The hypothetical cuticular protein, CPH19, is involved in cuticle formation during molt of silkworm Bombyx mori

The hypothetical cuticular protein 19 (CPH19) of the silkworm Bombyx mori, was highly expressed in the cuticle during larval molt. Injection of CPH19 double-stranded RNA (dsRNA) into the hemolymph of 2-day-old third instar larvae (2dLa3), accelerated insect molting at the La3-La4 and La4-La5 transitions, but larvae had difficulty shedding their cuticle and suffered from molt defects, and their exuviae were larger and heavier than those of the control group. A proximal promoter near the transcription start site of CPH19 with strong transcriptional activity that may be involved in an RNA-based promoter targeting mechanism mediated by small activating RNAs (saRNAs), which led to the mRNA levels of CPH19 were significantly increased in the CPH19 dsRNA-injected insects compared to the control, the expression of other CP genes such as CPH18, CPH20, CPR69, CPR96, CPR97, CPR98 and CPR100, as well as chitinase genes such as chs-2 and chsA were all increased, resulted in the heavier exuviae of molting larvae. Here we found that CPH19 is a crucial component of the larval molting cuticle and may contribute to insecticide resistance in silkworm larvae by affecting cuticle thickness. [Display omitted] •CPH19 can play roles in the cuticle formation of molting larvae in silkworm.•dsRNAs function as saRNAs to induce the expression of CPH19 in molting larva of silkworm.•Overexpression of CPH19 thicken the cuticle of molting larva.•Silkworms with CPH19 dsRNA injection were more resistant to insecticide decamethrin than control. The cuticle supports the insect body and serves as a protective barrier against pathogens and pesticides. We found that the gene CPH19, encoding the hypothetical cuticular protein 19 (CPH19) of the silkworm Bombyx mori, was highly expressed in the cuticle during larval molt. Injection of CPH19 double-stranded RNA (dsRNA) into the hemolymph of 2-day-old third instar larvae (2dLa3) accelerated insect molting at the La3-La4 and La4-La5 transitions. Nevertheless, the larvae injected with CPH19 dsRNA had difficulty shedding their cuticle and suffered from molt defects, and their exuviae were larger and heavier than those of the control group. Morphological comparison of the exuviae between CPH19 dsRNA-injected and control larvae showed that the exocuticle-endocuticle layer was thicker in the former. The effect of CPH19 dsRNA injection on gene expression was further investigated by quantitative real-time polymerase-chain reaction (qRT-PCR). Surprisingly, th