Cyclin G regulates hemocyte proliferation and antimicrobial peptide expression in the Chinese mitten crab (Eriocheir...

Mammalian cyclins G1 and G2 function in DNA damage repair, apoptosis, and cell cycle arrest. In contrast, Drosophila melanogaster possesses a single cyclin G essential for development and negatively regulating cell growth. However, the functions of cyclin G in crustaceans remain undefined. Here, we characterize Cyclin G (EsCycG) in the Chinese mitten crab (Eriocheir sinensis). EsCycG features a 1440-bp open reading frame encoding a 479-amino acid polypeptide, containing a 94-residue cyclin domain and seven low-complexity segments. Phylogenetic analysis revealed that invertebrate cyclin G forms a distinct clade separate from vertebrates. EsCycG expression, low in unchallenged hemocytes, increased rapidly in hemocytes following Vibrio parahaemolyticus infection. Immunofluorescence and flow cytometry demonstrated that EsCycG expression knockdown inhibited hemocyte proliferation upon V. parahaemolyticus challenge. Furthermore, EsCycG knockdown suppressed the infection-induced expression of antimicrobial peptides, including anti-lipopolysaccharide factors (ALF1, ALF2, ALF3) and lysozyme (Lys), in hemocytes. In vivo, EsCycG knockdown impaired bacterial clearance capacity, increasing susceptibility to infection and mortality. Thus, EsCycG positively regulates hemocyte proliferation and antimicrobial peptide expression, protecting against bacterial infection. These findings demonstrate the functional plasticity of the evolutionarily conserved cyclin gene family and provide novel insights for anti-infective strategies targeting cell cycle-immune crosstalk.