β-catenin translocation into nuclei demarcates the dorsalizing centers in frog and fish embryos

Abstract

The question of how dorsal-ventral polarity is established in vertebrates is central to our understanding of their early development. Several lines of evidence suggest that wnt-signaling is involved in the induction of dorsal-specific gene expression in the Spemann Organizer of amphibians. Here, we show that beta-catenin, acting as a component of the wnt-pathway, transiently accumulates in nuclei on the dorsal side of Xenopus and zebrafish blastulae. The spatially restricted nuclear translocation of beta-catenin precedes the expression of dorsal-specific genes. In experimentally ventralized frog embryos the dorsal ventral pattern of beta-catenin nuclear staining is abolished; in contrast, embryos hyperdorsalized by Li-ions or by injection of Xwnt8 mRNA exhibit an enhanced nuclear accumulation of beta-catenin. The results show that translocation of beta-catenin into nuclei in the wake of wnt-signaling is an early step in the establishment of the dorsal-ventral axis in frog and fish embryos.

Regulation of the early expression patterns of the zebrafish Dishevelled-interacting proteins Dapper1 and Dapper2

“…In zebrafish, the asymmetric localization of maternally supplied ␤-catenin determines the dorsal side of the embryo (Schneider et al, 1996;Dougan et al, 2003). To determine whether the early dorsal dpr1 and/or dpr2 expression is regulated by ␤-catenin signaling, constitutively active ␤-catenin (Molenaar et al, 1996) mRNA was injected into zebrafish embryos, and the expression of dpr genes was assayed by in situ hybridization at dome through 30% epiboly.…”

“…2 compare A,B with C,D, and I,J with K,L). Dorsal asymmetric ␤-catenin nuclear accumulation and signaling are thought to be the earliest dorsal specifying events (Schneider et al, 1996;Dougan et al, 2003;Leung et al, 2003b). To test whether initiation of dorsal dpr1 expression and dpr2 expression is downstream of ␤-catenin signaling, I injected embryos with dominant negative tcf3 (dn-tcf3) RNA (Molenaar et al, 1996) and assayed dpr expression at the sphere stage.…”

Wnt Signaling in Vertebrate Axis Specification

“…These observations indicated that the movement of the dorsalizing activity is essential for the establishment of the primary dorsoventral axis in both Xenopus and zebrafish. One of the important outcomes of the cortical rotation is the accumulation of b-catenin in dorsal nuclei of early blastulae, whereas bcatenin remains largely cytoplasmic and cortical in ventral cells (Schneider et al 1996;Schohl and Fagotto 2002). This difference in b-catenin localization can be detected as early as the 2-to 4-cell stage (Larabell et al 1997).…”

Nuclear particles containing RNA polymerase III complexes associated with the junctional plaque protein plakophilin 2

“…23). The inclusion of plakophilin 2 in nucleoplasmic assembly forms of the pol III transcription machinery would be compatible with the widespread and constitutive occurrence of plakophilin 2 in nuclei (6)(7)(8), a situation that is fundamentally different from the transient signal-induced nuclear translocation reported for other proteins of the arm-repeat family such as ␤-catenin and plakoglobin (24)(25)(26)(27)(28)(29)(30)(31) and suggests that it serves some general nuclear function. The human pol III of Ϸ700 kDa representing the core complex contains 16 subunits that remain tightly associated with each other even under partially denaturing conditions (e.g., see refs.…”