Reversible Influence of Hemipiperazine Photochromism on the Early Development of Zebrafish Embryo.

This study explores the potential of controlling organismal development with light by using reversible photomodulation of activity in bioactive compounds. Specifically, our research focuses on plinabulin 1, an inhibitor of tubulin dynamics that contains a photochromic motif called hemipiperazine. The two isomeric forms, Z-1 and E-1, can partially interconvert with light, yet show remarkable thermal stability in darkness. The Z-isomer exhibits higher cytotoxicity due to stronger binding to α-tubulin's colchicine site. The less toxic E-1 form, considered a "pro-drug", can be isolated in vitro and stored. Upon activation by blue or cyan light, it predominantly generates the more toxic Z-1 form. Here we demonstrate that 1 can effectively photomodulate epiboly, a critical microtubule-dependent cell movement during gastrulation in zebrafish embryos. This research highlights the potential of photomodulation for precise and reversible control of cellular activities and organismal development.

Caveolae disassemble upon membrane lesioning and foster cell survival.

Repair of lesions in the plasma membrane is key to sustaining cellular homeostasis. Cells maintain cytoplasmic as well as membrane-bound stores of repair proteins that can rapidly precipitate at the site of membrane lesions. However, little is known about the origins of lipids and proteins for resealing and repair of the plasma membrane. Here we study the dynamics of caveolar proteins after laser-induced lesioning of plasma membranes of mammalian C2C12 tissue culture cells and muscle cells of intact zebrafish embryos. Single-molecule diffusivity measurements indicate that caveolar clusters break up into smaller entities after wounding. Unlike Annexins and Dysferlin, caveolar proteins do not accumulate at the lesion patch. In caveolae-depleted cavin1a knockout zebrafish embryos, lesion patch formation is impaired, and injured cells show reduced survival. Our data suggest that caveolae disassembly releases surplus plasma membrane near the lesion to facilitate membrane repair after initial patch formation for emergency sealing.

sox1a:eGFP transgenic line and single-cell transcriptomics reveal the origin of zebrafish intraspinal serotonergic neurons.

Sox transcription factors are crucial for vertebrate nervous system development. In zebrafish embryo, sox1 genes are expressed in neural progenitor cells and neurons of ventral spinal cord. Our recent study revealed that the loss of sox1a and sox1b function results in a significant decline of V2 subtype neurons (V2s). Using single-cell RNA sequencing, we analyzed the transcriptome of sox1a lineage progenitors and neurons in the zebrafish spinal cord at four time points during embryonic development, employing the Tg(sox1a:eGFP) line. In addition to previously characterized sox1a-expressing neurons, we discovered the expression of sox1a in late-developing intraspinal serotonergic neurons (ISNs). Developmental trajectory analysis suggests that ISNs arise from lateral floor plate (LFP) progenitor cells. Pharmacological inhibition of the Notch signaling pathway revealed its role in negatively regulating LFP progenitor cell differentiation into ISNs. Our findings highlight the zebrafish LFP as a progenitor domain for ISNs, alongside known Kolmer-Agduhr (KA) and V3 interneurons.

Smuggling on the Nanoscale-Fusogenic Liposomes Enable Efficient RNA-Transfer with Negligible Immune Response In Vitro and In Vivo.

The efficient and biocompatible transfer of nucleic acids into mammalian cells for research applications or medical purposes is a long-standing, challenging task. Viral transduction is the most efficient transfer system, but often entails high safety levels for research and potential health impairments for patients in medical applications. Lipo- or polyplexes are commonly used transfer systems but result in comparably low transfer efficiencies. Moreover, inflammatory responses caused by cytotoxic side effects were reported for these transfer methods. Often accountable for these effects are various recognition mechanisms for transferred nucleic acids. Using commercially available fusogenic liposomes (Fuse-It-mRNA), we established highly efficient and fully biocompatible transfer of RNA molecules for in vitro as well as in vivo applications. We demonstrated bypassing of endosomal uptake routes and, therefore, of pattern recognition receptors that recognize nucleic acids with high efficiency. This may underlie the observed almost complete abolishment of inflammatory cytokine responses. RNA transfer experiments into zebrafish embryos and adult animals fully confirmed the functional mechanism and the wide range of applications from single cells to organisms.

Fat Grafts Show Higher Hypoxia, Angiogenesis, Adipocyte Proliferation, and Macrophage Infiltration than Flaps in a Pilot Mouse Study.

