Abstract
Centriole structure and function in the sea urchin zygote parallel those in mammalian somatic cells. Here, I briefly introduce the properties and attributes of the sea urchin system that make it an attractive platform for the study of centrosome and centriole duplication. These attributes apply to all echinoderms readily available from commercial suppliers: sea urchins, sand dollars, and starfish. I list some of the practical aspects of the system that make it a cost- and time-effective system for experimental work and then list properties that are a “tool kit” that can be used to conduct studies that would not be practical, or in some cases not possible, with mammalian somatic cells. Since centrioles organize and localize the pericentriolar material that nucleates the astral arrays of microtubules (Bobinnec et al. in J Cell Biol 143(6):1575–1589, 1998), the pattern of aster duplication over several cell cycles can be used as a reliable measure for centriole duplication (Sluder and Rieder in J Cell Biol 100(3):887–896, 1985). Descriptions of the methods my laboratory has used to handle and image echinoderm zygotes are reviewed in Sluder et al. (Methods Cell Biol 61:439–472, 1999). Also included is a bibliography of papers that describe additional methods.
Highlights
Sperm and egg The sea urchin sperm contains two centrioles
The unfertilized egg is believed to be devoid of centrioles as none have been reported from ultrastructural studies
Centrosome inheritance in echinoderms is paternal; both centrioles in the sperm are contributed to the zygote and after duplication they organize the centrosomes used in development
Summary
Sperm and egg The sea urchin sperm contains two centrioles. One serves as the basal body of the flagellum and has a prominent electron-dense cap on the proximal end where it is firmly anchored in a hof at the base of the sperm nucleus (Fig. 1a, b). Since the investigation of centrosome/centriole duplication often requires following the cells for multiple cell cycles, echinoderm zygotes allow one to do an experiment in a morning or afternoon, not the several days needed for somatic cells. Zygotes can be fragmented by passing them through a plastic screen shortly after the fertilization envelope is removed Since this is done before pronuclear fusion, one obtains a mixture of viable cycling enucleated cell fragments; fragments that contain just a male or a female pronucleus or fragments with both pronuclei [5]. One of the easiest and most controllable methods is to transiently raise their internal pH with ammoniated sea water [16] Such activated eggs, or experimentally produced fragments of fertilized eggs that contain only the female pronucleus, organize at mitosis a single radial array of microtubules (a monaster) at the site of the female pronucleus. This system could be used to study the properties and composition of pericentriolar material free from centrioles
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