Neuronal-Specific TUBB3 Is Not Required for Normal Neuronal Function but Is Essential for Timely Axon Regeneration

Abstract

SUMMARYWe generated a knockout mouse for the neuronalspecific β-tubulin isoform Tubb3 to investigate its role in nervous system formation and maintenance. Tubb3−/− mice have no detectable neurobehavioral or neuropathological deficits, and upregulation of mRNA and protein of the remaining β-tubulin isotypes results in equivalent total b-tubulin levels in Tubb3−/− and wild-type mice. Despite similar levels of total β-tubulin, adult dorsal root ganglia lacking TUBB3 have decreased growth cone microtubule dynamics and a decreased neurite outgrowth rate of 22% in vitro and in vivo. The effect of the 22% slower growth rate is exacerbated for sensory recovery, where fibers must reinnervate the full volume of the skin to recover touch function. Overall, these data reveal that, while TUBB3 is not required for formation of the nervous system, it has a specific role in the rate of peripheral axon regeneration that cannot be replaced by other β-tubulins.

Tubulin mutations in brain development disorders: Why haploinsufficiency does not explain TUBA1A tubulinopathies

“…Indeed, in channelopathy models where expression of one channel subunit is reduced, expression of similar channel subunits increases (Dahal et al, ). This result is reminiscent of recent findings revealing that when the β‐tubulin isotype Tubb3 is knocked out in mouse models, the expression of other β‐tubulin isotypes increases (Latremoliere et al, ).…”

“…Here, with a systemic loss of the single tubulin isotype, it was possible to study how losing Tubb3 impacts cellular β-tubulin isotype expression. Intriguingly, equivalent total β-tubulin mRNA and protein levels were observed in Tubb3 null mice (Latremoliere et al, 2018). Complete deletion of Tubb3, long thought to be a critical neuronal β-tubulin isotype, was readily compensated for via upregulation of the remaining neuronal β-tubulin isotypes.…”

“…Human TUBB3 mutations have been associated with a spectrum of developmental brain disorders and progressive neuropathy, and share many clinical features with TUBA1A-associated tubulinopathy (Tischfield, Cederquist, Gupta, & Engle, 2011). Greater flexibility afforded by the increased sequence divergence of β-tubulin isotypes has allowed researchers to generate Tubb3 knock-in mouse models of patient TUBB3 mutations as well as generate a full Tubb3 knock-out mouse (Latremoliere et al, 2018;Tischfield et al, 2010;Whitman & Engle, 2017). Tubb3-R262C homozygous knock-in mice exhibit lower Tubb3 protein levels, reduced heterodimer levels, altered microtubule stability, and decreased interactions with the kinesin motor Kif21a, resulting in axon guidance defects in vivo (Tischfield et al, 2010).…”

Cyclin-dependent-like kinase 5 is required for pain signalling in both human neurons and mouse models

“…Cdkl5 controls peripheral nociception 5 We found that altered pain sensitivity in their children was reported by 53.0% (122/230) of caregivers. Amongst these a total of 57.4% (70/122) specifically reported decreased pain sensitivity, 19.7% (24/122) specifically reported enhanced sensitivity and 22.9% (28/122) reported both. 202 caregivers provided specific responses including either reduced (70/202, 34.7%) or enhanced nociception (24/202, 11.9%) ( Table 1).…”

“…S3C-F), supporting the physiological relevance of our pool of interactors. Top ranked Cdkl5 co-immunoprecipitating proteins included CaMKIIα, putatively the strongest interactor of Cdkl5, and some proteins associated with the neuronal cytoskeleton, such as Myh10 (18), Tubb3 (19) and Dynch1h1 (20-23) ( fig. S3G).…”