Cloning of the full-length cDNA of the gene encoding complement C5 from grass carp (Ctenopharyngodon idella) and its expression in different tissues by following grass carp reovirus infection

Grass carp (Ctenopharyngodon idella) is the most widely produced freshwater aquaculture product worldwide. However, its susceptibility to microbial infections during its cultivation restricts its development. The complement system plays an important role in immune defence. To investigate the transcription of the complement factor C5 and production of its cleavage product C5a in grass carp infected with grass carp reovirus (GCRV), the full-length C5 gene sequence was cloned and sequenced using the rapid amplification of cDNA ends method, and C5 transcription and C5a production in different grass carp tissues at different GCRV infection stages were determined by RT-qPCR and western blotting, respectively. Our results showed that the full-length cDNA of the C5 gene was 5365-bp long, encoding 1687 amino acids. Signal peptide prediction showed that C5 had a secretory signal peptide. After artificial infection with GCRV, C5 transcription in grass carp liver increased significantly before the appearance of symptoms. C5a generation in the liver increased significantly from the onset of disease symptoms, and continued to increase until recovery. GCRV induced C5 cleavage in grass carp, with C5a production.