Identification and functional analysis of transforming growth factor-β type I receptor (TβR1) from Scylla paramamosain: The first evidence of TβR1 involved in development and innate immunity in crustaceans.

The transforming growth factor-β (TGF-β) receptor-mediated TGF-β signaling cascade plays important roles in diverse cellular processes, including cell proliferation, differentiation, growth, apoptosis and inflammation in vertebrates. In the present study, the type I TGF-β receptor (TβR1) was firstly identified and characterized in mud crab Scylla paramamosain. The full-length cDNA of SpTβR1 was 1, 986 bp with a 1, 608 bp open reading frame, which encoded a putative protein of 535 amino acids including a typical transmembrane region, a conserved glycine-serine (GS) motif and a S_TKc domain (Serine/Threonine protein kinases, catalytic domain). Real-time PCR analysis showed that SpTβR1 was predominantly expressed at early embryonic development stage and was highly expressed at postmolt stages during molt cycle, suggesting its participation in development and growth. Moreover, the expression levels of SpTβR1 in hepatopancreas and hemocytes were positively induced after the challenges of Vibro alginolyticus and Poly (I:C), indicating the involvement of SpTβR1 in responding to both bacterial and viral infections. The in vivo RNA interference assays demonstrated that the expression levels of two NF-κB members (SpRelish and SpDorsal) and six antimicrobial peptide (AMP) genes (SpCrustin and SpALF2-6) were significantly suppressed when the SpTβR1 was silenced. Additionally, the expression levels of SpTβR1, SpRelish, SpDorsal and AMPs were consistently down-regulated or up-regulated when the primary cultured hemocytes were treated with TβR1 antagonist or agonist for 24 h. These results indicated that TβR1 not only contributed to the crabs' development and growth but also played vital role in the innate immunity of S. paramamosain, and it also provided new insights into the origin or evolution of TGF-β receptors in crustacean species and even in invertebrates.