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Title: Towards an understanding of the role of Ca2+ signalling in neural stem cell activation
Author: Zhao, Mo
ISNI:       0000 0004 7968 503X
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2019
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Regeneration of the adult human brain is a long time clinical challenge. The adult mammalian brain contains neural stem cells (NSCs) that are capable of brain repair, but they are mostly in a mitotically quiescent state. Identifying novel regulators of neural stem cell quiescence will provide more molecular targets for brain regeneration therapies. Drosophila melanogaster is an excellent model for understanding NSC quiescence. The NSCs in Drosophila transit between quiescence and proliferation. The transcriptional profiles of quiescent and active NSCs have been determined, which reveal genes that are specifically expressed during quiescence. In this project, I analysed two quiescence- specific genes, slowpoke and mulet, in the context of NSC quiescence and activation. I also investigated if the adult Drosophila brain contained quiescent NSCs. Slowpoke is the α subunit of Big-Potassium channel that is required in neurons for membrane potential repolarisation. I have shown that it is required for NSC activation. Loss of Slo in NSCs significantly extends the life span of neuroblasts, leading many of them to persist until adulthood. Slo acts largely independent of the insulin signalling pathway, a canonical pathway required for NSC activation. Since Slo is a negative regulator of Ca2+ signalling, I investigated Ca2+ levels in quiescent and active NSCs. I have found that quiescent NSCs have significantly higher intracellular Ca2+ compared to active NSCs. Upregulation of intracellular Ca2+ phenocopies loss of Slo, repressing NSC activation. The second quiescence-specific gene I have assayed is mulet, a tubulin cofactor that destabilises microtubule. I have shown that in NSCs, mulet expresses exclusively at the quiescent stage. Loss of mulet results in growth defects at the whole organismal level, but does not affect NSC quiescence and activation. Therefore, mulet can be used as a marker for quiescent NSCs, although its function in regulating quiescence is yet unclear. I hypothesised that astrocytes in the adult Drosophila brain were quiescent NSCs as some of them expressed the NSC marker, deadpan. In rodents, adult NSCs are astrocytes that can be triggered into proliferation by brain hyperactivation. I have found that hyperactivation of astrocytes, but not neurons, triggers cell cycle re-entry in the adult Drosophila brain. The cells that re-enter the cell cycle are mostly glia. However, these cells are arrested in the cell cycle and do not proceed to proliferate. Therefore, I have not found evidence that astrocytes function as NSCs in the adult Drosophila brain.
Supervisor: Brand, Andrea Sponsor: China Scholarship Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Neural stem cell ; neuroblasts ; quiescence ; Calcium signalling ; Drosophila development