MicroRNA let-7 targets BmCDK1 to regulate cell proliferation and endomitosis of silk gland in the silkworm,Bombyx mori

MicroRNAs play critical roles in multiple developmental processes in insects.Our previous study showed that CRISPR/Cas9-mediated knock down of the microRNA let-7 in silkworms increased the size of larvae and silk glands,thereby improving the silk production capacity.In this study,we elucidate the molecular mechanism underlying of let-7 regulates growth.Identification of differentially expressed genes in response to let-7 knock down revealed enrichment of pathways associated with cell proliferation and DNA replication.let-7 dysregulation affected the cell cycle and proliferation of the Bombyx mori cell line BmN.Dual-luciferase and target site mutation assays showed that BmCDK1 is a direct target gene of let-7,with only 1 binding site on its 3′-untranslated region.RNA interference of BmCDK1 inhibited cell proliferation,but this effect was counteracted by co-transfection with let-7 antagomir.Moreover,let-7 knock down induced BmCDK1 expression and promoted cell proliferation in multiple tissues,and further induced endomitosis in the silk gland in vivo.Knock down of BmCDK1 resulted in abnormal formation of a new epidermis,and larval development was arrested at the 2nd or 3rd molt stage.Taken together,our results demonstrated that BmCDK1 is a novel target of let-7 in cell fate determination,possessing potential for improving silk yield in silkworm.