Dynamic chromatin conformation and accessibility changes mediate the spatial-specific gene regulatory network in Bombyx mori

Silk gland genes of Bombyx mori can have strict spatial expression patterns, which impact their functions and silk quality. However, our understanding of their regulation mechanisms is currently insufficient. To address this, the middle silk gland (MSG) and posterior silk gland (PSG) of the silkworm were investigated. Gene ontology annotation showed that spatially specific expressed genes were involved in the formation of H3k9me and chromatin topology. Chromatin conformation data generated by Hi-C showed that the topologically associated domain boundaries around FibL and Sericin1 genes were significantly different between MSG and PSG. Changes in chromatin conformation led to changes in chromatin activity, which significantly affected the expression of nearby genes in silkworm. Chromatin accessibility regions of MSG and PSG were analyzed using FAIRE-seq, and 1006 transcription factor motifs were identified in open chromatin regions. Furthermore, the spatial-specific expression patterns of silk gland genes were mainly associated with homeobox-contained transcription factors, such as POU-M2, which was specifically bound and relatively highly expressed in the MSG. The regulatory network mediated by POU-M2 regulated most of the spatial-specific expressed genes in MSG, such as ADH1. These results can aid in improving silk performance, optimizing silkworm breeding, and improving the gene spatial regulatory model research for insects.