Real-time PCR analysis of Rspo1 , 2 and 3 in various tissues of adult medaka. B, brain; H, heart; L, liver; O, ovary; T, testis; K, kidney; I, intestine. Relative mRNA level (copy number of each gene/EF1-α) represents the mean ± S.E. of samples from at least 3 different fish. Values with different letters indicate significant difference (P < 0.05) of each gene in different tissues.