Department of Biochemistry and Molecular Biophysics, Columbia University, College of Physicians and Surgeons, New York, New York 10032, USA.
Genetics. 2011 Aug;188(4):847-58. doi: 10.1534/genetics.111.128389. Epub 2011 May 19.
lag-2 encodes a ligand for LIN-12/Notch and is a component of the lateral signal that activates LIN-12/Notch during Caenorhabditis elegans vulval precursor cell (VPC) fate patterning. lag-2 is specifically transcribed in one VPC, named P6.p, in response to activation of EGFR/Ras/MAPK by the inductive signal that initiates vulval development. Here, we show that a critical molecular event linking inductive and lateral signaling is the relief of VPC-wide lag-2 repression in P6.p. We find that the lag-2 promoter contains an element, VPCrep, which mediates repression in all VPCs when the inductive signal is absent, and another promoter element, VPCact, which is required for activation when repression is relieved by the inductive signal. We show that repression through VPCrep is mediated by the Elk1 ortholog LIN-1, and that the level and subcellular accumulation of a functional LIN-1::GFP protein is similar in all six VPCs before and after vulval induction, suggesting that relief of LIN-1-mediated repression in P6.p is likely due to the known MAPK-dependent phosphorylation of LIN-1. We also provide evidence that the factor(s) acting through VPCact is present in all VPCs but is not modulated by the inductive signal, and that transcription of lag-2 requires the Hth/Meis ortholog UNC-62 and the Mediator complex component SUR-2. Relief of repression of lag-2 in P6.p offers a plausible mechanistic basis for spatial restriction of lag-2 in generating the precise spatial pattern of VPC fates.
lag-2 编码了 LIN-12/Notch 的配体，是激活 LIN-12/Notch 的侧向信号的组成部分，该信号在秀丽隐杆线虫的外阴前体细胞（VPC）命运模式形成过程中发挥作用。lag-2 特异性地在外阴发育起始诱导信号激活 EGFR/Ras/MAPK 途径后，在一个名为 P6.p 的 VPC 中被转录。在这里，我们表明，连接诱导信号和侧向信号的关键分子事件是在 P6.p 中解除 VPC 范围的 lag-2 抑制。我们发现，lag-2 启动子包含一个元件 VPCrep，当诱导信号不存在时，它介导所有 VPC 的抑制，另一个启动子元件 VPCact，当诱导信号通过解除抑制时，它是激活所必需的。我们表明，通过 VPCrep 介导的抑制是由 Elk1 同源物 LIN-1 介导的，并且在诱导前后，所有六个 VPC 中功能性 LIN-1::GFP 蛋白的水平和亚细胞积累相似，这表明 P6.p 中 LIN-1 介导的抑制的解除可能归因于已知的 MAPK 依赖性 LIN-1 磷酸化。我们还提供了证据表明，通过 VPCact 作用的因子存在于所有 VPC 中，但不受诱导信号的调节，并且 lag-2 的转录需要 Hth/Meis 同源物 UNC-62 和 Mediator 复合物成分 SUR-2。在 P6.p 中解除 lag-2 的抑制为 lag-2 在产生 VPC 命运的精确空间模式中的空间限制提供了合理的机制基础。
