auditory hindbrain; calyx of Held; micro-RNA; synaptic transmission
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 Mir-183/96dko mice of both sexes. In this mouse model, the genomically clustered miR-183 and miR-96 are constitutively deleted. It shows significantly and specifically reduced volumes of auditory hindbrain nuclei, because of decreases in cell number and soma size. Electrophysiological analysis of the calyx of Held synapse in the medial nucleus of the trapezoid body (MNTB) demonstrated strongly altered synaptic transmission in young-adult mice. We observed an increase in quantal content and readily releasable vesicle pool size in the presynapse while the overall morphology of the calyx was unchanged. Detailed analysis of the active zones (AZs) revealed differences in its molecular composition and synaptic vesicle (SV) distribution. Postsynaptically, altered clustering and increased synaptic abundancy of the AMPA receptor subunit GluA1 was observed resulting in an increase in quantal amplitude. Together, these presynaptic and postsynaptic alterations led to a 2-fold increase of the evoked excitatory postsynaptic currents in MNTB neurons. None of these changes were observed in deaf Cldn14ko mice, confirming an on-site role of miR-183 and miR-96 in the auditory hindbrain. Our data suggest that the Mir-183/96 cluster plays a key role for proper synaptic transmission at the calyx of Held and for the development of the auditory hindbrain. - SIGNIFICANCE STATEMENT The calyx of Held is the outstanding model system to study basic synaptic physiology. Yet, genetic factors driving its morphologic and functional maturation are largely unknown. Here, we identify the Mir-183/96 cluster as an important factor to regulate its synaptic strength. Presynaptically, Mir-183/96dko calyces show an increase in release-ready synaptic vesicles (SVs), quantal content and abundance of the proteins Bassoon and Piccolo. Postsynaptically, the quantal size as well as number and size of GluA1 puncta were increased. The two microRNAs (miRNAs) are thus attractive candidates for regulation of synaptic maturation and long-term adaptations to sound levels. Moreover, the different phenotypic outcomes of different types of mutations in the Mir-183 cluster corroborate the requirement of mutation-tailored therapies in patients with hearing loss.
The journal of neuroscience Washington, DC : Soc., 1981 41(2021), 32, Seite 6796-6811 Online-Ressource
Die Analyse einer miR-183/96 knockout Mauslinie belegt die Bedeutung von miR-183/96 für die Entwicklung und Funktion des auditorischen Hirnstammes bei Säugern. Neben einer essentiellen Rolle für die Histogenese zeigte die funktionelle Analyse der miR-183/96 ko Mauslinie Funktionsgewinne und Verluste der miR-96 Dmdo Mutation auf molekularer Ebene. Das Ausschalten von miR-183/96 beeinflusst zudem die synaptische Übertragung an der Calyx von Held, einer gut untersuchten Riesensynapse des zentralen auditorischen Systems. Diese Ergebnisse tragen zum Verständnis der Regulation synaptischer Funktion bei.Desweiteren wurden durch eine Kombination von Next-Generation-Sequencing (NGS) und Bioinformatik 32 möglicherweise auditorische miRNAs identifiziert. Diese repräsentieren miRNA Kandidaten für weitere Analysen in knockout Mausmodellen und können zum Verständnis der genetischen Regulation von Entwicklung und Pathologie des auditorischen Systems beitragen.
Analysis of a miR-183/96 knockout mouse line demonstrated the importance of miR-183/96 for development and function of the mammalian auditory hindbrain. Besides an essential role in its histogenesis, functional analysis of the miR-183/96 ko mouse line delivered data on gain and loss of function consequences of the miR-96 Dmdo mutation on a molecular level. miR-183/96 ko interfered with synaptic transmission at the calyx of Held, a well- studied giant central synapse in the central auditory system. These results contribute to the understanding of the regulation of key synaptic properties. Furthermore, a combination of next generation sequencing (NGS) and bioinformatics identified 32 miRNAs being possibly auditory-related. They represent thus a set of miRNA candidates for further analysis in knockout mouse models and could contribute to the gross understanding of genetic regulation underlying development and disease of the auditory system.