TCF Is the Nuclear Effector of the β-Catenin Signal That Patterns the Sea Urchin Animal–Vegetal Axis

• Published in: Developmental biology Vol. 217; no. 2; pp. 230 - 243
• Main Authors: Vonica, Alin, Weng, Wei, Gumbiner, Barry M., Venuti, Judith M.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 15-01-2000
• Subjects: Animals; animal–vegetal axis; Antigens, Differentiation; beta Catenin; Body Patterning; Cadherins - metabolism; Calcium-Calmodulin-Dependent Protein Kinases - metabolism; Cell Communication; Cell Differentiation; Cytoskeletal Proteins - metabolism; dominant negative; Echinoidea; Gene Expression Regulation, Developmental; Genes, Reporter; Glucocorticoids - pharmacology; Glycogen Synthase Kinase 3; HMGB Proteins; Lithium Chloride - pharmacology; Microinjections; Protein Binding; sea urchin embryos; Sea Urchins - embryology; TCF Transcription Factors; TCF/LEF; Time Factors; Trans-Activators; Transcription Factor 7-Like 1 Protein; Transcription Factors - metabolism; VP-16; Xtcf-3; β-catenin; β-catenin; sea urchin embryos; TCF/LEF; VP-16; animal–vegetal axis; Xtcf-3; dominant negative
• ISSN: 0012-1606; 1095-564X
• DOI: 10.1006/dbio.1999.9551

The mechanism of animal–vegetal (AV) axis formation in the sea urchin embryo is incompletely understood. Specification of the axis is thought to involve a combination of cell–cell signals and as yet unidentified maternal determinants. In Xenopus the Wnt pathway plays a crucial role in defining the embryonic axes. Recent experiments in sea urchins have shown that at least two components of the Wnt signaling pathway, GSK3β and β-catenin, are involved in embryonic AV axis patterning. These results support the notion that the developmental network that regulates axial patterning in deuterostomes is evolutionarily conserved. To further test this hypothesis, we have examined the role of β-catenin nuclear binding partners, members of the TCF family of transcriptional regulators, in sea urchin AV axis patterning. To test the role of TCFs in mediating β-catenin signals in sea urchin AV axis development we examined the consequences of microinjecting RNAs encoding altered forms of TCF on sea urchin development. We show that expression of a dominant negative TCF results in a classic “animalized” embryo. In contrast, microinjected RNA encoding an activated TCF produces a highly “vegetalized” embryo. We show that the transactivational activity of endogenous sea urchin TCF is potentiated by LiCl treatment, which vegetalizes embryos by inhibiting GSK3, consistent with an in vivo interaction between endogenous β-catenin and TCF. We also provide evidence indicating that all of β-catenin's activity in patterning the sea urchin AV axis is mediated by TCF. Using a glucocorticoid-responsive TCF, we show that TCF transcriptional activity affects specification along the AV axis between fertilization and the 60-cell stage.