Imaginal disc growth factor maintains cuticle structure and controls melanization in the spot pattern formation ofBombyx mori

Author summary The diverse stripe patterns of animals are usually used for warning or camouflage. However, the actual mechanisms underlying diverse stripe pattern formation remains largely unknown. This study provides direct evidence that imaginal disc growth factor (IDGF) maintains cuticle structure and controls melanization in the spot pattern formation. Our exhaustive knockout experiments reveal that BmIDGF is involved in the melanin pigmentation ofBombyx mori. We demonstrate that IDGF impacts the expression levels of the 20E-inducible transcription factorE75Aand pleiotropic factorsapt-likeandToll8/spz3, to further affect the melanin metabolism. Furthermore, the metabolome ofBmIDGFgene deletion connects metabolism to gene function. Thus, this study shed light on not only the unique function of IDGF but also, the molecular mechanism of spot pattern formation. The complex stripes and patterns of insects play key roles in behavior and ecology. However, the fine-scale regulation mechanisms underlying pigment formation and morphological divergence remain largely unelucidated. Here we demonstrated that imaginal disc growth factor (IDGF) maintains cuticle structure and controls melanization in spot pattern formation ofBombyx mori. Moreover, our knockout experiments showed that IDGF is suggested to impact the expression levels of the ecdysone inducible transcription factor E75A and pleiotropic factors apt-like and Toll8/spz3, to further control the melanin metabolism. Furthermore, the untargeted metabolomics analyses revealed that BmIDGF significantly affected critical metabolites involved in phenylalanine, beta-alanine, purine, and tyrosine metabolism pathways. Our findings highlighted not only the universal function of IDGF to the maintenance of normal cuticle structure but also an underexplored space in the gene function affecting melanin formation. Therefore, this study furthers our understanding of insect pigment metabolism and melanin pattern polymorphisms.