Biology subjects

Fath, T.

Publications and source records attributed to Fath, T..

4 recordsLinked to original sources

bioRxiv2025

Fluorescence recovery after photobleaching reveals different 1 behaviour2 of tropomyosin isoforms Tpm3.1 and Tpm4.2 in dendritic spines

Actin is the predominant cytoskeletal structure in both the pre- and the post-synaptic compartment of excitatory synapses in the brain, which are formed between the distal part of the axon and the distal site of dendritic spines. Tropomyosin (Tpm) is regarded a master regulator of actin dynamics in mammalian cells. Tpm isoforms, found in neurons are encoded by the Tpm1, Tpm3 and Tpm4 genes, and have a distinct temporal and spatial distribution of expression. Tpm3 and Tpm4 gene products have been found to segregate to the postsynaptic region of central nervous system synapses. Functional differences between Tpm3.1 and Tpm4.2 in neurons have been reported in previous studies. However, these were lacking a detailed analysis of the molecular mobility and dynamics of these two Tpm isoforms in the dendritic compartment. Here, we investigated the kinetic properties of Tpm3.1 and Tpm4.2 via a Fluorescent Recovery After Photobleaching (FRAP) approach and have discovered that Tpm3.1 and Tpm4.2 have distinct kinetic features in dendritic spines. Moreover, we investigated the dynamics of actin in the presence of either Tpm3.1 or Tpm4.2 isoform overexpression, using F-tractin as a reporter of filamentous actin. We have shown that the kinetics of actin turnover is significantly different in response to Tpm3.1 overexpression when compared the actin turnover in response to Tpm4.2 overexpression. Our study further elucidates the roles of Tpm3.1 and Tpm4.2 and provides important conclusions for future studies that are focused on discerning the molecular pathways of Tpm3.1 and Tpm4.2 segregation into different neuronal compartments.

cell biology↗

bioRxiv2025

Knock-out of Tpm4.2/actin filaments alters neuronal signaling, neurite outgrowth and behavioral phenotypes in mice.

Tropomyosins (Tpm) are master regulators of actin dynamics through forming co-polymers with filamentous actin. Despite the well-understood function of muscle Tpms in the contractile apparatus of muscle cells, much less is known about the diverse physiological function of cytoplasmic Tpms in eukaryotic cells. Here, we investigated the role of the Tpm4.2 isoform in neuronal processes including signaling, neurite outgrowth and receptor recycling using primary neurons from Tpm4.2 knock-out mice. Live imaging of calcium and electro-physiology data demonstrated increased frequency, yet reduced strength of single neuron spikes. Calcium imaging further showed increase in neuronal networks. In vitro assays of Tpm4.2 knock-out neurons displayed impaired recycling of the AMPA neurotransmitter receptor subunit GluA1. Morphometric analysis of neurite growth showed increased dendritic complexity and altered dendritic spine morphology in Tpm4.2 knock-out primary neurons. Behavioral analysis of Tpm4.2 knock-out mice displayed heightened anxiety in Open field test whilst Elevated Plus maze displayed heightened anxiety only in females. A sex-dependent phenotype was also seen in the Social Preference test with impaired social memory and socialization in female Tpm4.2 knock-out mice, whilst male and female knock-out mice had impaired recognition memory in a Novel Object Recognition test. Our study depicts the multi-faceted role of the Tpm4.2 isoform and its co-polymer F-actin population in neurons, with potential implications for better understanding diseases of the nervous system which involve actin cytoskeleton dys-function.

neuroscience↗

bioRxiv2023

Dysregulated actin dynamics and cofilin correlate with TDP-43 pathology in sporadic amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal, rapidly progressive neurodegenerative disorder affecting motor neurons, that overlaps significantly with frontotemporal dementia (FTD). Most cases are sporadic (90%) with undefined aetiology, but pathological forms of TAR-binding protein 43 (TDP-43), involving its misfolding, aggregation and mislocalisation from the nucleus to the cytoplasm, are present in motor neurons in almost all cases (97%) and [~]45% FTD cases. Actin is the most abundant protein in eukaryotic cells, with structural roles in the cytoskeleton and diverse signalling functions. This includes neuronal-specific roles in dendritic spines, synapses, axonal growth cones, and plasticity. Actin is in constant dynamic equilibrium between two forms: free monomeric, globular actin (G-actin) and polymeric, filamentous actin (F-actin). Actin dynamics is regulated by several key actin-binding proteins, including tropomyosin 4.2 (Tpm4.2) and cofilin, which depolymerises actin filaments. Cofilin is activated by phosphorylation at Ser3 via LIM domain kinase1/2 (LIMK1/2), which is also regulated by phosphorylation via Rac1/cdc42. Here we demonstrate that actin dynamics is closely associated with pathological TDP-43 in ALS. More F-actin relative to G-actin was detected in lumbar spinal cords from both sporadic ALS patients and a mouse model displaying TDP-43 pathology (rNLS), and in neuronal cells expressing cytoplasmic TDP-43. Hence actin dynamics is dysregulated in sporadic ALS, resulting in more actin polymerization. We also detected increased levels of Tpm 4.2, Rac1/cdc42, and increased phosphorylation of both LIMK1/2 and cofilin, in sporadic ALS patients. TDP-43 also physically interacted with actin in vitro and in cell lysates, providing additional insights into actin dysregulation in ALS. rNLS mice display motor neuron loss and key ALS/MND behavioural phenotypes, and increased cofilin phosphorylation was also detected in these animals at symptom onset, implying that actin dynamics actively contributes to neurodegeneration. Moreover, pharmacological induction of actin polymerization produced features typical of pathological TDP-43 (cytoplasmic mis-localisation and formation of inclusions and stress granules) implying that actin dysregulation contributes to TDP-43 pathology in ALS. Importantly, we also detected more cofilin phosphorylation in spinal motor neurons from sporadic patients compared to healthy controls, revealing that our observations are clinically relevant and present in the relevant cell type. This study therefore identifies dysregulated actin dynamics as a novel disease mechanism associated with TDP-43 pathology and hence most ALS cases. It also implies that regulating cofilin or LIMK1/2 phosphorylation may be a novel therapeutic strategy in ALS, FTD and other diseases involving TDP-43 pathology.

neuroscience↗

bioRxiv2019

Tropomyosin Tpm3.1 is required to maintain the structure and function of the axon initial segment

The axon initial segment (AIS) is the site of action potential initiation and serves as a vesicular filter and diffusion barrier that help maintain neuronal polarity. Recent studies have revealed details about a specialized structural complex in the AIS. While an intact actin cytoskeleton is required for AIS formation, pharmacological disruption of actin polymerization compromises the AIS vesicle filter but does not affect overall AIS structure. In this study, we found that the tropomyosin isoform Tpm3.1 decorates a population of relatively stable actin filaments in the AIS. Inhibiting Tpm3.1 in cultured hippocampal neurons led to the loss of AIS structure, the AIS vesicle filter, the clustering of sodium ion channels, and reduced firing frequency. We propose that Tpm3.1-decorated actin filaments form a stable actin filament network under the AIS membrane which provides a scaffold for membrane organization and AIS proteins.

neuroscience↗