The AF-2 domain of estrogen-related receptor interacts with PPRC1 to modulate larval epidermal marking in Bombyx mori

Estrogen-related receptors (ERRs) have no natural ligands, vertebrate ERRs rely on their activation function-2 (AF-2) structural domain to recruit coactivators for transcriptional regulation. While metabolic regulation in insects differs significantly from that in vertebrates, it remains unclear whether the regulatory function of insect ERR requires coactivators. Using silkworms as the research subject, this study aims to analyze the molecular mechanisms of ERR-regulated metabolism in insects and refine the metabolic regulatory network. This study applied CRISPR/Cas9 gene editing technology to knock out the AF-2 domain of BmERR in the lepidopteran silkworms and examined its effects on functional role, associated interacting factors, and related physiological processes. Disruption of the BmERR AF-2 domain inhibited the expression of melanin metabolism-related genes BmTH , BmDDC , BmAA-NAT , Bmebony , and Bmtan , leading to the accumulation of tyrosine and dopa, thereby causing aberrant melanin metabolism and loss of epidermal markings. By contrast, BmERR overexpression enhanced the pathway, resulting in intensification of epidermal markings. The homologous gene of the ERR coactivator, BmPPRC1, showed highly consistent expression with BmERR in the epidermis. The immunofluorescence signal of BmPPRC1 was localized to the nucleus and highly overlapped with that of BmERR. BmPPRC1 interacts with the AF-2 domain of BmERR, and deletion of this region weakens the regulation of melanin metabolism-related genes in silkworm embryonic cells. The ERR function and mode of action are evolutionarily conserved, and its AF-2 structural domain binds equally well to the coactivator BmPPRC1, providing new perspectives for studying the modulability of insect mottle formation.