Functional C1q is present in the skin mucus of Siberian sturgeon (Acipenser baerii)

Abstract

The skin mucus of fish acts as the first line of self-protection against pathogens in the aquatic environment and comprises a number of innate immune components. However, the presence of the critical classical complement component C1q, which links the innate and adaptive immune systems of mammalians, has not been explored in a primitive actinopterygian fish. In this study, we report that C1q is present in the skin mucus of the Siberian sturgeon (Acipenser baerii). The skin mucus was able to inhibit the growth of Escherichia coli. The bacteriostatic activity of the skin mucus was reduced by heating and by pre-incubation with EDTA or mouse anti-human C1q antibody. We also detected C1q protein in skin mucus using the western blot procedure and isolated a cDNA that encodes the Siberian sturgeon C1qC, which had 44.7-51.4% identity with C1qCs in teleosts and tetrapods. A phylogenetic analysis revealed that Siberian sturgeon C1qC lies at the root of the actinopterygian branch and is separate from the tetrapod branch. The C1qC transcript was expressed in many tissues as well as in skin. Our data indicate that C1q is present in the skin mucus of the Siberian sturgeon to protect against water-borne bacteria, and the C1qC found in the sturgeon may represent the primitive form of teleost and tetrapod C1qCs.

Molecular ontogeny of larval immunity in European eel at increasing temperatures

“…This is reflected in the expression pattern observed in the analysed healthy eel tissue where c1qc expression was very low in the liver but high in spleen, kidney, and head kidney. This pattern seems to be conserved across many fish species and orders as it was also observed in Siberian sturgeon (Acipenser baerii), mandarin fish (Siniperca chuatsi), and zebrafish (Danio rerio) [50][51][52]. Both investigated complement factors c3 and c1qc were not significantly up-regulated during AngHV-1, which is in line with results from common carp gills infected with cyprinid herpesvirus 3 (CyHV-3), which has been shown to be able to modulate the immune response of the host [53].…”

Biological and Ecological Roles of External Fish Mucus: A Review

“…Different types of proteases (trypsins, metalloproteases, cathepsins, and aminopeptidases) have been identified in fish skin mucus, with serine and metalloproteases being the most predominant [15]. Several complement components such as C7, C3, and C1q have been identified in skin and intestine mucus of several fish species [112,113]. Immunoglobulins (IgM and IgT/IgZ) are major components in fish mucus, with IgT/IgZ playing major roles in fish mucosal immunity [100,114,115].…”

Epidermal mucus as a potential biological matrix for fish health analysis

“…In the epidermal mucus, lectins play active roles in the mucosal defence system with its activity on the external surface of the body (Dash et al, 2018). Some complementary proteins such as C7, C3, and C1q have been identified in the epidermal and intestinal mucus of several fish species (Shen et al, 2012;Fan et al, 2015;Salinas, 2015;Reverter et al, 2018). Immunoglobulins (IgM and IgT/IgZ) are the key components of innate immunity in the epidermal mucus, with IgT/IgZ having the primary activity in fish mucosal immunity (Xu et al, 2013;Sunyer, 2013;Xia et al, 2016;Reverter et al, 2018;Pietrzak et al, 2020).…”