Abstract
De novo heterozygous missense variants in the γ-tubulin gene TUBG1 have been linked to human malformations of cortical development associated with intellectual disability and epilepsy. Here, we investigated through in-utero electroporation and in-vivo studies, how four of these variants affect cortical development. We show that TUBG1 mutants affect neuronal positioning, disrupting the locomotion of new-born neurons but without affecting progenitors’ proliferation. We further demonstrate that pathogenic TUBG1 variants are linked to reduced microtubule dynamics but without major structural nor functional centrosome defects in subject-derived fibroblasts. Additionally, we developed a knock-in Tubg1Y92C/+ mouse model and assessed consequences of the mutation. Although centrosomal positioning in bipolar neurons is correct, they fail to initiate locomotion. Furthermore, Tubg1Y92C/+ animals show neuroanatomical and behavioral defects and increased epileptic cortical activity. We show that Tubg1Y92C/+ mice partially mimic the human phenotype and therefore represent a relevant model for further investigations of the physiopathology of cortical malformations.
Highlights
De novo heterozygous missense variants in the γ-tubulin gene TUBG1 have been linked to human malformations of cortical development associated with intellectual disability and epilepsy
To investigate the effect of pathogenic TUBG1 variants on neuronal positioning in vivo, we used in utero electroporation to induce overexpression of the four pathogenic variants (Fig. 1a) under the control of a CAG promoter, together with a GFPencoding reporter in progenitors
Mice cortices were electroporated at E14.5 and the distribution of electroporated cells was analyzed after 4 days
Summary
To our data at E18.5, abnormally localized cells in the white matter express only upper-layer markers (Fig. 1e and Supplementary Fig. 1e). This indicates that the phenotype is not a transient phenomenon and is probably due to an arrest rather than a delay in neuronal migration. Downregulation of Tubg[1] leads to misplacement of neurons, which at E18.5 are mainly localized in the IZ This phenotype was significantly recovered when WT-TUBG1 was expressed but barely modified by TUBG2 co-expression, and even accentuated by co-electroporation of TUBG1-Tyr92Cys (Supplementary Fig. 2c). TUBG2 rescue was significant for other mutants (Supplementary Fig. 2e) These results suggest limited functional overlap between the two isoforms during cortical development
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