Adult NeurogenesisDr. Francesca Ciccolini
Proliferation and differentiation of neural stem cells
Our group has a long-standing interest in neural stem cells (NSCs) and adult neurogenesis. We have developed and optimized various experimental approaches in the identification ex vivo and in vivo of different pools of NSCs in the developing and adult murine brain to determine various NSC hallmarks such as genetic signatures, cilia extension and electrophysiological properties. Our recent work points to the existence of apical and basal of NSCs in the ventricular-subventricular zone, the largest neurogenic niche of the adult brain. Apical and basal NSCs differ in terms of cytoarchitecture, gene expression and crucially their ability to contribute to olfactory bulb neurogenesis.
Other than the identification of different pools of NSCs, we are also interested in studying intrinsic, as for example the stem cell gene tailless, as well as extrinsic mechanisms, like neurotransmitter and intracellular interactions, regulating their cell cycle entry and exit into quiescence.
Our overall goal is to understand how this network of regulatory mechanisms integrates the various NSC pools thereby achieving niche homeostasis.
Research Foci
NSC proliferation and maintenance
During aging the number of neural stem cells and their ability to proliferate progressively decrease. The mechanisms underlying these changes are not clear. While proliferating stem cells can generate two different daughter cells by undergoing asymmetric cell division or identical progeny by dividing symmetrically. In addition, stem cells are capable of self-renewing as well as differentiating cell divisions. Symmetric self-renewing, asymmetric selfrenewing and symmetric differentiating cell divisions will lead respectively to expansion, maintenance and depletion of the stem cell pool. In adult tissues a further layer of control of the stem cell pool homeostasis is represented by the ability of stem cells to undergo transitions between active and quiescent states of proliferation. Therefore, to fully understand how any factor may affect stem cell proliferation it is not enough to determine its mitogenic activity but also to consider how it may affect stem cells self-renewa land whether it acts at the levels of actively proliferating or quiescent stem cells.A major obstacle to such studies is represented by the fact that due to the absence of specific markers stem cell identification is mostly based on retrospective attribution of stem cell properties. Defining characteristics of NSC sare their ability to maintain long-term self-renewal and multipotency and they are tested in vivo by means of clonal assays. Reports from several laboratories, including ours, have shown that Epidermal Growth Factor not only is the main mitogen inducing clone formation from perinatal and postnatal adult NSCs but also that levels of EGF (EGFR)receptor expression specifically increase during development in NSCs and that FGF-2 increases expression EGFR in NSCs.In addition, using a fluorescently tagged EGF and flow cytomentry (Fig.1). We have isolated cell populations expressing high levels of EGFR (EGFRhigh) from different regions of the embryonic and adult telencephalon and have shown that they are highly enriched for NSCs. We are using this direct mean of NSC identification to investigate regional and temporal specification of NSCs and the mechanisms underlying the effect of growth factors on NSC proliferation and maintenance.
Effect of neural activity on NSC proliferation and differentiation
It is well known that the behaviour of NSC is not only modulated by growth factors and cell interactions but also by neural activity. Changes in neural activity affect not only the proliferation and differentiation of NSC derived progenitors but they may also regulate the proliferation of the primitive NSCs. A growing body of evidence indicates that non-synaptic release of neurotransmitters such as GABA and glutamate affects the proliferation of NSC, probably by modulation of intracellular calcium homeostasis. However, due to the problems associated with NSC identification it is not known whether these effects are direct or indirect .It is also not clear how neural activity interacts with other identified signalling components of the stem cell niche. We are using calcium imaging and electrophysiology to functionally characterize the membrane properties of isolated NSCs. This functional characterisation is combined with the analysis of gene expression in NSCs of relevant neurotransmitters and the effect of their activation on NSC function.
