Neural stem cells and their interaction with the brain environment

The NS culture system is an innovative yet not fully characterized method of culturing neural stem cells (NSCs). Previous reports have described the possibility of isolation of a virtually pure NSC culture from embryonic, fetal or adult NSCs (Conti et al., 2005; Pollard et al., 2006; Sun et al., 2008). These cells, grown in adhesion, are called NS cells and show radial glial characteristics. The present thesis aims to characterize the in vitro and in vivo behaviour of human and mouse NS cells. In the first study, we describe the isolation of a new strain of human striatal NS cells. They show unique features in vitro, and can be efficiently differentiated into neurons. After transplantation in newborn rats, they survive, migrate and differentiate in the host brain. In the second part of the thesis, we show that mouse ES-derived NS cells fuse with cortical pyramidal neurons after transplantation in mice or rats. This process is mediated by microglia, which first fuse with the NS cells and then with the neurons. This NS-microglia-neuron fusion has not been previously described, although it occurs both in vivo and in vitro. In summary, we report here previously undescribed features of the NS cells; our results are relevant to better understanding of NSCs in general and their behaviour after transplantation in the brain.