Identification of Hc-β-catenin in freshwater mussel Hyriopsis cumingii and its involvement in innate immunity and sex determination

β-catenin is a multifunctional protein that participates in a variety of physiological activities, including immune regulation, sex determination, nervous system development and, cell differentiation. However, the function of β-catenin in freshwater mussel Hyriopsis cumingii remains unclear. Herein, the gene encoding β-catenin from H. cumingii (Hc-β-catenin) was cloned and characterised. The full-length 5544 bp gene includes an open reading frame (ORF) of 2463 bp encoding a putative protein of 820 amino acids residues containing 12 armadillo (ARM) repeats. After injecting H. cumingii with Aeromonas hydrophila or lipopolysaccharides, Hc-β-catenin transcription was induced in hemocytes and gills, and the greatest responses occurred at 24 h after bacterial challenge, confirming an important role in immune responses. Quantitative real-time PCR analysis showed that Hc-β-catenin mRNA was distributed in the gill, foot, liver, kidney, mantle, adductor muscle and gonad of male and female mussels. In gonad, Hc-β-catenin expression was markedly higher in females than males. During the embryonic period, Hc-β-catenin expression was highest at 3 day. In 1-, 2- and 3-year-old mature mussels, Hc-β-catenin expression in female gonad tissue was notably higher than in males. In situ hybridisation revealed a significant hybridisation signal in female gonads, indicating that Hc-β-catenin is a pro-ovarian, anti-testis gene. Our findings demonstrate that Hc-β-catenin is important in immune regulation and sex determination in freshwater mussel.