Samuel Lunenfeld Research Institute, Mount Sinai Hospital, 600 University Avenue, Toronto, ON M5G 1X5, Canada.
Development. 2011 Jan;138(1):65-74. doi: 10.1242/dev.058727. Epub 2010 Nov 23.
An interplay of transcription factors interprets signalling pathways to define anteroposterior positions along the vertebrate axis. In the hindbrain, these transcription factors prompt the position-appropriate appearance of seven to eight segmental structures, known as rhombomeres (r1-r8). The evolutionarily conserved Cdx caudal-type homeodomain transcription factors help specify the vertebrate trunk and tail but have not been shown to directly regulate hindbrain patterning genes. Mafb (Kreisler, Krml1, valentino), a basic domain leucine zipper transcription factor, is required for development of r5 and r6 and is the first gene to show restricted expression within these two segments. The homeodomain protein vHnf1 (Hnf1b) directly activates Mafb expression. vHnf1 and Mafb share an anterior expression limit at the r4/r5 boundary but vHnf1 expression extends beyond the posterior limit of Mafb and, therefore, cannot establish the posterior Mafb expression boundary. Upon identifying regulatory sequences responsible for posterior Mafb repression, we have used in situ hybridization, immunofluorescence and chromatin immunoprecipitation (ChIP) analyses to determine that Cdx1 directly inhibits early Mafb expression in the neural tube posterior of the r6/r7 boundary, which is the anteriormost boundary of Cdx1 expression in the hindbrain. Cdx1 dependent repression of Mafb is transient. After the 10-somite stage, another mechanism acts to restrict Mafb expression in its normal r5 and r6 domain, even in the absence of Cdx1. Our findings identify Mafb as one of the earliest direct targets of Cdx1 and show that Cdx1 plays a direct role in early hindbrain patterning. Thus, just as Cdx2 and Cdx4 govern the trunk-to-tail transition, Cdx1 may regulate the hindbrain-to-spinal cord transition.
转录因子的相互作用解释信号通路，从而确定沿脊椎动物轴的前后位置。在后脑中，这些转录因子促使适当位置出现七个到八个节段结构，称为菱脑节（r1-r8）。进化上保守的 Cdx 尾部同源域转录因子有助于指定脊椎动物的躯干和尾巴，但尚未显示其直接调节后脑模式基因。Mafb（Kreisler、Krml1、valentino），一种基本结构域亮氨酸拉链转录因子，是 r5 和 r6 发育所必需的，是第一个在这两个节段内表现出受限表达的基因。同源域蛋白 vHnf1（Hnf1b）直接激活 Mafb 的表达。vHnf1 和 Mafb 在 r4/r5 边界处具有共同的前表达限制，但 vHnf1 的表达延伸超过 Mafb 的后限，因此无法建立 Mafb 的后表达边界。在确定负责 Mafb 后抑制的调节序列后，我们使用原位杂交、免疫荧光和染色质免疫沉淀（ChIP）分析来确定 Cdx1 直接抑制 r6/r7 边界后神经管中早期 Mafb 的表达，这是 Cdx1 在后脑中的前表达边界。Cdx1 依赖的 Mafb 抑制是短暂的。在 10 体节阶段之后，另一种机制作用于限制 Mafb 在其正常 r5 和 r6 域中的表达，即使在没有 Cdx1 的情况下也是如此。我们的研究结果确定 Mafb 是 Cdx1 的最早直接靶标之一，并表明 Cdx1 在早期后脑模式形成中发挥直接作用。因此，就像 Cdx2 和 Cdx4 控制躯干到尾部的转变一样，Cdx1 可能调节后脑到脊髓的转变。
