Schweitzer R, Shaharabany M, Seger R, Shilo B Z
Department of Molecular Genetics and Virology, Weizmann Institute of Science, Rehovot, Israel.
Genes Dev. 1995 Jun 15;9(12):1518-29. doi: 10.1101/gad.9.12.1518.
The spitz gene encoding a TGF-alpha homolog, has been shown to affect a subset of developmental processes that are similar to those regulated by DER, the Drosophila EGF receptor homolog. This work demonstrates that Spitz triggers the DER signaling cascade. Addition of a secreted, but not the membrane-associated form of Spitz to S2 Drosophila cells expressing DER gives rise to a rapid tyrosine autophosphorylation of DER. Following autophosphorylation, DER associates with the Drk adapter protein. Consequently, activation of MAP kinase is observed. The profile of MAP kinase activation provides a quantitative assay for DER activation. A dose response between the levels of Spitz and MAP kinase activity was observed. The secreted Spitz protein was expressed in embryos to assess its biological activity. An alteration in cell fates was observed in the ventral ectoderm, such that lateral cells acquired the ventral-most fates. The result indicates that graded activation of the DER pathway may normally give rise to a repertoire of discrete cell fates in the ventral ectoderm. Spatially restricted processing of Spitz may be responsible for this graded activation. The Rhomboid (Rho) and Star proteins were suggested, on the basis of genetic interactions, to act as modulators of DER signaling. No alteration in DER autophosphorylation or the pattern of MAP kinase activation by secreted Spitz was observed when the Rho and Star proteins were coexpressed with DER in S2 cells. In embryos mutant for rho or Star the ventralizing effect of secreted Spitz is epistatic, suggesting that Rho and Star may normally facilitate processing of the Spitz precursor.
编码转化生长因子α同源物的spitz基因已被证明会影响一部分发育过程，这些过程与由果蝇表皮生长因子受体同源物DER调控的过程相似。这项研究表明，Spitz可触发DER信号级联反应。将分泌型而非膜结合型的Spitz添加到表达DER的S2果蝇细胞中，会导致DER迅速发生酪氨酸自磷酸化。自磷酸化后，DER与Drk衔接蛋白结合。因此，可观察到丝裂原活化蛋白激酶（MAP激酶）的激活。MAP激酶激活情况可提供一种定量检测DER激活的方法。观察到Spitz水平与MAP激酶活性之间存在剂量反应关系。在胚胎中表达分泌型Spitz蛋白以评估其生物学活性。在腹侧外胚层观察到细胞命运的改变，即外侧细胞获得了最腹侧的命运。结果表明，DER信号通路的分级激活可能通常会导致腹侧外胚层中一系列离散的细胞命运。Spitz在空间上受到限制的加工过程可能是这种分级激活的原因。基于遗传相互作用，菱形（Rho）蛋白和星状（Star）蛋白被认为是DER信号传导的调节因子。当Rho和Star蛋白与DER在S2细胞中共表达时，未观察到分泌型Spitz对DER自磷酸化或MAP激酶激活模式的改变。在rho或Star基因发生突变的胚胎中，分泌型Spitz的腹侧化作用具有上位性，这表明Rho和Star可能通常促进Spitz前体的加工。
