ROLE OF CHANNEL CATFISH CLCA IN FISH BACTERIAL DISEASES

The stringent regulations on the use of antibiotics call for new solutions to treat bacterial infections. Mucus is the first line of defense that fights pathogens in fish. Mucus consists of humoral factors that include metalloproteases that act as antibacterial peptides. In this study, we investigate  the Channel catfish CLCA gene family that is secreted in the fish mucus.

CLCA genes are well conserved across species, including fish. CLCAs are expressed at cell-cell junctions of epithelial cells and required for maintenance of epithelial integrity. There are three different forms of CLCA variants in zebrafish. The catfish CLCAs have never been explored . We have identified a catfish EST similar to zCLCA5.2 isoform, which is a putative soluble protein secreted in the fish mucus. CLCAs are known to be stress- inducible genes in other species and  are shown to induce c ytokines  in the  Staphylococcus aureus disease model. The CLCA protein family is intimately tied to mucus secretion and goblet cells. For example, CLCA1 is found in mucus granules and mucus barrier of airways and regulates the level of mucus secretion. CLCAs are Zn+2 metalloproteases in other species, and this metal-binding motif is highly conserved across species.

Interestingly,  we find that cCLCA 5.2  expression is  significantly higher in  gills and mucus, which is directly correlated with stress-inducible genes P53 and P21 .  We speculate that cCLCA5.2, like other CLCAs,  is a Zn+2 dependent metalloprotease expressed at cell-cell junctions of gills . Although we dint see high expression in skin, we did evidence its presence in the mucus collected from skin. Therefore, we speculate that cCLCA5.2 in the mucus is a potential antibacterial peptide that can fight catfish pathogens.