Molecular cloning and functional characterization of a QM protein in large yellow croaker (Larimichthys crocea)

• A QM gene was cloned and the protein was expressed in Escherichia coli and purified.
• LycQM protein shared the conserved structures with the reported QM proteins.
• LycQM mRNA expresses ubiquitously in multi-tissues with the highest in head kidney.
• LycQM gene was significantly up-regulated by pathogens challenge.
• LycQM protein could regulate the activity of phenoloxidase revealed by RNAi assays.

Since it was proposed to be a tumor suppressor in 1991, QM protein has attracted intensive and wide attention in plants, animals and fungi research fields. Up to date, however, the function of QM protein in fish immunity remains unknown. In this investigation, a QM gene (named as LycQM gene) was cloned from large yellow croaker (Larimichthys crocea), and LycQM protein was expressed in Escherichia coli and purified. The LycQM gene was ubiquitously transcribed in multi-tissues, including spleen, muscle, heart, liver, intestine, blood and head kidney. By quantitative real-time RT-PCR analysis, we found the highest and the lowest expression level of LycQM gene in head kidney and in heart, respectively. Time course analysis showed that LycQM expression was obviously up-regulated in blood and head kidney after immunization with polyinosinic polycytidynic acid (poly I:C), formalin-inactive Gram-negative bacterium Vibrio parahaemolyticus and bacterial lipopolysaccharides (LPS). Moreover, as demonstrated by RNAi assays, LycQM protein could regulate the activity of phenoloxidase, a key enzyme in the proPO activation system of immunity. These results suggested that LycQM protein might play an important role in the immune response against microorganisms in large yellow croaker.