Abstract
Poc1 (Protein of Centriole 1) proteins are highly conserved WD40 domain-containing centriole components, well characterized in the alga Chlamydomonas, the ciliated protazoan Tetrahymena, the insect Drosophila and in vertebrate cells including Xenopus and zebrafish embryos. Functions and localizations related to the centriole and ciliary axoneme have been demonstrated for Poc1 in a range of species. The vertebrate Poc1 protein has also been reported to show an additional association with mitochondria, including enrichment in the specialized “germ plasm” region of Xenopus oocytes. We have identified and characterized a highly conserved Poc1 protein in the cnidarian Clytia hemisphaerica. Clytia Poc1 mRNA was found to be strongly expressed in eggs and early embryos, showing a punctate perinuclear localization in young oocytes. Fluorescence-tagged Poc1 proteins expressed in developing embryos showed strong localization to centrioles, including basal bodies. Anti-human Poc1 antibodies decorated mitochondria in Clytia, as reported in human cells, but failed to recognise endogenous or fluorescent-tagged Clytia Poc1. Injection of specific morpholino oligonucleotides into Clytia eggs prior to fertilization to repress Poc1 mRNA translation interfered with cell division from the blastula stage, likely corresponding to when neosynthesis normally takes over from maternally supplied protein. Cell cycle lengthening and arrest were observed, phenotypes consistent with an impaired centriolar biogenesis or function. The specificity of the defects could be demonstrated by injection of synthetic Poc1 mRNA, which restored normal development. We conclude that in Clytia embryos, Poc1 has an essentially centriolar localization and function.
Highlights
Centrioles are intruiging cellular organelles that have fascinated biologists for over a century
Understanding the centriole has long been a major challenge in cell biology, since this complex organelle is essential in its basal body form for the genesis and function of cilia and flagella across the eukaryotic world, and, as a cytoplasmic structure, can be a key player in cell division [18]
Poc1 is a Highly Conserved Centriole Protein Tagged fluorescent Poc1 proteins expressed in Clytia embryos proved to be excellent in vivo centriole markers, with bright staining confined to cytoplasmic centrosome and basal bodies
Summary
Centrioles are intruiging cellular organelles that have fascinated biologists for over a century. The WD40 repeat-containing protein Poc is an integral component of the centriole and is required for basal body stability and cilia formation. It has been exceptionally well conserved through eukaryotic evolution, being identified in most species in a wide genome survey [1], and has been consistently identified in centriole proteomics studies, for instance basal bodies of the unicellular alga Chlamydomonas [2], the ciliated protozoan Tetrahymena [3], human centrioles [4] and the mouse sensory cilium complex [5]. Poc shows a precise localization to the microtubule cylinder wall and the proximal/ basal cartwheel structure, and is a very early marker for proximal centriole and basal body assembly [3,6,7]
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