Hearing sensitivity in mammals is enhanced by more than 40 dB (that is, 100-fold) by mechanical amplification thought to be generated by one class of cochlear sensory cells, the outer hair cells. In addition to the mechano-electrical transduction required for auditory sensation, mammalian outer hair cells also perform electromechanical transduction, whereby transmembrane voltage drives cellular length changes at audio frequencies in vitro. This electromotility is thought to arise through voltage-gated conformational changes in a membrane protein, and prestin has been proposed as this molecular motor. Here we show that targeted deletion of prestin in mice results in loss of outer hair cell electromotility in vitro and a 40-60 dB loss of cochlear sensitivity in vivo, without disruption of mechano-electrical transduction in outer hair cells. In heterozygotes, electromotility is halved and there is a twofold (about 6 dB) increase in cochlear thresholds. These results suggest that prestin is indeed the motor protein, that there is a simple and direct coupling between electromotility and cochlear amplification, and that there is no need to invoke additional active processes to explain cochlear sensitivity in the mammalian ear.

Humans have evolved intimate symbiotic relationships with a consortium of gut microbes (microbiome) and individual variations in the microbiome influence host health, may be implicated in disease etiology, and affect drug metabolism, toxicity, and efficacy. However, the molecular basis of these microbe-host interactions and the roles of individual bacterial species are obscure. We now demonstrate a''transgenomic'' approach to link gut microbiome and metabolic phenotype (metabotype) variation. We have used a combination of spectroscopic, microbiomic, and multivariate statistical tools to analyze fecal and urinary samples from seven Chinese individuals (sampled twice) and to model the microbialhost metabolic connectivities. At the species level, we found structural differences in the Chinese family gut microbiomes and those reported for American volunteers, which is consistent with population microbial cometabolic differences reported in epidemiological studies. We also introduce the concept of functional metagenomics, defined as ''the characterization of key functional members of the microbiome that most influence host metabolism and hence health.'' For example, Faecalibacterium prausnitzii population variation is associated with modulation of eight urinary metabolites of diverse structure, indicating that this species is a highly functionally active member of the microbiome, influencing numerous host pathways. Other species were identified showing different and varied metabolic interactions. Our approach for understanding the dynamic basis of host-microbiome symbiosis provides a foundation for the development of functional metagenomics as a probe of systemic effects of drugs and diet that are of relevance to personal and public health care solutions. covariation analysis ͉ gut microbiota ͉ metabonomics ͉ metabotype ͉ metagenomics

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Lurcher (Lc) is a spontaneous, semidominant mouse neurological mutation. Heterozygous Lurcher mice (Lc/+) display ataxia as a result of a selective, cell-autonomous and apoptotic death of cerebellar Purkinje cells during postnatal development. Homozygous Lurcher mice (Lc/Lc) die shortly after birth because of a massive loss of mid- and hindbrain neurons during late embryogenesis. We have used positional cloning to identify the mutations responsible for neurodegeneration in two independent Lc alleles as G-to-A transitions that change a highly conserved alanine to a threonine residue in transmembrane domain III of the mouse delta2 glutamate receptor gene (GluR delta2). Lc/+ Purkinje cells have a very high membrane conductance and a depolarized resting potential, indicating the presence of a large, constitutive inward current. Expression of the mutant GluR delta2(Lc) protein in Xenopus oocytes confirmed these results, demonstrating that Lc is inherited as a neurodegenerative disorder resulting from a gain-of-function mutation in a glutamate receptor gene. Thus the activation of apoptotic neuronal death in Lurcher mice may provide a physiologically relevant model for excitotoxic cell death.

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It is a central tenet of cochlear neurobiology that mammalian ears rely on a local, mechanical amplification process for their high sensitivity and sharp frequency selectivity. While it is generally agreed that outer hair cells provide the amplification, two mechanisms have been proposed: stereociliary motility and somatic motility. The latter is driven by the motor protein prestin. Electrophysiological phenotyping of a prestin knockout mouse intimated that somatic motility is the amplifier. However, outer hair cells of knockout mice have significantly altered mechanical properties, making this mouse model unsatisfactory. Here, we study a mouse model without alteration to outer hair cell and organ of Corti mechanics or to mechanoelectric transduction, but with diminished prestin function. These animals have knockout-like behavior, demonstrating that prestin-based electromotility is required for cochlear amplification.

