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Mimicking fish lateral line for hydrodynamic sensing, various artificial lateral line systems have been developed for underwater robotics. However, previous studies of artificial lateral line systems for underwater source localization were based on a single sensing modality of either pressure or flow velocity. Inspired by the functions of flow and pressure receptors of fish, we developed an artificial lateral line system integrated with pressure sensors and flow velocity sensors. A dual-sensor fusion modality was proposed to locate near-field dipole source by measuring hydrodynamic signals. A multilayer perceptron neural network was constructed to process the pressure and flow velocity signals and to predict near-field dipole coordinates in two and three dimensions. In a two-dimensional plane, compared with a single pressure- or velocity-sensing modality, the dual-sensor fusion modality reduced the mean localization error by 30%. In a three-dimensional space, the mean localization error based on the dual-sensor fusion modality was approximately 0.1 body lengths, when considering a source located within one body length from the artificial lateral line. In addition, we studied the influence of the number of sensors on the localization accuracy via analysis of variance. Our experimental results indicated that the bio-inspired dual-sensor fusion modality is beneficial for improving the performance of artificial lateral line systems for underwater source localization.

In all fishes and aquatic-stage amphibians, lines of mechanosensory lateral line organs ('neuromasts' containing hair cells), distributed over the head and trunk, detect local water movement. Many species also have electrosensory lateral line organs that detect weak electric fields, such as those surrounding other animals. In electroreceptive non-teleost jawed fishes and amphibians, electroreceptor cells reside within ‘ampullary organs’ (AOs) distributed in fields flanking some or all neuromast lines on the head. Both AOs and neuromasts develop from lateral line placodes that elongate over the head to form sensory ridges. Their shared origin makes the system a useful model to investigate cell fate decisions during development. Electroreception was lost in the lineages leading to teleost ray-finned fishes and frogs, so the electrosensory (AO) vs. mechanosensory (neuromast) fate-choice cannot be studied in the standard anamniote models, zebrafish and Xenopus. To identify genes involved in AO vs. neuromast development, the lab previously used differential RNAseq in late-larval stages of a chondrostean ray-finned fish, the Mississippi paddlefish (Polyodon spathula), to generate a dataset of around 500 genes putatively enriched in lateral line organs. Candidate gene expression analysis suggested electroreceptors and hair cells are closely related cell types. To gain insight into signalling pathways potentially involved in AO and/or neuromast development, I cloned cDNA fragments of 50 signalling pathway-related genes from the paddlefish gene-set and 26 other signalling pathway-related genes selected via a candidate approach, in an experimentally tractable chondrostean, the sterlet (Acipenser ruthenus, a sturgeon). Overall, I cloned cDNA fragments of 33 genes encoding receptors, 27 encoding ligands and 16 encoding, for example, secreted inhibitors, scaffold proteins and co-receptors. In situ hybridisation identified 32 genes expressed in the developing lateral line system. Of these, five (Dner, Fgf10, Ngfr, Cbln18 and Kit) were expressed within developing neuromasts but not AOs, and four (Dll4, Axin2, Omg and Gpr52) within developing AOs but not neuromasts. (Other genes with specific expression patterns were expressed in non-lateral line structures such as gill filaments and taste buds.) I explored the Bmp signalling pathway in the most depth. I identified lateral line organ expression of genes encoding two ligands (Bmp5, Bmp4), an activin type II receptor (Acvr2a) that can complex with type I Bmp receptors, and two secreted dual-Bmp/Wnt inhibitors (Sostdc1, Apcdd1). CRISPR/Cas9-mediated mutagenesis targeting Bmp5 in F0-injected sterlet embryos led to fewer AOs forming, primarily in the posterior preopercular fields. Conversely, DMH1-mediated inhibition of Bmp signalling for 20 hours when AOs normally start to develop, led to precocious AO formation generally, plus ectopic AOs in the three dorsal-most fields. This suggested that Bmp signalling inhibits, while Bmp5 promotes, AO development., Anatomical Society

The lateral line system and its innervation were examined in the masu salmon Oncorhynchus masou masou. The species has 8 cephalic canals (supraorbital, infraorbital, otic, preopercular, mandibular, postotic, supratemporal, and temporal portion of trunk), 1 trunk canal and 9 superficial neuromast groups (rostral, nostril, preinfraorbital, postocular, cheek and supratemporal groups in the cephalic groups, and predorsal, trunk accessory and caudal fin groups in the trunk groups). The components are generally similar to those in many other teleosts, the lateral line system of O. m. masou is distinctive in having a preinfraorbital superficial neuromast group and lacking infraorbital, mandibular and opercular superficial neuromast groups. The lateral line system of O. m. masou is compared with some other species of Oncorhynchus.

Machine vision and learning analysis of rheotaxis behavior (orientation and swimming to water flow) in larval zebrafish, Danio rerio.

Threespine stickleback exhibit a row of superficial neuromasts that project through the bony plates on each side of the trunk and which constitute an important sensory modality for detection of near-field water motion. Previously, we have shown that numbers of neuromasts on each structural plate are highly variable among populations. In the current paper, we expand this study to evaluate the extent of deviation from bilateral symmetry of 4344 fish in 57 natural and three transplant populations of threespine stickleback from lakes, streams and oceanic habitats of coastal British Columbia, predicting that neuromasts would be largely bilaterally symmetrical for optimal detection of external stimuli. In contrast, we found asymmetry in all populations, the greatest amount occurring on the anterior buttressing lateral plates and on populations with the fewest neuromasts. We found no consistent trends of signed (directional) asymmetry (SA) among the populations while relative absolute asymmetry (RAA) is lower in dystrophic (stained) habitats than in clearwater habitats (p

Any phenomenon in nature is potential to be an inspiration for us to propose new ideas. Lateral line is a typical example which has attracted more interest in recent years. With the aid of lateral line, fish is capable of acquiring fluid information around, which is of great significance for them to survive, communicate and hunt underwater. In this paper, we briefly introduce the morphology and mechanism of the lateral line first. Then we focus on the development of artificial lateral line which typically consists of an array of sensors and can be installed on underwater robots. A series of sensors inspired by the lateral line with different sensing principles have been summarized. And then the applications of artificial lateral line systems in hydrodynamic environment sensing and vortices detection, dipole oscillation source detection, and autonomous control of underwater robots have been reviewed. In addition, the existing problems and future foci in this field have been further discussed in detail. The current works and future foci have demonstrated that artificial lateral line has great potentials of applications and contributes to the development of underwater robots.

The lateral line system and its innervation were examined in two paedomorphic species of Apogonidae, Gymnapogon japonicus and Pseudamiops cf. springeri, both of which have been included in Gymnapogonini (Apogoninae) characterized by a small translucent body lacking canalized lateral line scales, but with many superficial neuromasts (total SNs: 2,691 and 2,197 in G. japonicus and Pseudamiops cf. springeri, respectively). Although scales are entirely absent in G. japonicus, the innervation pattern of the trunk lateral line system is basically similar to that in other apogonids having a single lateral line scale series. In comparison, Pseudamiops cf. springeri (and P. gracilicauda) have three series of inconspicuous lateral line scales with a distinct innervation pattern, implying a phylogenetic affinity with Pseudamia (Pseudamiinae). The monophyly of Pseudamiops and Pseudamia was also supported strongly by a molecular phylogenetic analysis, thus the paedomorphic nature is considered homoplasy between Pseudamiops and Gymnapogon. The innervation of head lateral line system in G. japonicus and Pseudamiops cf. springeri is basically the same with that of other apogonids, supporting homology of the presence of many head SNs among the species. The SN pattern and head canals of adult Pseudamiops cf. springeri are similar to those in juvenile Pseudamia gelatinosa, implying a paedomorphic truncation of lateral line system development in Pseudamiops cf. springeri.

