Analysis of cell identity, morphology, apoptosis and mitotic activity in a primary neural cell culture system in Drosophila

Neurogenesis in Drosophila is a biphasic process consisting of an embryonic and a postembryonic period of neurogenesis. During embryogenesis primary neurons are generated, that form the functional larval central nervous system (CNS). Subsequently, during postembryonic neurogenesis secondary neurons are generated, which build up the adult brain during larval and pupal stages. During embryonic stages neural precursor cells termed neuroblasts (NBs) divide asymmetrically in a stem cell-like fashion thereby self-renewing and producing smaller ganglion mother cells (GMCs). The GMCs have a limited mitotic potential and divide only once more, to generate a pair of neurons and/or glial cells. At the end of embryogenesis, NBs undergo a quiescent phase and only a subset of NBs enter mitosis again to generate secondary neurons during larval development, reviewed in [1-3].Depending on their mode of proliferation, larval NBs can be further subdivided into Type I and Type II NBs. In contrast to Type I NBs, in which the GMCs divide once to form two postmitotic cells, Type II NBs give rise to an intermediate progenitor that can divide multiple times. Therefore, Type II lineages are substantially larger than Type I lineages [4-6]. A third type of neurogenesis occurs in the developing optic lobe, where NBs derive from neuroepithelial precursors. Neuroepithelial cells initially divide symmetrically to increase the pool of precursor cells. Later, during larval development, neuroepithelial cells gradually transform to NBs and switch to an asymmetric division mode [7].In contrast from what we know about mammalian neural stem cell behavior, most knowledge about precursor cells in the Drosophila nervous system is based on findings in vivo. It has been difficult to study defined neural Drosophila cells in vitro over a longer culture period [8]. Dissociation of neural tissue into individual cells allows studying how neural precursors, differentiating neurons and glial cells behave outside the