Molecular cloning, characterization and effects of catechol-o-methyltransferase (comt) mrna and protein on aggressive behavior in the swimming crab portunus trituberculatus

In the present study, a cDNA that encodes catechol-O-methyltransferase (COMT) was cloned from the muscle of the swimming crab Portunus trituberculatus and named PtCOMT. PtCOMT was proven to be a conserved gene that encodes a protein of 222 amino acid residues with a molecular mass 25.4 kDa that constitutes only the signature motif “SAM_OMT_I.” The RT-PCR results showed that PtCOMT was expressed in all five larval stages (zoea stage I, Z1; zoea stage II, Z2; zoea stage III, Z3; zoea stage IV, Z4; and megalopa, M) of P. trituberculatus. The PtCOMT mRNA levels were higher (P < 0.05) in the Z4 and M stages than in the Z1, Z2, and Z3 stages. In addition, PtCOMT was expressed in the tissues of healthy crabs, namely, ganglion, muscle, and hepatopancreas. On the basis of the RT-PCR and immunohistochemistry analyses, the level of expression in the ganglion and muscle was significantly higher than that in the hepatopancreas (P < 0.05). Aggressiveness of DA injected crabs was tested through a behavioral study where dopamine-treated crabs walked through the “middle” of the pool more frequently than control crabs. When compared with the control group, PtCOMT expression level was significantly upregulated (P < 0.05) at 2 h and significantly downregulated at 4 h in the muscles after dopamine (DA) injection (P < 0.05), whereas it was significantly downregulated (P < 0.05) at 2 h and upregulated after 4 h (P < 0.05) in the ganglia. These results show that DA promotes the release of PtCOMT. Our findings indicate that the expression level of PtCOMT may be directly related to aggressiveness and affect the central nervous system of P. trituberculatus to act on its aggressive behavior. Our results can help further studies on the aggressive behavior mechanism of P. trituberculatus.