This study was carried out to analyze the architecture of the skin of the upper lip region in silver carp fishes using light, scanning, and transmission electron microscopies. The skin was composed of epidermis, dermis, and hypodermis. The epidermis of the upper lip was characterized by the presence of large number of metachromatic mucous goblet cells, which showed positive reaction with Periodic Acid-Schiff (PAS), Alcian blue (AB), and toluidine blue. The electroreceptive lateral line system was organized into ampullary and tuberous organs. The scanning electron microscopy showed that the surface of the skin of upper lip was covered by microridges and characterized by the presence of taste buds and openings of lateral line system. As observed by transmission electron microscopy, the cytoplasm of the epidermal layers appeared electron-dense except for the superficial layer, where the cytoplasm was electron-lucent and contained many vacuoles and few profiles of rER. Moreover, the epidermis contained rodlet cells and stem cells. Few organelles were found within the cytoplasm of club cells. Neutrophils and eosinophilic granular cells were also demonstrated as important immune cells in the epidermis of the upper lip. Furthermore, lymphocytes and basophils could be identified with macrophage in the epidermal layer of the upper lip. Numerous telocytes were demonstrated between the collagen fibers of the dermis and bundles of myelinated nerve fibers. In conclusion, the skin of the upper lip region of silver carp displayed many sensory and immunological characteristic features.

The lateral line system of fishes is composed of neuromast mechanoreceptors that detect movement through vibration and changes in pressure gradients in the water. Although mechanosensory information has been shown to be important in the contexts of predator escape and foraging, little is known about the role of the lateral line system during intraspecific interactions, such as reproduction. However, many species of fish demonstrate complex courtship and aggressive repertoires that involve movement of the body and fins, resulting in local displacement of the surrounding water. This displacement has the potential to function as a signal that contains information about the sender. In this study, we conducted two behavioural experiments using fathead minnows, Pimephales promelas, to test the hypothesis that the outcomes of male–male contests and male–female courtship interactions are influenced by hydrodynamic flows generated during conspecific interactions. In the first experiment, we pitted control males against those with an ablated lateral line system and assessed both overall aggression and the likelihood of territory acquisition. In the second experiment, we conducted dual-choice female mate choice experiments to determine whether control females and those without access to mechanosensory information (ablated females) differed in patterns of discrimination and the use of courtship as a criterion of choice. In experiment 1, control males won a significantly greater proportion of territorial contests than expected by chance and were more likely to use noncontact threat displays during aggressive interactions compared with ablated males. In experiment 2, females with access to the mechanosensory information channel showed enhanced mate discrimination compared to ablated females. These data are among the first to show that mechanosensory signals are an important criterion of territorial and reproductive success in fishes and are likely important contributors to multimodal communication in this group.

In vertebrate animals, motor and sensory efferent neurons carry information from the central nervous system (CNS) to peripheral targets. These two types of efferent systems sometimes bear a close resemblance, sharing common segmental organization, axon pathways, and chemical messengers. Here, we focus on the development of the octavolateral efferent neurons (OENs) and their interactions with the closely-related facial branchiomotor neurons (FBMNs) in zebrafish. Using live-imaging approaches, we investigate the birth, migration, and projection patterns of OENs. We find that OENs are born in two distinct groups: a group of rostral efferent neurons (RENs) that arises in the fourth segment, or rhombomere (r4), of the hindbrain and a group of caudal efferent neurons (CENs) that arises in r5. Both RENs and CENs then migrate posteriorly through the hindbrain between 18 and 48 hours post-fertilization, alongside the r4-derived FBMNs. Like the FBMNs, migration of the r4-derived RENs depends on function of the segmental identity gene hoxb1a; unlike the FBMNs, however, both OEN populations move independently of prickle1b. Further, we investigate whether the previously described ‘pioneer’ neuron that leads FBMN migration through the hindbrain is an r4-derived FBMN/REN or an r5-derived CEN. Our experiments verify that the pioneer is an r4-derived neuron and reaffirm its role in leading FBMN migration across the r4/5 border. In contrast, the r5-derived CENs migrate independently of the pioneer. Together, these results indicate that the mechanisms OENs use to navigate the hindbrain differ significantly from those employed by FBMNs.

Anesthesia is used to sedate aquatic animals during transportation or to immobilize them for surgery. However, most studies have focused on the behavioral effects of induction and recovery, without addressing the effect of anesthetic on neural activity. This study investigated the neural response of anterior lateral line afferent fibers in the oyster toadfish, Opsanus tau, during exposure to incremental increases of AQUI-S 20E (0.001-0.006%), to determine if eugenol (the active ingredient of AQUI-S 20E) influences neural activity of the fish lateral line system. Ventilation rate significantly decreased following AQUI-S 20E exposure with the surgical plane of anesthesia reached at 0.003%, characterized by shallow ventilation, equilibrium loss, and no response to tactile stimuli. Spontaneous and evoked firing rates of anterior lateral line fibers also significantly decreased following exposure, although the effect was transitory as neural activity recovered in the majority of fibers (70%) within 30 min of anesthetic withdrawal. While AQUI-S 20E proved effective in inducing the surgical plane of anesthesia without compromising survival, it is not recommended for acute neural preparations due to its depression of neural activity. However, the depression of lateral line sensitivity at low concentrations could play a role in reducing the stress response during fish transport.

In this letter, we present a distributed pressure sensory system, inspired by the lateral line found in fish, for estimating hydrodynamic forces acting on an autonomous underwater vehicle. By canceling these forces using the vehicle control system, the dynamics of the vehicle can be decoupled from the state of the surrounding fluid. We discuss a control scheme which combines the measured hydrodynamic forces with a feedback controller that is robust to disturbances and measurement errors, achieving asymptotic tracking in the presence of bounded disturbances and errors. We compare this robust lateral line controller to a baseline robust controller not using the lateral line system and to a controller using the lateral line with simple PD feedback. We simulate a spatially and time varying velocity flow field on the scale of the vehicle and show that the robust lateral line controller has improved performance compared to both the baseline robust controller and the PD controller using the lateral line system.

A new species of Astyanax is described from the rio Salobra, tributary of rio Cuiabá, rio Paraguai basin. The new taxon can be distinguished from its congeners by having a well-defined dark midlateral stripe on body extending from the posterior margin of the opercle to the base of middle caudal-fin rays and a single vertical elongate humeral blotch. Although the new species is described in Astyanax, some specimens present an incomplete or a discontinuous series of perforated scales in the lateral line. Therefore, a discussion on its generic allocation is presented. Comments on different patterns of coloration among dark-striped species of Astyanax are also provided. The discovery of a new species in an underwater tourist point relatively near a large urban center underscores that even fish species daily observed by hundreds of people in limpid waters may lack a formal taxonomic identity. Such finding also highlights how the megadiverse Brazilian freshwater ichthyofauna still needs efforts and investments to identify and describe new taxa.

