Identification of CTNNB1 in the lined seahorse, Hippocampus erectus, and its function in innate immunity and cell proliferation

β-Catenin (CTNNB) is a core downstream mediator in the Wnt/β-catenin signaling pathway, which plays a role in immune regulation and cell differentiation. In the present study, two CTNNB genes were identified by genomic analysis of Hippocampus erectus and named He-CTNNB1 and He-CTNNB2. He-CTNNB1 was more conserved than He-CTNNB2. The full length of He-CTNNB1 was 2369 bp, including an open reading frame of 2275 bp that encoded 737 amino acids containing 12 armadillo repeats. Phylogenetic analysis revealed that He-CTNNB1 clusters had homologs in other bony fishes. Tissue distribution analysis showed the highest mRNA expression of He-CTNNB1 in the ovary, liver, and kidney of the lined seahorse under normal physiological conditions. The transcription level of He-CTNNB1 was significantly increased in the liver and kidney in response to LPS, poly I:C, and Edwardsiella tarda challenge (p < 0.05). In vitro overexpression of He-CTNNB1 significantly upregulated the expression of key genes of the canonical Wnt/β-catenin signaling pathway, such as axin2, cMyc, and cyclinD (p < 0.05), which increased cell proliferation during the wound-healing process. Taken together, our results suggest that He-CTNNB1 is essential for cell proliferation and the innate immune response in H. erectus.