Maternal Transfer And Protective Role Of Antibodies In Zebrafish Danio Rerio

Fish eggs are in most cases cleidoic, i. e. closed free-living systemfollowing fertilization. In water, the embryos of fish with unmaturedimmune system are threaten by numerous pathogens including bacteria,virus and parasite; therefore, they are supposed to depend upon thematernal provision of immune-relevant molecules for protection againstinvading pathogens. Maternal transfer of antibodies from mother to eggshas been reported in various species of fishes, and these antibodies havebeen proposed to play immune roles in developing embryos and larvae.However, firm evidence supporting this remains lacking. Zebrafish(Danio rerio) has been used as a good model in research of immunesystem of vertebrates. However, the maternal transfer of antibodies inzebrafish has not been reported and whether antibodies involve inprotection against pathogenic bacteria in embryo is unknown.In the first part of this study,(1) we clearly demonstrated thatimmunization of female zebrafish with the hapten-carrier complex,trinitrophenylated bovine serum albumin (TNP-BSA), induced a significant increase in anti-TNP antibodies production in the mothers,which in turn caused a marked increase in anti-TNP antibodies level intheir eggs.(2) Western blot was used to show the catabolic trend of thismolecule. The result showed that at5dpf, maternally-derived IgM wasexhausted, coninciding the absorbance of yolk sac.(3) Microinjection ofanti-zebrafish IgM antibody into early embryos (to neutralizematernally-derived antibodies action) resulted in a remarkable decrease inthe resistance of recipient embryos to pathogenic Aeromonas hydrophila,whereas injection of BSA or anti-β-actin monoclonal antibody intoembryos had little effect on their resistance to the pathogen. Moreover,the content of maternally-derived antibodies in eggs was clearlycorrelated with their anti-bacterial activity against A. hydrophila.Consequently，this is the first report showing that maternally transferredantibodies in eggs of zebrafish can protect early emabyros/larvae from theattack of A. hydrophila.In the second part of this study, we tried to explore the anti-bacterialfactors stored in eggs of zebrafish Danio rerio. We incubated E.coli withthe egg cytosol, and then the proteins bound to E.coli were eluted. AfterSDS-PAGE, some protein bands were cut and subjected to mass spectrum(MS). Totally, seven proteins bound to E.coli were indentified: they aremyosin, plectin, chitinase, vitellogenin, myosin light chain kinase, ser/thrprotein kinase and LFI protein. The possible anti-bacterial activities of these proteins were discussed.In sum, this study has verified the transfer of maternlly-derived IgMin Danio rerio, and its anti-bacterial function in embryos. Moreover, aseries of potential innate immune factors were found in egg of Daniorerio.