The lateral line system is a mechanosensory organ of fish and amphibians that detects changes in water flow and is formed by the coordinated action of many signalling pathways. These signalling pathways can easily be targeted in zebrafish using pharmacological inhibitors to decipher their role in lateral line system development at cellular and molecular level. We have identified two uncharacterized proteins, whose mRNA are expressed in the lateral line system of zebrafish. One of these proteins, uncharacterized protein LOC564095 precursor, is conserved across vertebrates and its mRNA is expressed in posterior lateral line primordium (pLLP). The other uncharacterized protein, LOC100536887, is present only in the teleost fishes and its mRNA is expressed in neuromasts. We show that inhibition of retinoic acid (RA) signalling reduces the expression of both of these uncharacterized genes. It is reported that inhibition of RA signalling during gastrulation starting at 7 hours post fertilization (hpf) abrogates pLLP formation, and inhibition of RA signalling at 10 hpf delays the initiation of pLLP migration. Here, we show that inhibition of RA signalling before and during segmentation (9-16 hpf) results in delayed initiation and reduced speed of pLLP migration, as well as inhibition of posterior neuromasts formation.

Hair cells are the sensory receptors in the auditory and vestibular systems of all vertebrates, and in the lateral-line system of aquatic vertebrates. During development, spontaneous activity in hair cells shapes the formation of these sensory systems. In auditory hair cells of mice, coordinated waves of spontaneous activity can be triggered by concomitant activity in nearby supporting cells. But in mammals, developing auditory and vestibular hair cells can also autonomously generate spontaneous events independent of supporting cell activity. To date, significant progress has been made studying spontaneous activity in the auditory and vestibular systems of mammals, in isolated cultures. The purpose of this work is to explore the zebrafish lateral-line system as a model to study and understand spontaneous activity in vivo. Our work applies genetically encoded calcium indicators along with light-sheet fluorescence microscopy to visualize spontaneous calcium activity in the developing lateral-line system. Consistent with our previous work, we show that spontaneous calcium activity is present in developing lateral-line hair cells. We now show that supporting cells that surround hair cells, and cholinergic efferent terminals that directly contact hair cells are also spontaneously active. Using two-color functional imaging we demonstrate that spontaneous activity in hair cells does not correlate with activity in either supporting cells or cholinergic terminals. We find that during lateral-line development, hair cells autonomously generate spontaneous events. Using localized calcium indicators, we show that within hair cells, spontaneous calcium activity occurs in two distinct domains–the mechanosensory bundle and the presynapse. Further, spontaneous activity in the mechanosensory bundle ultimately drives spontaneous calcium influx at the presynapse. Comprehensively, our results indicate that in developing lateral-line hair cells, autonomously generated spontaneous activity originates with spontaneous mechanosensory events. Overall, with robust spontaneous activity three different cell types, the developing lateral line is a rich model to study these activities in an intact sensory organ. Future work studying this model may further our understanding of these activities and their role in sensory system formation, function and regeneration.

Flow field detection plays a crucial role in flying and swimming robots by providing information for navigation, active flow control, and disturbance rejection in complex fluid environments. Nature creatures have evolved flow receptors with extreme sensing performances such as fish lateral line system and sensory hairs of insects, which inspire engineers to develop artificial flow sensors. With the introduction to the high-sensitive mechanisms in fish lateral line and sensory hairs, we focus on recent progress on bio-inspired flexible sensors, which can be mounted on curved surfaces for flow field detection and analysis. The engineered sensors have reached the detection limit comparable to that of the biological receptors, which is a great breakthrough for bio-inspired sensors.

Lateral lines, a major sensory modality in fishes, are diverse among taxa, but their intraspecific variation has received limited attention. We examined numbers of superficial neuromasts on the buttressing lateral plates (LP) of 1910 threespine stickleback (Gasterosteus aculeatus Linnaeus, 1758) from 26 ecologically and morphologically diverse populations on the Haida Gwaii archipelago, western Canada. Extending from previous studies, we predicted that (i) highly stained dystrophic localities would have threespine stickleback with elevated numbers of neuromasts per plate due to a greater reliance on non-visual sensory modalities and (ii) that LP count and neuromast numbers per plate would functionally covary with predatory assemblage. We found that there were no differences in neuromast count across major habitats (marine, lake, stream), but clear-water populations and those with predatory fish had significantly more neuromasts per plate than most populations in highly stained dystrophic lakes, the effects being accentuated on the first buttressing plate (LP4). We also report the first evidence that neuromast counts per plate are sexually dimorphic, with males having a greater density of neuromasts in most populations. Two transplant experiments between ecologically opposite habitats indicate that within 12 generations, neuromast counts per plate can rapidly shift in response to a change in habitat.

The lateral-line system has been traditionally recognized as an important source of phylogenetic information for different groups of fishes. Although extensively studied in Siluriformes and Cypriniformes, the lateral-line system of Characiformes remained underexplored. In the present study, the anatomy of the cephalic lateral-line canals of characiforms is described in detail and a unifying terminology that considers the ontogeny and homologies of the components of this system is offered. Aspects of the arrangement of lateral-line canals, as well as the number, location and size of canal tubules and pores, resulted in the identification of novel putative synapomorphies for Characiformes and several of its subgroups. The study also revised synapomorphies previously proposed for different characiform families and provided comments on their observed distribution across the order based on extensive taxon sampling. Information from the ontogenetic studies of the cephalic lateral-line canal system and a proposal for the proper use of these data to detect truncations in the development of the lateral-line canals across the order is also offered.

Summary A new root-knot nematode, parasitizing Robusta coffee in Dak Lak Province, Western Highlands of Vietnam, is described as Meloidogyne moensi n. sp. Morphological and molecular analyses demonstrated that this species differs clearly from other previously described root-knot nematodes. Morphologically, the new species is characterized by a swollen body of females with a small posterior protuberance that elongated from ovoid to saccate; perineal patterns with smooth striae, continuous and low dorsal arch; lateral lines marked as a faint space or linear depression at junction of the dorsal and ventral striate; distinct phasmids; perivulval region free of striae; visible and wide tail terminus surrounding by concentric circles of striae; medial lips of females in dumbbell-shaped and slightly raised above lateral lips; female stylet is normally straight with posteriorly sloping stylet knobs; lip region of second stage juvenile (J2) is not annulated; medial lips and labial disc of J2 formed dumbbell shape; lateral lips are large and triangular; tail of J2 is conoid with rounded unstriated tail tip; distinct phasmids and hyaline; dilated rectum. Meloidogyne moensi n. sp. is most similar to M. africana, M. ottersoni by prominent posterior protuberance. Results of molecular analysis of rDNA sequences including the D2–D3 expansion regions of 28S rDNA, COI, and partial COII/16S rRNA of mitochondrial DNA support for the new species status.

