Transcriptome analysis provides insights into the mechanism of albinism during different pigmentation stages of the albino sea cucumber Apostichopus japonicus

The sea cucumber Apostichopus japonicus (Selenka), which has nutritive and medical properties, is considered the most valuable commercial marine species in many parts of Asia. Of the different color morphs, the albino sea cucumber is rare and has great appeal to consumers. Identification of factors contributing to albinism in the sea cucumber is therefore likely to provide a scientific basis for improving the cultivability of this morph. In this study, illumina sequencing was performed on three pigmentation stages of the albino sea cucumber: the early pigmentation stage (Wa), the mid pigmentation stage (Wb) and the late pigmentation stage (Wc). In total, 120,365 unigenes were generated with an N50 length of 3360 bp and 60,224 unigenes were annotated from seven functional databases (NR, NT, GO, COG, KEGG, Swissprot and Interpro). In addition, 39,285 SSRs were detected, distributed on 26,156 unigenes. Compared with sea cucumbers during the early pigmentation stage, 842 genes were identified as differentially expressed in the body wall of albino sea cucumbers during the mid-pigmentation stage, including 331 upregulated and 511 downregulated genes. Additionally, compared with sea cucumbers in the mid-pigmentation stage, 247 genes were identified as differentially expressed in the body wall of albino sea cucumbers during the late-pigmentation stage, including 67 upregulated and 180 downregulated genes. GO and KEGG analyses revealed possible differentially expressed genes, including “melanogenesis”, “Ras-signaling pathway”, “cAMP signaling pathway” and “epithelium development” involved in albinism formation in albino sea cucumbers. In conclusion, these studies identified many candidate albinism-related and pigmentation-related genes and signaling pathways. In addition, a comparative analysis was conducted of the differentially expressed genes from albino sea cucumber body walls in different pigmentation stages. The results should be highly useful in further elucidating the mechanisms underlying albinism in sea cucumbers.