Identification of a CREB-regulated transcription coactivator (CRTC) in Crassostrea gigas and its role in regulating melanin production.

Abstract

Shell pigmentation is a critical economic trait that influences the commercial value of aquacultural oyster, with coloration primarily governed by melanin deposition. In melanin biosynthesis, the cAMP-CREB-MITF signaling axis serves as the core regulatory pathway, wherein the CREB-regulated transcription coactivator (CRTC) functions as an important coactivator for CREB. In this study, we identified and functionally characterized the CRTC homologous gene CgCRTC from the Pacific oyster (Crassostrea gigas). The CgCRTC gene encodes a 669-amino-acid protein with three conserved functional domains: an N-terminal CREB-binding domain (CBD), a central regulatory domain (REG), and a C-terminal trans-activating domain (TAD). Phylogenetic analysis confirmed its close evolutionary grouping with other molluscan orthologs. While CgCRTC transcripts were ubiquitously detected across all examined tissues, expression levels peaked in the gill and smooth adductor muscle. Subcellular localization revealed that the CgCRTC protein is predominantly cytoplasmic. RNAi-mediated silencing of CgCRTC led to a significant transcriptional downregulation of key melanogenic genes CgMITF, CgTYR and CgOCA2 in oysters. Furthermore, dual-luciferase assays demonstrated that CgCRTC activates the promoters of CgMITF, CgTYR and CgOCA2, and overexpression of CgCRTC in mouse B16F10 melanoma cells leads to an increase in melanin deposition. Collectively, our findings demonstrate that CgCRTC acts as a positive regulator of melanogenesis by transcriptionally upregulating the expression of CgMITF, CgTYR and CgOCA2.