In-depth proteomic analysis of Boleophthalmus pectinirostris skin mucus

Abstract

Fish skin mucus serves as the first line of defence against pathogens and external stressors. The mudskipper Boleophthalmus pectinirostris inhabits intertidal mudflats containing abundant and diverse microbial populations; thus, the skin and mucus of B. pectinirostris are very important for immune defence. However, the molecules involved in the immune response and mucus secretion in the skin of this fish are poorly understood. To explore the proteomic profile of the skin mucus and understand the molecular mechanisms underlying B. pectinirostris adaption to amphibious environments, the microstructure of B. pectinirostris skin was analysed, and a series of histochemical procedures were employed for mucous glycoprotein localization and characterization. In addition, the antibacterial activity of B. pectinirostris skin mucus was studied, and the transcriptome of the skin and in-depth proteome of the mucus were determined. These studies revealed the hierarchical structure of B. pectinirostris skin and different types of glycoproteins (GPs) in the dermal bulge (DB) of the B. pectinirostris skin epidermis. The mucus has a broad antimicrobial spectrum and significant effects on the bacterial morphology. Furthermore, 93,914 unigenes were sequenced from B. pectinirostris skin tissue, and a total of 559 proteins were identified from B. pectinirostris skin mucus. Significancei)In this paper, the microstructure of B. pectinirostris skin was analysed and a series of histochemical procedures were employed for mucous glycoprotein localization and characterization. The results revealed the presence of glycoproteins with acidic oligosaccharides in the dermal bulges, indicating the important roles of this structure in mucus secretion and storage.ii)The antibacterial molecules of B. pectinirostris skin mucus had significant effects on the morphology of E. coli and M. luteus, as observed with TEM.iii)This paper establishes the first proteome map of mudskipper (B. pectinirostris) skin mucus, and a total of 559 proteins were identified, of which, many were not previously described in fish skin mucus.iv)Metabolic and structural proteins are predominant in B. pectinirostris skin mucus, and proteins involved in the immunologic defence, molecular transport, stress response, and signal transduction are also represented.v)This study would be useful for understanding the role of mucus associated with various function in mudskipper skin. The identified mucosal protein set from B. pectinirostris skin mucus could provide a clue for exploring the mechanism of immune function and screening for novel immune markers.