Cell Lineage and Brain Development
Our objective is to understand where brains come from. More specifically, we aim to reveal the mechanisms underlying the emergence of primitive neural stem cells from the pluripotent embryonic stem (ES) cells of the mammalian blastocyst. Furthermore, we plan to address the questions of how the neural stem cell fate is maintained, how definitive (brain derived) neural stem cells acquire regional identity, and whether this regional identity (and indeed even the neural stem cell state itself) is plastic.
Four specific hypotheses will be tested...
1. The default state for ES cells is to become neural stem cells. The test of this hypothesis will involve a screen for genes that are expressed during and may be functionally important for the in vitro transition from ES cells to neural stem cells. Will all of the identified candidates work to inhibit this transition (as predicted by the default hypothesis) or will some actually facilitate the transition when tested experimentally?
2. Some cell death genes selectively act on primitive neural stem cells. The first gene to come through our genetic screen (#1 above) increases the numbers of neural stem cells emerging from ES cells by twenty fold when mutated. The hypothesis will be tested by comparing a number of ES cell mutations in cell death genes in terms of their effects on the survival of ES cells versus the survival of the primitive neural stem cells that emerge from these ES cells.
3. The Notch signalling pathway serves to maintain the neural stem cell state. Preliminary data suggest that mutations in this pathway appear not to effect the initial determination of neural stem cells, but result in a later depletion of embryonic and adult neural stem cells. We will test the in vivo and in vitro self-renewal ability of embryonic and adult neural stem cells in mice with homozygous and heterozygous mutations of genes in the Notch signalling pathway.
4. Primitive (ES derived) neural stem cells show considerable non-neural tissue plasticity. However, definitive (brain derived) neural stem cells have less non-neural tissue plasticity, but still show plasticity in their commitment to a neural regional fate along the anterioposterior neuraxis. The possible non-neural tissue fates of neural stem cells will be tested in blastocyst chimeric mice and the neuraxis regional fates of neural stem cells will be tested in slice cocultures and with in vivo transplantation.
Related Publications
Clarke, L., van der Kooy, D. The adult mouse dentate gyrus contains populations of committed progenitor cells that are distinct from subependymal zone neural stem cells. Stem Cells 29 (2011) 1448-58. (clarke...2011...)
Akamatsu, W., Cooney, A.J., van der Kooy, D. Suppression of Oct4 by germ cell nuclear factor promotes the development of the early neural stem cell lineage. Journal of Neuroscience. 29 (2009) 2113-2124. (akamatsu...2009...)
Smukler SR, Runciman SB, Xu S, van der Kooy D. Embryonic stem cells assume a primitive neural stem cell fate in the absence of extrinsic influences. Journal of Cell Biology 172 (2006) 79-90. (smukler...2006...)
Hitoshi S, Seaberg RM, Koscik C, Alexson T, Kusunoki S, Kanazawa I, Tsuji S, van der Kooy D.Primitive neural stem cells from the mammalian epiblast differentiate to definitive neural stem cells under the control of Notch signaling. Genes Dev. 2004 Aug 1;18(15):1806-11. (hitoshi...2004)
V. Tropepe, S. Hitoshi, C. Sirard, T. Mak, J. Rossant, van der Kooy D. Direct neural fate specification from embryonic stem cells: a primitive mammalian neural stem cell stage acquired through a default mechanism. Neuron. 2001 Apr;30(1):65-78. (tropepe...2001)
**photo credit: Sandrine Willaime-Morawek**