Molecular Characterization and Expression of the LAP3 Gene and Its Association with Growth Traits in the Blood Clam Tegillarca granosa

Abstract

Leucine aminopeptidase 3 (LAP3) is a metallopeptidase that cleaves N-terminal residues and is involved in protein maturation and degradation. In this study, we characterized the leucine aminopeptidase 3 (LAP3) gene from Tegillarca granosa (Tg-LAP3 for short), which appeared to consist of 15,731 nucleotides encoding 530 amino acids. We identified 12 introns and 13 exons in the Tg-LAP3 gene, suggesting a highly conserved genomic structure. The proximal promoter sequence consists of 1922 bps with a typical TATA box structure, which is the general structural characteristic of core promoters in eukaryotes. We found two functional domains in the Tg-LAP3 protein, including an N-terminal domain (41–174aa) and a peptidase_M17 catalytic domain (209–522aa). Multiple alignment showed that Tg-LAP3 shares 73.4% identity with LAP3 of Mizuhopecten yessoensis and 55.2–70.7% identity with LAP3 of other species. Quantitative analysis of Tg-LAP3 in embryos/larvae and adult tissues indicated that the highest expression occurred in eyebot larva, with limited expression in other stages; among tissues, the highest expression was found in the liver (p < 0.05). Association analysis found that three single-nucleotide polymorphisms (SNPs) (g.-488A > G, g.-1123C > T, and g.-1304C > A) in the proximal promoter were successfully typed, but there was no significant difference in growth traits (body weight, shell length, shell width, and shell height) among these genotypes. The results of our study demonstrate the functional roles of the Tg-LAP3 gene and provide valuable information for molecular marker-assisted selection (MAS) of the blood clam.