract surgery. The learning curves presented here can reassure residents who are progressing normally and help identify those who need a further personalized training program. TRIAL REGISTRATION: ClinicalTrials registration number: NCT05722080 (first submitted 22/12/2022, first posted 10/02/2023).http://clinicaltrials.gov/show/NCT0572208