Studies on mechanisms of morphogen action in shaping the body pattern

形态发生素是一种分泌性分子，它从一个不连续的来源发出，产生一个浓度梯度，在靶细胞中激发浓度依赖性反应，并组织发育区域的模式和生长。Hedgehog（Hh）和Decapentaplegic（Dpp）分别作为短程和长程形态发生素，指导发育中果蝇翅膀的前后方向模式。我们发现，DPP的活动是分级的，并动态调节的Engrailed（En）和HH依赖的机制。Dpp与受体复合物结合，并通过磷酸化主要信号转导剂母体（mother）来发出信号，所述主要信号转导剂母体针对dpp（Mad），其在磷酸化后易位到细胞核中并调节靶基因的转录。因此，Dpp信号传导活性的水平可以通过使用特异性抗体检测磷酸化形式的Mad（p-Mad）来原位监测。p-Mad的分布揭示了发展中机翼中Dpp活动的一种出乎意料的复杂模式; Dpp活动的梯度沿A/P轴沿着是不对称的。Hh下调Dpp活性沿着A/P室边界，En也参与产生Dpp活性梯度的不对称分布。梯度的这种模式似乎很大程度上取决于Dpp的主要I型受体thickveins（txl）的水平，即Hh和En的调节靶点是txl。我们发现，这种基因的转录水平受到我们命名为“粗脉大师”（mtv）的基因的负调控。Hh和Enact通过mtv调控果蝇的转录表达模式，因此mtv在形成果蝇发育翅中Dpp形态原的活性梯度中起重要作用，我们还鉴定了一个抑制Dpp靶基因的新基因brinker（brk）。由于brk被dpp下调，因此Dpp似乎通过下调brk来激活靶基因表达。

Morphogens have been defined as secreted molecules that emanate from a discrete source, generate a concentration gradient that elicits concentration-dependent responses in target cells and organize pattern and growth of the developmental field Hedgehog (Hh) and Decapentaplegic (Dpp) direct anteroposterior patterning in the developing Drosophila wing by functioning as short-and long-range morphogens, respectively. We show that the activity of Dpp is graded and is dynamically regulated by Engrailed (En)-and Hh-dependent mechanisms. Dpp binds to the receptor complex and signals by phosphorylating the major signal hansducer Mothers against dpp (Mad), which upon phosphorylation translocates into the nucleus and regulates transcription of target genes. Thus the levels of Dpp signaling activity can be monitored in situ by detecting the phospshorylated form of Mad (p-Mad) using a specific antibody. The distribution of p-Mad revealed an unexpectedly complex pattern of Dpp activity in the developing wing ; the gradient of Dpp activity is asymmetric along the A/P axis. Hh downregulates Dpp activity along the A/P compartment border and En is also involved in generating the asymmetric distribution of the Dpp activity gradient. This pattern of the gradient appears to depend largely on the levels of the major type I receptor of Dpp, thickveins (tkv), i.e. the regulatory target of Hh and En is tkv. We found that tkv transcription levels are negatively regulated by a gene that we named master of thick veins (mtv). Hh and Enact through mtv to control the tkv expression pattern, hence mtv plays an important role in shaping the activity gradient of the Dpp morphogen in the developing wing of Drosophila.We have also identified a new gene brinker (brk) that represses the Dpp target genes. Since brk is downregulated by dpp, it appears that Dpp activates target gene expression by downregulating brk.