![]() Sea urchins cells, like mammalian cells, contain abundant quantities of vaults, which are ~13MDa ribonucleoprotein particles of as yet unknown function. Therefore sea urchins provide a system that avoids the problem of functional redundancies between multiple paralogues that often occurs in vertebrates, and serves as a useful comparison for assessing the significance of conserved genes and regulatory linkages within the genome. In addition, the echinoderm lineage leading to sea urchins diverged from chordates prior to the large scale gene duplication events that occurred early in the evolution of the vertebrates, and because of this many of the genes that are found as multiple paralogues in vertebrates have only a single homolog in sea urchins. Sea urchins occupy an important phylogenetic position as basal deuterostomes, and are thus more closely related to humans than are other invertebrate model organisms such as Drosophila and C. Sea urchin embryos are well suited for biochemical approaches to studying the cell biology of development, as large quantities of eggs can easily be obtained, and their fertilization initiates the synchronous development of optically transparent embryos. The sea urchin Strongylocentrotus purpuratus is an important model system in developmental biology and its genome is currently being sequenced by the Human Genome Sequencing Center at the Baylor College of Medicine under the auspices of the National Human Genome Research Institute (NHGRI). These results are suggestive of a role for the vault in delivering macromolecules to the nucleus during development. Confocal experiments indicate a dramatic relocalization of MVP from the cytoplasm to the nucleus during sea urchin embryogenesis. The sea urchin vault appears to have additional protein components in the molecular weight range of 14–55 kDa that might correspond to molecular contents. Analysis of the molecular composition of the sea urchin vault indicates that it contains components that may be homologs of the mammalian vault RNA component (vRNA) and protein components (VPARP and TEP1). A cryoelectron microscopy (cryoEM) reconstruction of isolated sea urchin vaults reveals the assembly to have a barrel-shaped external structure that is nearly identical to the rat vault structure. Sea urchin MVP includes seven ~50 residue repeats in the N-terminal half of the protein and a predicted coiled coil domain in the C-terminus, as does rat MVP. The sequence of the sea urchin major vault protein (MVP) was assembled from expressed sequence tags and genome traces, and the predicted protein was found to have 64% identity and 81% similarity to rat MVP. ![]() ![]() Here we compare the structures of sea urchin and mammalian vaults and analyze the subcellular distribution of vaults during sea urchin embryogenesis. elegans, neither of which possesses vaults. The Pacific coast sea urchin, Strongylocentrotus purpuratus, is an invertebrate model organism that is evolutionarily closer to humans than Drosophila and C. Vaults are intriguing ribonucleoprotein assemblies with an unknown function that are conserved among higher eukaryotes. ![]()
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