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

昆虫头部的形态极其多样，许多针对不同生活方式的关键适应塑造了昆虫头部的解剖结构（例如，捕食、舔烂水果、吸血）。它是由多个节段组织和非节段组织组成的复合结构，是由复杂的形态发生运动形成的。几条缝合线标志着昆虫的头部，这些缝合线起着头囊稳定、肌肉附着或蜕皮的作用。人们普遍认为，大多数缝合线不反映节段边界，但它们的发育和进化起源仍然不清楚。昆虫前头图案不涉及配对规则或Hox簇基因表达。因此，它一定与躯干不同，但对头部模式的基因调控网络仍然知之甚少。引人注目的是，一组高度保守的基因分布在所有双侧动物的前侧区域。我们以红粉甲虫Tribolium castaneum及其昆虫典型的非卷曲头为模型来理解昆虫头的发育及其潜在的遗传原理。我们在Tribolium中收集到的见解与果蝇、其他昆虫、节肢动物和脊椎动物进行了比较，以追溯前模式的进化。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。后者使我们提出了冠状和额状缝合线（表皮线）来源于胚胎上皮融合事件的假设。在这个项目中，我们希望用荧光蛋白对细胞进行体内成像和非侵入性标记，以生成精确的命运图，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，我们想分析tc -同源脑的功能，tc -同源脑是一种新的头部模式基因，在早期囊胚的前帽中表达，后来在头原中表达。这与果蝇相似，表明其功能是保守的。然而，在飞行中没有可用的功能数据。在Tribolium的RNAi中，整个背头缺失。作为该项目的一部分，将构建几个转基因系，这将对其他研究有价值。这包括一个系统，以遗传永久标记表皮细胞，几个Gal4驱动程序和响应结构与荧光蛋白，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.