The homeobox gene <i>Distal</i> ‐ <i>less</i> is critical for the development of adult body appendages in <i>Bombyx mori</i>

The development of adult body appendages is critical for insects. The homeobox gene Distal-less (Dll) is known for its role in proximodistal patterning, and its role in the development of the appendage has been well studied in the model organism Drosophila melanogaster. However, the biological function of Dll in other insects still remains to be further verified. In this study, we investigated the biological function of Dll in the lepidoptera model insect Bombyx mori. Similar to the expression patterns observed in D. melanogaster, BmDll was highly expressed in the tibia and tarsus of the legs. The BmDll mutants obtained through the binary transgenic CRISPR/Cas9 system appeared to thrive normally and no apparent deleterious phenotypes were observed throughout the embryonic and larval stages. Nevertheless, mutants exhibited severe defects in the development of the appendage, especially at the distal end of legs, from pupal stage to adult stage. RNA-seq analysis revealed that metabolism pathways, extracellular matrix (ECM)-receptor interaction and structural constituent of the cuticle were dysregulated in mutant silkworms. Our study provided genetic evidence that Dll plays an important role in the development of B. mori adult body appendages.