MITF Contributes to the Body Color Differentiation of Sea Cucumbers Apostichopus japonicus through Expression Differences and Regulation of Downstream Genes

SIMPLE SUMMARY: The sea cucumber Apostichopus japonicus is an ecologically significant echinoderm with considerable nutritional and therapeutic value. Color variation of A. japonicus is one of its most important cultivation traits, as color affects its bioactive compounds, taste, and market price. Microphthalmia-associated transcription factor (MITF) is one of the most critical genes in melanocyte development and melanin synthesis pathways. However, how MITF regulates body color and differentiation in sea cucumbers is poorly understood. Here, we analyzed the expression level and location of MITF in white, purple, and green sea cucumbers and identified the genes regulated by MITF using chromatin immunoprecipitation followed by sequencing. Our findings suggested that MITF contributed to the body color differentiation of green, purple, and white sea cucumbers A. japonicus through expression differences and regulation of downstream genes. These findings give researchers a foundation for further research into the processes that underlie the development of body color in sea cucumbers and provide light on how genes are regulated. The results will also provide support for sea cucumber breeding and a useful theoretical basis in order to contribute to the development of the sea cucumber industry. ABSTRACT: Melanin, which is a pigment produced in melanocytes, is an important contributor to sea cucumber body color. MITF is one of the most critical genes in melanocyte development and melanin synthesis pathways. However, how MITF regulates body color and differentiation in sea cucumbers is poorly understood. In this study, we analyzed the expression level and location of MITF in white, purple, and green sea cucumbers and identified the genes regulated by MITF using chromatin immunoprecipitation followed by sequencing. The mRNA and protein expression levels of MITF were all highest in purple morphs and lowest in white morphs. In situ hybridization indicated that MITF mRNA were mainly expressed in the epidermis. We also identified 984, 732, and 1191 peaks of MITF binding in green, purple, and white sea cucumbers, which were associated with 727, 557, and 887 genes, respectively. Our findings suggested that MITF contributed to the body color differentiation of green, purple, and white sea cucumbers through expression differences and regulation of downstream genes. These results provided a basis for future studies to determine the mechanisms underlying body color formation and provided insights into gene regulation in sea cucumbers.