Biology subjects

Whitwam, T.

Publications and source records attributed to Whitwam, T..

4 recordsLinked to original sources

bioRxiv2023

Activity-Induced MeCP2 Phosphorylation Regulates Retinogeniculate Synapse Refinement

Mutations in MECP2 give rise to Rett syndrome (RTT), an X-linked neurodevelopmental disorder that results in broad cognitive impairments in females. While the exact etiology of RTT symptoms remains unknown, one possible explanation for its clinical presentation is that loss of MeCP2 causes miswiring of neural circuits due to defects in the brains capacity to respond to changes in neuronal activity and sensory experience. Here we show that MeCP2 is phosphorylated at four residues in the brain (S86, S274, T308, and S421) in response to neuronal activity, and we generate a quadruple knock-in (QKI) mouse line in which all four activity-dependent sites are mutated to alanines to prevent phosphorylation. QKI mice do not display overt RTT phenotypes or detectable gene expression changes in two brain regions. However, electrophysiological recordings from the retinogeniculate synapse of QKI mice reveal that while synapse elimination is initially normal at P14, it is significantly compromised at P20. Notably, this phenotype is distinct from that previously reported for Mecp2 null mice, where synapses initially refine but then regress after the third postnatal week. We thus propose a model in which activity-induced phosphorylation of MeCP2 is critical for the proper timing of retinogeniculate synapse maturation specifically during the early postnatal period. SIGNIFICANCE STATEMENTRett syndrome (RTT) is an X-linked neurodevelopmental disorder that predominantly affects girls. RTT is caused by loss of function mutations in a single gene MeCP2. Girls with RTT develop normally during their first year of life, but then experience neurological abnormalities including breathing and movement difficulties, loss of speech, and seizures. This study investigates the function of the MeCP2 protein in the brain, and how MeCP2 activity is modulated by sensory experience in early life. Evidence is presented that sensory experience affects MeCP2 function, and that this is required for synaptic pruning in the brain. These findings provide insight into MeCP2 function, and clues as to what goes awry in the brain when the function of MeCP2 is disrupted.

neuroscience↗

bioRxiv2018

OSCA/TMEM63 are an Evolutionarily Conserved Family of Mechanically Activated Ion Channels

IntroductionMechanotransduction, the conversion of mechanical cues into biochemical signals, is crucial for many biological processes in plants and animals1,2. In mammals, some mechanosensory processes such as touch sensation and vascular development are mediated by the PIEZO family of mechanically activated (MA) ion channels3-5. In plants, the impact of gravity or soil properties on root development, wind on stem growth, and turgor pressure on plant-cell size and shape are proposed to involve activation of MA ion channels6,7. Homologues of the bacterial MA channel MscS (MSLs) exist in plants, and MSL8 is shown to be involved in pollen hydration8; however, the identity of the MA channels required for most mechanotransduction processes in plants have remained elusive9. Here, we identify various members of the 15 OSCA proteins from Arabidopsis thaliana (previously reported as hyperosmolarity sensors10,11) as MA ion channels. Purification and reconstitution of OSCA1.2 in liposomes induced stretch-activated currents, suggesting that OSCAs are inherently mechanosensitive, pore-forming ion channels. This conclusion is confirmed by a high-resolution electron microscopy structure of OSCA1.2 described in a companion paper12. Beyond plants, we present evidence that fruit fly, mouse, and human TMEM63 family of proteins, homologues of OSCAs, induce MA currents when expressed in naive cells. Our results suggest that OSCA/TMEM63 proteins are the largest family of MA ion channels identified, and are conserved across eukaryotes. We anticipate that further characterization of OSCA isoforms which have diverse biophysical properties, will help gain substantial insight on the molecular mechanism of MA ion channel gating and permeation. OSCA1.1 mutant plants have impaired leaf and root growth under stress, potentially linking this ion channel to a mechanosensory role11. We expect future studies to uncover novel roles of OSCA/TMEM63 channels in mechanosensory processes across plants and animals.

biophysics↗

bioRxiv2018

Structure of the Human Volume Regulated Anion Channel

SWELL1 (LRRC8A) is the only essential subunit of the Volume Regulated Anion Channel (VRAC), which regulates cellular volume homeostasis and is activated by hypotonic solutions. SWELL1, together with four other LRRC8 family members, forms a vastly heterogeneous cohort of VRAC channels with different properties; however, SWELL1 alone is also functional. Here, we report a high-resolution cryo-electron microscopy structure of full-length human homo-hexameric SWELL1. The structure reveals a trimer of dimers assembly with symmetry mismatch between the pore-forming domain and the cytosolic leucine-rich repeat (LRR) domains. Importantly, mutational analysis demonstrates that a charged residue at the narrowest constriction of the homomeric channel is an important pore determinant of heteromeric VRAC. This structure provides a scaffold for further dissecting the heterogeneity and mechanism of activation of VRAC.

biochemistry↗

bioRxiv2017

Common Piezo1 allele in African populations causes xerocytosis and attenuates Plasmodium infection

Hereditary xerocytosis (HX) is thought to be a rare genetic condition characterized by red blood cell (RBC) dehydration with mild hemolysis. Gain-of-function (GOF) mutations in mechanosensitive Piezo1 ion channels are identified in HX patients. RBC dehydration is linked to reduced Plasmodium infection rates in vitro. We engineered a Piezo1 mouse model of HX and show that Plasmodium infection fails to cause experimental cerebral malaria in these mice. Furthermore, we identified a novel GOF human Piezo1 variant, E756del, present in a third of African population. Remarkably, RBCs from individuals carrying this allele are dehydrated and protected against Plasmodium infection in vitro. The presence of an HX-causing Piezo1 mutation at such high frequencies in African population is surprising, and suggests an association with malaria resistance.

physiology↗