Unlike non-mammalian vertebrates, mammals cannot convert inner ear cochlear supporting cells (SCs) into sensory hair cells (HCs) after damage, thus causing permanent deafness. Here, we achieved in vivo conversion of two SC subtypes, pillar cells (PCs) and Deiters’ cells (DCs), into HCs by inducing targeted expression of Atoh1 at neonatal and juvenile ages using novel mouse models. The conversion only occurred in ~10% of PCs and DCs with ectopic Atoh1 expression and started with reactivation of endogenous Atoh1, followed by expression of 11 HC and synaptic markers; a process that took at least 3 weeks in vivo. These new HCs resided in the outer HC region, formed stereocilia, contained mechanoelectrical transduction channels, and survived for more than 2 months in vivo; however, they surprisingly lacked prestin and oncomodulin expression and mature HC morphology. In contrast, adult PCs and DCs no longer responded to ectopic Atoh1 expression, even after outer HC damage. Finally, permanent Atoh1 expression in endogenous HCs did not affect prestin expression, but caused cell loss of mature HCs. Together our results demonstrate that in vivo conversion of PCs and DCs into immature HCs by Atoh1 is age-dependent, and resembles normal HC development. Therefore combined expression of Atoh1 with additional factors holds therapeutic promise to convert PCs and DCs into functional HCs in vivo for regenerative purposes.

There was an error published in Development 141, 816-829. Edwin W. Rubel was omitted from the authorship of the paper. The correct author list and affiliations appears above.In addition the Acknowledgements and Author contributions sections should read as follows. AcknowledgementsWe thank L. Tong and R. Palmiter (University of Washington) for Pou4f3DTR/+ mice and discussion; S. Baker (St. Jude) for Atoh1-CreERTM mice and discussion; R. Kageyama (Kyoto University) for Hes5-nlsLacZ mice; P. Chambon (Institut Genetique Biologie Moleculaire Cellulaire) for the CreERT2 construct; S. Heller (Stanford University) for the anti-espin antibody and critical reading, J. Corwin, J. Burns and other members of the Corwin laboratory (University of Virginia) as well as members of our laboratories for discussion and critical comments; S. Connell, V. Frohlich, Y. Ouyang and J. Peters (St. Jude) for expertise in confocal imaging; A. Xue, V. Nookala, N. Pham, A. Vu, G. Huang and W. Liu (Stanford University) for excellent technical support; and L. Boykins (University of Memphis), R. Martens and J. Goodwin (University of Alabama) for assistance and expertise in scanning electron microscopy. Author contributionsB.C.C., R.C., E.W.R., A.G.C. and J.Z. developed the concepts or approach; B.C.C., R.C., A.L., Z.L., L.Z., D.-H.N., K.C., K.A.S., J.F., A.G.C. and J.Z. performed experiments or data analysis; B.C.C., R.C., A.G.C. and J.Z. prepared or edited the manuscript prior to submission.The authors apologise to readers for this mistake. DTA/+ alleles allowed selective and inducible hair cell ablation. After hair cell loss was induced at birth, we observed spontaneous regeneration of hair cells. Fate-mapping experiments demonstrated that neighboring supporting cells acquired a hair cell fate, which increased in a basal to apical gradient, averaging over 120 regenerated hair cells per cochlea. The normally mitotically quiescent supporting cells proliferated after hair cell ablation. Concurrent fate mapping and labeling with mitotic tracers showed that regenerated hair cells were derived by both mitotic regeneration and direct transdifferentiation. Over time, regenerated hair cells followed a similar pattern of maturation to normal hair cell development, including the expression of prestin, a terminal differentiation marker of outer hair cells, although many new hair cells eventually died. Hair cell regeneration did not occur when ablation was induced at one week of age. Our findings demonstrate that the neonatal mouse cochlea is capable of spontaneous hair cell regeneration after damage in vivo. Thus, future studies on the neonatal cochlea might shed light on the competence of supporting cells to regenerate hair cells and on the factors that promote the survival of newly regenerated hair cells. 816© 2014. Published by The Company of Biologists Ltd | Development (2014) 141, 816-829 doi