Molecular cloning, sequencing and tissue-level expression of complement C3 of Labeo rohita (Hamilton, 1822)

Complement component C3 plays a central role in all known complement activation pathways. In the present study, we cloned, sequenced and analyzed the full-length cDNA sequence of Labeo rohita complement C3 (LRC3). The expression pattern of complement C3 mRNA in different tissues of healthy rohu and after challenge with Aeromonas hydrophila were evaluated using real-time PCR. The LRC3 cDNA sequence of rohu comprised of 5081 bp encoding a predicted protein of 1645 amino acids. The deduced amino acid sequence had the characteristic domain architecture. About eight domains specific to complement C3 are present in the sequence starting from signal peptide to netrin C345C (NTR) domain. The post-translational processing signal sequence (RKRR), the C3-convertase cleavage site sequence (LAR) and the canonical thiol-ester motif (GCGEQ) were found to be conserved in the LRC3. Real-time PCR analysis revealed the highest expression of C3 in liver and extra-hepatic expression of C3 was also observed in all the tissues studied. A. hydrophila challenge resulted in significant up-regulated expression of C3 transcripts in both liver and kidney at 6, 12, 24, 48 and 72 h post-infection.