Chitin, a polysaccharide of N-acetylglucosamine, is the primary building material for both insect exoskeletons and the bristles of marine bristle worms. Bristles enable the worms to move in their aquatic environment. The mechanism, however, by which this material is formed into bristles has, to date, remained enigmatic. Group leader Florian Raible explains: "Chaetoblasts, specialized cells with long surface structures known as microvilli, play a pivotal role in this process. These microvilli harbor a specific enzyme responsible for chitin synthesis, crucial for bristle building." The researchers’ findings reveal a dynamic cell surface characterized by geometrically arranged microvilli. Bristle formation entails both extension and disassembly processes.
These dynamic processes operate on a material jetting principle. Florian elaborates: "Our analysis indicates that bristles are not cast, but chitin is ejected by the chaetoblasts. The microvilli of the cells play a crucial role in shaping the distinct geometric structure.” Bristle biosynthesis usually takes place in two days and gives rise to different shapes, depending on the developmental stage of the worm. Starting with the production of the bristle tip, followed by the middle section, and finally the base, the process resembles 3D printing, where an object is generated layer by layer.
Besides local collaborations with the Hellmich group of the Technical University of Vienna and imaging specialists at the University of Brno, the cooperation with the Jokitalo lab from the University of Helsinki proved to be a significant asset for the Raible group. With their expertise in serial block-face scanning electron microscopy (SBF-SEM), the researchers examined microvillar arrangements during bristle biogenesis and proposed a 3D model of the synthesis of nascent bristles. First author Kyojiro Ikeda explains: " Standard electron tomography is very labor-intensive, as the cutting of the samples and their examination in the electron microscope must be done manually. With this approach, however, we can reliably automate the analysis of thousands of layers." The layers are aligned to generate 3D electron micrographs, but the technique is limited in resolution.
The Raible group is currently working on a new approach with enhanced resolution to visualize the entire process of bristle biogenesis. Chitin synthase also holds translational potential, in particular with respect to the printing of other polysaccharide materials or geometries, and the associated production of recyclable products. Understanding bristle biogenesis is therefore not only valuable for biology but may have potential future applications in material science.
DOI: 10.1038/s41467-024-48044-3
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