The Effects of Chemical Animalizing and Vegetalizing Agents and of Cell Dissociation on the Synthesis of 5S RNA and Transfer RNA in Cleaving Sea Urchin Embryos. (animalization/vegetalization/cell dissociation/5S RNA and tRNA synthesis/sea urchin embryo)

Gastrulation is a universal process in the morphogenesis of many animal embryos. In sea urchin embryos, it involves the invagination of single-layered vegetal plate into blastocoel. Although morphological and molecular events have been well studied for gastrulation, the mechanical driving forces and their regulatory mechanism underlying the gastrulation is not fully understood. In this study, structural features and cytoskeletal distributions were studied in sea urchin embryo using an "exogastrulation" model induced by inhibiting the H+/K+ ion pump with omeprazole. The vegetal pole sides of the exogastrulating embryos had reduced roundness indices, intracellular pH polarization, and intracellular F-actin polarization at the pre-early gastrulation compared with the normal embryo. Gastrulation stopped when F-actin polymerization or degradation was inhibited by RhoA or YAP1 knockout, although pH distributions were independent of such a knockout. A mathematical model of sea urchin embryos at the early gastrulation reproduced the shapes of both normal and exogastrulating embryos using cell-dependent cytoskeletal features based on F-actin and pH distributions. Thus, gastrulation required appropriate cell position-dependent intracellular F-actin distributions regulated by the H+/K+ ion pump through pH control.

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

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.95.16.9343 ◽

1998 ◽

Vol 95 (16) ◽

pp. 9343-9348 ◽

Cited By ~ 162

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.

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