scholarly journals Functional Gap Junctions in the Early Sea Urchin Embryo Are Localized to the Vegetal Pole

1999 ◽  
Vol 212 (2) ◽  
pp. 503-510 ◽  
Author(s):  
Ikuko Yazaki ◽  
Brian Dale ◽  
Elisabetta Tosti
Keyword(s):  
Gap Junctions ◽  
Sea Urchin ◽  
Sea Urchin Embryo ◽  
Vegetal Pole

GSK3beta/shaggy mediates patterning along the animal-vegetal axis of the sea urchin embryo

Development ◽  
1998 ◽  
Vol 125 (13) ◽  
pp. 2489-2498 ◽  
Author(s):  
F. Emily-Fenouil ◽  
C. Ghiglione ◽  
G. Lhomond ◽  
T. Lepage ◽  
C. Gache
Keyword(s):  
Sea Urchin ◽  
Wnt Pathway ◽  
Dominant Negative ◽  
Early Gene ◽  
Expression Domain ◽  
Animal Pole ◽  
Axial Patterning ◽  
Sea Urchin Embryo ◽  
Vegetal Pole ◽  
Dominant Negative Activity

In the sea urchin embryo, the animal-vegetal axis is defined before fertilization and different embryonic territories are established along this axis by mechanisms which are largely unknown. Significantly, the boundaries of these territories can be shifted by treatment with various reagents including zinc and lithium. We have isolated and characterized a sea urchin homolog of GSK3beta/shaggy, a lithium-sensitive kinase which is a component of the Wnt pathway and known to be involved in axial patterning in other embryos including Xenopus. The effects of overexpressing the normal and mutant forms of GSK3beta derived either from sea urchin or Xenopus were analyzed by observation of the morphology of 48 hour embryos (pluteus stage) and by monitoring spatial expression of the hatching enzyme (HE) gene, a very early gene whose expression is restricted to an animal domain with a sharp border roughly coinciding with the future ectoderm / endoderm boundary. Inactive forms of GSK3beta predicted to have a dominant-negative activity, vegetalized the embryo and decreased the size of the HE expression domain, apparently by shifting the boundary towards the animal pole. These effects are similar to, but even stronger than, those of lithium. Conversely, overexpression of wild-type GSK3beta animalized the embryo and caused the HE domain to enlarge towards the vegetal pole. Unlike zinc treatment, GSK3beta overexpression thus appeared to provoke a true animalization, through extension of the presumptive ectoderm territory. These results indicate that in sea urchin embryos the level of GSKbeta activity controls the position of the boundary between the presumptive ectoderm and endoderm territories and thus, the relative extent of these tissue layers in late embryos. GSK3beta and probably other downstream components of the Wnt pathway thus mediate patterning both along the primary AV axis of the sea urchin embryo and along the dorsal-ventral axis in Xenopus, suggesting a conserved basis for axial patterning between invertebrate and vertebrate in deuterostomes.

Specification of endoderm and mesoderm in the sea urchin

Zygote ◽  
1999 ◽  
Vol 8 (S1) ◽  
pp. S41-S41 ◽  
Author(s):  
David R. McClay
Keyword(s):  
Sea Urchin ◽  
Wnt Pathway ◽  
Special Significance ◽  
Nuclear Entry ◽  
Cell Stage ◽  
Animal Pole ◽  
Secondary Axis ◽  
Sea Urchin Embryo ◽  
Vegetal Pole

It has long been recognized that micromeres have special significance in early specification events in the sea urchin embryo. Micromeres have the ability to induce a secondary axis if transferred to the animal pole at the 16-cell stage of sea urchin embryos (Hörstadius, 1939). Without micromeres an isolated animal hemisphere develops into an ectodermal ball called a dauer blastula. Addition of micromeres to an animal half rescues a normal pluteus larva, including endoderm (Hörstadius, 1939). Despite these well-known experiments, however, neither the molecular basis of that induction nor the endogenous inductive role of micromeres in development was known. In recent experiments we learned that if one eliminates micromeres from the vegetal pole at the 16-cell stage the resulting embryo makes no secondary mesenchyme. Earlier it had been found that β-catenin is crucial for specification events that lead to mesoderm and endoderm (Wikra-manayake et al., 1998; Emily-Fenouil et al., 1998; Logan et al., 1999). We noticed that at the 16-cell stage β-catenin enters the nuclei of micromeres, then enters the nuclei of macromeres at the 32-cell stage (Logan et al., 1999). Since nuclear entry of β-catenin is known to be important for its signalling function in the Wnt pathway, we asked whether β-catenin functions in the micromere induction pathway.

