Perception of sound and gravity by TMC1 and TMC2

Recent advances in cochlear hair cell nanophysiology: subcellular compartmentalization of electrical signaling in compact sensory cells

In recent years, genetics, physiology, and structural biology have advanced into the molecular details of the sensory physiology of auditory hair cells. Inner hair cells (IHCs) and outer hair cells (OHCs) mediate two key functions: active amplification and non-linear compression of cochlear vibrations by OHCs and sound encoding by IHCs at their afferent synapses with the spiral ganglion neurons. OHCs and IHCs share some molecular physiology, e.g. mechanotransduction at the apical hair bundles, ribbon-type presynaptic active zones, and ionic conductances in the basolateral membrane. Unique features enabling their specific function include prestin-based electromotility of OHCs and indefatigable transmitter release at the highest known rates by ribbon-type IHC active zones. Despite their compact morphology, the molecular machineries that either generate electrical signals or are driven by these signals are essentially all segregated into local subcellular structures. This review provides a brief account on recent insights into the molecular physiology of cochlear hair cells with a specific focus on organization into membrane domains.

KCNQ1 rescues TMC1 plasma membrane expression but not mechanosensitive channel activity

Transmembrane channel-like protein isoform 1 (TMC1) is essential for the generation of mechano-electrical transducer currents in hair cells of the inner ear. TMC1 disruption causes hair cell degeneration and deafness in mice and humans. Although thought to be expressed at the cell surface in vivo, TMC1 remains in the endoplasmic reticulum when heterologously expressed in standard cell lines, precluding determination of its roles in mechanosensing and pore formation. Here, we report that the KCNQ1 Kv channel forms complexes with TMC1 and rescues its surface expression when coexpressed in Chinese Hamster Ovary cells. TMC1 rescue is specific for KCNQ1 within the KCNQ family, is prevented by a KCNQ1 trafficking-deficient mutation, and is influenced by KCNE β subunits and inhibition of KCNQ1 endocytosis. TMC1 lowers KCNQ1 and KCNQ1-KCNE1 K⁺ currents, and despite the surface expression, it does not detectably respond to mechanical stimulation or high salt. We conclude that TMC1 is not intrinsically mechano- or osmosensitive but has the capacity for cell surface expression, and requires partner protein(s) for surface expression and mechanosensitivity. We suggest that KCNQ1, expression of which is not thought to overlap with TMC1 in hair cells, is a proxy partner bearing structural elements or a sequence motif reminiscent of a true in vivo TMC1 hair cell partner. Discovery of the first reported strategy to rescue TMC1 surface expression should aid future studies of the TMC1 function and native partners.

Voltage-gated calcium channel activity and complex related genes and schizophrenia: A systematic investigation based on Han Chinese population

Schizophrenia (SCZ) is a devastating mental disorder affecting approximately 1% of the worldwide population. Early studies have indicated that genetics plays an important role in the onset and development of SCZ. Accumulating evidence supports that SCZ is linked to abnormalities of synapse transmission and synaptic plasticity. Voltage-gated calcium channel (VGCC) subunits are critical for mediating intracellular Ca^2 + influx and therefore are responsible for changing neuronal excitability and synaptic plasticity. To systematically investigate the role of calcium signaling genes in SCZ susceptibility, we conducted a case-control study that included 2518 SCZ patients and 7521 healthy controls with Chinese Han ancestry. Thirty-seven VGCC genes, including 363 tag single nucleotide polymorphisms (SNPs), were examined. Our study replicated the following previously identified susceptible loci: CACNA1C, CACNB2, OPRM1, GRM7 and PDE4B. In addition, several novel loci including CACNA2D1, PDE4D, NALCN, and CACNA2D3 were also identified to be associated with SCZ in our Han Chinese sample. Combined with GTEx eQTL data, we have shown that CASQ2, ITGAV, and TMC2 can be also added into the prioritization list of SCZ susceptible genes. Two-way interaction analyses identified widespread gene-by-gene interactions among VGCC activity and complex-related genes for the susceptibility of SCZ. Further sequencing based studies are still needed to unravel potential contributions of schizophrenia risk from rare or low frequency variants of these candidate genes.

Detection of Regional Variation in Selection Intensity within Protein-Coding Genes Using DNA Sequence Polymorphism and Divergence

Numerous approaches have been developed to infer natural selection based on the comparison of polymorphism within species and divergence between species. These methods are especially powerful for the detection of uniform selection operating across a gene. However, empirical analyses have demonstrated that regions of protein-coding genes exhibiting clusters of amino acid substitutions are subject to different levels of selection relative to other regions of the same gene. To quantify this heterogeneity of selection within coding sequences, we developed Model Averaged Site Selection via Poisson Random Field (MASS-PRF). MASS-PRF identifies an ensemble of intragenic clustering models for polymorphic and divergent sites. This ensemble of models is used within the Poisson Random Field framework to estimate selection intensity on a site-by-site basis. Using simulations, we demonstrate that MASS-PRF has high power to detect clusters of amino acid variants in small genic regions, can reliably estimate the probability of a variant occurring at each nucleotide site in sequence data and is robust to historical demographic trends and recombination. We applied MASS-PRF to human gene polymorphism derived from the 1,000 Genomes Project and divergence data from the common chimpanzee. On the basis of this analysis, we discovered striking regional variation in selection intensity, indicative of positive or negative selection, in well-defined domains of genes that have previously been associated with neurological processing, immunity, and reproduction. We suggest that amino acid-altering substitutions within these regions likely are or have been selectively advantageous in the human lineage, playing important roles in protein function.

Features of autosomal recessive non-syndromic hearing impairment: a review to serve as a reference

OBJECTIVE

Non-syndromic sensorineural hearing impairment is inherited in an autosomal recessive fashion in 75-85% of cases. To date, 61 genes with this type of inheritance have been identified as related to hearing impairment, and the genetic heterogeneity is accompanied by a large variety of clinical characteristics. Adequate counselling on a patient's hearing prognosis and rehabilitation is part of the diagnosis on the genetic cause of hearing impairment and, in addition, is important for the psychological well-being of the patient.

TYPE OF REVIEW

Traditional literature review.

DATA SOURCE

All articles describing clinical characteristics of the audiovestibular phenotypes of identified genes and related loci have been reviewed.

CONCLUSION

This review aims to serve as a summary and a reference for counselling purposes when a causative gene has been identified in a patient with a non-syndromic autosomal recessively inherited sensorineural hearing impairment.

Fetus sound stimulation: cilia memristor effect of signal transduction

Background. This experimental study evaluates fetal middle cerebral artery (MCA) circulation after the defined prenatal acoustical stimulation (PAS) and the role of cilia in hearing and memory and could explain signal transduction and memory according to cilia optical-acoustical properties. Methods. PAS was performed twice on 119 no-risk term pregnancies. We analyzed fetal MCA circulation before, after first and second PAS. Results. Analysis of the Pulsatility index basic (PIB) and before PAS and Pulsatility index reactive after the first PAS (PIR 1) shows high statistical difference, representing high influence on the brain circulation. Analysis of PIB and Pulsatility index reactive after the second PAS (PIR 2) shows no statistical difference. Cilia as nanoscale structure possess magnetic flux linkage that depends on the amount of charge that has passed between two-terminal variable resistors of cilia. Microtubule resistance, as a function of the current through and voltage across the structure, leads to appearance of cilia memory with the “memristor” property. Conclusion. Acoustical and optical cilia properties play crucial role in hearing and memory processes. We suggest that fetuses are getting used to sound, developing a kind of memory patterns, considering acoustical and electromagnetically waves and involving cilia and microtubules and try to explain signal transduction.