Tubb3 expression levels are sensitive to neuronal activity changes and determine microtubule growth and kinesin-mediated transport

Abstract

Microtubules are dynamic polymers of α/β-tubulin. They regulate cell structure, cell division, cell migration, and intracellular transport. However, functional contributions of individual tubulin isotypes are incompletely understood. The neuron-specific β-tubulin Tubb3 displays highest expression around early postnatal periods characterized by exuberant synaptogenesis. Although Tubb3 mutations are associated with neuronal disease, including abnormal inhibitory transmission and seizure activity in patients, molecular consequences of altered Tubb3 levels are largely unknown. Likewise, it is unclear whether neuronal activity triggers Tubb3 expression changes in neurons. In this study, we initially asked whether chemical protocols to induce long-term potentiation (cLTP) affect microtubule growth and the expression of individual tubulin isotypes. We found that growing microtubules and Tubb3 expression are sensitive to changes in neuronal activity and asked for consequences of Tubb3 downregulation in neurons. Our data revealed that reduced Tubb3 levels accelerated microtubule growth in axons and dendrites. Remarkably, Tubb3 knockdown induced a specific upregulation of Tubb4 gene expression, without changing other tubulin isotypes. We further found that Tubb3 downregulation reduces tubulin polyglutamylation, increases KIF5C motility and boosts the transport of its synaptic cargo N-Cadherin, which is known to regulate synaptogenesis and long-term potentiation. Due to the large number of tubulin isotypes, we developed and applied a computational model based on a Monte Carlo simulation to understand consequences of tubulin expression changes in silico. Together, our data suggest a feedback mechanism with neuronal activity regulating tubulin expression and consequently microtubule dynamics underlying the delivery of synaptic cargoes.

Expanding the genetics and phenotypes of ocular congenital cranial dysinnervation disorders

“…Moreover, downregulation of the oCCDD gene TUBB3 increases KIF5C motility and cargo transport. 33 While this is an intriguing candidate, all pedigrees with KIF5C variants in our cohort are singletons, and the syndromic phenotypes in the two DRS probands are disparate from one another and from known KIF5C -associated syndromic findings.…”

Taxol acts differently on different tubulin isotypes

“…β3 tubulin is largely neuron-specific. Recent work indicates that downregulating human tubulin β3 boosts kinesin motility in neurons (without taxol) 44 . Perhaps relatedly, we see in vitro that a small decrease in the proportion of α1β3 tubulin in α1β3: α1β4 mixed isotype microtubules substantially accelerates kinesin transport in the presence of 10 μM taxol ( Fig.…”

Taxol acts differently on different tubulin isotypes

“…In neurons, kinesin-1 is a processive, axon-speci c transporter of neurotransmitter vesicles. β3 tubulin is largely neuron-speci c. Recent work indicates that downregulating human tubulin β3 boosts kinesin motility in neurons (without taxol) 44 . Perhaps relatedly, we see in vitro that a small decrease in the proportion of α1β3 tubulin in α1β3:α1β4 mixed isotype microtubules substantially accelerates kinesin stepping in 10 µM taxol (Fig.…”