Antimicrobial peptide hepcidin contributes to restoration of the intestinal flora after Aeromonas hydrophila infection in Acrossocheilus fasciatus.

Hepcidin is a cysteine-rich antimicrobial peptide that serves an important role in the immunity system of fishes. It exhibits antibacterial, antifungal, antiviral, and antitumor activities. However, the exact role of fish hepcidin in the regulation of the intestinal flora still remains a mystery. In our study, we sequenced and characterized hepcidin from the liver of Acrossocheilus fasciatus. Phylogenetic tree analysis showed that A. fasciatus hepcidin and Gobiocypris rarus hepcidin were the most closely related, and both belonged to the fish HAMP1 cluster. Studies conducted on in vivo tissue distribution showed that the expression of hepcidin was highest in healthy A. fasciatus liver. Aeromonas hydrophila infection was confirmed by the increased expression of pro-inflammatory cytokine genes and bacterial loads in A. fasciatus tissues. After A. hydrophila infection, hepcidin expression significantly increased in the liver, spleen, and head kidney. In vitro antibacterial assays showed that hepcidin exhibits strong broad spectrum antibacterial activity. Furthermore, we examined the regulatory effect of hepcidin on the intestinal flora and found that A. fasciatus hepcidin restored the reduced diversity and compositional changes in intestinal flora caused by A. hydrophila infection. Our results suggest that hepcidin could regulate the intestinal flora in fishes; however, the underlying mechanisms need to be explored in greater detail.

Transcriptomic analysis of intermuscular bone development in barbel steed (Hemibarbus labeo).

Intermuscular bones (IBs), which are little, bony spicules in muscle, are embedded in lower teleosts' myosepta. Despite the importance of studying IB development in freshwater aquaculture species, the genes associated with IB development need to be further explored. In the present study, we identified four stages of IB development in barbel steed (Hemibarbus labeo), namely stage 1: IBs have not emerged, stage 2: a few small IBs have emerged in the tail, stage 3: longer IBs gradually emerged in the tail and stage 4: all of the IBs in the tail are mature and long, via Alizarin red staining. Subsequently, we used the HiseqXTen platform to sequence and de novo assemble the transcriptome of epaxial muscle (between 35th and 40th myomere) of barbel steed at 29 days (stage 1) and 42 days (stage 3) after hatching. A total of 190,814 unigenes were obtained with an average length and N50 of 648 bp and 1027 bp, respectively. We found 2174 differentially expressed genes (DEGs) between stages 1 and 3, of which 378 and 1796 were up- and down-regulated, respectively. Functional enrichment analysis showed that several DEGs functioned in ossification, positive regulation of osteoblast differentiation, osteoblast differentiation, and BMP signaling pathway, and were further enriched in signal pathway, including osteoclast differentiation, TGF-ß signaling pathway, cytokine-cytokine receptor interaction, Jak-STAT signaling pathway, and other KEEG pathways. In conclusion, we identified genes that may be related to IB development, such as kazal type serine peptidase inhibitor domain 1 (KAZALD1), extracellular matrix protein 1 (ECM1), tetranectin, bone morphogenetic protein 1 (bmp1), acid phosphatase 5 (ACP5), collagen type XI alpha 1 chain (COL11A1), matrix metallopeptidase 9 (MMP9), pannexin-3 (PANX3), sp7 transcription factor (Sp7), and c-x-c motif chemokine ligand 8 (CXCL8), by comparing the transcriptomes of epaxial muscle before and after IB ossification. This study provided a theoretical basis for identifying the molecular mechanisms underlying IB development in fish.