Maintenance of a central high frequency synapse in the absence of synaptic activity.

Activity has long been considered essential for circuit formation and maintenance. This view has recently been challenged by proper synaptogenesis and only mildly affected synapse maintenance in the absence of synaptic activity in forebrain neurons. Here, we investigated whether synaptic activity is necessary for the development and maintenance of the calyx of Held synapse.

Serine 937 phosphorylation enhances KCC2 activity and strengthens synaptic inhibition.

The potassium chloride cotransporter KCC2 is crucial for Cl extrusion from mature neurons and thus key to hyperpolarizing inhibition. Auditory brainstem circuits contain well-understood inhibitory projections and provide a potent model to study the regulation of synaptic inhibition. Two peculiarities of the auditory brainstem are (i) posttranslational activation of KCC2 during development and (ii) extremely negative reversal potentials in specific circuits.

Shared and organ-specific gene-expression programs during the development of the cochlea and the superior olivary complex.

The peripheral and central auditory subsystems together form a complex sensory network that allows an organism to hear. The genetic programs of the two subsystems must therefore be tightly coordinated during development. Yet, their interactions and common expression pathways have never been systematically explored.

Comparative expression analysis of the Atoh7 gene regulatory network in the mouse and chicken auditory hindbrain.

The mammalian and avian auditory brainstem likely arose by independent evolution. To compare the underlying molecular mechanisms, we focused on Atoh7, as its expression pattern in the mammalian hindbrain is restricted to bushy cells in the ventral cochlear nucleus. We thereby took advantage of an Atoh7 centered gene regulatory network (GRN) in the retina including upstream regulators, Hes1 and Pax6, and downstream targets, Ebf3 and Eya2.

NKCC1 and KCC2: Structural insights into phospho-regulation.

Inhibitory neurotransmission plays a fundamental role in the central nervous system, with about 30-50% of synaptic connections being inhibitory. The action of both inhibitory neurotransmitter, gamma-aminobutyric-acid (GABA) and glycine, mainly relies on the intracellular Cl concentration in neurons. This is set by the interplay of the cation chloride cotransporters NKCC1 (Na, K, Cl cotransporter), a main Cl uptake transporter, and KCC2 (K, Cl cotransporter), the principle Cl extruder in neurons.

Loss of miR-183/96 Alters Synaptic Strength via Presynaptic and Postsynaptic Mechanisms at a Central Synapse.

A point mutation in miR-96 causes non-syndromic progressive peripheral hearing loss and alters structure and physiology of the central auditory system. To gain further insight into the functions of microRNAs (miRNAs) within the central auditory system, we investigated constitutive mice of both sexes. In this mouse model, the genomically clustered miR-183 and miR-96 are constitutively deleted.

Differential expression of microRNAs in the developing avian auditory hindbrain.

The avian auditory hindbrain is a longstanding model for studying neural circuit development. Information on gene regulatory network (GRN) components underlying this process, however, is scarce. Recently, the spatiotemporal expression of 12 microRNAs (miRNAs) was investigated in the mammalian auditory hindbrain.

Structural changes in the extracellular loop 2 of the murine KCC2 potassium chloride cotransporter modulate ion transport.

K-Cl cotransporters (KCCs) play important roles in physiological processes such as inhibitory neurotransmission and cell-volume regulation. KCCs exhibit significant variations in K affinities, yet recent atomic structures demonstrated that K- and Cl-binding sites are highly conserved, raising the question of whether additional structural elements may contribute to ion coordination. The termini and the large extracellular domain (ECD) of KCCs exhibit only low sequence identity and were already discussed as modulators of transport activity.

The Lbx1 lineage differentially contributes to inhibitory cell types of the dorsal cochlear nucleus, a cerebellum-like structure, and the cerebellum.

The dorsal cochlear nucleus (DCN) is a mammalian-specific nucleus of the auditory system. Anatomically, it is classified as a cerebellum-like structure. These structures are proposed to share genetic programs with the cerebellum.

Expression pattern of cochlear microRNAs in the mammalian auditory hindbrain.

The auditory system comprises the auditory periphery, engaged in sound transduction and the central auditory system, implicated in auditory information processing and perception. Recently, evidence mounted that the mammalian peripheral and central auditory systems share a number of genes critical for proper development and function. This bears implication for auditory rehabilitation and evolution of the auditory system.

Staurosporine and NEM mainly impair WNK-SPAK/OSR1 mediated phosphorylation of KCC2 and NKCC1.

The pivotal role of KCC2 and NKCC1 in development and maintenance of fast inhibitory neurotransmission and their implication in severe human diseases arouse interest in posttranscriptional regulatory mechanisms such as (de)phosphorylation. Staurosporine (broad kinase inhibitor) and N-ethylmalemide (NEM) that modulate kinase and phosphatase activities enhance KCC2 and decrease NKCC1 activity. Here, we investigated the regulatory mechanism for this reciprocal regulation by mass spectrometry and immunoblot analyses using phospho-specific antibodies.

Loss of inner hair cell ribbon synapses and auditory nerve fiber regression in Cldn14 knockout mice.

Proper functioning of the auditory nerve is of critical importance for auditory rehabilitation by cochlear implants. Here we used the Cldn14 mouse to study in detail the effects of Claudin 14 loss on auditory synapses and the auditory nerve. Mutations in the tight junction protein Claudin 14 cause autosomal recessive non-syndromic hearing loss (DFNB29) in humans and mice, due to extensive degeneration of outer and inner hair cells.

