Molecular Cloning, Characterization, and Expression Analysis of Cathepsin A in the Chinese Giant Salamander Andrias davidianus

Identification of two immunoglobulin light chain types and expression of immunoglobulin diversity in Chinese giant salamander (Andrias davidianus)

Lacking research on immunoglobulins in the Chinese giant salamanders (Andrias davidianus) has left their populations vulnerable to pathogen infections, contributing to a sharp decline in their numbers. In this study, we employed the rapid amplification of cDNA ends (RACE) technique along with paired-end 300 bp read length (PE300) sequencing. This approach was used to construct a DNA library, which enabled us to investigate the diversity of immunoglobulin gene expression. Through this approach, we identified structural features of immunoglobulin light chains. Our results revealed the presence of Igλ and Igσ. Similar to other vertebrates, the immunoglobulin light chains of Chinese giant salamanders are composed of variable (V) and constant (C) domains connected by recombination activating gene (RAG) mediated V-J (joining) recombination. This canonical gene organization allows combinatorial diversity through rearrangement of multiple V and J gene segments. The IgLC features FPPS and FYP motifs, showing high similarity to both mammalian IgLC sequences and the IgLC of the Chinese Alligator (Alligator sinensis). The IgSC, characterized by SSYL structures, showed strong homology with fish and amphibian IgSC sequences, notably the axolotl (Ambystoma mexicanum) IgSC. Both the IgLV and IgSV sequences exhibit a YYCXX fold in the last five residues of framework region 3 (FR3). FR3 is a critical framework region within the V domain that anchors the antigen binding complementarity determining regions. Notably, the FPPS/FYP motifs in Igλ and SSYL motifs in Igσ exhibited evolutionary conservation patterns consistent with those in other vertebrates. In terms of gene expression diversity, the IgH is composed of 7 IgHV, 7 IgHD, and 6 IgHJ subgroups, while the Igλ consists of 10 IgLV and 7 IgLJ subgroups, and the Igσ comprises 5 IgSV and 7 IgSJ subgroups. Dominant IgH combinations are IgHV4-IgHD3-IgHJ4 and IgHV4-IgHD2-IgHJ4. The Igλ shows high usage of IgLV8, IgLV3, IgLJ7, and IgLJ3, while the Igσ is predominantly characterized by IgSV3-IgSJ3. Notably, Cys utilization in the complementarity determining region 3 (CDR3) region was extremely low, suggesting that gene conversion plays a significant role in immune adaptation. This research enriches the immune genetic map of the Chinese giant salamanders and enhances our understanding of immunoglobulin evolution in tetrapods.

Characterization, expression signatures and microbial binding analysis of cathepsin A in turbot, Scophthalmus maximus L.(SmCTSA)

Mucosal immune system is one of the most vital components in the innate immunity and constitutes the first line of host defense against bacterial infections, especially for the teleost, which live in the pathogen-rich aquatic environment. Cathepsins, a superfamily of hydrolytic enzymes produced and enclosed within lysosomes, play multiple roles at physiological and pathological states. In this regard, we sought here to identify Cathepsin A in turbot (SmCTSA), characterize its mucosal expression patterns following Vibrio anguillarum and Streptococcus iniae infections in mucosal tissues, and explore its binding ability with three microbial ligands for the first time. The SmCTSA was 2631 bp long containing a 1422 bp open reading frame (ORF) that encoded 473 amino acids. Phylogenetic analysis revealed that SmCTSA showed the closest relationship to half-smooth tongue sole (Cynoglossus semilaevis). In addition, SmCTSA was ubiquitously expressed in all examined healthy tissues, with high expression levels in head kidney (HK) and intestine, while the lowest expression level in blood. Moreover, SmCTSA was significantly differentially expressed at least two timepoints in each mucosal tissue, suggesting its potential important roles in innate immune responses of turbot. Finally, in vitro assays showed that recombinant SmCTSA bound Lipopolysaccharide (LPS) with high affinity, and lipoteichoic acid (LTA) and peptidoglycan (PGN) with relatively low affinity. This study provides valuable data for understanding the roles of ctsa in the host defense against bacterial infections.