On ‘the Stationary Surface Ring’ in Heart-Shaped Cleavage

1958 ◽  
Vol 35 (2) ◽  
pp. 400-406
Author(s):  
KATSUMA DAN
Keyword(s):  
Cell Surface ◽  
Sea Urchin ◽  
Mitotic Spindle ◽  
Cleavage Furrow ◽  
Sand Dollar ◽  
Animal Pole ◽  
Sea Urchin Eggs ◽  
Stationary Surface ◽  
Vegetal Pole

1. The eggs of the sand dollar, Astriclypeus manni, and the medusa, Spirocodon saltatrix, were used for the reason that they cleave in heart shape, the cleavage furrow appearing earlier at the animal than at the vegetal pole. 2. By the superposition of drawings showing contours and astral centres as well as the positions of carbon markers on the cell surface, the presence of a pair of stationary circular zones of the cortex can be demonstrated. These remain absolutely stationary through successive stages of cleavage, as was shown to be true of regularly cleaving sea-urchin eggs. 3. The two planes determined by this pair of stationary surface rings tilt toward each other on the animal pole side in linear proportion to the eccentricity of the mitotic spindle within the cell, and the loci of the astral centres tend to slant toward the animal pole. 4. The above phenomena can be explained by the previously proposed theory for heart-shaped cleavage; i.e. the primary cause of heart-shaped cleavage is the eccentric position of the spindle, which in turn causes the rotation of the asters and the bending of the spindle.

Studies of the cleavage in the frog egg

Development ◽  
1969 ◽  
Vol 21 (1) ◽  
pp. 119-129
Author(s):  
T. Kubota
Keyword(s):  
Sea Urchin ◽  
Sea Urchins ◽  
Cleavage Furrow ◽  
Mitotic Apparatus ◽  
Animal Pole ◽  
Sea Urchin Eggs ◽  
Rana Nigromaculata ◽  
Vegetal Pole ◽  
Egg Cortex

In sea-urchin eggs, once karyokinesis reaches metaphase or anaphase, the cleavage furrow can be formed even if the mitotic apparatus is destroyed (Swann & Mitchison, 1953) or removed (Hiramoto, 1956). A similar result was obtained in frog eggs (Kubota, 1966). In amphibian eggs a much longer time is available for performing experiments than in sea urchins as the furrow first appears at the animal pole and slowly travels toward the vegetal pole. Taking advantage of this situation, Waddington (1952) and Dan & Kuno-Kojima (1963) performed various kinds of operations to elucidate the roles of the egg cortex and the inner cytoplasm in furrow formation, and Selman & Waddington (1955) also made cytological observations of the process. In the present paper a shift of the inner cytoplasm relative to the cortex and its influence on the course of the furrow was analysed for eggs of the frog Rana nigromaculata.

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.

Isolation of the Cleavage Furrow from Dividing Sea Urchin Eggs

1990 ◽  
Vol 582 (1 Cytokinesis) ◽  
pp. 318-320 ◽  
Author(s):  
SHIGENOBU YONEMURA ◽  
ISSEI MABUCHI ◽  
SCHOICHIRO TSUKITA
Keyword(s):  
Sea Urchin ◽  
Cleavage Furrow ◽  
Sea Urchin Eggs

Roles of Cortical and Subcortical Components in Cleavage Furrow Formation in Amphibia

1972 ◽  
Vol 11 (2) ◽  
pp. 543-556
Author(s):  
TSUYOSHI SAWAI
Keyword(s):  
Surface Layer ◽  
Xenopus Laevis ◽  
Species Specificity ◽  
Cleavage Furrow ◽  
Entire Surface ◽  
Animal Pole ◽  
The Future ◽  
Vegetal Pole ◽  
Triturus Pyrrhogaster

