Deletion of the Actin-Associated Tropomyosin Tpm3 Leads to Reduced Cell Complexity in Cultured Hippocampal Neurons—New Insights into the Role of the C-Terminal Region of Tpm3.1

Abstract

Tropomyosins (Tpms) have been described as master regulators of actin, with Tpm3 products shown to be involved in early developmental processes, and the Tpm3 isoform Tpm3.1 controlling changes in the size of neuronal growth cones and neurite growth. Here, we used primary mouse hippocampal neurons of C57/Bl6 wild type and Bl6Tpm3flox transgenic mice to carry out morphometric analyses in response to the absence of Tpm3 products, as well as to investigate the effect of C-terminal truncation on the ability of Tpm3.1 to modulate neuronal morphogenesis. We found that the knock-out of Tpm3 leads to decreased neurite length and complexity, and that the deletion of two amino acid residues at the C-terminus of Tpm3.1 leads to more detrimental changes in neurite morphology than the deletion of six amino acid residues. We also found that Tpm3.1 that lacks the 6 C-terminal amino acid residues does not associate with stress fibres, does not segregate to the tips of neurites, and does not impact the amount of the filamentous actin pool at the axonal growth cones, as opposed to Tpm3.1, which lacks the two C-terminal amino acid residues. Our study provides further insight into the role of both Tpm3 products and the C-terminus of Tpm3.1, and it forms the basis for future studies that aim to identify the molecular mechanisms underlying Tpm3.1 targeting to different subcellular compartments.

Cofilin and Actin Dynamics: Multiple Modes of Regulation and Their Impacts in Neuronal Development and Degeneration

“…It seems likely that, in addition to these mechanisms, some direct modifications of actin within a filament or an interplay with other F-actin binding partners sort out Tpm isoform specificity. One such possibility is through specific lysine modifications on actin catalyzed by different lysine acetyltransferases (KATs) [177]. Of course, this just pushes our understanding further down the road since the question then becomes "how do KATs recognize the different filaments for modification?…”

“…A specific KAT acetylates K50 and K61 on actin [185]. More than 20 different KATs have been identified based on sequence homology [177], suggesting that KAT/KDAC mediated modifications of F-actin might form an "actin code" that can modulate actin assembly pools differentially. HDAC6 plays an important role in neuronal polarity and, in AD, possibly by increasing Hsp90 acetylation and/or tau phosphorylation [274,275].…”

“…Determining if different actin KATs modify filaments in ways that allow differential binding of specific isoforms of Tpms, coronins, or ADF/cofilins is also of importance. There are 19 lysines on cytoplasmic actins, at least seven of which have been reported to be acetylated [177].…”

A novel DNA damage repair-related gene signature predicting survival, immune infiltration and drug sensitivity in cervical cancer based on single cell sequencing

“…TPM is a filamentous actin-binding protein that can bind to actin. TPM3 is an important member of the TPM family and stabilizes the cell skeleton microfilaments ( 33 ). Studies on glioma, colon cancer, and liver cancer have shown that TPM3 affects tumor occurrence and development through gene fusion and epithelial-mesenchymal transition (EMT), and has high expression levels ( 34 ).…”

Overexpression of Tropomyosin Isoform Tpm3.1 Does Not Alter Synaptic Function in Hippocampal Neurons

“…Pharmacological inhibition of Tpm3.1/2 has been found to decrease the uniformity of actin rings in axons, reduce the accumulation of proteins at the axon initial segment, and reduce the action potential firing frequency [19]. Knockout of Tpm3.1 reduces branching and the total neurite length in developing neurons [20].…”