Chemokines are best known for their vital role in leukocyte chemotaxis, as part of the larger inflammatory response. Expression analysis and functional characterization of
chemokines in mammalian species have often overlooked the role of these
proteins under homeostatic conditions. Recent investigations of
chemokine diversity in teleost fish have also centered on the immune-related functions of
chemotactic cytokines, such as CXCL8 and CXCL10. While a disease-based approach to
chemokines is essential to the development of remediative
therapies for both human and animal
infections, it may be a poor measure of the overall complexity of
chemokine functions. As part of a larger effort to assess the conservation of
chemokine diversity in teleost fish, we report here the identification of three novel, constitutively expressed
CXC chemokines from channel catfish (Ictalurus punctatus). Phylogenetic analyses indicated that two of the three
CXC chemokines were orthologues for mammalian CXCL12 and CXCL14, respectively. Whereas a clear orthology could not yet be established for the third
CXC chemokine, it shared highest
amino acid identity with mammalian CXCL2. All three
CXC chemokines show expression in a wide range of tissues, and early expression during development was observed for CXCL12. The expression of this new set of catfish
CXC chemokines was not induced during challenge by
infection of Edwardsiella ictaluri, the causative agent of the fish pathogen enteric
septicemia of catfish. In contrast to the gene duplication of CXCL12 in carp and zebrafish, Southern blot analysis indicated that all three catfish
CXC chemokines exist as single copy genes in the catfish genome suggesting that gene duplication of
CXC chemokines in specific teleost fish was a recent evolutionary event.