and analyses of a novel variant in 6 identified in a family with postlingual non-syndromic hearing loss from Argentina.

Hereditary hearing loss stands as the most prevalent sensory disorder, with over 124 non-syndromic genes and approximately 400 syndromic forms of deafness identified in humans. The clinical presentation of these conditions spans a spectrum, ranging from mild to profound hearing loss. The aim of this study was to identify the genetic cause of hearing loss in a family and functionally validate a novel variant identified in the 6 gene.

Key role of the TM2-TM3 loop in calcium potentiation of the α9α10 nicotinic acetylcholine receptor.

The α9α10 nicotinic cholinergic receptor (nAChR) is a ligand-gated pentameric cation-permeable ion channel that mediates synaptic transmission between descending efferent neurons and mechanosensory inner ear hair cells. When expressed in heterologous systems, α9 and α10 subunits can assemble into functional homomeric α9 and heteromeric α9α10 receptors. One of the differential properties between these nAChRs is the modulation of their ACh-evoked responses by extracellular calcium (Ca).

An in vivo functional assay to characterize human STAT5B genetic variants during zebrafish development.

Growth hormone (GH) binding to GH receptor activates janus kinase 2 (JAK2)-signal transducer and activator of transcription 5b (STAT5b) pathway, which stimulates transcription of insulin-like growth factor-1 (IGF1), insulin-like growth factor binding protein 3 (IGFBP3) and insulin-like growth factor acid-labile subunit (IGFALS). Although STAT5B deficiency was established as an autosomal recessive disorder, heterozygous dominant-negative STAT5B variants have been reported in patients with less severe growth deficit and milder immune dysfunction. We developed an in vivo functional assay in zebrafish to characterize the pathogenicity of three human STAT5B variants (p.

The Cholinergic Lateral Line Efferent Synapse: Structural, Functional and Molecular Similarities With Those of the Cochlea.

Vertebrate hair cell (HC) systems are innervated by efferent fibers that modulate their response to external stimuli. In mammals, the best studied efferent-HC synapse, the cholinergic medial olivocochlear (MOC) efferent system, makes direct synaptic contacts with HCs. The net effect of MOC activity is to hyperpolarize HCs through the activation of α9α10 nicotinic cholinergic receptors (nAChRs) and the subsequent activation of Ca-dependent SK2 potassium channels.

Loss of Choline Agonism in the Inner Ear Hair Cell Nicotinic Acetylcholine Receptor Linked to the α10 Subunit.

The α9α10 nicotinic acetylcholine receptor (nAChR) plays a fundamental role in inner ear physiology. It mediates synaptic transmission between efferent olivocochlear fibers that descend from the brainstem and hair cells of the auditory sensory epithelium. The α9 and α10 subunits have undergone a distinct evolutionary history within the family of nAChRs.

Unraveling the Molecular Players at the Cholinergic Efferent Synapse of the Zebrafish Lateral Line.

The lateral line (LL) is a sensory system that allows fish and amphibians to detect water currents. LL responsiveness is modulated by efferent neurons that aid in distinguishing between external and self-generated stimuli, maintaining sensitivity to relevant cues. One component of the efferent system is cholinergic, the activation of which inhibits afferent activity.

Expression of acid-labile subunit (ALS) in developing and adult zebrafish and its role in dorso-ventral patterning during development.

Mammalian acid-labile subunit (ALS) is a serum protein that binds binary complexes between Insulin-like growth factors (IGFs) and Insulin-like growth factor-binding proteins (IGFBPs) extending their half-life and keeping them in the vasculature. Human ALS deficiency (ACLSD), due to homozygous or compound heterozygous mutations in IGFALS, leads to moderate short stature with reduced levels of IGF-I and IGFBP-3. There is only one corresponding zebrafish ortholog gene and it has not yet been studied.

Distinct Evolutionary Trajectories of Neuronal and Hair Cell Nicotinic Acetylcholine Receptors.

The expansion and pruning of ion channel families has played a crucial role in the evolution of nervous systems. Nicotinic acetylcholine receptors (nAChRs) are ligand-gated ion channels with distinct roles in synaptic transmission at the neuromuscular junction, the central and peripheral nervous system, and the inner ear. Remarkably, the complement of nAChR subunits has been highly conserved along vertebrate phylogeny.

Differential Contribution of Subunit Interfaces to α9α10 Nicotinic Acetylcholine Receptor Function.

Nicotinic acetylcholine receptors can be assembled from either homomeric or heteromeric pentameric subunit combinations. At the interface of the extracellular domains of adjacent subunits lies the acetylcholine binding site, composed of a principal component provided by one subunit and a complementary component of the adjacent subunit. Compared with neuronal nicotinic acetylcholine cholinergic receptors (nAChRs) assembled from α and β subunits, the α9α10 receptor is an atypical member of the family.

Activity-dependent competition regulates motor neuron axon pathfinding via PlexinA3.

The role of electrical activity in axon guidance has been extensively studied in vitro. To better understand its role in the intact nervous system, we imaged intracellular Ca(2+) in zebrafish primary motor neurons (PMN) during axon pathfinding in vivo. We found that PMN generate specific patterns of Ca(2+) spikes at different developmental stages.

