Echinobase Image ID: 208617

FIGURE 8. Proposed model of microtubule structure and function throughout sea urchin larval skeletogenesis. (A) An illustration of a 25hpf sea urchin embryo with skeletogenic cells marked in blue, the biomineral marked in light orange. (B) An enlargement of the triradiate spicule area showing the skeletogenic cells around the spicule with nuclei marked in white, and the Golgi apparatus marked in pink. At the Golgi apparatus matrix proteins SM50 (marked in yellow) and SM30 (marked in purple) are being sorted and packed inside vesicles. Around the spicule FAK is activated (marked in red). The microtubule filaments elongate from perinuclear region into the biomineralization compartment in all the skeletogenic cells, and the microtubule filaments are anchored around the outer membrane of the spicule. In the region of the mineral‐free pseudopodia, microtubule filaments transport vesicles bearing SM50 from the Golgi into the pseudopodia cable while SM30 is only found in the Golgi. At the growing tip of the spicule, both SM30 and SM50 are trafficked on microtubules from the Golgi apparatus to the spicule outer membrane. (C) Illustration of a sea urchin embryo at 48hpf, similar color codes to A. (D) An enlargement of the body tip area. The microtubule filaments elongate from perinuclear region into the biomineralization compartment, possible mediating the transport of SM30 and SM50 bearing vesicles. The density of the microtubule filaments appears to higher at cells near the growing tips compared to cells at the back of the rods. Image courtesy of Shanduo Chen. Image published in: Qassem A et al. (2025) Image downloaded from an Open Access article in PubMed Central. © 2025 The Author(s). Larger Image Printer Friendly View

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