Scanning laser optical tomography in a neuropathic mouse model : Visualization of structural changes.

Background: In the field of hearing research a variety of imaging techniques are available to study molecular and cellular structures of the cochlea. Most of them are based on decalcifying, embedding, and cutting of the cochlea. By means of scanning laser optical tomography (SLOT), the complete cochlea can be visualized without cutting.

[Scanning laser optical tomography in a neuropathic mouse model : Visualization of structural changes. German version].

Background: In the field of hearing research a variety of imaging techniques are available to study molecular and cellular structures of the cochlea. Most of them are based on decalcifying, embedding, and cutting of the cochlea. By means of scanning laser optical tomography (SLOT), the complete cochlea can be visualized without cutting.

Evolution of Endolymph Secretion and Endolymphatic Potential Generation in the Vertebrate Inner Ear.

The ear of extant vertebrates reflects multiple independent evolutionary trajectories. Examples include the middle ear or the unique specializations of the mammalian cochlea. Another striking difference between vertebrate inner ears concerns the differences in the magnitude of the endolymphatic potential.

Phosphoregulation of the intracellular termini of K-Cl cotransporter 2 (KCC2) enables flexible control of its activity.

The pivotal role of K-Cl cotransporter 2 (KCC2) in inhibitory neurotransmission and severe human diseases fosters interest in understanding posttranslational regulatory mechanisms such as (de)phosphorylation. Here, the regulatory role of the five phosphosites Ser, Thr, Ser, Thr, and Thr was investigated by the use of alanine and aspartate mutants. Tl-based flux analyses in HEK-293 cells demonstrated increased transport activity for S932D (mimicking phosphorylation) and T1008A (mimicking dephosphorylation), albeit to a different extent.

miR-96 is required for normal development of the auditory hindbrain.

The peripheral deafness gene Mir96 is expressed in both the cochlea and central auditory circuits. To investigate whether it plays a role in the auditory system beyond the cochlea, we characterized homozygous Dmdo/Dmdo mice with a point mutation in miR-96. Anatomical analysis demonstrated a significant decrease in volume of auditory nuclei in Dmdo/Dmdo mice.

Activity-dependent formation of a vesicular inhibitory amino acid transporter gradient in the superior olivary complex of NMRI mice.

Background: In the mammalian superior olivary complex (SOC), synaptic inhibition contributes to the processing of binaural sound cues important for sound localization. Previous analyses demonstrated a tonotopic gradient for postsynaptic proteins mediating inhibitory neurotransmission in the lateral superior olive (LSO), a major nucleus of the SOC. To probe, whether a presynaptic molecular gradient exists as well, we investigated immunoreactivity against the vesicular inhibitory amino acid transporter (VIAAT) in the mouse auditory brainstem.

Molecular cloning and biochemical characterization of two cation chloride cotransporter subfamily members of Hydra vulgaris.

Cation Chloride Cotransporters (CCCs) comprise secondary active membrane proteins mainly mediating the symport of cations (Na+, K+) coupled with chloride (Cl-). They are divided into K+-Cl- outward transporters (KCCs), the Na+-K+-Cl- (NKCCs) and Na+-Cl- (NCCs) inward transporters, the cation chloride cotransporter interacting protein CIP1, and the polyamine transporter CCC9. KCCs and N(K)CCs are established in the genome since eukaryotes and metazoans, respectively.

Differences in molecular mechanisms of K clearance in the auditory sensory epithelium of birds and mammals.

Mechanoelectrical transduction in the vertebrate inner ear is a highly conserved mechanism that is dependent on K influx into hair cells. Here, we investigated the molecular underpinnings of subsequent K recycling in the chicken basilar papilla and compared them with those in the mammalian auditory sensory epithelium. As in mammals, the avian auditory hair cell uses KCNQ4, KCNMA1 and KCNMB1 in its K efflux system.

Scanning laser optical tomography for in toto imaging of the murine cochlea.

The mammalian cochlea is a complex macroscopic structure due to its helical shape and the microscopic arrangements of the individual layers of cells. To improve the outcomes of hearing restoration in deaf patients, it is important to understand the anatomic structure and composition of the cochlea ex vivo. Hitherto, only one histological technique based on confocal laser scanning microscopy and optical clearing has been developed for in toto optical imaging of the murine cochlea.

Comparative Analysis of Gene Regulatory Network Components in the Auditory Hindbrain of Mice and Chicken.

The neurons in the mammalian and avian auditory hindbrain nuclei share a number of significant morphological and physiological properties for fast, secure and precise neurotransmission, such as giant synapses, voltage-gated K+ channels and fast AMPA receptors. Based on the independent evolution of the middle ear in these two vertebrate lineages, on different embryonic origins of the nuclei and on marked differences on the circuit level, these similarities are assumed to reflect convergent evolution. Independent acquisition of similar phenotypes can be produced by divergent evolution of genetic mechanisms or by similar molecular mechanisms.

Molecular bases of K secretory cells in the inner ear: shared and distinct features between birds and mammals.

In the cochlea, mammals maintain a uniquely high endolymphatic potential (EP), which is not observed in other vertebrate groups. However, a high [K] is always present in the inner ear endolymph. Here, we show that Kir4.