The α1 subunit of nicotinic acetylcholine receptors in the inner ear: transcriptional regulation by ATOH1 and co-expression with the γ subunit in hair cells.

Acetylcholine is a key neurotransmitter of the inner ear efferent system. In this study, we identify two novel nAChR subunits in the inner ear: α1 and γ, encoded by Chrna1 and Chrng, respectively. In situ hybridization shows that the messages of these two subunits are present in vestibular and cochlear hair cells during early development.

Inhibition of the alpha9alpha10 nicotinic cholinergic receptor by neramexane, an open channel blocker of N-methyl-D-aspartate receptors.

In this study we report the effects of neramexane, a novel amino-alkyl-cyclohexane derivative that is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist, on recombinant rat alpha9alpha10 nicotinic acetylcholine receptors expressed in Xenopus laevis oocytes. We compared its effects with those of memantine, a well-studied pore blocker of NMDA receptors, currently used in therapeutics for the treatment of Alzheimer's disease. Our results indicate that both compounds block acetylcholine-evoked responses at micromolar concentrations with a rank order of potency of neramexane>memantine, P<0.

Stoichiometry of the alpha9alpha10 nicotinic cholinergic receptor.

The alpha9 and alpha10 nicotinic cholinergic subunits assemble to form the receptor that mediates synaptic transmission between efferent olivocochlear fibers and hair cells of the cochlea. They are the latest vertebrate nicotinic cholinergic receptor (nAChR) subunits that have been cloned, and their identification has established a distant early divergent branch within the nAChR gene family. The alpha10 subunit serves as a "structural" component leading to heteromeric alpha9alpha10 nAChRs with distinct properties.

A novel alpha-conotoxin, PeIA, cloned from Conus pergrandis, discriminates between rat alpha9alpha10 and alpha7 nicotinic cholinergic receptors.

The alpha9 and alpha10 nicotinic cholinergic subunits assemble to form the receptor believed to mediate synaptic transmission between efferent olivocochlear fibers and hair cells of the cochlea, one of the few examples of postsynaptic function for a non-muscle nicotinic acetylcholine receptor (nAChR). However, it has been suggested that the expression profile of alpha9 and alpha10 overlaps with that of alpha7 in the cochlea and in sites such as dorsal root ganglion neurons, peripheral blood lymphocytes, developing thymocytes, and skin. We now report the cloning, total synthesis, and characterization of a novel toxin alpha-conotoxin PeIA that discriminates between alpha9alpha10 and alpha7 nAChRs.

Effects of quinine, quinidine, and chloroquine on alpha9alpha10 nicotinic cholinergic receptors.

In this study, we report the effects of the quinoline derivatives quinine, its optical isomer quinidine, and chloroquine on alpha9alpha10-containing nicotinic acetylcholine receptors (nAChRs). The compounds blocked acetylcholine (ACh)-evoked responses in alpha9alpha10-injected Xenopus laevis oocytes in a concentration-dependent manner, with a rank order of potency of chloroquine (IC50 = 0.39 microM) > quinine (IC50 = 0.

Key roles of hydrophobic rings of TM2 in gating of the alpha9alpha10 nicotinic cholinergic receptor.

We have performed a systematic mutagenesis of three hydrophobic rings (17', 13' and 9') within transmembrane region (TM) 2 of the alpha9alpha10 nicotinic cholinergic receptor (nAChR) to a hydrophilic (threonine) residue and compared the properties of mutant receptors reconstituted in Xenopus laevis oocytes. Phenotypic changes in alpha9alpha10 mutant receptors were evidenced by a decrease in the desensitization rate, an increase in both the EC(50) for ACh as well as the efficacy of partial agonists and the reduction of the allosteric modulation by extracellular Ca(2+). Mutated receptors exhibited spontaneous openings and, at the single-channel level, an increased apparent mean open time with no major changes in channel conductance, thus suggesting an increase in gating of the channel as the underlying mechanism.

Functional expression and properties of a nicotinic alpha9/5-HT3A chimeric receptor.

We describe the functional properties of a nicotinic alpha9/serotonin subtype 3A (5HT3A) chimeric receptor expressed in Xenopus laevis oocytes. The chimera preserved ligand-binding properties of alpha9 and channel properties of 5HT3A. Thus, it responded to acetylcholine in a concentration-dependent manner with an EC50 of 70 microM but not to serotonin.

Direct interaction of serotonin type 3 receptor ligands with recombinant and native alpha 9 alpha 10-containing nicotinic cholinergic receptors.

In the present work, we characterized the effects of serotonin type 3 receptor ligands on recombinant and native alpha 9 alpha 10-containing nicotinic acetylcholine receptors (nAChRs). Our results indicate that the recombinant alpha 9 alpha 10 nAChR shares striking pharmacological properties with 5-HT(3) ligand-gated ion channels. Thus, 5-HT(3) receptor antagonists block ACh-evoked currents in alpha 9 alpha 10-injected Xenopus laevis oocytes with a rank order of potency of tropisetron (IC(50), 70.