Elasticity and Thermal Stability are Key Determinants of Hearing Rescue by Mini-Protocadherin-15 Proteins.

Protocadherin-15 is a core protein component of inner-ear hair-cell tip links pulling on transduction channels essential for hearing and balance. Protocadherin-15 defects can result in non-syndromic deafness or Usher syndrome type 1F (USH1F) with hearing loss, balance deficits, and progressive blindness. Three rationally engineered shortened versions of protocadherin-15 (mini-PCDH15s) amenable for gene therapy have been used to rescue function in USH1F mouse models. Two can successfully or partially rescue hearing, while another one fails. Here we show that despite varying levels of hearing rescue, all three mini-PCDH15 versions can rescue hair-cell mechanotransduction. Negative-stain electron microscopy shows that all three versions form dimers like the wild-type protein, while crystal structures of some engineered fragments show that these can properly fold and bind calcium ions essential for function. In contrast, simulations predict distinct elasticities and nano differential scanning fluorimetry shows differences in melting temperature measurements. Our data suggest that elasticity and thermal stability are key determinants of sustained hearing rescue by mini-PCDH15s.

Implications of a temperature-dependent heat capacity for temperature-gated ion channels.

Temperature influences dynamics and state-equilibrium distributions in all molecular processes, and only a relatively narrow range of temperatures is compatible with life-organisms must avoid temperature extremes that can cause physical damage or metabolic disruption. Animals evolved a set of sensory ion channels, many of them in the family of transient receptor potential cation channels that detect biologically relevant changes in temperature with remarkable sensitivity. Depending on the specific ion channel, heating or cooling elicits conformational changes in the channel to enable the flow of cations into sensory neurons, giving rise to electrical signaling and sensory perception. The molecular mechanisms responsible for the heightened temperature-sensitivity in these ion channels, as well as the molecular adaptations that make each channel specifically heat- or cold-activated, are largely unknown. It has been hypothesized that a heat capacity difference (ΔCp) between two conformational states of these biological thermosensors can drive their temperature-sensitivity, but no experimental measurements of ΔCp have been achieved for these channel proteins. Contrary to the general assumption that the ΔCp is constant, measurements from soluble proteins indicate that the ΔCp is likely to be a function of temperature. By investigating the theoretical consequences for a linearly temperature-dependent ΔCp on the open-closed equilibrium of an ion channel, we uncover a range of possible channel behaviors that are consistent with experimental measurements of channel activity and that extend beyond what had been generally assumed to be possible for a simple two-state model, challenging long-held assumptions about ion channel gating models at equilibrium.

Ghost cell odontogenic tumor associated with odontoma--report of two rare cases.

The ghost cell odontogenic tumor (GCOT) is a neoplastic/cystic lesion with a diverse histopathological and clinical behavior It was formerly known as calcified odontogenic cyst, but in 2005 the World Health Organization categorized this lesion as an odontogenic, benign tumor rather than a cyst; nominating this neoplasm as calcifying cystic odontogenic tumor. A later comprehensive classification named it ghost cell odontogenic tumor because the most remarkable histopathologic characteristic is the presence of a mass of ghost cells embedded in the epithelium. We report two cases of a rare variant of a ghost cell odontogenic tumor associated with odontoma; to our knowledge, one is the youngest patient (four month old) reported in the English literature.