Mutations in the murine homologue ofTUBB5cause microcephaly by perturbing cell cycle progression and inducing p53 associated apoptosis

Abstract

Microtubules play a crucial role in the generation, migration and differentiation of nascent neurons in the developing vertebrate brain. Mutations in the constituents of microtubules, the tubulins, are known to cause an array of neurological disorders, including lissencephaly, polymicrogyria and microcephaly. In this study we explore the genetic and cellular mechanisms that cause TUBB5-associated microcephaly by exploiting two new mouse models: a conditional E401K knock-in, and a conditional knockout animal. These mice present with profound microcephaly due to a loss of upper-layer neurons that correlates with massive apoptosis and upregulation of p53. This phenotype is associated with a delay in cell cycle progression and ectopic DNA elements in progenitors, which is dependent on the dosage of functional Tubb5. Strikingly, we report ectopic Sox2-positive progenitors and defects in spindle orientation in our knock-in mouse line, which are absent in knockout animals. This work sheds light on the functional repertoire of Tubb5, reveals that the E401K mutation acts by a complex mechanism, and demonstrates that the cellular pathology driving TUBB5-associated microcephaly is cell death.

Genetics and mechanisms leading to human cortical malformations

“…;Nestin-Cre), both presented significant reductions in total brain and cortical volume. Other brain regions were also affected, including the corpus callosum, cerebellum, hippocampus and putamen [186]. No major defects in the laminar structure of the cortex were detected, despite a significant reduction in Cux1-positive superficial neurons.…”

“…In order to analyze the effects of TUBB5 (also termed TUBB) during cortical development, the generation of two conditional Tubb5 transgenic mouse lines were reported: a conditional knock-in of the E401K patient mutation and a conditional KO [186]. Both lines were generated by crossing with Nestin-Cre mice to drive expression in progenitors.…”

In Vitro, Ex Vivo and In Vivo Techniques to Study Neuronal Migration in the Developing Cerebral Cortex

“…Altogether, gene function studies performed via in utero electroporation led to the discovery of novel genes implicated in the aetiology of neurodevelopmental disorders (for examples, refer to [13,87,88,89,90]) and provide an experimental platform to investigate genetic interactions and molecular mechanisms underpinning the cellular activities of such genes.…”

Ade novomissense mutation inTUBA1Aresults in reduced neural progenitor survival and differentiation

“…Similarly, recent findings on the b-tubulin gene TUBB5 show that alterations in mitotic spindle orientation can also result in a shift from cell survival to cell death (Breuss et al, 2016). Taken together, reduced cell survival and neuron production seem to be common features of tubulin mutations leading to cortical malformations of development.…”