BACKGROUND: Over 137,000 breast reconstructions are performed annually by American Society of Plastic Surgeons (ASPS) members. Vascularized flaps and avascular lipofilling each account for over 33,000 autologous reconstructions. Although clinical and experimental observations suggest biologic differences with diverging effects on locoregional tumor control, comparative animal models are lacking. The authors standardized existing techniques in immunocompetent mice, laying the foundation for in vivo models of autologous breast reconstruction combinable with orthotopic tumor implantations. METHODS: Twenty-five groin flaps and 39 fat grafts were transferred in female BALB/c-mice. Adipocytes were tracked via Hoechst-Calcein-DiI staining ( n = 2 per group), and postoperative volume retentions were compared via magnetic resonance imaging ( n = 3 per group) on days 1, 11, 21, and 31. Proliferation indices, microvessel densities, tissue hypoxia, and macrophage infiltrates were compared via Ki67, CD31, pimonidazole, and hematoxylin-eosin staining on days 5, 10, 15, 20, and 30 ( n = 4 per group). RESULTS: Viable adipocytes were present in both groups. Graft volumes plateaued at 42.7 ± 1.2% versus 81.8 ± 4.0% of flaps ( P < 0.001). Initially, grafts contained more hypoxic cells (day 5: 15.192 ± 1.249 versus 1.157 ± 192; P < 0.001), followed by higher proliferation (day 15: 25.2 ± 1.0% versus 0.0 ± 0.0%; P < 0.001), higher microvessel numbers (day 30: 307.0 ± 13.2 versus 178.0 ± 10.6; P < 0.001), and more pronounced macrophage infiltrates (graded 3 versus 2; P < 0.01). CONCLUSION: This comparative murine pilot study of vascularized flaps versus avascular lipofilling suggests differences in volume retention, proliferation, angiogenesis, hypoxia, and inflammation. CLINICAL RELEVANCE STATEMENT: The biological differences of fat grafting versus flap transfer are not fully understood because no single comparative experimental model has been established to date. The authors present the first comparative small animal model of both techniques, which will allow the gaining of deeper insights into their biological effects.

Phenotypic Discovery of Triazolo[1,5-c]quinazolines as a First-In-Class Bone Morphogenetic Protein Amplifier Chemotype.

Phenotypic drug discovery (PDD) continues to fuel the research and development pipelines with first-in-class therapeutic modalities, but success rates critically depend on the quality of the underlying model system. Here, we employed a stem cell-based approach for the target-agnostic, yet pathway-centric discovery of small-molecule cytokine signaling activators to act as morphogens during development and regeneration. Unbiased screening identified triazolo[1,5-c]quinazolines as a new-in-class in vitro and in vivo active amplifier of the bone morphogenetic protein (BMP) pathway. Cellular BMP outputs were stimulated via enhanced and sustained availability of BMP-Smad proteins, strictly dependent on a minimal BMP input. Holistic target deconvolution unveiled a unique mechanism of dual targeting of casein kinase 1 and phosphatidyl inositol 3-kinase isoforms as key effectors for efficient amplification of osteogenic BMP signaling. This work underscores the asset of PDD to discover unrecognized polypharmacology signatures, in this case significantly expanding the chemical and druggable space of BMP modulators.

Highly Fluorinated Peptide Probes with Enhanced In Vivo Stability for 19 F-MRI.

A labeling strategy for in vivo 19 F-MRI (magnetic resonance imaging) based on highly fluorinated, short hydrophilic peptide probes, is developed. As dual-purpose probes, they are functionalized further by a fluorophore and an alkyne moiety for bioconjugation. High fluorination is achieved by three perfluoro-tert-butyl groups, introduced into asparagine analogues by chemically stable amide bond linkages. d-amino acids and ß-alanine in the sequences endow the peptide probes with low cytotoxicity and high serum stability. This design also yielded unstructured peptides, rendering all 27 19 F substitutions chemically equivalent, giving rise to a single 19 F-NMR resonance with <10 Hz linewidth. The resulting performance in 19 F-MRI is demonstrated for six different peptide probes. Using fluorescence microscopy, these probes are found to exhibit high stability and long circulation times in living zebrafish embryos. Furthermore, the probes can be conjugated to bovine serum albumin with only amoderate increase in 19 F-NMR linewidth to ≈30 Hz. Overall, these peptide probes are hence suitable for in vivo 19 F-MRI applications.

Loss of the Bardet-Biedl protein Bbs1 alters photoreceptor outer segment protein and lipid composition.

