Molluskan fasciclin-1 domain-containing protein: Molecular characterizationand gene expression analysis of fasciclin 1-like protein from disk abalone (Haliotis discus discus)

• Complete fasciclin 1-like cDNA from disk abalone was identified.
• Characteristic features of FAS-1 proteins were identified in Abfac1.
• Abfac1 mRNA was primarily expressed in hepatopancreas and mantle.
• Abfac1 mRNA expressions were significantly induced by bacterial infections.
• Tissue injury significantly upregulated Abfac1 expressions in hemocytes and mantle.

Cell-to-cell contacts play a key role in multicellular systems and organisms. Fasciclin-1 (FAS-1) is a lipid-linked membrane associated glycoprotein that is a member of a newly recognized family of cell adhesion molecules sharing features with the immunoglobulins, cadherins, integrins, and selectins. Here, we report the identification and molecular characterization of a novel FAS-1 domain-containing cDNA from disk abalone (Haliotis discus discus), including its gene expression profile and immune response to bacterial stimuli and tissue injuries. Designated as Abfac1, the 909 bp open reading frame (ORF) encodes 303 amino acid (aa) residues with a predicted molecular mass of 33 kDa and isoelectric (pI) value of 4.9. The aa sequence contains two FAS-1 domains and three conserved regions, FRa motif, H-box, and FRb motif. Phylogenetic analysis showed the closest relation to Jellyfish cell adhesion protein. In healthy abalone, Abfac1 expression is highest in hepatopancreas followed by mantle and lowest in digestive gland. In immune-stimulated abalones, relative Abfac1 mRNA expression was increased in hemocytes by ~ 11-fold at 48 h after the Vibrio parahaemolyticus infection, by 3.1-fold at 6 h after the Listeria monocytogenes infection and by ~ 9-fold at 6 h after the LPS injection. Similarly, tissue injuries caused significant increase of relative mRNA expression by 3.5-fold in hemocytes and by ~ 10-fold in mantle at 12 h post-injury. These results suggest that the novel member of the FAS-1 domain-containing protein family, Abfac1, may be involved in immune response and cell adhesion in disk abalone.