Molecular Characterization and Phylogenetic Analysis of Antimicrobial Peptides From Cyprinid Fishes.

Abstract- Aquaculture is the most promising sector to satisfy the increasing protein need of future world. A number of Cyprinids family species including Catla Catla, Labeo rohita, Cirrhinus mrigala, Ctenopharyngodon idella, Hypopthalmichthys molitrix, H. nobilis, Cyprinus carpio and Carassius auratus are being investigated as future aquaculture species in countries around the world. However they face a number of issues and limitations which will need to be overcome to ensure future stability and growth, one of which is disease outbreak. However, very little has been done to understand the immune system of fishes and very few immune genes have been characterized. Antimicrobial peptides (AMP) are naturally occurring low molecular weight polypeptides that play a major role in an organism’s immune system and act effectively as a first line of defence.

In the present study, gene based approach was employed for identifying AMP genesin freshwater fishes belonging to Family Cyprinidae. Four fishes belonging to Family Cyprinidae viz. C. auratus, C. carpio carpio, Labeo rohita and C. catla, fishes were taken for identification and characterization of antimicrobial peptide genes present in these organisms. Three novel Histone H2A derived AMP genes could be identified and characterized from Cyprinid fishes viz. C. auratus, C. carpio carpio and C. catla from the current study. All the three AMP genes were the first report of these genes from these fish species. The AMP genes were named HIS – GI, HIS – KI and HIS – CI repectively.

An mRNA fragment of 174 bp encoding 58 amino acid corresponding to histone H2A gene could be amplified from the gold fish, C. auratus (HIS – GI), an mRNA fragment 166 bp encoding 55 amino acid corresponding to histone H2A genes could be amplified from the koi carp, C. carpio (HIS – KI), and an mRNA fragment of 124 bp encoding 41 amino acid corresponding to histone H2A gene could be amplified from C. catla (HIS – CI). Multiple alignment of these genes showed the presence of conserved regions in both nucleotide and amino acid sequences, Phylogenetic tree was constructed using histone H2A sequences and this also showed the basal placement of these AMPs along with other histone identified from other fishes belonging to Family Cyprinidae.

Examination of AMPs in significant fish families such as Cyprinidae, possessing aquaculture importance as food fish or ornamental fish can help understand the role of these peptides in innate host defense of the fish. Furthermore, they can provide important information for the better design of novel therapeutic agents, both for microbial infections as well as other conditions. Unique for the field of fish AMPs is the potential application to aquaculture.