Primary cilia are key sensory organelles whose dysfunction leads to ciliopathy disorders such as Bardet-Biedl syndrome (BBS). Retinal degeneration is common in ciliopathies, since the outer segments (OSs) of photoreceptors are highly specialized primary cilia. BBS1, encoded by the most commonly mutated BBS-associated gene, is part of the BBSome protein complex. Using a bbs1 zebrafish mutant, we show that retinal development and photoreceptor differentiation are unaffected by Bbs1-loss, supported by an initially unaffected transcriptome. Quantitative proteomics and lipidomics on samples enriched for isolated OSs show that Bbs1 is required for BBSome-complex stability and that Bbs1-loss leads to accumulation of membrane-associated proteins in OSs, with enrichment in proteins involved in lipid homeostasis. Disruption of the tightly regulated OS lipid composition with increased OS cholesterol content are paralleled by early functional visual deficits, which precede progressive OS morphological anomalies. Our findings identify a role for Bbs1/BBSome in OS lipid homeostasis, suggesting a pathomechanism underlying retinal degeneration in BBS.

Two plus one is almost three: a fast approximation for multi-view deconvolution.

Multi-view deconvolution is a powerful image-processing tool for light sheet fluorescence microscopy, providing isotropic resolution and enhancing the image content. However, performing these calculations on large datasets is computationally demanding and time-consuming even on high-end workstations. Especially in long-time measurements on developing animals, huge amounts of image data are acquired. To keep them manageable, redundancies should be removed right after image acquisition. To this end, we report a fast approximation to three-dimensional multi-view deconvolution, denoted 2D+1D multi-view deconvolution, which is able to keep up with the data flow. It first operates on the two dimensions perpendicular and subsequently on the one parallel to the rotation axis, exploiting the rotational symmetry of the point spread function along the rotation axis. We validated our algorithm and evaluated it quantitatively against two-dimensional and three-dimensional multi-view deconvolution using simulated and real image data. 2D+1D multi-view deconvolution takes similar computation time but performs markedly better than the two-dimensional approximation only. Therefore, it will be most useful for image processing in time-critical applications, where the full 3D multi-view deconvolution cannot keep up with the data flow.

Methylmercury-induced hair cell loss requires hydrogen peroxide production and leukocytes in zebrafish embryos.

Hearing impairment and deafness is frequently observed as one of the neurological signs in patients with Minamata disease caused by methylmercury (MeHg) poisoning. Loss of hair cells in humans and animals is a consequence of MeHg poisoning. However, it is still not clear how MeHg causes hearing deficits. We employed the hair cells of the lateral line system of zebrafish embryos as a model to explore this question. We exposed transgenic zebrafish embryos to MeHg (30-360 µg/L) at the different stages, and scored the numbers of hair cells. We find that MeHg-induced reduction of hair cells is in a concentration dependent manner. By employing antisense morpholino against to pu.1, we confirm that loss of hair cells involves the action of leukocytes. Moreover, hair cell loss is attenuated by co-treating MeHg-exposed embryos with pharmacological inhibitors of NADPH oxidases named diphenyleneiodonium (DPI) and VAS2870. In situ gene expression analysis showed that genes encoding the SQSTM1-Keap1-Nrf2 systems involved in combating oxidative stress and immune responses are highly expressed in the lateral line organs of embryos exposed to MeHg. This suggests that induction of hydrogen peroxide (H2O2) is the primary effect of MeHg on the hair cells. Genes induced by MeHg are also involved in regeneration of the hair cells. These features are likely related to the capacity of the zebrafish to regenerate the lost hair cells.

Neuron-Radial Glial Cell Communication via BMP/Id1 Signaling Is Key to Long-Term Maintenance of the Regenerative Capacity of the Adult Zebrafish Telencephalon.

