The hepatic lectin of zebrafish binds a wide range of bacteria and participates in immune defense.

C-type lectins (CTLs) have a diverse range of functions including cell-cell adhesion, immune response to pathogens and apoptosis. Asialoglycoprotein receptor (ASGPR), also known as hepatic lectin, a member of CTLs, was the first animal lectin identified, yet information regarding it remains rather limited in teleost. In this study, we identified a putative protein in zebrafish, named as the zebrafish hepatic lectin (Zhl). The zhl encoded a typical Ca2+-dependent carbohydrate-binding protein, and was mainly expressed in the liver in a tissue specific fashion. Challenge with LPS and LTA resulted in significant up-regulation of zhl expression, suggesting involvement in immune response. Actually, recombinant C-type lectin domain (rCTLD) of Zhl was found to be capable of agglutinating and binding to both Gram-negative and Gram-positive bacteria and enhancing the phagocytosis of the bacteria by macrophages. Moreover, rCTLD specifically bound to insoluble lipopolysaccharide (LPS), lipoteichoic acid (LTA) and peptidoglycan (PGN), which were inhibited by galactose. Interestingly, Zhl was located in the membrane, and its overexpression could inhibit the production of pre-inflammatory cytokines. Taken together, these results indicate that Zhl has immune activity capable of defending invading pathogens, enriching our understanding of the function of ASGPR/hepatic lectin.

Identification and expression of carbonic anhydrase 2, myosin regulatory light chain 2 and selenium-binding protein 1 in zebrafish Danio rerio: Implication for age-related biomarkers.

Proteomic study has determined age-related changes in synthesis of carbonic anhydrase 2, myosin regulatory light chain 2 and selenium-binding protein 1 in muscle of post-menopausal women. However, little information is available regarding the expression and role of these proteins in early development and life span. In this study we showed that zebrafish ca2, myl2a, myl2b and selenbp1 were highly identical to their mammalian counterparts in primary and tertiary structures as well as genomic organization and syntenic map. They displayed distinct spatiotemporal expression patterns in embryos and larvae of zebrafish. Moreover, their transcription levels in the respective tissues were obviously remodeled in an age-dependent fashion, i.e. some mRNA levels were increased, while others remained unchanged or even decreased, suggesting that CA2, MYL2a, MYL2b and SELENBP1 can be used as aging biomarkers. Our study also lays a foundation for further illumination of the functions of these genes in early development and aging processes.

Evolutionary and Expression Analyses Show Co-option of khdrbs Genes for Origin of Vertebrate Brain.

Genes generated by whole genome duplications (WGD) can be co-opted by changing their regulation process or altering their coding proteins, which has been shown contributable to the emergence of vertebrate morphological novelties such as vertebrate cartilage. Mouse khdrbs genes, differing from its invertebrate orthologs, were mainly expressed in brain, hinting that khdrbs gene family as a member of genetic toolkit may be linked to vertebrate brain development. However, the evolutionary relationship between khdrbs gene family and vertebrate brain development is unclear. First, we analyzed the evolutionary history of khdrbs gene family in metazoans, and then investigated their expression patterns during early development and in adulthood of zebrafish. We found that the duplication of khdrbs gene family by WGD took place in zebrafish, and all zebrafish khdrbs genes were predominantly expressed in the substructures of brain during early development. Given the expression of invertebrate khdrbs gene in germ line, the distinct expression domains of zebrafish khdrbs genes in brain suggested that the duplicated khdrbs genes are co-opted for promoting the evolutionary origin of vertebrate brain.

Heavy chain (LvH) and light chain (LvL) of lipovitellin (Lv) of zebrafish can both bind to bacteria and enhance phagocytosis.

Lipovitellin (Lv) is an apoprotein in oviparous animals. Lv consists of a heavy chain (LvH) and a light chain (LvL) which are traditionally regarded as energy reserves for developing embryos. Recently, Lv has been shown to be involved in immune defense of developing embryos in fish. However, it remains unknown if each of LvH and LvL possesses immune activity; and if so, whether or not they function similarly. Here we clearly demonstrated that recombinant LvH (rLvH) and LvL (rLvL) from zebrafish vg1 gene bound to both the Gram-negative bacteria Escherichia coli and Vibrio anguillarum and the Gram-positive bacteria Staphylococcus aureus and Micrococcus luteus as well as the pathogen-associated molecular patterns LPS, LTA and PGN. In addition, both rLvH and rLvL were able to enhance the phagocytosis of bacteria E. coli and S. aureus by macrophages. All these data suggest that both LvH and LvL, in addition to being energy reserves, are also maternal immune-relevant factors capable of interacting with invading bacteria in zebrafish embryos/larvae.