Biology subjects

Tzingounis, A. V.

Publications and source records attributed to Tzingounis, A. V..

4 recordsLinked to original sources

bioRxiv2026

Spatial organization of voltage-gated ion channel expression across molecularly defined neuronal populations in the mouse mammillary bodies

The mammillary bodies (MB) are a hypothalamic component of the limbic Papez circuit that plays a critical role in spatial and episodic memory in mammals. Degeneration of the MB occurs in disorders associated with cognitive impairment, including Korsakoff's syndrome and Alzheimer's disease, yet the molecular organization and intrinsic properties of MB neurons remain poorly understood. Recent single-cell RNA sequencing identified multiple transcriptionally distinct neuronal populations within the MB and suggested that they differentially express voltage-gated ion channels that regulate neuronal excitability. Here, we used fluorescence in situ hybridization (FISH) to define the anatomical organization of cluster-enriched molecular markers and determine the spatial distribution of transcripts encoding voltage-gated sodium (NaV), potassium (KV), and hyperpolarization-activated cyclic nucleotide-gated (HCN) channels among defined subregions of the mouse MB. We found that marker transcripts occupy characteristic but partially overlapping spatial domains that broadly correspond to classical anatomical subdivisions. In addition, several ion channel transcripts, including Scn1a, Scn2a, Kcnq2, Kcnq3, and Hcn1, exhibited distinct patterns of enrichment across molecularly defined neuronal populations and MB subregions. Multiplex FISH further revealed unexpected co-expression of Scn1a and Scn2a within Pvalb-enriched neuronal populations, while whole-cell recordings demonstrated distinct intrinsic firing properties of neurons in the lateral and medial mammillary nuclei. Together, these findings establish a molecular framework linking neuronal population identity with voltage-gated ion channel expression in the MB and provide a foundation for future studies investigating how cell type-specific differences in intrinsic excitability contribute to memory function and neurological disease.

neuroscience↗

bioRxiv2025

Homeostatic Neuronal Plasticity Alters Axon Initial Segment Actin Membrane Skeleton Periodicity

Homeostatic plasticity allows neurons to maintain their activity around a set point, contributing to neuronal network stability over time. Increasing or decreasing neuronal activity not only regulates the levels of ion channels in neurons, but also leads to structural plasticity of the axon initial segment (AIS), the site of action potential initiation. Although previous studies have shown that activity could change the length and position of the AIS along the axon to compensate for changes in neuronal activity, it is currently unknown whether homeostatic plasticity also regulates the periodicity of the AIS actin cytoskeleton. Actin filaments, which are components of the axon plasma membrane skeleton, form periodic rings with a 190-nm spacing. Here, we examined whether the integrity of the actin ring periodicity at the AIS is plastic, depending on prolonged changes in neuronal activity. To induce AIS homeostatic plasticity, we either increased neuronal activity chronically by blocking the AIS enriched Kv7 voltage-gated potassium channels with XE991 or chronically decreased it by using the pan-Kv7 channel opener retigabine (RTG), or alternatively, the voltage-gated sodium channel blocker TTX at different neuronal maturation stages (DIV10 and DIV16). We found that prolonged exposure to XE991 relocated AIS away from soma and disrupted the periodicity of actin rings at DIV10. However, the actin ring periodicity remained unaffected at DIV16. In comparison, long-term treatment with RTG or TTX induced relocation of AIS towards the soma and reduction in AIS length, respectively. In parallel, RTG and TTX disrupted the actin ring periodicity at both developmental stages. These observations suggest that homeostatic plasticity not only changes the AIS position and length, but it could also modulate the periodicity of the AIS actin membrane skeleton, raising the possibility that the mechanical properties of the AIS are also plastic. Statement of significanceHomeostatic plasticity allows neurons to maintain their activity around a set point, contributing to neuronal network stability over time. Although previous studies have shown that activity could change the length and position of the AIS along the axon to compensate for changes in neuronal activity, it is currently unknown whether homeostatic plasticity also regulates the periodicity of the AIS actin cytoskeleton. Here, using super-resolution microscopy, we show that either blocking or activating Kv7 channels could disrupt the periodicity of actin depending on the maturation stage of cultured neurons. In comparison, blocking voltage-gated sodium channels disrupted the actin ring periodicity independent of the age of neurons. These observations suggest that homeostatic plasticity also modulates the periodicity of the AIS actin cytoskeleton.

biophysics↗

bioRxiv2021

The Okur-Chung Neurodevelopmental Syndrome (OCNDS) mutation CK2K198R leads to a rewiring of kinase specificity

Okur-Chung Neurodevelopmental Syndrome (OCNDS) is caused by heterozygous mutations to the CSNK2A1 gene, which encodes the alpha subunit of casein kinase II (CK2). The most frequently occurring mutation is lysine 198 to arginine (K198R). To investigate the impact of this mutation, we first generated a high-resolution phosphorylation motif of CK2WT, including the first characterization of specificity for tyrosine phosphorylation activity. A second high resolution motif representing CK2K198R substrate specificity was also generated. Here we report for the first time the impact of the OCNDS associated CK2K198R mutation. Contrary to prior speculation, the mutation does not result in a loss of function, but rather shifts the substrate specificity of the kinase. Broadly speaking the mutation leads to 1) a decreased preference for acidic residues in the +1 position, 2) a decreased preference for threonine phosphorylation, 3) an increased preference for tyrosine phosphorylation, and 4) an alteration of the tyrosine phosphorylation specificity motif. To further investigate the result of this mutation we have developed a probability-based scoring method, allowing us to predict shifts in phosphorylation in the K198R mutant relative to the wild type kinase. As an initial step we have applied the methodology to the set of axonally localized ion channels in an effort to uncover potential alterations of the phosphoproteome associated with the OCNDS disease condition.

neuroscience↗

bioRxiv2021

The periodic axon membrane skeleton leads to high-density sodium nanodomains but does not impact action potentials

Recent work has established that axons have a periodic skeleton structure comprising of azimuthal actin rings connected via longitudinal spectrin tetramer filaments. This structure endows the axon with structural integrity and mechanical stability. Additionally, voltage-gated sodium channels follow the periodicity of the active-spectrin arrangement, spaced [~]190 nm segments apart. The impact of this periodic sodium channel arrangement on the generation and propagation of action potentials is unknown. To address this question, we simulated an action potential using the Hodgkin-Huxley formalism in a cylindrical compartment but instead of using a homogeneous distribution of voltage-gated sodium channels in the membrane, we applied the experimentally determined periodic arrangement. We found that the periodic distribution of voltage-gated sodium channels does not significantly affect the generation or propagation of action potentials, but instead leads to high-density sodium channel nanodomains. This work provides a foundation for future studies investigating the role of the voltage-gated sodium channel periodic arrangement in the axon.

biophysics↗