The lateral line system and its innervation were examined in two species of the family Apogonidae (Cercamia eremia [Apogoninae] and Pseudamia gelatinosa [Pseudamiinae]). Both species were characterized by numerous superficial neuromasts (SNs; total 2,717 in C. eremia; 9,650 in P. gelatinosa), including rows on the dorsal and ventral halves of the trunk, associated with one (in C. eremia) and three (in P. gelatinosa) reduced trunk canals. The pattern of SN innervation clearly demonstrated that the overall pattern of SN distribution had evolved convergently in the two species. In C. eremia, SN rows over the entire trunk were innervated by elongated branches of the dorsal longitudinal collector nerve (DLCN) anteriorly and lateral ramus posteriorly. In P. gelatinosa, the innervation pattern of the DLCN was mirrored on the ventral half of the trunk (ventral longitudinal collector nerve: VLCN). Elongated branches of the DLCN and VLCN innervated SN rows on the dorsal and ventral halves of the trunk, respectively. The reduced trunk canal(s) apparently had no direct relationship with the increase of SNs, because these branches originated deep to the lateral line scales, none innervating canal neuromast (CN) homologues on the surface of the scales. In P. gelatinosa, a CN (or an SN row: CN homologue) occurred on every other one of their small lateral line scales, while congeners (P. hayashii and P. zonata) had an SN row (CN homologue) on every one of their large lateral line scales.

Three species of the genus Tribolodon (T. hakonensis, T. brandtii, and T. sachalinensis) and hybrids between T. hakonensis and T. brandtii have been analyzed using the cephalic lateral-line system and four molecular genetic markers: nuclear DNA (Rho and ITS-1–5.8S–ITS-2) and mitochondrial DNA (Co-1 and Cyt-b). It was shown that the presence of a connection between postopercular and preopercularmandibular canals of the cephalic lateral line on one side of the head (such connection on both sides of the head is a characteristic of T. brandtii) and the absence of such a connection on the other side (such connection on both sides of the head is a characteristic of T. hakonensis), along with p-distances for markers Rho, ITS-1–5.8S–ITS-2, Co-1, and Cyt-b, can reveal hybrid individuals between T. hakonensis and T. brandtii.

Astyanax mexicanus is a well-established and widely used fish model system for evolutionary and developmental biology research. These fish exist as surface forms that inhabit rivers and 30 different populations of cavefish. The establishment of A. mexicanus as an emergent model organism for understanding the evolutionary basis of development and behavior has been accelerated by an increasing availability of genomic approaches to identify genotype-phenotype associations. Despite important progress in the deployment of new technologies, deep mechanistic insights into A. mexicanus evolution and development have been limited by a lack of transgenic lines commonly used in genetic model systems. Here, we expand the toolkit of transgenesis by characterizing two novel stable transgenic lines that were generated using the highly efficient Tol2 system, commonly used to generate transgenic zebrafish. A stable transgenic line consisting of the zebrafish ubiquitin promoter fused to eGFP expressed eGFP ubiquitously throughout development in a surface population of Astyanax. To define specific cell-types, we injected fish with a Cntnap2-mCherry construct that labels lateral line mechanosensory neurons in zebrafish. Strikingly, both constructs appear to label the predicted cell types, suggesting many genetic tools and defined promoter regions in zebrafish are directly transferrable to cavefish. The lines provide proof-of-principle for the application of Tol2 transgenic technology in A. mexicanus. Expansion on these initial transgenic lines will provide a platform to address broadly important problems in the quest to bridge the genotype to phenotype gap.

The cephalic lateral line system of the Normanicthyidae family monotypic species, Normanichthys crockeri from Corral Bay, Chile was studied. N. crockeri is a small, schooling and pelagic fish from the southeast Pacific coast between Chimbote, Perú and Mocha Island, Chile. Normanichthys displays a cephalic latero sensorial system constituted by pores and canals. The pores are in six cephalic zones: five preopercular pores (pr.p), five mandibular pores (m.p), three supraorbital pores (so.p), eight infraorbital pores (io.p), three postorbital pores (po.p), three supratemporal pores (st.p) and only one coronary pore (c.p). The high number of pores distributed along the anterior, middle and posterior zones of the orbit stands out, making it a quite sensitive area. In the jaw, five elongated pores join those present in the preoperculum that, along with the rest of the cephalic pores in the supraorbital, supratemporal and postorbital regions make yet another area sensitive to the water flow. These pores are connected with eight narrow, continuous and simple canals: preopercular canal (PR), mandibular canal (MD), supraorbital canal (SO), infraorbital canal (IO), supratemporal canal (ST), otic canal (OT), post-otic canal (PO) and temporal canal (T). This type of canal is the most common pattern found among bony fishes and is designed to respond maximally to water flow velocity along the axis of the canal. These results will help understand part of the cephalic sensorial lateral line biology of this species, which has been barely considered in the ichthyological literature.

Cynoglossus yokomaru sp. nov., previously known as Cynoglossus sp., called “Otafuku-genko” (the standard Japanese name), is described based on 15 specimens [64–226 mm in standard length (SL)] collected at depths of 73–157 m in the East China Sea and Yellow Sea. The new species belongs to the Cynoglossus kopsii complex as redefined in this paper and clearly differs from its congeners by the following combination of characters: two ocular-side lateral lines (dorsolateral and midlateral lines present, ventrolateral line absent); no blind-side lateral line; ctenoid scales present on both sides; two ocular-side nostrils; ocular-side posterior nostril immediately anterior to a point between eyes; head length (HL) shorter than its depth; posterior margin of upper jaw on ocular side not reaching below posterior margin of lower eye; body depth 25.8–30.2% SL; upper supraorbital length 35.5–47.3% HL; lower supraorbital length 48.8–64.3% HL; horizontal diameter of lower eye 10.1–17.4% HL; a long and continuous dorsolateral line with 61–70 scales; midlateral-line scales 4–5 + 65–68 = 69–73; scales above dorsolateral line 3–4; scales between dorsolateral line and midlateral line 10–12; cephalodorsal-line scales 8; dorsal-fin rays 115–119; anal-fin rays 90–94; caudal-fin rays 10 (rarely 8 or 9); and vertebrae 9 + 47–48 = 56–57.

POU genes are characterized by a conserved POU DNA-binding domain, and are divided into six subclasses. Class III and IV POU genes are predominantly expressed in the developing nervous system. POU class III genes are critical for several neuronal cell differentiation and class IV POU genes serve important functions in the differentiation and survival of sensory neurons. In this study, we attempted to identify POU genes in the zebrafish and pufferfish genomes by using existing bioinformatics tools. We analysed the expression of zebrafish brn1.2 and brn3a genes (brn3a1 and brn3a2)) using whole-mount in situ hybridisation. Similarly to the mammalian orthologue, zebrafish brn1.2 was widely expressed in the forebrain, midbrain and hindbrain. During the late stages of embryogenesis, brn1.2 expressing cells were located in the preoptic area and in the auditory vesicles. Expression of both zebrafish brn3a genes was detected in trigeminal ganglia, cranial sensory ganglia, sensory neurons along the dorsal spinal cord, in the anterior and posterior lateral line placodes (ALL and PLL), retinal ganglion cell layer, optic tectum and in small cell clusters in the forebrain and hindbrain. Similar to mammalian Brn3a, zebrafish brn3a genes were detected in the retina and sensory structures. However, different domains of expression were also observed, namely in spinal sensory neurons, and lateral line system.