The central nervous system of adult zebrafish displays an extraordinary neurogenic and regenerative capacity. In the zebrafish adult brain, this regenerative capacity relies on neural stem cells (NSCs) and the careful management of the NSC pool. However, the mechanisms controlling NSC pool maintenance are not yet fully understood. Recently, Bone Morphogenetic Proteins (BMPs) and their downstream effector Id1 (Inhibitor of differentiation 1) were suggested to act as key players in NSC maintenance under constitutive and regenerative conditions. Here, we further investigated the role of BMP/Id1 signaling in these processes, using different genetic and pharmacological approaches. Our data show that BMPs are mainly expressed by neurons in the adult telencephalon, while id1 is expressed in NSCs, suggesting a neuron-NSC communication via the BMP/Id1 signaling axis. Furthermore, manipulation of BMP signaling by conditionally inducing or repressing BMP signaling via heat-shock, lead to an increase or a decrease of id1 expression in the NSCs, respectively. Induction of id1 was followed by an increase in the number of quiescent NSCs, while knocking down id1 expression caused an increase in NSC proliferation. In agreement, genetic ablation of id1 function lead to increased proliferation of NSCs, followed by depletion of the stem cell pool with concomitant failure to heal injuries in repeatedly injured mutant telencephala. Moreover, pharmacological inhibition of BMP and Notch signaling suggests that the two signaling systems cooperate and converge onto the transcriptional regulator her4.1. Interestingly, brain injury lead to a depletion of NSCs in animals lacking BMP/Id1 signaling despite an intact Notch pathway. Taken together, our data demonstrate how neurons feedback on NSC proliferation and that BMP1/Id1 signaling acts as a safeguard of the NSC pool under regenerative conditions.

In Vivo Behavior of the Antibacterial Peptide Cyclo[RRRWFW], Explored Using a 3-Hydroxychromone-Derived Fluorescent Amino Acid.

Labeling biomolecules with fluorescent labels is an established tool for structural, biochemical, and biophysical studies; however, it remains underused for small peptides. In this work, an amino acid bearing a 3-hydroxychromone fluorophore, 2-amino-3-(2-(furan-2-yl)-3-hydroxy-4-oxo-4H-chromen-6-yl)propanoic acid (FHC), was incorporated in a known hexameric antimicrobial peptide, cyclo[RRRWFW] (cWFW), in place of aromatic residues. Circular dichroism spectropolarimetry and antibacterial activity measurements demonstrated that the FHC residue perturbs the peptide structure depending on labeling position but does not modify the activity of cWFW significantly. FHC thus can be considered an adequate label for studies of the parent peptide. Several analytical and imaging techniques were used to establish the activity of the obtained labeled cWFW analogues toward animal cells and to study the behavior of the peptides in a multicellular organism. The 3-hydroxychromone fluorophore can undergo excited-state intramolecular proton transfer (ESIPT), resulting in double-band emission from its two tautomeric forms. This feature allowed us to get insights into conformational equilibria of the labeled peptides, localize the cWFW analogues in human cells (HeLa and HEK293) and zebrafish embryos, and assess the polarity of the local environment around the label by confocal fluorescence microscopy. We found that the labeled peptides efficiently penetrated cancerous cells and localized mainly in lipid-containing and/or other nonpolar subcellular compartments. In the zebrafish embryo, the peptides remained in the bloodstream upon injection into the cardinal vein, presumably adhering to lipoproteins and/or microvesicles. They did not diffuse into any tissue to a significant extent during the first 3 h after administration. This study demonstrated the utility of fluorescent labeling by double-emission labels to evaluate biologically active peptides as potential drug candidates in vivo.

MondoA regulates gene expression in cholesterol biosynthesis-associated pathways required for zebrafish epiboly.

The glucose-sensing Mondo pathway regulates expression of metabolic genes in mammals. Here, we characterized its function in the zebrafish and revealed an unexpected role of this pathway in vertebrate embryonic development. We showed that knockdown of mondoa impaired the early morphogenetic movement of epiboly in zebrafish embryos and caused microtubule defects. Expression of genes in the terpenoid backbone and sterol biosynthesis pathways upstream of pregnenolone synthesis was coordinately downregulated in these embryos, including the most downregulated gene nsdhl. Loss of Nsdhl function likewise impaired epiboly, similar to MondoA loss of function. Both epiboly and microtubule defects were partially restored by pregnenolone treatment. Maternal-zygotic mutants of mondoa showed perturbed epiboly with low penetrance and compensatory changes in the expression of terpenoid/sterol/steroid metabolism genes. Collectively, our results show a novel role for MondoA in the regulation of early vertebrate development, connecting glucose, cholesterol and steroid hormone metabolism with early embryonic cell movements.

