Functional characterization of a calcium-dependent bacterial-binding C-type lectin from amphioxus

Area of Science:

• Innate immunity
• Comparative immunology
• Marine biology

Background:

• C-type lectins (CTLs) are crucial pattern recognition receptors (PRRs) in innate immunity.
• Amphioxus possesses a vast repertoire of CTL genes, yet few are functionally characterized.
• Understanding CTL function in basal chordates like amphioxus provides insights into immune evolution.

Purpose of the Study:

• To characterize a novel CTL, AmphiCTL6, from Branchiostoma japonicum (B. japonicum).
• To investigate the immune functions and binding capabilities of AmphiCTL6.
• To explore the role of AmphiCTL6 in the innate immune system of amphioxus.

Main Methods:

• Gene prediction and genomic analysis identified AmphiCTL6.
• In situ hybridization and single-cell RNA-seq determined AmphiCTL6 expression patterns.
• Recombinant protein expression, carbohydrate-binding assays, bacterial agglutination, and domain-truncation analyses were performed.

Main Results:

• AmphiCTL6 exhibits a unique structure with tandem EGF-like domains and a CTLD.
• High expression was observed in the hepatic cecum, intestine, gills, and gonads, particularly in gut epithelial cells.
• AmphiCTL6 demonstrated calcium-dependent binding and agglutination of diverse bacteria, with the CTLD mediating these interactions.

Conclusions:

• AmphiCTL6 functions as a broad-spectrum pattern recognition receptor (PRR) in amphioxus.
• This finding expands the known functional diversity of CTLs in basal chordates.
• AmphiCTL6 plays a significant role in gut immune surveillance and innate immunity.