Swimming in schools has long been hypothesized to allow fish to save energy. Fish must exploit the energy from the wakes of their neighbors for maximum energy savings, a feat that requires them to both synchronize their tail movements and stay in certain positions relative to their neighbors. To maintain position in a school, we know that fish use multiple sensory systems, mainly their visual and flow sensing lateral line system. However, how fish synchronize their swimming movements in a school is still not well understood. Here, we test the hypothesis that this synchronization may depend on functional differences in the two branches of the lateral line sensory system that detects water movements close to the fish’s body. The anterior branch, located on the head, encounters largely undisturbed free-stream flow, while the posterior branch, located on the trunk and tail, encounters flow that has been affected strongly by the tail movement. Thus, we hypothesize that the anterior branch may be more important for regulating position within the school, while the posterior branch may be more important for synchronizing tail movements. Our study examines functional differences in the anterior and posterior lateral line in the structure and tail synchronization of fish schools. We used a widely available aquarium fish that schools, the giant danio, Devario equipinnatus. Fish swam in a large circular tank where stereoscopic videos recordings were used to reconstruct the 3D position of each individual within the school and to track tail kinematics to quantify synchronization. For one fish in each school, we ablated using cobalt chloride either the anterior region only, the posterior region only, or the entire lateral line system. We observed that ablating any region of the lateral line system causes fish to swim in a “box” or parallel swimming formation, which was different from the diamond formation observed in normal fish. Ablating only the anterior region did not substantially reduce tail beat synchronization but ablating only the posterior region caused fish to stop synchronizing their tail beats, largely because the tail beat frequency increased dramatically. Thus, the anterior and posterior lateral line system appears to have different behavioral functions in fish. Most importantly, we showed that the posterior lateral line system played a major role in determining tail beat synchrony in schooling fish. Without synchronization, swimming efficiency decreases, which can have an impact on the fitness of the individual fish and group.

Animals have a remarkable ability to use local cues to orient in space in the absence of a panoramic fixed reference frame. Here we use the mechanosensory lateral line in larval zebrafish to understand rheotaxis, an innate oriented swimming evoked by water currents. We generated a comprehensive light-microscopy cell-resolution projectome of lateralis afferent neurons (LANs), and used clustering techniques for morphological classification. We find surprising structural constancy among LANs. Laser-mediated microlesions indicate that precise topographic mapping of lateral-line receptors is not essential for rheotaxis. Recording neuronal-activity during controlled mechanical stimulation of neuromasts reveals unequal representation of water-flow direction in the hindbrain. We explored potential circuit architectures constrained by anatomical and functional data to suggest a parsimonious model under which the integration of lateralized signals transmitted by direction-selective LANs underlies the encoding of water-flow direction in the brain. These data provide a new framework to understand how animals use local mechanical cues to orient in space.

The lateral line system and its innervation were examined in the Nurseryfish Kurtus gulliveri (family Kurtidae). The system is characterized by ca. 373,000 superficial neuromasts (SNs; at 152 mm standard length) occurring over one side of the entire body surface, including the dorsal, anal, and caudal fins. A fine-grid pattern of SNs is spread regularly over the surface, comprising many longitudinal and transverse SN rows, with the axis of best physiological sensibility perpendicular to the long axis of the neuromasts. On the head, rami of the anterior lateral line nerve are similar to those in typical percomorphs, each innervating numerous SNs by extensive ramification. On the trunk, 22 elongated dorsal ramules of the lateral ramus (of the posterior lateral line nerve) supply SNs on the dorsal half of the trunk and dorsal fin, and the dorsal longitudinal collector nerve innervates 22 canal neuromasts along the short (incomplete) trunk lateral line canal. Sixteen ventral ramules arise from the lateral ramus to supply SNs on the ventral half of the trunk and anal fin, which is similar to the pattern of the dorsal ramules. Innervation of the trunk and fins is distinctive, differing from all percomorphs known thus far.

The lateral line system and its innervation were examined in the Japanese eel Anguilla japonica. Although the species has seven lateral line canals and 13 superficial neuromast groups, the components are generally similar to those in many other teleosts. The lateral line system of A. japonica is distinctive in having a rostral commissure connecting the left and right supraorbital canals, pouches in the cephalic lateral line canals and superficial neuromasts along the lower lip, and lacking a postotic canal. Four tube-like elements, two along the supratemporal canal and the other two along the temporal portion of the trunk canal, respectively, are also reported. The functional significance of cephalic lateral line pouches, homologies of the four tube-like elements, and other distinctive characters are discussed.

A key challenge in contemporary biology is connecting genotypic variation to phenotypic diversity. Quantitative genetics provides a powerful technique for identifying regions of the genome that covary with phenotypic variation. Here, we present a quantitative trait loci (QTL) analysis of a natural freshwater fish system, Astyanax mexicanus, that harbors two morphs corresponding to a cave and surface fish. Following their divergence ~500 Kya, cavefish have adapted to the extreme pressures of the subterranean biome. As a consequence, cavefish have lost numerous features, but evolved gains for a variety of constructive features including behavior. Prior work found that sensory tissues (neuromasts) present in the “eye orbit” region of the skull associate with sensitivity to vibrations in water. This augmented sensation is believed to facilitate foraging behavior in the complete darkness of a cave, and may impact on evolved lateral swimming preference. To this point, however, it has remained unclear how morphological variation integrates with behavioral variation through heritable factors. Using a QTL approach, we discovered the genetic architecture of neuromasts present in the eye orbit region, demonstrating that this feature is under genetic control. Interestingly, linked loci were asymmetric–signals were detected using only data collected from the right, but not left, side of the face. This finding may explain enhanced sensitivity and/or feedback of water movements mediating a lateral swimming preference. The locus we discovered based on neuromast position maps near established QTL for eye size and a facial bone morphology, raising the intriguing possibility that eye loss, sensory expansion, and the cranial skeleton may be integrated for evolving adaptive behaviors. Thus, this work will further our understanding of the functional consequence of key loci that influence the evolutionary origin of changes impacting morphology, behavior, and adaptation.

Sensory systems gather cues essential for directing behavior, but animals must decipher what information is biologically relevant. Locomotion generates reafferent cues that animals must disentangle from relevant sensory cues of the surrounding environment. For example, when a fish swims, flow generated from body undulations is detected by the mechanoreceptive neuromasts, comprising hair cells, that compose the lateral line system. The hair cells then transmit fluid motion information from the sensor to the brain via the sensory afferent neurons. Concurrently, corollary discharge of the motor command is relayed to hair cells to prevent sensory overload. Accounting for the inhibitory effect of predictive motor signals during locomotion is, therefore, critical when evaluating the sensitivity of the lateral line system. We have developed an in vivo electrophysiological approach to simultaneously monitor posterior lateral line afferent neuron and ventral motor root activity in zebrafish larvae (4-7 days post fertilization) that can last for several hours. Extracellular recordings of afferent neurons are achieved using the loose patch clamp technique, which can detect activity from single or multiple neurons. Ventral root recordings are performed through the skin with glass electrodes to detect motor neuron activity. Our experimental protocol provides the potential to monitor endogenous or evoked changes in sensory input across motor behaviors in an intact, behaving vertebrate.

