Cloning of interleukin-10 gene in the Indian major carp, Labeo rohita (Hamilton 1822) and its functional characterization following Aeromonas hydrophila infection

Abstract

Interleukin-10 (IL-10) is a pleiotropic cytokine, expressed in various species of fish and higher vertebrates, and is activated
during infection. In this report, we describe the identification and characterization of IL-10 in the Indian major carp (IMC),
rohu (Labeo rohita), which is the most preferred and commercially important species in the Indian subcontinent. The rohu
IL-10 cDNA consisted of 1103 bp nucleotides, having 65 bp and 495 bp un-translated regions at the 5’ and 3’ end respectively.
The open reading frame consisted of 543 bases, encoding 180 amino acids with a putative signal peptide of 22 amino acids.
Deduced amino acid sequence of rohu IL-10 showed highest similarity (97.8%) and identity (91.7%) with common carp
(Cyprinus carpio) IL-10. Phylogenetic analysis indicated that the rohu IL-10 amino acid sequence resembles common carp
IL-10, more closely related to silver carp (Hypophthalmichthys molitrix) and zebra fish (Danio rerio). Basal IL-10 expression
analysis in ten different tissues of healthy fish by quantitative real-time PCR (qRT-PCR) assay showed its constitutive
expressions among the tested tissues; with highest expression in the muscle, intestine and brain followed by gill, kidney and
the lowest expression in heart. Following Aeromonas hydrophila infection, IL-10 mRNA transcripts were analysed in gill,
liver and kidney by qRT-PCR assay, and it showed significant induction (p<0.05) of IL-10 and down-regulation of IL-1β and
TNF-∞ in gill and liver of the treated fish compared to control fish. The results partly explain the function of IL-10 as an
anti-inflammatory cytokine and could aid in comprehending the disease progression in fish.