Dissecting and manipulating regulatory feedback circuitry in Drosophila BMP morphogen signaling

动物发育过程中的组织生长和模式受到形态原的严格控制，形态原是一种分泌的信号分子，建立了信号活动的梯度。形态原信号的重要性反映在控制信号范围的多种调节机制和信号梯度的形状上。这些机制的核心是调节反馈环，它将信号响应耦合到梯度建立和维持，并已被建议配备具有精确度、稳健性和在给定上下文中随组织生长而缩放的能力的形态发生信号。拟议的项目侧重于骨形态发生蛋白(BMP)形态原信号转导，旨在解决如何重新连接调节反馈电路，以在不同背景下产生不同的信号特征和输出。作为一个模型，我们将关注果蝇的两个背部附属物，翅膀和龟头，它们在大小和形状上截然不同，尽管它们有共同的发育历史和依赖于DPP(十五叉神经节，一种果蝇BMP)的梯度来生长和分化。以前的工作已经确定，DPP梯度的差异是两个器官大小差异的关键原因。遗传学研究还表明，BMP信号的不同部分是由于BMP对BMP受体细静脉(Tkv)的依赖调节的不同。在幼虫翅膀中，BMP信号抑制TKV转录，从而允许有效的配体扩散和建立长距离的BMP信号梯度。相反，在幼虫Hatere前体中，同源蛋白Ultrabithorax(UBx)和高Tkv水平的Trap DPP阻止了对BMP依赖的Tkv的抑制，导致了短距离和紧凑的BMP信号梯度。在这个项目中，我们希望了解并挑战解释这种监管反馈中差异的机制。具体地说，我们希望了解在翅膀中将Tkv产生与BMP信号耦合的分子机制，以及Ubx如何与这些机制相结合来解偶联Hatere发育过程中的反馈调节。我们希望达到一个理解的水平，使我们能够在项目的第二部分，改变这个反馈环的属性，并评估这种操纵在体内信号活动水平(DPP梯度的轮廓)和信号输出(器官大小)的影响。我们的研究将为调节反馈电路重新布线以使信号活动适应组织特定的“需求”的机制提供见解。

Tissue growth and patterning during animal development is critically controlled by morphogens, secreted signaling molecules that establish gradients of signaling activity. The importance of morphogen signaling is reflected by the multitude of regulatory mechanisms that control the range, and the shape of the signaling gradient. Central amongst such mechanisms are regulatory feedback loops that couple signaling responses to gradient establishment and maintenance and have been suggested to equip morphogen signaling with precision, robustness and the ability to scale with tissue growth in a given context. The proposed project focuses on BMP (Bone Morrphogenetic Protein) morphogen signaling and aims at addressing how regulatory feedback circuitries might be rewired to produce differential signaling profiles and output in different contexts. As a model we will focus on two dorsal appendages of Drosophila, the wing and the haltere, which drastically differ in size and form despite sharing developmental history and dependence on a gradient of Dpp (Decapentaplegic, a Drosophila BMP) for growth and differentiation. Previous work has established that differences in the Dpp gradient critically contribute to size differences between the two organs. Genetic studies also suggested that the differences in BMP signaling are partly due to differences in BMP-dependent regulation of the BMP-receptor Thickveins (Tkv). In the larval wing, BMP signaling represses tkv transcription which allows for efficient ligand spreading and establishment of a long-range BMP signaling gradient. In contrast, in the larval haltere precursor, BMP-dependent repression of tkv is blocked by the homeotic Protein Ultrabithorax (Ubx) and high Tkv levels trap Dpp resulting in a short-range and compacted BMP signaling gradient. In this project, we wish to understand and challenge the mechanisms that account for the differences in this regulatory feedback. Specifically, we wish to understand the molecular mechanisms that couple Tkv production to BMP signaling in the wing and how Ubx integrates with such mechanisms to uncouple feedback regulation during haltere development. We wish to reach a level of understanding that will allow us, in a second part of the project, to alter the properties of this feedback-loop and assess effects of such manipulations at both the level of signaling activity (profile of the Dpp gradient) and signaling output (organ size) in vivo. Our studies will provide insights in the mechanisms by which regulatory feedback circuitries can be rewired to adapt signaling activity to tissue-specific 'demands'.