The anatomy, neurophysiology, and behavioral roles of the mechanosensory lateral line system of cichlid fishes are reviewed. The lateral line system of cichlids shares fundamental anatomical features characteristic of all bony fishes and is composed of cranial lateral line canals, a trunk canal (or canals) containing canal neuromasts, and superficial neuromasts on the skin of the head, trunk, and tail. Cichlids typically have narrow cranial lateral line canals, but several genera have reduced or widened canals. A single, continuous trunk canal, which is common among bony fishes, is rare among cichlids, which typically have a disjunct trunk canal (or variations thereof) that is otherwise rare among other teleost families. Lateral line neuroanatomy and neurophysiology is well known in only a small number of cichlid species that serve as models for the study of the neuroethology of feeding and social behavior. The ability to study cichlids in the field and in the laboratory and carry out genetic and genomic analyses of complex phenotypes provides unique opportunities for novel integrative studies of the behavior and sensory ecology of these extraordinary fishes.

A new species of Moenkhausia is described from the rio Machado drainage, Amazon basin, Brazil. It is diagnosed from congeners by its color pattern, consisting of the concentration of chromatophores on the anterior portion of body scales, the horizontally elongate blotch on caudal peduncle, a bright golden coloration of the dorsal portion of eye when alive, and a dark line crossing the eye horizontally. The new species has variable morphology regarding trunk lateral-line canals. Most fully grown individuals do not have enclosed bony tube in many lateral line scales, resembling early developmental stages of tube formation of other species. This paedomorphic condition is interpreted as a result of developmental truncation. Such evolutionary process may have been responsible for the presence of distinct levels of trunk lateral line reductions in small characids. Variation in this feature is common, even between the sides of the same individual. We reassert that the degree of trunk lateral-line tube development must be used with care in taxonomic and phylogenetic studies, because reductions in the laterosensory system may constitute parallel loss in the Characidae. We suggest the new species to be categorized Near Threatened due to the restricted geographical distribution and continuing decline in habitat quality. Resumo Uma espécie nova de Moenkhausia é descrita da drenagem do rio Machado, bacia Amazônica, Brasil. É diagnosticada das congêneres pelo padrão de coloração, que consiste na concentração de cromatóforos na porção anterior das escamas do corpo, em uma mancha horizontalmente alongada no pedúnculo caudal, na coloração dourada brilhante da porção dorsal do olho quando vivo e na faixa escura que atravessa o olho horizontalmente. A nova espécie apresenta variação na morfologia do canal da linha lateral do corpo. A maioria dos indivíduos totalmente desenvolvidos não possuem tubo ósseo fechado em muitas escamas da linha lateral, assemelhando-se aos estágios iniciais do desenvolvimento da formação do tubo de outras espécies. Essa condição pedomórfica é interpretada como resultado do truncamento do desenvolvimento. Tal processo evolutivo pode ter sido responsável pelos diferentes níveis de redução do canal sensorial de pequenos caracídeos. A variação neste caráter é comum, até entre os lados do mesmo indivíduo. Por isso, reafirmamos que o grau de desenvolvimento do canal sensorial do corpo deve ser usado com cuidado em estudos taxonômicos e filogenéticos, porque reduções no sistema látero-sensorial podem significar perdas paralelas em Characidae. Sugerimos que a espécie nova seja categorizada como Quase Ameaçada devido à distribuição geográfica restrita e ao declínio contínuo da qualidade do habitat.

Each hair cell (HC) precursor of zebrafish neuromasts divides to form two daughter HCs of opposite hair bundle orientations. Previously, we showed that transcription factor Emx2, expressed in only one of the daughter HCs, generates this bidirectional HC pattern (Jiang et al., 2017). Here, we asked whether Emx2 mediates this effect by changing location of hair bundle establishment or positions of HCs since daughter HCs are known to switch positions with each other. We showed this HC rearrangement, redefined as two processes named Rock and Roll, is required for positional acquisition of HCs. Apical protrusion formation of nascent HCs and planar polarity signaling are both important for the Rock and Roll. Emx2 facilitates Rock and Roll by delaying apical protrusion of its nascent HCs but it does not determine HCs’ ultimate positions, indicating that Emx2 mediates bidirectional HC pattern by changing the location where hair bundle is established in HCs.

Gobies (family Gobiidae) have a complex mechanosensory lateral line system characterized by reduced lateral line canals and a dramatic proliferation of small superficial neuromasts (on “sensory papillae”), which are arranged in lines on the head, trunk, and tail. A suite of morphological methods was used to describe the distribution and morphology of canal and superficial neuromasts in the neon goby, Elacatinus lori, and to describe the ontogeny of the lateral line system for the first time for any gobiiform fish. Portions of only three cranial lateral line canals are retained and they contain a total of eight canal neuromasts. In addition, 128–155 superficial neuromasts are found in six head series (comprising 33 neuromast lines or rows). Superficial neuromasts are found in one body series (65–80 neuromasts arranged in three groups of vertical lines or “stitches”) and one caudal fin series (3 lines, each located between fin rays and comprised of many small neuromasts; total of 27–53 neuromasts) extending to the tip of the caudal fin. The general distribution of neuromasts is established early during the larval stage, and neuromast numbers increase within and among lines resulting in an increase in overall complexity of the system. On day-of-hatch, a total of 22 neuromasts are present. At ∼15 days post-hatch, all eight cranial canal neuromasts are present, and, in post-settlement juveniles (“settlers”), they are enclosed in canals and a total of ∼185 neuromasts are found on the head, trunk, and tail. All neuromasts are small (∼40 lm long) and diamond-shaped, but three subpopulations (canal neuromasts, canal neuromast homologs, superficial neuromasts) are defined based on their location and their arrangement within lines (“tip-to-tip” or “side-by-side”). The ontogeny of the lateral line system and distinctions among neuromast subpopulations help to reveal the structural and functional organization of the complex lateral line system in Elacatinus and will contribute to the interpretation of neuromast patterns in other gobiiforms. A comparison of superficial neuromast number in 12 species of Elacatinus and Tigrigobius (sister genera) revealed variation among species that live in different reef microhabitats, which suggests that adaptive evolution in the lateral line system is evident among closely related taxa.

Mammalian inner ear and fish lateral line sensory hair cells depend on fluid motion to transduce environmental signals and elicit a response. In mammals, actively maintained ionic homeostasis of the cochlear and vestibular fluid (endolymph) is essential for hair cell function and numerous mammalian hearing and vestibular disorders arise from disrupted endolymph ion homeostasis. Lateral line hair cells, however, are openly exposed to the aqueous environment with fluctuating ionic composition. How sensory transduction in the lateral line is maintained during environmental changes of ionic composition is not fully understood. Using lineage labeling,in vivotime lapse imaging and scRNA-seq, we discovered highly motile skin-derived cells that invade mature mechanosensory organs of the zebrafish lateral line and differentiate into Neuromast-associated (Nm) ionocytes. Furthermore, the invasive behavior is adaptive as it is triggered by drastic fluctuations in environmental stimuli. Our findings challenge the notion of an entirely placodally-derived lateral line and identify Nm ionocytes as regulators of mechanosensory hair cell function by modulating the ionic microenvironment. The discovery of lateral line ionocytes provides an experimentally accessiblein vivosystem to study cell invasion and migration, as well as the physiological adaptation of vertebrate organs to changing environmental conditions.

