Shared mechanisms regulate transcription-factor activity to control cell fate in neural stem cells and the embryo

摘要 发展需要细胞稳健地离开一个细胞的命运，进入另一个细胞的命运。在早期胚胎中，指定的 生殖细胞必须迅速重新编程为多能细胞，这样才能随后产生完全 新的有机体。相反，在不对称干细胞分裂之后，两个子细胞必须采用不同的 一个再生干细胞，另一个退出多能状态并启动分化的命运。 这些基本的发育转变要求驱动多能性的那些因素的活性 精确控制，因为太多和太少的干细胞对机体都是有害的。而当 决定干细胞命运的转录因子已经在培养中得到了很好的表征，但关于它是如何 这些因子的活性在发育中的有机体中受到严格控制。我们的预赛 数据表明，转录因子Zelda(ZLD)作为多能性的主要调节因子具有共同的作用 在果蝇早期胚胎和幼虫神经干细胞中的状态。我们最近做了 证明了在胚胎和幼虫中，ZLD都可以重新编程细胞以适应多潜能的命运 ZLD活性增加是有害的。因此，必须严格控制ZLD活动，以允许开发 继续吧。我们的初步数据表明，染色质结构可能限制了ZLD与 基因组和重新编程细胞命运。ZLD活性还受到转录后机制的额外调节，该机制 控制ZLD水平。基于这些初步数据，我们可以很好地阐明一般机制。 通过它，干细胞命运的主要调节者的活动被精确地控制，以维持平衡 在自我更新和差异化之间。我们将使用遗传、基因组和生化策略来(1) 确定染色质结构影响ZLD活性的机制和(2)确定后 ZLD RNA的转录调控控制着神经干细胞和早期胚胎中ZLD蛋白的水平。 综上所述，这些结果将对理解 多能和分化状态在发育过程中受到精确控制。

ABSTRACT Development requires that cells robustly exit one cell fate and enter another. In the early embryo the specified germ cells must be rapidly reprogrammed to the pluripotent cells that can subsequently generate an entirely new organism. Conversely, following asymmetric stem-cell division the two daughter cells must adopt different fates with one regenerating the stem cell and the other exiting the multipotent state and initiating differentiation. These essential developmental transitions require that the activity of those factors that drive pluripotency be precisely controlled as both too many and too few stem cells are detrimental to the organism. While the transcription factors that drive stem-cell fate have been well characterized in culture, less is known about how the activity of these factors is tightly controlled within the context of a developing organism. Our preliminary data demonstrate a shared role for the transcription factor Zelda (ZLD) as a master regulator of the mulitpotent state in both the early embryo and larval neural stem cells of Drosophila melanogaster. We have recently demonstrated that in both the embryo and the larva ZLD can reprogram cells to a multipotent fate and increased ZLD activity is deleterious. Thus, ZLD activity must be tightly controlled to allow for development to proceed. Our preliminary data suggest that chromatin structure may limit the ability of ZLD to engage the genome and reprogram cell fate. ZLD activity is additionally regulated by post-transcriptional mechanisms that control ZLD levels. Based on these preliminary data we are well positioned to elucidate general mechanisms by which the activities of master regulators of stem-cell fate are precisely controlled to maintain a balance between self-renewal and differentiation. We will use genetic, genomic, and biochemical strategies to (1) identify mechanisms by which chromatin structure influences ZLD activity and (2) determine how post- transcriptional regulation of zld RNA controls ZLD protein levels in both neural stem cells and the early embryo. Together these results will have important implications for understanding how the balance between the multipotent and differentiated states are precisely controlled during development.