scholarly journals β-Catenin is essential for patterning the maternally specified animal-vegetal axis in the sea urchin embryo

1998 ◽  
Vol 95 (16) ◽  
pp. 9343-9348 ◽  
Author(s):  
Athula H. Wikramanayake ◽  
Ling Huang ◽  
William H. Klein
Keyword(s):  
Sea Urchin ◽  
Molecular Mechanisms ◽  
Early Embryo ◽  
Cell Fates ◽  
Cell Stage ◽  
Signal Transduction Cascade ◽  
Sea Urchin Embryos ◽  
Sea Urchin Embryo ◽  
Vegetal Pole ◽  
Vegetal Cell

In sea urchin embryos, the animal-vegetal axis is specified during oogenesis. After fertilization, this axis is patterned to produce five distinct territories by the 60-cell stage. Territorial specification is thought to occur by a signal transduction cascade that is initiated by the large micromeres located at the vegetal pole. The molecular mechanisms that mediate the specification events along the animal–vegetal axis in sea urchin embryos are largely unknown. Nuclear β-catenin is seen in vegetal cells of the early embryo, suggesting that this protein plays a role in specifying vegetal cell fates. Here, we test this hypothesis and show that β-catenin is necessary for vegetal plate specification and is also sufficient for endoderm formation. In addition, we show that β-catenin has pronounced effects on animal blastomeres and is critical for specification of aboral ectoderm and for ectoderm patterning, presumably via a noncell-autonomous mechanism. These results support a model in which a Wnt-like signal released by vegetal cells patterns the early embryo along the animal–vegetal axis. Our results also reveal similarities between the sea urchin animal–vegetal axis and the vertebrate dorsal–ventral axis, suggesting that these axes share a common evolutionary origin.

scholarly journals Exogenous hyalin and sea urchin gastrulation, Part II: hyalin, an interspecies cell adhesion molecule

Zygote ◽  
2008 ◽  
Vol 16 (1) ◽  
pp. 73-78 ◽  
Author(s):  
M. Alvarez ◽  
J. Nnoli ◽  
E.J. Carroll ◽  
V. Hutchins-Carroll ◽  
Z. Razinia ◽  
...  
Keyword(s):  
Sea Urchin ◽  
Cell Adhesion Molecule ◽  
Cellular Interaction ◽  
Adhesive Interaction ◽  
Lytechinus Pictus ◽  
Developmental Effects ◽  
Sea Urchin Embryo ◽  
Repeat Domain ◽  
Precise Quantification ◽  
Main Component

SummaryThe 330 kDa fibrillar glycoprotein hyalin is a well known component of the sea urchin embryo extracellular hyaline layer. Only recently, the main component of hyalin, the hyalin repeat domain, has been identified in organisms as widely divergent as bacteria and humans using the GenBank database and therefore its possible function has garnered a great deal of interest. In the sea urchin, hyalin serves as an adhesive substrate in the developing embryo and we have recently shown that exogenously added purified hyalin from Strongylocentrotus purpuratus embryos blocks a model cellular interaction in these embryos, archenteron elongation/attachment to the blastocoel roof. It is important to demonstrate the generality of this result by observing if hyalin from one species of sea urchin blocks archenteron elongation/attachment in another species. Here we show in three repeated experiments, with 30 replicate samples for each condition, that the same concentration of S. purpuratus hyalin (57 μg/ml) that blocked the interaction in living S. purpuratus embryos blocked the same interaction in living Lytechinus pictus embryos. These results correspond with the known crossreactivity of antibody against S. purpuratus hyalin with L. pictus hyalin. We propose that hyalin–hyalin receptor binding may mediate this adhesive interaction. The use of a microplate assay that allows precise quantification of developmental effects should help facilitate identification of the function of hyalin in organisms as divergent as bacteria and humans.

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