Mechanism of Action of the Lissencephaly Gene LIS-1

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Type I lissencephaly is a severe brain developmental disease which involves defects in neural progenitor cell migration during the formation of the cerebral cortex. It is caused by LIS1 haploinsufficiency, resulting from sporadic mutations in the LIS1 gene. LIS1 has been implicated in the platelet activating factor and cytoplasmic dynein pathways, but current evidence suggests that defects in the latter are responsible for the brain developmental disease. Work from this lab has indicated that LIS1 functions together with cytoplasmic dynein at kinetochores and the cortex of dividing cells, at the leading edge of migrating fibroblasts, and during growth cone remodeling. Recent results from this lab have identified severe effects of LIS1 RNAi on the behavior of neural progenitor cells from neurogenesis through the entire course of radial migration by live imaging of brain slices. Aim I of this project will be to characterize further functional interactions between LIS1 and cytoplasmic dynein and their mutual binding partners NudE, and NudEL. The role of protein phosphorylation in regulating these interactions, and the effects of LIS1, NudE, and NudEL on dynein mechanochemical activity will be'determined. Aim II will be to define the role of LIS1, NudE and NudEL in the morphogenesis and locomotion of bipolar neural progenitors. Aim III will be to define the role of LIS1, NudE and NudEL in the interkinetic nuclear oscillations and cell division cycle of neural progenitor cells at the radial glial stage. Live imaging of embryonic rodent brain slices and isolated neural progenitors will be performed on control, mutant, or RNAi-treated animals to evaluate effects on nucleokinesis, cell division, control of division by nuclear position, glial guided migration, and process dynamics. The behavior of the microtubule cytoskeleton, centrosomes, nuclei, LIS1, NudE, and NudEL will be monitored to understand the underlying cellular causes for observed brain phenotypic effects. These studies are of considerable relevance to understanding normal and abnormal brain development, cell migration, cell division, the causes of mental retardation, and stem cell behavior.