Sequence information, ontogeny and tissue-specific expression of complement component C3 in Indian major carp, Labeo rohita (Hamilton).

The complement system is one of the first line of immune defence mechanisms as well as a modifier of acquired immunity. C3 is the central complement component primarily synthesized in liver. The local synthesis of C3 in tissues other than liver may play an important role in local inflammatory processes. The present study aims at looking into ontogeny of C3 in Labeo rohita and its tissue-specific expression that is yet to be explored for Indian carps. Unfertilised eggs, and eggs after 0, 1, 3, 6, 12 h post-fertilization and hatchlings at 24 h, and 3 and 7 days post-fertilization were collected from three brood fish of L. rohita (rohu). Total RNA was extracted from approximately 50 mg of tissue and subjected to RT-PCR using heterologous carp primers to amplify C3 fragment. A product of 155 bp size of rohu C3 was amplified, the deduced amino acid sequence of which had 91.1% similarity to that of Cyprinus carpio C3. C3 mRNA was not detected in unfertilized and 6 h post-fertilised eggs. C3 transcripts were detected 12 h post-fertilisation. Similarly, tissues from liver, spleen, kidney, muscle, brain, gonads, intestine, blood, heart and gills collected from juveniles of rohu were subjected to detection of C3 transcripts by RT-PCR and C3 mRNA was detected in all the tissues. Thus, it is concluded that there is extra-hepatic synthesis of complement (C3) in L. rohita and the synthesis of this component occurs only 6 h post-fertilisation.