Mice do not require auditory input for the normal development of their ultrasonic vocalizations

<p>Abstract</p> <p>Background</p> <p>Transgenic mice have become an important tool to elucidate the genetic foundation of the human language faculty. While learning is an essential prerequisite for the acquisition of human speech, it is still a matter of debate whether auditory learning plays any role in the development of species-specific vocalizations in mice. To study the influence of auditory input on call development, we compared the occurrence and structure of ultrasonic vocalizations from deaf otoferlin-knockout mice, a model for human deafness DFNB9, to those of hearing wild-type and heterozygous littermates.</p> <p>Results</p> <p>We found that the occurrence and structure of ultrasonic vocalizations recorded from deaf otoferlin-knockout mice and hearing wild-type and heterozygous littermates do not differ. Isolation calls from 16 deaf and 15 hearing pups show the same ontogenetic development in terms of the usage and structure of their vocalizations as their hearing conspecifics. Similarly, adult courtship 'songs' produced by 12 deaf and 16 hearing males did not differ in the latency to call, rhythm of calling or acoustic structure.</p> <p>Conclusion</p> <p>The results indicate that auditory experience is not a prerequisite for the development of species-specific vocalizations in mice. Thus, mouse models are of only limited suitability to study the evolution of vocal learning, a crucial component in the development of human speech. Nevertheless, ultrasonic vocalizations of mice constitute a valuable readout in studies of the genetic foundations of social and communicative behavior.</p

Identification of genetic variants associated with Huntington's disease progression: a genome-wide association study

Background Huntington's disease is caused by a CAG repeat expansion in the huntingtin gene, HTT. Age at onset has been used as a quantitative phenotype in genetic analysis looking for Huntington's disease modifiers, but is hard to define and not always available. Therefore, we aimed to generate a novel measure of disease progression and to identify genetic markers associated with this progression measure. Methods We generated a progression score on the basis of principal component analysis of prospectively acquired longitudinal changes in motor, cognitive, and imaging measures in the 218 indivduals in the TRACK-HD cohort of Huntington's disease gene mutation carriers (data collected 2008–11). We generated a parallel progression score using data from 1773 previously genotyped participants from the European Huntington's Disease Network REGISTRY study of Huntington's disease mutation carriers (data collected 2003–13). We did a genome-wide association analyses in terms of progression for 216 TRACK-HD participants and 1773 REGISTRY participants, then a meta-analysis of these results was undertaken. Findings Longitudinal motor, cognitive, and imaging scores were correlated with each other in TRACK-HD participants, justifying use of a single, cross-domain measure of disease progression in both studies. The TRACK-HD and REGISTRY progression measures were correlated with each other (r=0·674), and with age at onset (TRACK-HD, r=0·315; REGISTRY, r=0·234). The meta-analysis of progression in TRACK-HD and REGISTRY gave a genome-wide significant signal (p=1·12 × 10−10) on chromosome 5 spanning three genes: MSH3, DHFR, and MTRNR2L2. The genes in this locus were associated with progression in TRACK-HD (MSH3 p=2·94 × 10−8 DHFR p=8·37 × 10−7 MTRNR2L2 p=2·15 × 10−9) and to a lesser extent in REGISTRY (MSH3 p=9·36 × 10−4 DHFR p=8·45 × 10−4 MTRNR2L2 p=1·20 × 10−3). The lead single nucleotide polymorphism (SNP) in TRACK-HD (rs557874766) was genome-wide significant in the meta-analysis (p=1·58 × 10−8), and encodes an aminoacid change (Pro67Ala) in MSH3. In TRACK-HD, each copy of the minor allele at this SNP was associated with a 0·4 units per year (95% CI 0·16–0·66) reduction in the rate of change of the Unified Huntington's Disease Rating Scale (UHDRS) Total Motor Score, and a reduction of 0·12 units per year (95% CI 0·06–0·18) in the rate of change of UHDRS Total Functional Capacity score. These associations remained significant after adjusting for age of onset. Interpretation The multidomain progression measure in TRACK-HD was associated with a functional variant that was genome-wide significant in our meta-analysis. The association in only 216 participants implies that the progression measure is a sensitive reflection of disease burden, that the effect size at this locus is large, or both. Knockout of Msh3 reduces somatic expansion in Huntington's disease mouse models, suggesting this mechanism as an area for future therapeutic investigation

Differential dependence of phasic transmitter release on synaptotagmin 1 at GABAergic and glutamatergic hippocampal synapses

Previous studies revealed that synaptotagmin 1 is the major Ca2+ sensor for fast synchronous transmitter release at excitatory synapses. However, the molecular identity of the Ca2+ sensor at hippocampal inhibitory synapses has not been determined. To address the functional role of synaptotagmin 1 at identified inhibitory terminals, we made paired recordings from synaptically connected basket cells (BCs) and granule cells (GCs) in the dentate gyrus in organotypic slice cultures from wild-type and synaptotagmin 1-deficient mice. As expected, genetic elimination of synaptotagmin 1 abolished synchronous transmitter release at excitatory GC–BC synapses. However, synchronous release at inhibitory BC–GC synapses was maintained. Quantitative analysis revealed that elimination of synaptotagmin 1 reduced release probability and depression but maintained the synchrony of transmitter release at BC–GC synapses. Elimination of synaptotagmin 1 also increased the frequency of both miniature excitatory postsynaptic currents (measured in BCs) and miniature inhibitory postsynaptic currents (recorded in GCs), consistent with a clamping function of synaptotagmin 1 at both excitatory and inhibitory terminals. Single-cell reverse-transcription quantitative PCR analysis revealed that single BCs coexpressed multiple synaptotagmin isoforms, including synaptotagmin 1–5, 7, and 11–13. Our results indicate that, in contrast to excitatory synapses, synaptotagmin 1 is not absolutely required for synchronous release at inhibitory BC–GC synapses. Thus, alternative fast Ca2+ sensors contribute to synchronous release of the inhibitory transmitter GABA in cortical circuits

A dual‐AAV approach restores fast exocytosis and partially rescues auditory function in deaf otoferlin knock‐out mice

Abstract Normal hearing and synaptic transmission at afferent auditory inner hair cell (IHC) synapses require otoferlin. Deafness DFNB9, caused by mutations in the OTOF gene encoding otoferlin, might be treated by transferring wild‐type otoferlin cDNA into IHCs, which is difficult due to the large size of this transgene. In this study, we generated two adeno‐associated viruses (AAVs), each containing half of the otoferlin cDNA. Co‐injecting these dual‐AAV2/6 half‐vectors into the cochleae of 6‐ to 7‐day‐old otoferlin knock‐out (Otof−/−) mice led to the expression of full‐length otoferlin in up to 50% of IHCs. In the cochlea, otoferlin was selectively expressed in auditory hair cells. Dual‐AAV transduction of Otof−/− IHCs fully restored fast exocytosis, while otoferlin‐dependent vesicle replenishment reached 35–50% of wild‐type levels. The loss of 40% of synaptic ribbons in these IHCs could not be prevented, indicating a role of otoferlin in early synapse maturation. Acoustic clicks evoked auditory brainstem responses with thresholds of 40–60 dB. Therefore, we propose that gene delivery mediated by dual‐AAV vectors might be suitable to treat deafness forms caused by mutations in large genes such as OTOF