Cloning and Expression Analysis of TGF-β Type I Receptor Gene in Hyriopsis cumingii

The TGF-β signaling pathway plays an important role in wound healing and immune response. In this study, a TGF-β type I receptor (TGF-βRI) homolog was cloned and characterized from freshwater mussel <i>Hyriopsis cumingii</i>. The full-length cDNA of the <i>TGF-β RI</i> gene was 2017 bp, with a 1554 bp open reading frame (ORF), and encoded 517 amino acids. The predictive analysis further identified distinct regions within the TGF-βRI protein: a signal peptide, a membrane outer region, a transmembrane region, and an intracellular region. Real-time quantitative PCR results showed that the <i>TGF-β RI</i> gene was expressed in all tissues of healthy mussels. The transcripts of <i>TGF-β RI</i> in hemocytes and hepatopancreas were significantly up-regulated at different periods after stimulation with <i>Aeromonas hydrophila</i> and peptidoglycan (PGN) (<i>P</i> < 0.05). The mRNA expression of <i>TGF-β RI</i> progressively increased from day 1 to day 10 after trauma (<i>P</i> < 0.05), and it returned to the initial level by day 15. The expression levels of <i>TGF-β</i> , <i>Smad5</i>, <i>MMP1/19</i>, <i>and TIMP1/2</i>, but not <i>Smad3/4</i>, were significantly up-regulated at different time points after trauma. However, the expression levels of <i>TGF-β</i> , <i>MMP1/19</i>, and <i>TIMP2</i> were decreased after treatment with the inhibitor SB431542. Furthermore, the recombinant TGF-βRI proteins were expressed in vitro and existed in the form of inclusion bodies. Western blotting results showed that TGF-βRI proteins were expressed constitutively in various tissues of mussels, and their expression was up-regulated after trauma, which was consistent with the mRNA expression trend. These results indicate that <i>TGF-β RI</i> is involved in the process of wound repair and immune response.