Isolation and characterization of β-catenin downstream genes in early embryos of the ascidian Ciona savignyi

Abstract

Nuclear localization of β-catenin is most likely the first step of embryonic axis formation or embryonic cell specification in a wide variety of animal groups. Therefore, the elucidation of β-catenin target genes is a key research subject in understanding the molecular mechanisms of the early embryogenesis of animals. In Ciona savignyi embryos, nuclear accumulation of β-catenin is the first step of endodermal cell specification. Previous subtractive hybridization screens of mRNAs between β-catenin-overexpressed embryos and nuclear β-catenin-depleted embryos have resulted in the identification of β-catenin downstream genes in Ciona embryos. In the present study, I characterize seven additional β-catenin downstream genes, Cs-cadherinII, Cs-protocadherin, Cs-Eph, Cs-βCD1, Cs-netrin, Cs-frizzled3/6, and Cs-lefty/antivin. All of these genes were expressed in vegetal blastomeres between the 16-cell and 110-cell stages, although their spatial and temporal expression patterns were different from one another. In situ hybridizations and real-time PCR revealed that the expression of all of these genes was up-regulated in β-catenin-overexpressed embryos, and down-regulated in β-catenin-suppressed embryos. Therefore, the accumulation of β-catenin in the nuclei of vegetal blastomeres activates various vegetally expressed genes with potentially important functions in the specification of these cells.