Histone demethylase PHF8 is crucial for multiple developmental processes, and hence, the awareness of its function in developing auditory organs needs to be increased. Using in situ hybridization (ISH) labeling, the mRNA expression of PHF8 in the zebrafish lateral line system and otic vesicle was monitored. The knockdown of PHF8 by morpholino significantly disrupted the development of the posterior lateral line system, which impacted cell migration and decreased the number of lateral line neuromasts. The knockdown of PHF8 also resulted in severe malformation of the semicircular canal and otoliths in terms of size, quantity, and position during the inner ear development. The loss of function of PHF8 also induced a defective differentiation in sensory hair cells in both lateral line neuromasts and the inner ear. ISH analysis of embryos that lacked PHF8 showed alterations in the expression of many target genes of several signaling pathways concerning cell migration and deposition, including the Wnt and FGF pathways. In summary, the current findings established PHF8 as a novel epigenetic element in developing auditory organs, rendering it a potential candidate for hearing loss therapy.

Hair cells are the mechanosensory receptors of the inner ear and can be damaged by noise, aging, and ototoxic drugs. This damage often results in permanent sensorineural hearing loss. Hair cells have high energy demands and rely on mitochondria to produce ATP as well as contribute to intracellular calcium homeostasis. In addition to generating ATP, mitochondria produce reactive oxygen species, which can lead to oxidative stress, and regulate cell death pathways. Zebrafish lateral-line hair cells are structurally and functionally analogous to cochlear hair cells but are optically and pharmacologically accessible within an intact specimen, making the zebrafish a good model in which to study hair-cell mitochondrial activity. Moreover, the ease of genetic manipulation of zebrafish embryos allows for the study of mutations implicated in human deafness, as well as the generation of transgenic models to visualize mitochondrial calcium transients and mitochondrial activity in live organisms. Studies of the zebrafish lateral line have shown that variations in mitochondrial activity can predict hair-cell susceptibility to damage by aminoglycosides or noise exposure. In addition, antioxidants have been shown to protect against noise trauma and ototoxic drug–induced hair-cell death. In this review, we discuss the tools and findings of recent investigations into zebrafish hair-cell mitochondria and their involvement in cellular processes, both under homeostatic conditions and in response to noise or ototoxic drugs. The zebrafish lateral line is a valuable model in which to study the roles of mitochondria in hair-cell pathologies and to develop therapeutic strategies to prevent sensorineural hearing loss in humans.

Mechanosensory-cued hatching (MCH) is widespread, diverse, and improves survival in many animals. From flatworms and insects to frogs and turtles, embryos use mechanosensory cues and signals to inform hatching timing, yet mechanisms mediating mechanosensing in ovo are largely unknown. The arboreal embryos of red-eyed treefrogs, Agalychnis callidryas, hatch prematurely to escape predation, cued by physical disturbance in snake attacks. When otoconial organs in the developing vestibular system become functional, this response strengthens, but its earlier occurrence indicates another sensor must contribute. Post-hatching, tadpoles use lateral line neuromasts to detect water motion. We ablated neuromast function with gentamicin to assess their role in A. callidryas’ hatching response to disturbance. Prior to vestibular function, this nearly eliminated the hatching response to a complex simulated attack cue, egg-jiggling, revealing that neuromasts mediate early MCH. Vestibular function onset increased hatching, independent of neuromast function, indicating young embryos use multiple mechanosensory systems. MCH increased developmentally. All older embryos hatched in response to egg-jiggling, but neuromast function reduced response latency. In contrast, neuromast ablation had no effect on timing or level of hatching in motion-only vibration playbacks. It appears only a subset of egg-disturbance cues stimulate neuromasts; thus embryos in attacked clutches may receive uni- or multimodal stimuli. A. callidryas embryos have more neuromasts than described for any other species at hatching, suggesting precocious sensory development may facilitate MCH. Our findings provide insight into the behavioral roles of two mechanosensory systems in ovo and open possibilities for exploring sensory perception across taxa in early life stages.

The lateral line system is composed of a series of mechanoreceptors called neuromasts, which are found on the head and trunk in specific patterns. On the head, larger canal neuromasts (CNs) are enclosed in cranial canals and smaller superficial neuromasts (SNs) are embedded in the skin in lines or clusters. Among species the lateral line canals can be narrow, widened, branched, or reduced. Through the use of fluorescent stains, Scanning Electron Microscopy, and cleared and stained specimens the distribution and ontogenetic appearance of SNs and CNs were mapped in two species of Lake Malawi cichlids with divergent adult lateral line morphologies: Tramitichromis sp. (narrow canals) and A. stuartgranti stuartgranti (widened canals).This study provides: 1) the first description of cranial neuromast distributions in representatives of the genera Tramitichromis and A. stuartgranti , 2) evidence that CN patterning is the same in the 2 taxa despite differences in adult canal morphology, 3) evidence that SN patterns (e.g., 9 groups of NM) are the same, but SN numbers vary between the two taxa, and 4) evidence that the timing and appearance of some SN groups varies between the two species. Chemical and pharmacological ablation of neuromasts are methods frequently used to inactive the lateral line system. Fluorescent staining of neuromasts is also a common technique used to visually assess the effects of ablation on neuormasts. The two techniques, however, have only been used sequentially once before to verify that lateral line ablation occurred and that the behavior of the fish was a reflection of this. The interpretation of the use of these methods and how they might differentially affect SNs and CNs is very ambiguous. This study provides the first detailed description of the ablation effects of Cobalt (II) chloride heptahydrate and Gentamicin on superficial and canal neuromasts using fluorescence staining (4-Di-2ASP). Two species of Lake Malawi cichlids, Tramitichromis sp. and A. stuartgranti stuartgranti, were used in this study. Following treatment, it was determined that: 1) CoCl2 in Ca ++ free water and Gentamicin had comparable effects on SNs and CNs in both species, 2) Treatment with CoCl2 in Ca ++ free water and Gentamicin resulted in full recovery of both superficial and canal neuromasts by Day 4 or Day 7, 3) Treatment with CoCl2 in tank water with Ca ++ did not effectively ablate SNs and CNs on Day 0, when compared to CoCl2 in Ca ++ free water and Gentamicin, 4) Gentamicin does, in fact, affect SNs, which refutes previous experiments. The stain 4-Di-2-ASP proved to be a reliable and effective means of visually documenting the effects of Cobalt (II) chloride heptahydrate and Gentamicin on ablation and recovery of superficial and canal neuromasts in two cichlid species.

