Reconstruction of Starfish Eggs by Electric Cell Fusion: A New Method of Detect the Cytoplasmic Determinant for Archenteron Formation

Kiyomoto, Masato; Shirai, Hiroko

doi:10.1111/j.1440-169x.1993.00107.x

Cited by 13 publications

(3 citation statements)

References 18 publications

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“…More recent studies in the starfish showed that a relatively small region of the vegetal hemisphere contained the material necessary for endoderm specification (Kuraishi and Osanai, 1994). If that small vegetal region was removed, an archenteron failed to appear (Kiyomoto and Shirai, 1993). Those studies, and others like them, extending to vertebrates, strongly suggested that information near the vegetal pole was important for activating endomesoderm specification, but the identity of the active principle in the vegetal region remained unknown.…”

Section: Introductionmentioning

confidence: 96%

Wnt6 activates endoderm in the sea urchin gene regulatory network

Croce

Range

et al. 2011

Development

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SUMMARYIn the sea urchin, entry of -catenin into the nuclei of the vegetal cells at 4th and 5th cleavages is necessary for activation of the endomesoderm gene regulatory network. Beyond that, little is known about how the embryo uses maternal information to initiate specification. Here, experiments establish that of the three maternal Wnts in the egg, Wnt6 is necessary for activation of endodermal genes in the endomesoderm GRN. A small region of the vegetal cortex is shown to be necessary for activation of the endomesoderm GRN. If that cortical region of the egg is removed, addition of Wnt6 rescues endoderm. At a molecular level, the vegetal cortex region contains a localized concentration of Dishevelled (Dsh) protein, a transducer of the canonical Wnt pathway; however, Wnt6 mRNA is not similarly localized. Ectopic activation of the Wnt pathway, through the expression of an activated form of -catenin, of a dominant-negative variant of GSK-3 or of Dsh itself, rescues endomesoderm specification in eggs depleted of the vegetal cortex. Knockdown experiments in whole embryos show that absence of Wnt6 produces embryos that lack endoderm, but those embryos continue to express a number of mesoderm markers. Thus, maternal Wnt6 plus a localized vegetal cortical molecule, possibly Dsh, is necessary for endoderm specification; this has been verified in two species of sea urchin. The data also show that Wnt6 is only one of what are likely to be multiple components that are necessary for activation of the entire endomesoderm gene regulatory network.

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Section: Introductionmentioning

confidence: 96%

Wnt6 activates endoderm in the sea urchin gene regulatory network

Croce

Range

et al. 2011

Development

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“…As materials for analyzing nucleocytoplasmic relations, starfish eggs are preferable to sea urchin eggs in several respects: (i) the large size of the starfish egg makes the bisection easier; (ii) lack of a rigid hyaline layer facilitates the dissociation of blastomeres; and (iii) the ploidy of embryos can be doubled by blocking the formation of polar bodies (Obata & Nemoto 1984). Moreover, routine procedures for the electric fusion of starfish eggs have been described (Kiyomoto & Shirai 1993; Yoneda 1997), by which we can increase the volume of the cytoplasm of an egg. The last method has never been used in analyzing the timing mechanism operating during cleavage stages; we are the first to use it.…”

Section: Introductionmentioning

confidence: 99%

Nucleus : cell volume ratio directs the timing of the increase in blastomere adhesiveness in starfish embryos

Masui

Yoneda²,

Kominami

2001

Dev Growth Differ

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Blastomeres of starfish embryos begin to increase in adhesiveness after the eighth cleavage and form a monolayered hollow blastula. To investigate factors that affect the timing of the adhesiveness increase, we changed the volume of the cytoplasm or the ploidy of embryos and examined the morphologic changes in the descendent blastomeres during early cleavage stages. In parthenogenetic embryos, in which the ploidy is doubled, the timing of the increase in adhesiveness was accelerated by one cell cycle. In contrast, the timing was delayed by approximately one cell cycle in a large-sized embryo formed by the fusion of an egg and a non-nucleate egg fragment. These two sets of observations are in accord with the expectation from the classical concept that the DNA: cytoplasmic ratio may direct the timing of events in early development. However, observations of small-sized embryos with a reduced amount of cytoplasm were contradictory to the expectation based on the DNA: cytoplasmic ratio; the timing of the increase in adhesiveness in half-sized embryos was almost the same as in control embryos and the timing was delayed by only one cell cycle in quarter-sized embryos. Measurement of the diameters of nuclei showed that the size of nuclei was variable, depending on the stage of development, the volume of cytoplasm and ploidy. We calculated a volume ratio of nucleus to cytoplasm (N: C volume ratio) for tetraploid, large-, half- and quarter-sized embryos. We found that the embryonic cells begin to adhere always when their N: C volume ratio reaches 0.06. A plausible model for the cellular timing mechanism of cell contact is proposed.

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“…Over the past decades several methods have been introduced to fuse oocytes of different organisms, for instance with (Vassetzky 1983;Gulyas et al 1984), electrofusion (Kiyomoto and Shirai 1993;Yoneda 1997) or inactivated Sendai virus (Nogue et al 1994). For the questions we addressed here these methods are not suitable because the body size and construction of nematodes with a single-chamber hydroskeleton do not permit removal, manipulation and re-implantation of the small, sensitive oocytes (>50 µm long), as can be done in mouse.…”

Section: Experimental Cell Fusionmentioning

confidence: 98%

Developmental potential of fused Caenorhabditis elegans oocytes: generation of giant and twin embryos

Irle

Schierenberg

2002

Dev Genes Evol

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With their first cleavage blastomeres in Caenorhabditis elegans are fixed to very different developmental programs going along with differential segregation of maternal gene products. To investigate whether indications for a prelocalization of cytoplasmic components can already be found in unfertilized egg cells, we fused mature C. elegans oocytes with the help of a laser microbeam. Fertilization of two fused oocytes resulting in triploid zygotes showed an essentially normal early cleavage pattern with the establishment of five somatic cell lineages and a germline and also a normal spatial arrangement of blastomeres. A considerable fraction of such embryos hatched and developed into fertile giant nematodes. The numbers of cell nuclei in freshly hatched and adult giant animals were found to be essentially the same as in untreated controls. When three fused oocytes were fertilized, two alternative patterns of early embryogenesis were observed. Half of the embryos followed the normal cleavage mode. The other half, however, developed in a twin-like fashion with all cells present in two copies, apparently due to fertilization by two sperm. In such embryos, two areas of gastrulation were established, resulting in the generation of two separate gut primordia. In summary, our results suggest that (1) in contrast to the uncleaved zygote in the mature oocyte of C. elegans no cytoplasmic regionalization exists, (2) the invariable cell numbers typical for the C. elegans embryo are not controlled via cell size, and (3) the entry of a second sperm can induce a cascade of events in the egg leading to the formation of two complete embryo anlagen.

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Reconstruction of Starfish Eggs by Electric Cell Fusion: A New Method of Detect the Cytoplasmic Determinant for Archenteron Formation

Cited by 13 publications

References 18 publications

Wnt6 activates endoderm in the sea urchin gene regulatory network

Wnt6 activates endoderm in the sea urchin gene regulatory network

Nucleus : cell volume ratio directs the timing of the increase in blastomere adhesiveness in starfish embryos

Developmental potential of fused Caenorhabditis elegans oocytes: generation of giant and twin embryos

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