Biology subjects

Falzone, T. L.

Publications and source records attributed to Falzone, T. L..

3 recordsLinked to original sources

bioRxiv2026

Tau isoforms modulate the axon initial segment controlling axonal trafficking and neuronal excitability

The axon initial segment (AIS) is a specialized neuronal compartment integrating action potential initiation with selective control of axonal trafficking. The microtubule associated protein tau is a central regulator of cytoskeletal organization and transport, yet how distinct tau isoforms contribute to AIS development and function remains unclear. Here, we examined the role of tau isoform relative abundance in regulating AIS establishment, maturation, excitability, and transport selectivity using murine primary neurons and human induced pluripotent stem cell (hiPSC)-derived neurons combined with super resolution imaging, electrophysiology, and live trafficking assays. We found that tau expression levels and isoform content modulate the timing and robustness of AIS maturation. In murine neurons, tau deficiency or predominance of 3 repeat (3R) tau delays Ankyrin G accumulation and AIS stabilization without preventing AIS formation. hiPSC-derived neurons display an intrinsic AIS developmental program accompanied by progressive changes in tau isoform content. Super resolution DNA PAINT reveals that endogenous tau decorates axonal microtubules in discrete nanoclusters with compartment specific distributions. Modulation of the endogenous 3R/4R tau balance in hiPSC-derived neurons shows that isoform composition, independently of tau levels, regulates AIS positioning and Ankyrin G organization. Functionally, shifts towards 3R-tau reduce sodium currents, impair action potential firing, and alter lysosomal transport dynamics within the AIS. Together, these findings identify tau isoform balance as a developmental regulator of AIS maturation, linking cytoskeletal organization to neuronal excitability and transport gating. Because the aberrant alternative tau splicing of exon 10 is a defining feature of primary tauopathies, our results provide mechanistic insight into how imbalanced tau isoforms may contribute to neuronal dysfunction.

cell biology↗

bioRxiv2026

Huntingtin is a cell-autonomous regulator of neuropeptide trafficking and clock output

Huntingtons disease is a severe neurodegenerative condition arising from an abnormal CAG repeat expansion in the HTT gene, which leads to the production of a mutant Huntingtin protein carrying an extended polyglutamine stretch. Although the field has largely centred on the toxic effects gained by this mutant protein, growing evidence points to the loss of normal wild-type Huntingtin function as an additional contributor to disease progression. Despite this, the cell-intrinsic roles of wild-type Huntingtin in neuronal biology remain poorly defined, in part because disentangling its specific contributions from broader network-level effects has proven technically challenging. To address this knowledge gap, we took advantage of the Drosophila huntingtin homolog (htt) and selectively manipulated its expression in the small lateral ventral neurons (sLNvs), a discrete cluster of just eight circadian pacemaker neurons that govern behavioral rhythmicity and sleep. Through targeted genetic knock-down, we show that reducing htt levels in sLNvs weakens the robustness of free-running circadian rhythms and substantially increases sleep in female flies. These behavioral changes are not rooted in developmental abnormalities, as restricting htt knock-down to adult flies reproduces the sleep phenotype across both beam-crossing and video-based locomotion assays. At the cellular level, htt loss disrupts dense core vesicle trafficking along sLNv axons, altering the fraction of motile vesicles and their velocity, and abolishing the time-of-day-dependent fluctuations in vesicle dynamics observed in these neurons. Complementary electrophysiological recordings using whole-cell patch-clamp further reveal that htt knock-down lowers action potential firing rates without perturbing resting membrane potential. Together, these results identify huntingtin as a cell-autonomous regulator of neuropeptide trafficking, neuronal excitability and circadian output. Beyond advancing our understanding of wild-type huntingtin physiology, this work carries direct relevance for HD therapeutic strategies, particularly those involving huntingtin-lowering approaches, by highlighting functions that may be unintentionally compromised.

neuroscience↗

bioRxiv2021

DYRK1A role in microtubule-based axonal transport regulates the retrograde dynamics of APP vesicles in human neurons

In Alzheimers Disease (AD) the abnormal intracellular distribution of the amyloid precursor protein (APP) affects its processing and, consequently, the generation of A{beta}. Axonal transport plays key roles in the neuronal distribution of APP. The dual-specificity-tyrosine phosphorylation-regulated-kinase-1A (DYRK1A) has been associated with AD onset since its overexpression was found in Down syndrome and sporadic AD patients. Experimental evidence confirmed that APP and tau phosphorylations are mediated by DYRK1A. Moreover, DYRK1A can regulate the cytoskeletal architecture by phosphorylation of both tubulin subunits and microtubule-associated proteins. Therefore, we tested whether DYRK1A has a role in APP axonal transport regulation. We developed highly-polarized human-derived neurons in 2D cultures. At day 14 after terminal plating we inhibited DYRK1A for 48hs with harmine (7.5 M). DYRK1A overexpression was induced to perform live-cell imaging of APP-loaded vesicles in axons and analyzed transport dynamics. A custom-made MATLAB routine was developed to track and analyze single particle dynamics. Short-term harmine treatment reduced axonal APP vesicles density, due to a reduction in retrograde particles. Contrarily, DYRK1A overexpression enhanced axonal APP density, due to an increase in the retrograde and stationary component. Moreover, both harmine-mediated DYRK1A inhibition and DYRK1A overexpression revealed opposite phenotypes on single particle dynamics, affecting primarily dynein processivity. These results revealed an increased retrieval of distal APP vesicles in axons when DYRK1A is overexpressed and reinforce the suggestion that DYRK1A enhance APP endocytosis.. Taken together our results suggest that DYRK1A has a relevant role in the regulation of axonal transport and sub-cellular positioning of APP vesicles. Therefore, our work shed light on the role of DYRK1A in axonal transport regulation, and the putative use of harmine to restore axonal transport impairments.

neuroscience↗