In order for the brain to develop with proper size and structure, neural stem cells (NSCs) at early ages must make proliferative divisions and maintain their stemness to expand the stem cell pool, but then switch to undergo neurogenic divisions at the correct time to create neurons. However, the mechanism of this fate choice from remaining an NSC early on, to later choosing to exit the cell cycle and become a neuron, is still poorly understood. The last step of cell division is abscission, which severs the daughter from the mother cell. Abscission occurs during the time when the fate decision is made, and at the apical membrane, where many fate signals are located. We developed methods and tools to quantitatively analyze abscission in cortical NSCs, in vivo and in vitro. We found that abscission is not simply necessary to cut cells apart and keep them alive. Rather, we made the surprising discovery that both abscission duration and remnants of abscission (midbody remnants) are developmentally regulated, changing as development proceeds. Furthermore, we found that a small-brained mouse mutant with altered abscission duration has a reduced proportion of proliferative NSC divisions. These data led to our central hypothesis that changes in abscission duration and midbody remnant persistence can shift NSC daughter cells fate choices as development proceeds. We will test this hypothesis through the use of innovative genetic and cell biological approaches, on single NSC divisions and whole tissue analyses. We will utilize two mouse mutants that perturb abscission specifically, affecting duration and midbody remnants differentially. We will carry out three Specific Aims: 1) test whether abscission duration is correlated with daughter cell fate outcomes in vitro, 2) dissect the primary and secondary effects of dysregulated abscission on cortical NSC daughter cell fates, morphologies and lineage progression in vivo, and 3) investigate a candidate signaling mechanism at the apical membrane that could link abscission regulation to stem cell maintenance. The contributions of the proposed research will be to increase understanding of the fundamental question of how stem cells in developing tissues maintain high proliferative capacity early and then reduce it later in favor of differentiated daughter cell types. It will also elucidate how regulation of NSC divisions affect daughter cell fates, structures, and subsequent divisions. These contributions will be significant because they will reveal novel mechanisms and gene pathways that regulate how brain size and structure are controlled, and will elucidate how specific alterations in NSC division mechanisms during development can lead to brain malformations, or other neurodevelopment phenotypes.
The proposed research is relevant to public health because neurodevelopmental disorders such as brain malformations, epilepsy, or autism can be caused by abnormal stem cell divisions in the developing brain. The outcomes will be relevant to the mission of NINDS to reduce the burden of neurological disease. The fundamental knowledge gained will additionally impact many other areas of biology and health such as development or cancers of other organs.
