Organelle distribution and protein translation defects in radial glia cells with mutations in Eml1

Cerebral cortical development is a finely regulated process, depending on key neuronal progenitors, giving rise to post-mitotic neurons that migrate to superficial regions in the developing brain. Disruptions can give rise to severe cortical malformations that are associated with intellectual disability and intractable epilepsy. Mutations in EML1/Eml1, coding for a microtubule (MT)-associated protein, lead to subcortical heterotopia (SH) in both humans and mice. In developing mutant mouse brains, ectopic apical radial glia (aRG) progenitors were found outside the normal proliferative ventricular zone (VZ). The normal role of Eml1 in these cells remains to be precisely determined. Using proteomics and imaging approaches, we compared brain tissue from control and mutant mice and identified microtubule and organelle dysregulation. Eml1 influences the trafficking of organelles to different compartments of aRG, where they may be involved in local functions. Thus, we find that mitochondrial and polysome distribution are altered in mutant conditions. Indeed, Eml1 interacts with translational machinery, and an overall downregulation of translation is observed when analysing the translatome of Eml1 mutant aRG. Paradoxically, an upregulation of translation-related mRNAs is also observed. These new data uncover an unprecedented function of Eml1, as well as associating novel subcellular patho-mechanisms with severe heterotopia formation.