Biology subjects

Frolenkov, G. I.

Publications and source records attributed to Frolenkov, G. I..

4 recordsLinked to original sources

bioRxiv2025

A Myosin Nanomotor Essential for Stereocilia Maintenance Expands the Etiology of Hereditary Hearing Loss DFNB3

Cochlear hair cells transduce sound using stereocilia, and disruption to these delicate mechanosensors is a significant cause of hearing loss. Stereocilia architecture is dependent upon the nanomotor myosin 15. A short isoform (MYO15A-2) drives stereocilia development by delivering an elongation-promoting complex (EC) to stereocilia tips, and an alternatively spliced long isoform (MYO15A-1) tunes postnatal size in shorter stereocilia, which possess mechanosensitive ion channels. Disruption of these functions causes two distinct stereocilia pathologies, which underly human autosomal recessive non-syndromic hearing loss DFNB3. Here, we characterize a new isoform, MYO15A-3, that increases expression in postnatal hair cells as the developmental MYO15A-2 isoform wanes reciprocally. We show the critical EC complex is initially delivered by MYO15A-2, followed by a postnatal handover to MYO15A-3, which continues to deliver the EC. In a Myo15a-3 mutant mouse, stereocilia develop normally with correct EC targeting, but lack the EC postnatally and do not maintain their adult architecture, leading to progressive hearing loss. We conclude MYO15A-3 delivers the EC in postnatal hair cells and that the EC and MYO15A-3 are both required to maintain stereocilia integrity. Our results add to the spectrum of stereocilia pathology underlying DFNB3 hearing loss and reveal new molecular mechanisms necessary for resilient hearing during adult life.

neuroscience↗

bioRxiv2023

Calcium and Integrin-binding protein 2 (CIB2) controls force sensitivity of the mechanotransducer channels in cochlear outer hair cells

Calcium and Integrin-Binding Protein 2 (CIB2) is an essential subunit of the mechano-electrical transduction (MET) complex in mammalian auditory hair cells. CIB2 binds to pore-forming subunits of the MET channel, TMC1/2 and is required for their transport and/or retention at the tips of mechanosensory stereocilia. Since genetic ablation of CIB2 results in complete loss of MET currents, the exact role of CIB2 in the MET complex remains elusive. Here, we generated a new mouse strain with deafness-causing p.R186W mutation in Cib2 and recorded small but still measurable MET currents in the cochlear outer hair cells. We found that R186W variant causes increase of the resting open probability of MET channels, steeper MET current dependence on hair bundle deflection (I-X curve), loss of fast adaptation, and increased leftward shifts of I-X curves upon hair cell depolarization. Combined with AlphaFold2 prediction that R186W disrupts one of the multiple interacting sites between CIB2 and TMC1/2, our data suggest that CIB2 mechanically constraints TMC1/2 conformations to ensure proper force sensitivity and dynamic range of the MET channels. Using a custom piezo-driven stiff probe deflecting the hair bundles in less than 10 {micro}s, we also found that R186W variant slows down the activation of MET channels. This phenomenon, however, is unlikely to be due to direct effect on MET channels, since we also observed R186W-evoked disruption of the electron-dense material at the tips of mechanotransducing stereocilia and the loss of membrane-shaping BAIAP2L2 protein from the same location. We concluded that R186W variant of CIB2 disrupts force sensitivity of the MET channels and force transmission to these channels.

neuroscience↗

bioRxiv2022

TRPA1 activation in non-sensory supporting cells contributes to regulation of cochlear sensitivity after acoustic trauma

TRPA1 channels are expressed in nociceptive neurons, where they detect noxious stimuli, and in the mammalian cochlea, where their function is unknown. Here we show that TRPA1 activation in the supporting non-sensory Hensens cells causes prolonged Ca2+ responses, which propagate across the organ of Corti and cause long-lasting contractions of pillar and Deiters cells. Caged Ca2+ experiments demonstrated that, similar to Deiters cells, pillar cells also possess Ca2+-dependent contractile machinery. TRPA1 channels are activated by endogenous products of oxidative stress and by extracellular ATP. Since both these stimuli are present in vivo after acoustic trauma, TRPA1 activation after noise may affect cochlear sensitivity through supporting cell contractions. Consistently, TRPA1 deficiency results in larger but less prolonged noise-induced temporary shift of hearing thresholds, accompanied by permanent changes of latency and shape of the auditory brainstem responses. We conclude that TRPA1 contributes to the regulation of cochlear sensitivity after acoustic trauma.

neuroscience↗

bioRxiv2020

Modification of streptococcal cell wall polysaccharide spatially controls cell division

Bacterial cell division is driven by a tubulin homolog FtsZ, which assembles into the Z-ring structure leading to the recruitment of the cell division machinery. In ovoid-shaped Gram-positive bacteria, such as streptococci, MapZ guides Z-ring positioning at cell equators through an, as yet, unknown mechanism. The cell wall of the important dental pathogen Streptococcus mutans is composed of peptidoglycan decorated with Serotype c Carbohydrates (SCCs). Here, we show that an immature form of SCC, lacking the recently identified glycerol phosphate (GroP) modification, coordinates Z-ring positioning. Pulldown assays using S. mutans cell wall combined with binding affinity analysis identified the major cell separation autolysin, AtlA, as an SCC binding protein. Importantly, AtlA binding to mature SCC is attenuated due to GroP modification. Using fluorescently-labeled AtlA, we mapped SCC distribution on the streptococcal surface to reveal that GroP-deficient immature SCCs are exclusively present at the cell poles and equators. Moreover, the equatorial GroP-deficient SCCs co-localize with MapZ throughout the S. mutans cell cycle. Consequently, in GroP-deficient mutant bacteria, proper AtlA localization is abrogated resulting in dysregulated cellular autolysis. In addition, these mutants display morphological abnormalities associated with MapZ mislocalization leading to Z-ring misplacement. Altogether, our data support a model in which GroP-deficient immature SCCs spatially coordinate the localization of AtlA and MapZ. This mechanism ensures cell separation by AtlA at poles and Z-ring alignment with the cell equator.Competing Interest StatementThe authors have declared no competing interest.View Full Text

microbiology↗