Hair cells are mechanosensory cells that mediate the sense of hearing. These cells do not regenerate after damage in humans, but they are naturally replenished in non-mammalian vertebrates such as zebrafish. The zebrafish lateral line system is a useful model for characterizing sensory hair cell regeneration. The lateral line is comprised of hair cell-containing organs called neuromasts, which are linked together by a string of interneuromast cells (INMCs). INMCs act as progenitor cells that give rise to new neuromasts during development. INMCs can repair gaps in the lateral line system created by cell death. A method is described here for selective INMC ablation using a conventional laser-scanning confocal microscope and transgenic fish that express green fluorescent protein in INMCs. Time-lapse microscopy is then used to monitor INMC regeneration and determine the rate of gap closure. This represents an accessible protocol for cell ablation that does not require specialized equipment, such as a high-powered pulsed ultraviolet laser. The ablation protocol may serve broader interests, as it could be useful for the ablation of additional cell types, employing a tool set that is already available to many users. This technique will further enable the characterization of INMC regeneration under different conditions and from different genetic backgrounds, which will advance the understanding of sensory progenitor cell regeneration.

Hearing loss is the third most common chronic health condition in the United States and largely results from damage to sensory hair cells. Major causes of hair cell damage include aging, noise exposure, and medications such as aminoglycoside antibiotics. Due to their potent antibacterial properties and low cost, aminoglycosides are often used for the treatment of gram-negative bacterial infections, surpassing expensive antibiotics with fewer harmful side effects. However, their use is coupled with permanent hearing loss in over 20% of patients requiring these life-sustaining antibiotics. There are currently no FDA-approved drugs that prevent hearing loss from aminoglycosides. A previous study by our group identified the plant alkaloid berbamine as a strong protectant of zebrafish lateral line hair cells from aminoglycoside damage. This effect is likely due to a block of the mechanotransduction channel, thereby reducing aminoglycoside entry into hair cells. The present study builds on this previous work, investigating 16 synthetic berbamine analogs to determine the core structure underlying their protective mechanisms. We demonstrate that nearly all of these berbamine analogs robustly protect lateral line hair cells from ototoxic damage, with ED50 values nearing 20 nM for the most potent analogs. Of the 16 analogs tested, nine strongly protected hair cells from both neomycin and gentamicin damage, while one conferred strong protection only from gentamicin. These data are consistent with prior research demonstrating that different aminoglycosides activate somewhat distinct mechanisms of damage. Regardless of the mechanism, protection required the entire berbamine scaffold. Phenolic alkylation or acylation with lipophilic groups appeared to improve protection compared to berbamine, implying that these structures may be responsible for mitigating damage. While the majority of analogs confer protection by blocking aminoglycoside uptake, 18% of our analogs also confer protection via an uptake-independent mechanism; these analogs exhibited protection when delivered after aminoglycoside removal. Based on our studies, berbamine analogs represent a promising tool to further understand the pathology of aminoglycoside-induced hearing loss and can serve as lead compounds to develop otoprotective drugs.

Ammonia (including NH3 and NH4+) is a major pollutant of freshwater environments. However, the toxic effects of ammonia on the early stages of fish are not fully understood, and little is known about the effects on the sensory system. In this study, we hypothesized that ammonia exposure can cause adverse effects on embryonic development and impair the lateral line system of fish. Zebrafish embryos were exposed to high-ammonia water (10, 15, 20, 25, and 30 mM NH4Cl; pH 7.0) for 96 h (0–96 h post-fertilization). The body length, heart rate, and otic vesicle size had significantly decreased with ≥15 mM NH4Cl, while the number and function of lateral-line hair cells had decreased with ≥10 mM NH4Cl. The mechanoelectrical transduction (MET) channel-mediated Ca2+ influx was measured with a scanning ion-selective microelectrode technique to reveal the function of hair cells. We found that NH4+ (≥5 mM NH4Cl) entered hair cells and suppressed the Ca2+ influx of hair cells. Neomycin and La3+ (MET channel blockers) suppressed NH4+ influx, suggesting that NH4+ enters hair cells via MET channels in hair bundles. In conclusion, this study showed that ammonia exposure (≥10 mM NH4Cl) can cause adverse effects in zebrafish embryos, and lateral-line hair cells are sensitive to ammonia exposure.

Background The distribution of sensory organs is important for detecting environmental signals efficiently. The mechanosensory receptors of the lateral line system, neuromasts, are stereotypically distributed over the head and body surface of fish, although how neuromasts arise in these predetermined positions during development remains unclear. Results We investigated the development of the anterior lateral line (ALL) system in zebrafish head. The ALL neuromasts formed in the predetermined positions through proliferation and differentiation of (a) nonmigratory lateral line primordia, (b) migratory primordia, (c) interneuromast cells connecting preexisting neuromasts, and (d) budding primordia. We demonstrated that R-spondin2 (Rspo2), an activator of Wnt/β-catenin signaling, is required for the development of a particular set of neuromasts associated with hyomandibular cartilage. Further genetic analyses suggested that Rspo2, which emanates from the hyoid mesenchyme, acts on the adjacent neuromast progenitor cells to stimulate their proliferation through activating Wnt/β-catenin signaling. Conclusion This study has revealed novel mechanisms for neuromast positioning through local tissue-tissue interactions, providing insights into the development and evolution of the vertebrate head.

The peripheral nervous system of anuran larvae has traditionally been assumed to be largely invariant. Here, we describe the organization of cranial, spinal, and lateral line nerves at different larval stages of Lepidobatrachus spp. based on whole mounts. This is the first detailed description of cranial, spinal, and lateral lines innervation at premetamorphic stages of anuran larvae with notes on temporal variation. We distinguish three sources of morphological variation with respect to other anuran larvae: (a) the loss or reduction of some exclusively larval elements (i.e., the absence of the middle lateral line nerve); (b) spatial changes in the lateral line system (i.e., the supralabial arrangement of component of the anteroventral lateral line nerve); and (c) temporal changes in the disappearance of most of the lateral line system and in the premetamorphic repatterning of the spatial relationships of mandibularis ramus of the trigeminal (V) and hyomandibularis ramus of facial (VII). The innervation of limbs is achieved during late larval stages. Furthermore, comparisons among selected anurans reveal differences in tadpole brain morphology. The spatial and temporal variation found in the peripheral nerves of Lepidobatrachus larvae testifies to previously unappreciated variation in anuran larval morphology. Fil: Quinzio, Silvia Inés. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina Fil: Fabrezi, Marissa. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Salta. Instituto de Bio y Geociencias del NOA. Universidad Nacional de Salta. Facultad de Ciencias Naturales. Museo de Ciencias Naturales. Instituto de Bio y Geociencias del NOA; Argentina

Nature creatures have evolved excellent receptors, such as sensory hairs in arthropods, lateral line system of fishes. Researchers inspired by nature creatures have developed various mechanical sensors. Here, we provide an overview on the development of Artificial Hair-Like (AHL) sensors based on the inspiration of hair flow sensory receptors, especially sensory hairs in arthropods and lateral line systems of fishes. We classify the developed AHL sensors into several categories according to the operating principles they based on, for example, piezoresistive and piezoelectric effects. The current challenges and existing problems in the development of AHL sensors are also present, which were primarily restricted by the exploratory tools of sensing mechanism of creatures and current manufacturing technologies. In future, more efforts are required in order to further improve the performance of AHL sensors. We expect that intelligent multi-functional AHL sensors can be applied not only in applications like navigation of underwater automatic vehicles, underwater search and rescue, tap-water metering, air monitoring and even in medicare, but also potentially be used in space robots to detect complex topography.