BmILRUN plays an important role in the formation of wing scale in Bombyx mori

Wing scales are essential for insect flight, thermoregulation, camouflage, and mating behavior. During routine rearing of the bivoltine silkworm Qiufeng, a scaleless wing mutant, designated P33, was identified, in which adult wing scales were severely reduced or absent. However, the gene responsible for the scaleless wing mutation in the silkworm remains unknown. Here, Genetic analysis indicated that this phenotype is controlled by a single autosomal recessive locus. Positional cloning mapped the responsible locus to a 0.24 Mb interval on chromosome 13 of the Bombyx mori genome containing 21 predicted genes. qRT-PCR analysis of these candidate genes in the wing primordia of Qiufeng and P33 at pupal day 3-4 and pupal day 6-7 revealed that, among the 21 genes, BmILRUN(KWMTBOMO08006) displayed a stable upregulation expression in P33 compared to Qiufeng. Sequence analysis further revealed that the BmILRUN gene in P33 carries four synonymous substitutions in the coding region, together with a 284bp deletion in the third intron and a 633bp insertion in the fourth intron. 5' and 3' RACE results revealed that both the 5'-UTR and 3'-UTR regions of BmILRUN were truncated in P33 relative to Qiufeng. CRISPR-Cas9-mediated knockout of BmILRUN resulted in a significant reduction in its expression and a marked decrease in wing scales. Together, these results demonstrate that BmILRUN is essential for wing scale formation in Bombyx mori providing insight into the molecular regulation of wing scale development.