Cloning and characterization of a novel Lustrin A gene from Haliotis discus hannai

Lustrin A is the first nacre protein with specific structure and amino acid residue content that was identified in abalone; since its identification, homologs have been found in several abalone species. In this study, we isolated and cloned the complete cDNA of Lustrin A from Haliotis discus hannai, which was named Hdh-Lustrin A. Hdh-Lustrin A has characteristic cysteine- and proline-rich domains, glycine- and serine-rich domains, and a whey acidic protein (WAP)-like C-terminus. The cysteine- and proline-rich domains showed internal similarity repeats that arrayed in gene coding region, and the phylogenetic tree of these repeats indicated that the similarity of structural repetitive unit components in different abalone species, reflecting their evolutionary distance. A tissue distribution analysis showed that the mRNA level of Hdh-Lustrin A has tissue-specific expression in mantle. Under lipopolysaccharide (LPS) challenge, Hdh-Lustrin A showed a significantly increase, while it showed a more complex pattern with two peaks in the process of shell regeneration. Moreover, acidification and warming raised the expression level of Hdh-Lustrin A in shell regeneration in two different manners; acidification raised the gene expression in quick response, in contrast the long run in warming treatment. Similar pattern also has been detected in immune reaction and the thermal treatments. These results suggest that the Hdh-Lustrin A is a nacre protein, which can be distinguished by its cysteine- and proline-rich domain. It involves in shell regeneration and innate immunity in abalone, and its expression pattern during shell regeneration can be disrupted by physicochemical properties of the environment.