A c-type lectin with dual function of immunology and mineralization from the freshwater oyster ( Lea).

Background: Shell and pearl formation in bivalves is a sophisticated biomineralization process that encompasses immunological and mineralization aspects, particularly during shell repair and the initial stages of pearl cultivation when a nucleus is inserted. Here, we describe a novel C-type lectin, HcLec1, isolated and characterized from the freshwater pearl mussel Lea.

Methods: Immune challenge, RNA interference (RNAi) experiments, ELISA, and antibacterial assays were employed to investigate the role of HcLec1 in innate immunity. We also established shell damage repair and pearl nucleus insertion models to examine the impact of on the biomineralization process in Lea. In vitro calcium carbonate crystallization assays were conducted to explore the direct role of in calcium carbonate crystal formation.

Results: The gene sequence is a full-length cDNA of 1552 bp, encoding 240 amino acids. comprises an N-terminal signal peptide and a carbohydrate-recognition domain (CRD), with QPD (Gln-Pro-Asp) and MND (Met-Asn-Asp) motifs for polysaccharide binding. Tissue expression analysis showed that is predominantly expressed in the gill tissue of Lea under normal conditions, and its expression is significantly elevated in both gill and pearl sac tissues following nucleus insertion for pearl cultivation ( < 0.05). After immune stimulation with and lipopolysaccharides (LPS), expression levels significantly increased in both cases ( < 0.01), indicating a role in bivalve innate immunity. RNA interference (RNAi)-mediated knockdown of led to a significant decrease in the expression levels of immune-related genes (, , and ) and mineralization-related genes (, , , and ) ( < 0.05). In animal models for shell damage and nucleus insertion in pearl cultivation, showed a consistent expression pattern, with an initial significant decrease followed by a marked increase, peaking at day 14 ( < 0.05). This suggests a role for in pearl formation and shell repair. The recombinant HcLec1 protein demonstrated binding affinity to LPS and PGN, a robust ability to agglutinate , , , and , and significantly inhibited bacterial growth ( < 0.05). Moreover, rHcLec1 promoted calcite crystal formation in saturated calcium carbonate solutions and altered crystal morphology.

Discussion: The gene plays a pivotal role in both innate immunity and biomineralization in the triangle sail mussel. This study enhances our understanding of the functional diversity of C-type lectins and provides a foundation for future studies on shell repair and pearl growth.