Simeoni I, Gurdon J B
Wellcome Trust/Cancer Research UK, Gurdon Institute of Cancer and Development Biology, CB2 1QN Cambridge, UK.
Dev Biol. 2007 Aug 1;308(1):82-92. doi: 10.1016/j.ydbio.2007.05.010. Epub 2007 May 18.
Very little is known about how the extracellular binding of a morphogen is transduced to the nucleus of a cell in a concentration-related way, enabling cells to interpret their position in a concentration gradient. Here, we have analyzed when and how Xenopus embryo cells perceive and interpret a BMP signal. Dissociated embryo cells are exposed for short times to different concentrations of BMP4. We find that cells are already competent to receive a BMP4 signal at the blastula stage. They phosphorylate Smad1 very rapidly and express downstream genes less than half an hour after exposure to BMP. However, Smad1 is present in the nucleus even in the absence of BMP. To quantitate intracellular signaling after BMP exposure, we have constructed a chimeric type I receptor that registers BMP signaling as the intranuclear migration of Smad2, and as the transcription of Smad2 downstream genes. The combination of the chimeric receptor and GFP-Smad2 makes it possible to follow the transduction of BMP signaling to the nucleus. From our results, we conclude that an extracellular BMP concentration is interpreted by the steady state nuclear concentration of phosphorylated Smad1.
关于形态发生素的细胞外结合如何以浓度相关的方式传导至细胞核，使细胞能够在浓度梯度中确定自身位置，目前所知甚少。在此，我们分析了非洲爪蟾胚胎细胞何时以及如何感知和解读骨形态发生蛋白（BMP）信号。将解离的胚胎细胞短时间暴露于不同浓度的BMP4中。我们发现，囊胚期的细胞已具备接收BMP4信号的能力。暴露于BMP后不到半小时，它们就能迅速磷酸化Smad1并表达下游基因。然而，即使在没有BMP的情况下，Smad1也存在于细胞核中。为了定量BMP暴露后的细胞内信号传导，我们构建了一种嵌合I型受体，该受体将BMP信号传导记录为Smad2的核内迁移以及Smad2下游基因的转录。嵌合受体与绿色荧光蛋白标记的Smad2（GFP-Smad2）相结合，使得追踪BMP信号传导至细胞核成为可能。根据我们的结果，我们得出结论，细胞外BMP浓度是由磷酸化Smad1的稳态核浓度来解读的。
