Promoter G-quadruplex structures regulate tissue-specific gene expression and functional differentiation in Bombyx mori

BACKGROUND: DNA G-quadruplex structures (G4s) are noncanonical nucleic acid structures that play crucial roles in gene transcription regulation, particularly when located within promoter regions. Tissue-specific gene expression underlies the development and functional specialization of multicellular organisms. However, the potential role of G4s in tissue-specific transcriptional regulation remains largely unexplored. In this study, we conducted an integrative analysis of G-quadruplex (G4) distribution and function in the silkworm brain and fat body, two substantially differentiated tissues in terms of structure and function, using G4-CUT&Tag, ATAC-seq, RNA-seq, and histone modification datasets. RESULTS: We found that promoter G4s were highly enriched in regions of open chromatin and active histone modification, and that G4 folding showed a correlation with transcriptional activation in a tissue-specific manner. Even at identical genomic DNA sequences, G4 folding patterns differed markedly between the brain and fat body and were associated with tissue-specific gene expression profiles. Genes marked by brain-specific G4s were enriched in neural pathways, whereas genes with fat body-specific G4s were enriched in metabolic pathways, closely aligning with the physiological roles of each tissue. Moreover, chemical stabilization of G4s by pyridostatin disrupted gene expression and impaired tissue development, including neurogenesis in the brain and lipid metabolism in the fat body. CONCLUSIONS: Our results suggest that G4s may function as dynamic epigenetic modulators that shape tissue-specific gene expression and coordinate functional differentiation in insects.