In the eggs of the newt, Triturus pyrrhogaster, 2 separate factors are recognized which take part in cleavage furrow formation. (1) The inductive capacity for the furrow formation by the cytoplasm lying under the cortex along the cleavage furrow (FIC); and (2) the reactivity of the overlying cortex to form a furrow in response to FIC. (1) FIC. The inductive capacity is shown by the fact that FIC induces a furrow on whichever part of the surface under which FIC is transplanted. FIC is distributed along the cleavage furrow and even extends along the future furrow plane ahead of the furrow tip. The distance FIC precedes the furrow tip is about 1.0 mm in the animal hemisphere and is less in the vegetal hemisphere. In the direction at right angles to the furrow plane, FIC does not spread more than 0.1 mm. FIC is also present in the eggs of Xenopus laevis. Species specificity of FIC for induction is not found between Triturus and Xenopus. (2) Surface layer. At the onset of the first cleavage, the reactivity of the cortex to form the furrow in answer to FIC induction is localized on the animal pole region. The reactivity of the cortex propagates medially as a belt along the surface towards the vegetal pole with the advancing tip of the cleavage furrow. After the furrow is completed, the reactivity begins to be lost from the animal pole region, and eventually over the entire surface. The reactivity, however, reappears on the animal pole region simultaneously with the second cleavage.

Effect of wortmannin, an inhibitor of phosphatidylinositol 3-kinase, on the first mitotic divisions of the fertilized sea urchin egg

1998 ◽  
Vol 111 (17) ◽  
pp. 2507-2518 ◽  
Author(s):  
C. De Nadai ◽  
P. Huitorel ◽  
S. Chiri ◽  
B. Ciapa
Keyword(s):  
Sea Urchin ◽  
Mitotic Spindle ◽  
Second Messengers ◽  
Cellular Systems ◽  
Phosphatidylinositol 3 Kinase ◽  
Sea Urchin Eggs ◽  
Cellular Processes ◽  
Nuclear Envelope Breakdown ◽  
Sea Urchin Egg ◽  
Messenger System

We have reported earlier that the polyphosphoinositide messenger system may control mitosis in sea urchin eggs. Besides phospholipase C activation and its second messengers, phosphatidylinositol (PI) 3-kinase has been proposed to affect a wide variety of cellular processes in other cellular systems. Therefore, we have investigated whether PI 3-kinase could play a role in regulating the sea urchin early embryonic development. Our data presented here suggest that PI 3-kinase is present in sea urchin eggs. We found that wortmannin, an inhibitor of PI 3-kinase, led to arrest of the cell cycle. Chromosome condensation, nuclear envelope breakdown, microtubular aster polymerization, protein and DNA synthesis were not affected when fertilization was performed in the presence of the drug. However, maturation-promoting factor (MPF) activation was inhibited and centrosome duplication was perturbed preventing the formation of a bipolar mitotic spindle in wortmannin treated eggs. We discuss how PI 3-kinase might be involved in the cascade of events leading to the first mitotic divisions of the fertilized sea urchin egg.

scholarly journals AN INDIRECT METHOD TO ASSAY FOR MITOTIC CENTERS IN SAND DOLLAR (DENDRASTER EXCENTRICUS) EGGS

1966 ◽  
Vol 30 (3) ◽  
pp. 555-562 ◽  
Author(s):  
Hans A. Went
Keyword(s):  
Sea Urchin ◽  
De Novo ◽  
Sea Water ◽  
Early Prophase ◽  
Sand Dollar ◽  
Normal Pattern ◽  
Mitotic Apparatus ◽  
Sea Urchin Eggs ◽  
Dendraster Excentricus ◽  
Normal Controls

It is possible consistently to induce sea urchin and sand dollar eggs to cleave directly from one cell into four cells. This is done by exposing the fertilized eggs to benzimidazole for 20 to 30 min beginning about early metaphase. The mitotic apparatus regresses, the cells do not cleave, and shortly after they are returned to normal sea water an early-prophase-appearing nucleus is present in each cell. Each cell then organizes a tetrapolar tetrahedral mitotic apparatus de novo, instead of transforming a bipolar mitotic apparatus into a tetrapolar figure, and cleaves one-to-four. In another type of experiment, it appears that sand dollar eggs exposed to mercaptoethanol during the first period of mitotic center duplication have only half as many centers by first cleavage metaphase as the normal controls. This is consistent with an earlier report by Mazia et al (1960). Using this same experimental technique, it was demonstrated that benzimidazole, on the contrary, does not interfere with mitotic center duplication in sand dollar eggs. A labeling experiment demonstrated that benzimidazole does not interfere markedly with the normal pattern of incorporation of C14-thymidine into the DNA of sea urchin eggs. The data reported here suggest that judicious treatment of sand dollar eggs (and probably sea urchin eggs, too) with benzimidazole can induce the eggs to cleave into as many cells as there were mitotic centers sometime earlier, for example at early metaphase of the first cleavage division. This provides a very useful tool for studies on the process of mitotic center duplication.

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