The molecular mechanism of tissue boundary formation in animals

九头蛇是古老刺胞动物门的一员。对水螅和其他前两侧动物进行的基因组测序显示，控制哺乳动物胚胎发育和细胞稳态的主要信号通路，包括Notch信号，已经存在于这些早期后生动物中。notch信号的失调导致癌症和退行性疾病。在九头蛇中，阻断notch信号会导致间质干细胞谱系分化受阻，并导致严重的组织模式紊乱。在九头蛇中，有三种信号通路被证明调节着头到脚的模式。这些信号包括wnt通路、BMP和fgf信号。它们受可溶性配体的调节，这可能建立信号活动的梯度。相反，Notch信号依赖于细胞的直接接触，它导致两个相邻细胞之间信号状态的急剧切换。这允许在适应相反命运的细胞之间创造界限，例如触手区增殖细胞和触手中的分化细胞。水螅以其相对简单的身体计划和其独特的形态可塑性在成年动物中允许解剖整合扩散和接触依赖信号来塑造动物组织模式的分子原理。这是本提案的长期目标。在第一个阶段，我们希望在转录组研究的帮助下鉴定notch靶基因，并研究它们的表达模式。我们可能会在九头蛇中发现具有哺乳动物同源物的新的notch靶点。这可能与开发新的药物靶点来对抗人类的notch功能障碍有关。此外，在notch信号报告器的帮助下，我们希望检测在九头蛇头部再生和触手形成过程中接收notch信号的细胞。将这些信息与Notch配体和受体的半定量表达研究相结合，将解释Notch细胞接触依赖的信号事件如何被上游因子定位，以实现九头蛇体内结构模式所观察到的精度。

Hydra is a member of the ancient phylum Cnidaria. Genome sequencing carried out for Hydra and other pre-bilaterian animals has revealed that the major signalling pathways governing embryonal development and cellular homeostasis in mammals, including Notch signalling, were already present in these early metazoans. Dysregulation of Notch-signalling leads to cancer and degenerative disease. In Hydra, blocking Notch-signalling inflicts a differentiation block in the interstitial stem cell lineage and causes severe disturbances of tissue patterning. Three signalling pathways have previously been shown to regulate the head to foot patterning in Hydra. These include the Wnt-pathway, BMP- and FGF-signalling. They are regulated by soluble ligands, which may establish gradients of signalling activity. In contrast, Notch signalling depends on direct cell contact and it causes a sharp switch in signalling states between two neighbouring cells. This allows the creation of boundaries between cells adapting opposite fates, e.g proliferating cells in the tentacle zone and differentiating cells in the tentacles. Hydra with its relatively simple body plan and its unique morphological plasticity in adult animals allows to dissect the molecular principles of integrating diffusible and contact dependent signals for shaping tissue patterns in animals. This is the long-term aim of this proposal. In the first period we want to identify Notch-target genes with the help of a transcriptome study and investigate their expression patterns. We may discover novel Notch-targets in Hydra with homologs in mammals. These could be relevant for developing new drug targets to combat Notch-dysfunction in humans. In addition, with the help of a Notch-signalling reporter, we want to detect the cells where Notch-signals are received during Hydra head regeneration and tentacle patterning. Integrating this information with semi-quantitative expression studies of Notch-ligand and receptor will explain how Notch cell-contact dependent signalling events are positioned by upstream factors to achieve the observed precision in patterning body structures in Hydra.