The gene network underlying neural stem cell identity

描述（由申请人提供）：在果蝇和脊椎动物发育中的大脑中，神经干细胞增殖产生排列在柱状上皮中的干细胞群。在某个时间点上，分化波穿过上皮，细胞离开上皮层，不对称地分裂成一个自我更新的细胞和一个分化更大的神经元前体，后者将产生神经元。如果没有在适当的时间触发从增殖对称分裂到不对称分裂的转变，就无法实现正确的神经元数量和阵列。因此，有必要了解控制增殖和分化状态的潜在分子机制。在这里，我们关注果蝇幼虫大脑中调节神经干细胞维持的基因网络。尽管已知有几种信号通路参与其中，其中之一Notch已知在哺乳动物中是保守的，但对于维持干细胞身份的调控基因网络，以及干细胞在分化过程中如何变化，目前还没有全面的认识。我们最近发现转录因子Zelda是神经干细胞维持和抑制分化所必需的。我们之前已经确定Zelda是“合子基因组激活因子”，因为它的结合先于并预测了囊胚胚中几乎所有的转录活性。它组织子网络，建立多个前馈回路。Zelda还与模式转录因子一起建立其下游靶标的稳健和精确表达，从而在早期基因网络中发挥全面作用。Zelda就像一个先锋因子，早期结合目标增强因子并促进其他因子的结合

DESCRIPTION (provided by applicant): In the developing brain of flies and vertebrates alike, neural stem cells proliferate giving rise to a stem cell population arranged in a columnar epithelium. At some point in time, a wave of differentiation moves across the epithelium, whereby cells leave the epithelial sheet and split asymmetrically into a self-renewing cell and a more differentiated neuronal precursor that will produce neurons. If the transition from proliferative symmetric division to asymmetric division is not triggered at the proper time, the correct number and array of neurons is not achieved. It is therefore essential to understand the underlying molecular mechanisms controlling the proliferative versus differentiated states. Here we focus on the gene network that regulates neural stem cell maintenance in the Drosophila larval brain. Although several signaling pathways are known to be involved, one of which, Notch, is known to be conserved with mammals, there is no global view of the regulatory gene network that maintains stem cell identity, and how this changes upon differentiation. We recently found that the transcription factor Zelda is required for neural stem cell maintenance and inhibits differentiation. We had previously identified Zelda as the "zygotic-genome activator" as its binding precedes and predicts nearly all transcriptional activity in the blastoderm embryo. It organizes sub-networks and establishes many feed forward loops. Zelda also works together with the patterning transcription factors to establish robust and precise expression of their downstream targets, thus playing a comprehensive role in the early gene network. Zelda acts like a pioneer factor, binding target enhancers early and facilitating the binding of other factors that mediate stage and tissue specific activation. Here we hypothesize that Zelda plays a similar role in the neural stem cell gene network. In addition to genetic assays to determine how Zelda interacts with the known signaling pathways, we propose to use genome-wide approaches to identify all Zelda target genes in neural stem cells. This discovery-based approach will yield a comprehensive set of genes with which to build a global gene network. This pilot study is within the scope of the R03 mechanism as it will provide the basis for future studies to further delineate functional connections in the network, first in the Drosophila model system, and then in mammals, since important interactions are likely conserved. The studies outlined in this proposal have the potential to significantly advance our understanding of neural stem cell differentiation, with high impact in the field of developmental neurobiology.