In most animals, a protein called MondoA closely monitors the amount of glucose in the body, as this type of sugar is the fuel required for many life processes. Glucose levels also act as a proxy for the availability of other important nutrients. Once MondoA has detected glucose molecules, it turns genetic programmes on and off depending on the needs of the cell. So far, these mechanisms have mainly been studied in adult cells. However, recent studies have shown that proteins that monitor nutrient availability, and their associated pathways, can control early development. MondoA had not been studied in this context before, so Weger et al. decided to investigate its role in embryonic development. The experiments used embryos from zebrafish, a small freshwater fish whose early development is easily monitored and manipulated in the laboratory. Inhibiting production of the MondoA protein in zebrafish embryos prevented them from maturing any further, stopping their development at an early key stage. This block was caused by defects in microtubules, the tubular molecules that act like a microscopic skeleton to provide structural support for cells and guide transport of cell components. In addition, the pathway involved in the production of cholesterol and cholesterol-based hormones was far less active in embryos lacking MondoA. Treating MondoA-deficient embryos with one of these hormones corrected the microtubule defects and let the embryos progress to more advanced stages of development. These results reveal that, during development, the glucose sensor MondoA also controls pathways involved in the creation of cholesterol and associated hormones. These new insights into the metabolic regulation of development could help to understand certain human conditions; for example, certain patients with defective cholesterol pathway genes also show developmental perturbations. In addition, the work highlights a biological link between cholesterol production and cellular responses to glucose, which Weger et al. hope could one day help to identify new cholesterol-lowering drugs.

Pax6 organizes the anterior eye segment by guiding two distinct neural crest waves.

Cranial neural crest (NC) contributes to the developing vertebrate eye. By multidimensional, quantitative imaging, we traced the origin of the ocular NC cells to two distinct NC populations that differ in the maintenance of sox10 expression, Wnt signalling, origin, route, mode and destination of migration. The first NC population migrates to the proximal and the second NC cell group populates the distal (anterior) part of the eye. By analysing zebrafish pax6a/b compound mutants presenting anterior segment dysgenesis, we demonstrate that Pax6a/b guide the two NC populations to distinct proximodistal locations. We further provide evidence that the lens whose formation is pax6a/b-dependent and lens-derived TGFß signals contribute to the building of the anterior segment. Taken together, our results reveal multiple roles of Pax6a/b in the control of NC cells during development of the anterior segment.

Proteasome subunit PSMC3 variants cause neurosensory syndrome combining deafness and cataract due to proteotoxic stress.

The ubiquitin-proteasome system degrades ubiquitin-modified proteins to maintain protein homeostasis and to control signalling. Whole-genome sequencing of patients with severe deafness and early-onset cataracts as part of a neurological, sensorial and cutaneous novel syndrome identified a unique deep intronic homozygous variant in the PSMC3 gene, encoding the proteasome ATPase subunit Rpt5, which lead to the transcription of a cryptic exon. The proteasome content and activity in patient's fibroblasts was however unaffected. Nevertheless, patient's cells exhibited impaired protein homeostasis characterized by accumulation of ubiquitinated proteins suggesting severe proteotoxic stress. Indeed, the TCF11/Nrf1 transcriptional pathway allowing proteasome recovery after proteasome inhibition is permanently activated in the patient's fibroblasts. Upon chemical proteasome inhibition, this pathway was however impaired in patient's cells, which were unable to compensate for proteotoxic stress although a higher proteasome content and activity. Zebrafish modelling for knockout in PSMC3 remarkably reproduced the human phenotype with inner ear development anomalies as well as cataracts, suggesting that Rpt5 plays a major role in inner ear, lens and central nervous system development.

Bone morphogenetic protein signaling regulates Id1-mediated neural stem cell quiescence in the adult zebrafish brain via a phylogenetically conserved enhancer module.

In the telencephalon of adult zebrafish, the inhibitor of DNA binding 1 (id1) gene is expressed in radial glial cells (RGCs), behaving as neural stem cells (NSCs), during constitutive and regenerative neurogenesis. Id1 controls the balance between resting and proliferating states of RGCs by promoting quiescence. Here, we identified a phylogenetically conserved cis-regulatory module (CRM) mediating the specific expression of id1 in RGCs. Systematic deletion mapping and mutation of conserved transcription factor binding sites in stable transgenic zebrafish lines reveal that this CRM operates via conserved smad1/5 and 4 binding motifs under both homeostatic and regenerative conditions. Transcriptome analysis of injured and uninjured telencephala as well as pharmacological inhibition experiments identify a crucial role of bone morphogenetic protein (BMP) signaling for the function of the CRM. Our data highlight that BMP signals control id1 expression and thus NSC proliferation during constitutive and induced neurogenesis.

Correction to: Gene duplication and functional divergence of the zebrafish otospiralin genes.

In the originally published article, the first names and family names of the authors were interchanged, hence not correct. The correct presentation of names is presented above.

