Comparative Transcriptome Analysis of White and Orange Skin of Clownfish Identifying Differentially Expressed Genes (DEGs) Underlying Pigment Expression

Although the clownfish, Amphiprion ocellaris (A. ocellaris), is a popular ornamental marine fish worldwide, the mechanisms underlying color pattern variation remain unclear. Given that the Platinum-type clownfish, nearly entirely white, has high economic value, understanding the biological mechanism that accounts for the difference between orange and white colors in A. ocellaris is crucial. To investigate these coloration differences, we performed RNA sequencing analysis and identified differentially expressed genes (DEGs) by comparing white and orange skin samples from three A. ocellaris individuals. A total of 76 DEGs were detected, including 56 downregulated and 20 upregulated genes. DEG sequences were annotated using Danio rerio and Stegastus partitus as reference species, selecting the best hit based on the lowest E-value. A protein–protein interaction (PPI) network and Gene Ontology biological process terms were additionally analyzed. Several DEGs previously reported to be associated with pigmentation, including hpdb, cldn11b, sfrp5, slc2a9, slc2a11b, si:ch211-256m1.8, fhl2, rab38, and ttc39b were identified. Based on the functions of these DEGs, it is inferred that leucophores and xanthophores contribute to both white and orange coloration by modulating related genes, including slc2a11b and slc2a9. Additionally, sfrp5, sost, and sp7 genes were identified to interact with each other in the PPI analysis, with sfrp5 and sost being associated with the Wnt signaling pathway, which contributes to melanocyte specification and osteoblast differentiation. Based on these findings, we propose sost and sp7 as candidate genes that might provide insights relevant to extreme white pigmentation phenotypes, such as those observed in Platinum-type clownfish. For a clearer understanding, further studies integrating quantitative genetics and functional analyses are required.