Comprehensive transcriptomics comparison reveals switch of gene networks in the brain during silkworm domestication

As in other domestic animals, the silkworm Bombyx mori has evolved adaptive behavioral changes compared with its wild ancestor, Bombyx mandarina. Domestication may have significantly impacted the brain of the silkworm, but it remains unclear whether and how the brain has evolved in response to domestication. Here we systematically quantified and compared morphological differences in the brains of domestic and wild silkworms at 7 representative stages during metamorphosis, and revealed that the B. mori brain had a reduced brain area and a reduced degree of fusion compared with the B. mandarina brain. The 2 silkworm species exhibited divergent brain developmental transcriptomic landscapes, implying the reshaping of brain functions during domestication. Genes enriched in nervous system development were generally repressed in the domesticated brain, with a slight upregulation during the wandering stage. An upregulation of Toll and Imd and a disturbance of apoptotic homeostasis were identified in the domestic silkworm brain. Mapping a comprehensive interaction network of these pathways and nervous system-related processes identified one key gene, Stx1b, and several candidate domestication genes that may have coordinated the developmental changes in the brain of the silkworm during domestication.