Differential Nanoparticle Sequestration by Macrophages and Scavenger Endothelial Cells Visualized in Vivo in Real-Time and at Ultrastructural Resolution.

Despite the common knowledge that the reticuloendothelial system is largely responsible for blood clearance of systemically administered nanoparticles, the sequestration mechanism remains a "black box". Using transgenic zebrafish embryos with cell type-specific fluorescent reporters and fluorescently labeled model nanoparticles (70 nm SiO2), we here demonstrate simultaneous three-color in vivo imaging of intravenously injected nanoparticles, macrophages, and scavenger endothelial cells (SECs). The trafficking processes were further revealed at ultrastructural resolution by transmission electron microscopy. We also find, using a correlative light-electron microscopy approach, that macrophages rapidly sequester nanoparticles via membrane adhesion and endocytosis (including macropinocytosis) within minutes after injection. In contrast, SECs trap single nanoparticles via scavenger receptor-mediated endocytosis, resulting in gradual sequestration with a time scale of hours. Inhibition of the scavenger receptors prevented SECs from accumulating nanoparticles but enhanced uptake in macrophages, indicating the competitive nature of nanoparticle clearance in vivo. To directly quantify the relative contributions of the two cell types to overall nanoparticle sequestration, the differential sequestration kinetics was studied within the first 30 min post-injection. This revealed a much higher and increasing relative contribution of SECs, as they by far outnumber macrophages in zebrafish embryos, suggesting the importance of the macrophage:SECs ratio in a given tissue. Further characterizing macrophages on their efficiency in nanoparticle clearance, we show that inflammatory stimuli diminish the uptake of nanoparticles per cell. Our study demonstrates the strength of transgenic zebrafish embryos for intravital real-time and ultrastructural imaging of nanomaterials that may provide mechanistic insights into nanoparticle clearance in rodent models and humans.

Light-controllable dithienylethene-modified cyclic peptides: photoswitching the in vivo toxicity in zebrafish embryos.

This study evaluates the embryotoxicity of dithienylethene-modified peptides upon photoswitching, using 19 analogues based on the ß-hairpin scaffold of the natural membranolytic peptide gramicidin S. We established an in vivo assay in two variations (with ex vivo and in situ photoisomerization), using larvae of the model organism Danio rerio, and determined the toxicities of the peptides in terms of 50% lethal doses (LD50). This study allowed us to: (i) demonstrate the feasibility of evaluating peptide toxicity with D. rerio larvae at 3-4 days post fertilization, (ii) determine the phototherapeutic safety windows for all peptides, (iii) demonstrate photoswitching of the whole-body toxicity for the dithienylethene-modified peptides in vivo, (iv) re-analyze previous structure-toxicity relationship data, and (v) select promising candidates for potential clinical development.

Gene duplication and functional divergence of the zebrafish otospiralin genes.

Otospiralin (OTOSP) is a small protein of unknown function, expressed in fibrocytes of the inner ear and required for normal cochlear auditory function. Despite its conservation from fish to mammals, expression of otospiralin was only investigated in mammals. Here, we report for the first time the expression profile of OTOS orthologous genes in zebrafish (Danio rerio): otospiralin and si:ch73-23l24.1 (designated otospiralin-like). In situ hybridization analyses in zebrafish embryos showed a specific expression of otospiralin-like in notochord (from 14 to 48 hpf) and similar expression patterns for otospiralin and otospiralin-like in gut (from 72 to 120 hpf), swim bladder (from 96 to 120 hpf) and inner ear (at 120 hpf). Morpholino knockdown of otospiralin and otospiralin-like showed no strong change of the body structure of the embryos at 5 dpf and the inner ear was normally formed. Nevertheless, knockdown embryos showed a reduced number of kinocilia in the lateral crista, indicating that these genes play an important role in kinocilium formation. RT-qPCR revealed that otospiralin is highly expressed in adult zebrafish inner ear comparing to the others analyzed tissues as previously shown for mice. Interestingly, otospiralin-like was not detected in the inner ear which suggests that otospiralin have a more important function in hearing than otospiralin-like. Phylogenetic analysis of otospiralin proteins in vertebrates indicated the presence of two subgroups and supported the functional divergence observed in zebrafish for otospiralin and otospiralin-like genes. This study offers the first insight into the expression of otospiralin and otospiralin-like in zebrafish. Expression data point to an important role for otospiralin in zebrafish hearing and a specific role for otospiralin-like in notochord vacuolization.