Biology subjects

Boue-Grabot, E.

Publications and source records attributed to Boue-Grabot, E..

3 recordsLinked to original sources

bioRxiv2025

Medial olivocochlear efferent modulation of cochlear micromechanics requires P2X4 expression in outer hair cells

The role of P2X4, one of the most abundant ionotropic purinergic receptors in the central nervous system, is explored here in the context of auditory function. We observed, by using constitutive and conditional P2X4mCherryIN knock-in adult mouse models, a specific high expression of mCherry-tagged P2X4 in living cochlear outer hair cells (OHCs), from immature postnatal stages to adulthood. This P2X4-mCherry expression, confirmed by immuno-confocal fluorescence microscopy in wild-type mice, was mainly concentrated in the intracellular apical region of the OHCs, in the area of the Hensens body, a lysosomal rich region, specifically labeled with the fluorescent dye lysotracker. In addition, the basal cholinergic efferent synaptic region of the OHCs was found to express P2X4 at the cell membrane. Surprisingly, the assessment of the hearing function in constitutive P2X4 knock-out (P2X4KO) mice showed improved auditory brainstem responses with smaller latencies, larger amplitudes and smaller thresholds. These P2X4KO mice, as well as conditional P2X4KO-Myo15-Cre mice, displayed enhanced distortion product otoacoustic emissions (DPOAEs), suggesting an improved electromechanical amplification activity by OHCs. These mutant animals showed reduced inhibition of DPOAEs by contralateral noise, consistent with a weaker inhibitory effect of the medial cholinergic olivocochlear efferent circuit (MOC) on OHCs. We concluded that the MOC negative feedback modulation of cochlear micromechanics, in addition to involve Ca2+ permeable 9/10 nicotinic receptors, also requires the activation of postsynaptic P2X4 receptors in OHCs. SIGNIFICANCE STATEMENTOur study reveals a specific strong expression of P2X4 in mouse cochlear outer hair cells (OHCs), these cells being essential for generating the distortion products otoacoustic emissions (DPOAES) and tuning the sensitivity and frequency selectivity of the cochlea. Mice lacking P2X4 showed a deficient inhibitory control of their cochlear DPOAEs when activating the medial olivocochlear efferent pathway innervating the OHCs. We propose P2X4 receptors as an important Ca2+ regulatory component of the micromechanics of OHCs and that genetic defects in these purinergic receptors may potentially lead to hearing disorders such as tinnitus and hyperacusis.

neuroscience↗

bioRxiv2023

Purine biosynthesis pathways are required for myogenesisin Xenopus laevis

Purines are required for fundamental biological processes and alterations in their metabolism lead to severe genetic diseases associated with developmental defects whose etiology remains unclear. Here, we studied the developmental requirements for purine metabolism using the amphibian Xenopus laevis as a vertebrate model. We provide the first functional characterization of purine pathway-genes and show that these genes are mostly expressed in nervous and muscular embryonic tissues. Morphants were generated to decipher the functions of these genes, with a focus on the adenylosuccinate lyase (ADSL), an enzyme required for both salvage and de novo purine pathways. adsl.L knock-down leads to severe reduction in the expression of the Myogenic Regulatory Factors (MRFs: Myod1, Myf5 and Myogenin), thus resulting in defects in somitogenesis and in the formation and/or migration of both craniofacial and hypaxial muscle progenitors. Similar alterations were observed upon reduced expression of hprt1.L and ppat, two genes specific to the salvage and the de novo pathways, respectively. In conclusion, our data shows for the first time that de novo and recycling purine pathways are essential for myogenesis and highlight new mechanisms in the regulation of MRFs gene expression.

developmental biology↗

bioRxiv2021

The enpp4 ectonucleotidase regulates kidney patterning signalling networks in Xenopus embryos

The enpp ectonucleotidases regulate lipidic and purinergic signalling pathways by controlling the extracellular concentrations of purines and bioactive lipids. Although both pathways are key regulators of kidney physiology and linked to human renal pathologies, their roles during nephrogenesis remain poorly understood. We previously showed that the pronephros was a major site of enpp expression and now demonstrate an unsuspected role for the conserved vertebrate enpp4 protein during kidney formation in Xenopus. Enpp4 over-expression results in ectopic renal tissues and, on rare occasion, complete mini-duplication of the entire kidney. Enpp4 is required and sufficient for expression of the pronephric markers and regulates the expression of RA, Notch and Wnt pathway members. Enpp4 is a membrane protein that binds, without hydrolyzing, phosphatidylserine and its effects are mediated by the receptor s1pr5, although not via the generation of S1P. Finally, we propose a novel and surprising non-catalytic mechanism by which lipidic signalling regulates nephrogenesis.

developmental biology↗