Atoh1 Controls Primary Cilia Formation to Allow for SHH-Triggered Granule Neuron Progenitor Proliferation.

During cerebellar development, granule neuron progenitors (GNPs) proliferate by transducing Sonic Hedgehog (SHH) signaling via the primary cilium. Precise regulation of ciliogenesis, thus, ensures proper GNP pool expansion. Here, we report that Atoh1, a transcription factor required for GNPs formation, controls the presence of primary cilia, maintaining GNPs responsiveness to SHH. Loss of primary cilia abolishes the ability of Atoh1 to keep GNPs in a proliferative state. Mechanistically, Atoh1 promotes ciliogenesis by transcriptionally regulating Cep131, which facilitates centriolar satellite (CS) clustering to the basal body. Importantly, ectopic expression of Cep131 counteracts the effects of Atoh1 loss in GNPs by restoring proper localization of CS and ciliogenesis. This Atoh1-CS-primary cilium-SHH pro-proliferative pathway is also conserved in SHH-type medulloblastoma, a pediatric brain tumor arising from the GNPs. Together, our data reveal how Atoh1 modulates the primary cilium to regulate GNPs development.

Identification of genes associated with cortical malformation using a transposon-mediated somatic mutagenesis screen in mice.

Mutations in genes involved in the production, migration, or differentiation of cortical neurons often lead to malformations of cortical development (MCDs). However, many genetic mutations involved in MCD pathogenesis remain unidentified. Here we developed a genetic screening paradigm based on transposon-mediated somatic mutagenesis by in utero electroporation and the inability of mutant neuronal precursors to migrate to the cortex and identified 33 candidate MCD genes. Consistent with the screen, several genes have already been implicated in neural development and disorders. Functional disruption of the candidate genes by RNAi or CRISPR/Cas9 causes altered neuronal distributions that resemble human cortical dysplasia. To verify potential clinical relevance of these candidate genes, we analyzed somatic mutations in brain tissue from patients with focal cortical dysplasia and found that mutations are enriched in these candidate genes. These results demonstrate that this approach is able to identify potential mouse genes involved in cortical development and MCD pathogenesis.

Lis1 dysfunction leads to traction force reduction and cytoskeletal disorganization during cell migration.

Cell migration is a critical process during development, tissue repair, and cancer metastasis. It requires complex processes of cell adhesion, cytoskeletal dynamics, and force generation. Lis1 plays an important role in the migration of neurons, fibroblasts and other cell types, and is essential for normal development of the cerebral cortex. Mutations in human LIS1 gene cause classical lissencephaly (smooth brain), resulting from defects in neuronal migration. However, how Lis1 may affect force generation in migrating cells is still not fully understood. Using traction force microscopy (TFM) with live cell imaging to measure cellular traction force in migrating NIH3T3 cells, we showed that Lis1 knockdown (KD) by RNA interference (RNAi) caused reductions in cell migration and traction force against the extracellular matrix (ECM). Immunostaining of cytoskeletal components in Lis1 KD cells showed disorganization of microtubules and actin filaments. Interestingly, focal adhesions at the cell periphery were significantly reduced. These results suggest that Lis1 is important for cellular traction force generation through the regulation of cytoskeleton organization and focal adhesion formation in migrating cells.