BACKGROUND Kinases mTORC1 and AMPK act as energy sensors, controlling nutrient responses and cellular growth. Changes in nutrient levels affect diverse transcriptional networks, making it challenging to identify downstream paths that regulate cellular growth or a switch to development via nutrient variation. The life cycle of Dictyostelium presents an excellent model to study the mTORC1 signaling function for growth and development. Dictyostelium grow as single cells in nutrient-rich media, but, upon nutrient withdrawal, growth ceases and cells enter a program for multi-cell development. While nearly half the genome shows gene expression changes upon nutrient removal, we hypothesized that not all of these genes are required for the switch to program development. Through manipulation of mTORC1 activity alone, without nutrient removal, we focused on a core network of genes that are required for switching between growth and development for regulation of cell fate decisions. RESULTS To identify developmentally essential genes, we sought ways to promote development in the absence of nutrient loss. We first examined the activities of mTORC1 and AMPK in Dictyostelium during phases of rapid growth and starvation-induced development and showed they exhibited reciprocal patterns of regulation under various conditions. Using these as initial readouts, we identified rich media conditions that promoted rapid cell growth but, upon mTORC1 inactivation by rapamycin, led to a growth/development switch. Examination of gene expression during cell fate switching showed that changes in expression of most starvation-regulated genes were not required for developmental induction. Approximately 1000 genes which become downregulated upon rapamycin treatment comprise a cellular growth network involving ribosome biogenesis, protein synthesis, and cell cycle processes. Conversely, the upregulation of ~ 500 genes by rapamycin treatment defines essential signaling pathways for developmental induction, and ~ 135 of their protein products intersect through the well-defined cAMP/PKA network. Many of the rapamycin-induced genes we found are currently unclassified, and mutation analyses of 5 such genes suggest a novel gene class essential for developmental regulation. CONCLUSIONS We show that manipulating activities of mTORC1/AMPK in the absence of nutrient withdrawal is sufficient for a growth-to-developmental fate switch in Dictyostelium, providing a means to identify transcriptional networks and signaling pathways essential for early development.

中文翻译：

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mTORC1 / AMPK反应定义了发育细胞命运转换的核心基因集。

背景技术激酶mTORC1和AMPK充当能量传感器，控制养分响应和细胞生长。营养水平的变化会影响多种转录网络，因此很难确定调节细胞生长或通过营养变化转变为发育的下游途径。Dictyostelium的生命周期为研究mTORC1信号在生长和发育中的功能提供了一个极好的模型。Dictyostelium在富营养的培养基中以单细胞形式生长，但是在营养物质撤出后，生长停止，细胞进入多细胞发育程序。尽管近一半的基因组显示了去除营养后基因表达的变化，但我们假设并非所有这些基因都是转换程序开发所必需的。通过单独操纵mTORC1的活动，而没有去除营养，我们专注于基因的核心网络，这些基因在调节细胞命运决定的生长与发育之间进行切换。结果为了鉴定发育必需的基因，我们寻求了在没有营养损失的情况下促进发育的方法。我们首先研究了快速生长和饥饿诱导的发育过程中盘基网柄菌中mTORC1和AMPK的活性，并发现它们在各种条件下均表现出相互的调节模式。使用这些作为初始读数，我们确定了富媒体条件，该条件促进了细胞的快速生长，但是在雷帕霉素使mTORC1失活后，导致了生长/发育的转变。细胞命运转换过程中基因表达的检查表明，大多数饥饿调节基因的表达变化不需要发育诱导。雷帕霉素治疗后被下调的大约1000个基因包括一个涉及核糖体生物发生，蛋白质合成和细胞周期过程的细胞生长网络。相反，雷帕霉素处理对约500个基因的上调定义了发育诱导的基本信号通路，其约135个蛋白质产物通过定义明确的cAMP / PKA网络相交。我们发现许多雷帕霉素诱导的基因目前尚未分类，对5个此类基因的突变分析表明，这是发育调控必不可少的新型基因。结论我们证明，在不存在营养物质撤离的情况下，操纵mTORC1 / AMPK的活性足以使盘基网柄菌发生从生长到发育的命运，