Expression of PoCD9.1 and PoCD9.3 in flounder tissues. PoCD9.1 expression (A) and PoCD9.3 expression (B) in the muscle, spleen, blood, gill, heart, head kidney, liver, and intestine of flounder were determined by quantitative real-time RT-PCR. For convenience of comparison, the expression level in the spleen was set as 1 because its expression level was the lowest. Data are the mean of three independent assays and presented as the mean ± SEM (N = 3). N represents the number of times the experiment was performed.