Key downstream component of the canonical Wnt signaling pathway (By similarity). In the absence of Wnt, forms a complex with axin1, axin2, apc, csnk1a1 and gsk3b that promotes phosphorylation on N-terminal Ser and Thr residues and ubiquitination of ctnnb1 and its subsequent degradation by the proteasome (By similarity). In the presence of Wnt ligand, ctnnb1 is not ubiquitinated and accumulates in the nucleus, where it acts as a coactivator for transcription factors of the TCF/LEF family, leading to activate Wnt responsive genes (By similarity). Plays a key role in dorsoventral patterning: in prospective ventral blastomeres, its down-regulation by axin1 and axin2 leads to inhibit the Wnt signaling pathway, while in prospective dorsal blastomeres, degradation of axin results in stabilization and nuclear translocation of ctnnb1 (PubMed:8562427, PubMed:30467143). Cytoplasmic when it is unstabilized (high level of phosphorylation). Translocates to the nucleus when it is stabilized (low level of phosphorylation). The majority of beta-catenin is localized to the cell membrane. Expressed maternally and is widely distributed in the early embryo (PubMed:8562427). Expressed in the posterior ventral and lateral mesodermal, and ectodermal cells during gastrulation (PubMed:25371059). Phosphorylation by gsk3b promotes ubiquitination and subsequent degradation by the proteasome. Ubiquitinated when phosphorylated by gsk3b, leading to its degradation. Belongs to the beta-catenin family.