Molecular Characterization and Expression Analysis of NLRC3-like, ASC, and Caspase1 in Spotted Sea Bass (Lateolabrax maculatus)

Nucleotide-binding oligomerization domain (NOD)-like receptor (NLR) family members are innate immune sensors involved in the recognition of highly conserved pathogen-associated molecular patterns (PAMPs). Apoptosis-associated speck-like protein (ASC) is a critical adaptor molecule in multiple inflammasome protein complexes, mediating inflammation and host defense. Caspase1, an inflammatory caspase, has been documented to play important roles in the innate immune system. In this study, we identified and characterized NLRC3-like, ASC, and Caspase1 (referred to as LmNLRC3L, LmASC, and LmCaspase1) from the spotted sea bass (Lateolabrax maculatus). A sequence analysis revealed that LmNLRC3L, LmASC, and LmCaspase1 shared similar features with their fish counterparts. LmNLRC3L contained a FISNA domain, a NACHT domain, and four LRR motifs, followed by a C-terminal fish-specific B30.2 domain. LmASC possessed a PYRIN domain for interacting with inflammasome sensor proteins, as well as a CARD domain. LmCaspase1 had a CARD domain at its N-terminus and a CASC domain at its C-terminus. These three genes were ubiquitously distributed in the liver, spleen, head kidney, gill, intestine, skin, muscle, and brain. They share similar expression patterns, and all demonstrate the highest level of expression in the gill. We analyzed the expression changes in genes in the spleen, gill, and head kidney after stimulation experiments in vivo. After lipopolysaccharide (LPS) stimulation, the expression levels of these three genes were significantly upregulated in the short term, followed by significant downregulation at 48 and 72 h in some examined tissues. Following Edwardsiella tarda infection, these three genes were upregulated in various tissues. However, the expressions of these three genes were not affected by polyinosinic-polycytidylic acid (poly (I:C)) stimulation. Overall, our results indicate that these three genes are involved in the immune response against bacterial infection in the spotted sea bass, providing the foothold for understanding the immune function and mechanism of the fish inflammasome.