MicroRNA-277 regulates dopa decarboxylase to control larval-pupal and pupal-adult metamorphosis of Helicoverpa armigera.

Insect metamorphosis is a complex process involving many metabolic pathways, such as juvenile hormones and molting hormones, bioamines, microRNAs (miRNAs), etc. However, relatively little is known about the biogenic amines and their miRNAs to regulate cotton bollworm metamorphosis. Here we show that one miRNA, miR-277 regulates larval-pupal and pupal-adult metamorphosis of cotton bollworm by targeting the 3'UTR of Dopa decarboxylase (DDC), a synthetic catalytic enzyme of dopamine. Injection of miR-277 agomir inhibited the expression of DDC at the mRNA and protein levels, leading to defects in the pupation and emergence of H. armigera that was consistent with the phenotype obtained by injection of DDC double-stranded RNA (dsRNA). Injection of miR-277 antagomir induced the mRNA and protein expression of DDC and rescued the phenotype of pupation failure caused by DDC gene silencing. Unexpectedly, miR-277 antagomir can also cause failure of emergence of H. armigera and both agomir and antagomir of miR-277 injection could cause abnormal phenotypes in wing veins. This study reveals that elaborate regulation of miRNA and its target gene expression is prerequisite for insect development, which provides a new insight to study the developmental mechanisms of insect wing veins.