Patterning of an ascidian embryo along the anterior-posterior axis through spatial regulation of competence and induction ability by maternally localized PEM |
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Authors: | Gaku Kumano Hiroki Nishida |
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Affiliation: | Department of Biological Sciences, Graduate School of Science, Osaka University, Toyonaka, Osaka 560-0043, Japan |
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Abstract: | In ascidian embryos, anterior-posterior (A-P) patterning of the vegetal cells is regulated by posteriorizing activities of a localized egg region known as posterior-vegetal cortex/cytoplasm (PVC). PEM is an essential component of the PVC and is involved in the posterior-specific cell cleavage pattern. Here we report a novel function of PEM independently of its function in cleavage regulation; it controls cell fate by excluding competence to respond to the FGF signal for notochord induction from posterior-vegetal cells. PEM was found to regulate the nuclear accumulation of β-catenin, an upstream activator of the competence factor. PEM also influences A-P patterning in the animal hemisphere. It was found to regulate FGF signal expression and restrict the occurrence of brain induction only in the anterior region. Our results suggest a model in which PEM patterns the embryo along the A-P axis through regulation of the spatial distribution of competence and induction ability. |
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Keywords: | Anterior-posterior axis Ascidian β-catenin Competence FGF Induction PEM |
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