Patterning and morphogenesis of the insect head - origin of epicranial sutures and Tc-homeobrain

昆虫的头部形态极其多样，许多对不同生活方式的重要适应塑造了昆虫头部的解剖结构(例如，捕食、舔食腐烂的水果、吸血)。它是由多个节段和非节段组织构成的复合结构，是由复杂的形态发生运动形成的。昆虫的头部有几条缝线，在肌肉附着或蜕皮过程中起着稳定头部被膜的作用。人们普遍认为，大多数缝合不反映节段边界，但它们的发育和进化起源仍然不清楚。前部昆虫头部模式不涉及配对规则或HOX簇基因表达。因此，它一定不同于躯干，但头部模式的基因调控网络仍然知之甚少。引人注目的是，所有双边动物的前部都有一组高度保守的基因。我们使用具有昆虫典型的非渐开头部的赤粉甲虫作为模型来理解昆虫头部的发育和潜在的遗传原理。我们在Tribolium收集的见解被与果蝇、其他昆虫和节肢动物以及脊椎动物进行比较，以追溯前图案的演变。在过去，我们已经确定了头部模式形成所需的新基因，并建立了头部的临时命运图。后者使我们提出了一种假设，即冠状缝和额缝(蜕皮线)来自胚胎上皮融合事件。在这个项目中，我们希望用荧光蛋白对细胞进行活体成像和非侵入性标记，以便生成准确的命运图，并更好地了解头部的形态发生运动。使用这些工具，我们将测试缝合线是否确实来自胚胎融合事件。此外，我们想要分析一种新的头部模式基因--TC-Homeobrain的功能，该基因在早期胚芽胚中的前帽中表达，后来在头部原始细胞中表达。这与果蝇相似，表明其功能保守。然而，目前还没有可用的功能数据。在Tribolium的RNAi中，整个背部头部缺失。作为该项目的一部分，将构建几个转基因株系，这将对其他研究具有价值。这包括一个从基因上永久标记表皮细胞的系统，几个Gal4驱动程序和带有荧光蛋白的响应器结构，这些荧光蛋白标记细胞核或细胞轮廓。

Insect head morphology is extremely diverse and many crucial adaptations to different life styles have shaped the anatomy of insect heads (e.g. predating, licking on rotten fruit, sucking blood). It is a composite structure built by several segments and non-segmental tissue and it is formed by complex morphogenetic movements. Several sutures mark the insect head, which function in stabilization of the head capsule, in muscle attachment or ecdysis. It is well accepted that most of the sutures do not reflect segment boundaries, but their developmental and evolutionary origin remains obscure. Anterior insect head patterning does not involve pair rule or Hox cluster gene expression. Hence, it must be different from the trunk but the gene regulatory network of head patterning remains poorly understood. Strikingly, a set of highly conserved genes pattern the anterior region of all bilaterian animals. We use the red flour beetle Tribolium castaneum with its insect typical non-involuted head as a model for understanding the development of an insect head and the underlying genetic principles. The insights we gather in Tribolium are compared to Drosophila, other insects and arthropods and also vertebrates in order to trace back the evolution of anterior patterning. In the past, we have identified novel genes required for head pattern formation and have established a provisional fate map of the head. The latter led us to propose the hypothesis that the coronal and frontal sutures (the lines of ecdysis) are derived from embryonic epithelial fusion events. In this project, we want to perform in vivo imaging and non-invasive marking of cells with fluorescent proteins in order to generate an exact fate map and to better understand the morphogenetic movements of the head. Using these tools, we will then test, whether the sutures do indeed derive from embryonic fusion events. Further, we want to analyze the function of Tc-homeobrain, a novel head patterning gene, which is expressed in an anterior cap in the early blastoderm and later in the head anlagen. This is similar to Drosophila indicating a conserved function. However, no functional data is available in the fly. In RNAi in Tribolium, the entire dorsal head is missing. Several transgenic lines will be constructed as part of this project, which will be valuable for other studies. This includes a system to genetically permanently mark epidermal cells, several Gal4 drivers and responder constructs with fluorescent proteins, which mark nuclei or cell outlines.