beta-Catenin is essential for patterning the maternally specified animal-vegetal axis in the sea urchin embryo.
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 beta-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 beta-catenin is necessary for vegetal plate specification and is also sufficient for endoderm formation. In addition, we show that beta-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.
Department of Biochemistry and Molecular Biology, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA.
A H
AH
Wikramanayake
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L
Huang
W H
WH
Klein
D000818:Animals; D019521:Body Patterning; D003598:Cytoskeletal Proteins / Q000378:metabolism*; D004475:Ectoderm / Q000166:cytology; D004625:Embryo, Nonmammalian; D004707:Endoderm / Q000166:cytology; D005260:Female; D018392:Genomic Imprinting; D008094:Lithium / Q000494:pharmacology; D012617:Sea Urchins / Q000196:embryology*; D015398:Signal Transduction; D015534:Trans-Activators; D051176:beta Catenin
D003598:Cytoskeletal Proteins; D015534:Trans-Activators; D051176:beta Catenin; D008094:Lithium