Transcription factor FTZ-F1 regulates mosquito cuticular protein CPLCG5 conferring resistance to pyrethroids in Culex pipiens pallens

Abstract

Background Culex pipiens pallens poses a serious threat to human health because of its widespread distribution, high carrier capacity for several arboviruses, frequent human-biting, and growth in urban environments. Pyrethroid insecticides have been mainly used to control adult Cx. pipiens pallens during outbreaks of mosquito-borne diseases. Unfortunately, mosquitoes have developed resistance, rendering the insecticides ineffective. Cuticular resistance is the primary mechanism of pyrethroid resistance. Previously, we revealed that cuticular protein of low complexity CPLCG5 is a major cuticular protein associated with deltamethrin resistance in Cx. pipiens pallens, which is enriched in the cuticle of mosquitoes’ legs and participates in pyrethroid resistance by forming a rigid matrix. However, the regulatory mechanisms of its transcription remain unknown. Results First, qRT-PCR analysis revealed that the expression of FTZ-F1 (encoding Fushi tarazu-Factor 1) was ~ 1.8-fold higher in the deltamethrin-resistant (DR) than deltamethrin-susceptible (DS) strains at 24 h post-eclosion (PE) and ~ 2.2-fold higher in the DR strain than in the DS strain at 48 h PE. CPLCG5 and FTZ-F1 were co-expressed in the legs, indicating that they might play an essential role in the legs. Dual luciferase reporter assays and EMSA (electrophoretic mobility shift experiments) revealed that FTZ-F1 regulates the transcription of CPLCG5 by binding to the FTZ-F1 response element (− 870/− 864). Lastly, knockdown of FTZ-F1 not only affected CPLCG5 expression but also altered the cuticle thickness and structure of the legs, increasing the susceptibility of the mosquitoes to deltamethrin in vivo. Conclusions The results revealed that FTZ-F1 regulates the expression of CPLCG5 by binding to the CPLCG5 promoter region, altering cuticle thickness and structure, and increasing the susceptibility of mosquitoes to deltamethrin in vivo. This study revealed part of the mechanism of cuticular resistance, providing a deeper understanding of insecticide resistance.

Genomic and Transcriptomic Analysis Reveals Cuticular Protein Genes Responding to Different Insecticides in Fall Armyworm Spodoptera frugiperda

“…The over-expression of CP genes in resistant strains led to the increased thickness of cuticle, resulting in a cuticular penetration resistance to insecticide. Due to CP genes that exhibit higher expressions in resistant strains than in susceptible strains with the most potential to be implicated in insecticide resistance [19,21,36,42], CP genes of FAW up regulated here are worth being focused on to investigate their role in insecticide resistance. In addition to induction, CP genes can also be reduced by insecticides.…”

“…Due to the mixture of CPs, they greatly contribute to determine the properties of the insect cuticles for defending against environmental stresses [16,17]. Previous reports have shown that the changed expression of CP genes is associated with the exposure to insecticides, indicating that CPs participate in insecticide resistance [18][19][20][21]. However, the precise roles served by CPs in response to insecticides remain largely unknown.…”

CPR63 Promotes Pyrethroid Resistance by Increasing Cuticle Thickness in Culex Pipiens Pallens

“…Cuticle proteins play an important role in insect cuticle resistance, by thickening the cuticle to prevent the penetration of insecticides, and changing the density, thickness and insect morphological development of the cuticle. There is increasing evidence that alteration of the cuticle plays a role in insecticide resistance, based on analysis of CP transcripts and measurement of cuticle thickness [19,21,22,23,24,25]. For example, CYP4G16, CPLCG3, CPLCG5 and CPLC8 have been implicated in insecticide resistance by contributing to a thicker cuticle and thereby slowing penetration of insecticides [21,25,26].…”

“…The thickness of the cuticle was examined using image J software. The other detailed steps of the TEM experiment have been described in previous studies [14,19].…”

“…The mosquito leg is composed of the femur, tibia and tarsus, the tarsus is divided into T1, T2, T3, T4 and T5, and the cross section was at T1 (Fig. 4a) [19,20]. The same number of specimens was assessed in siCPR63 and siNC groups (n = 4).…”