Involvement of cecropin B in the formation of the Aedes aegypti mosquito cuticle

Wei-Ting Liu,Wu-Chun Tu,Ueng-Cheng Yang,Cheng-Chen Chen,Chao-Hsiung Lin

doi:10.1038/s41598-017-16625-6

Abstract

In this study, we found a mosquito antimicrobial peptide (AMP), Aedes aegypti cecropin B (Aacec B), was expressed constitutively in pupae. Knockdown in the pupae of Aacec B using double-stranded RNA (dsRNA) resulted in high mortality, the emergence of deformed adults and an impairment of pharate adult cuticle formation with fewer lamellae being deposited and the helicoidal pattern of the chitin microfibrils being disorganized. Simultaneous injection of Aacec B dsRNA and Aacec B peptide into pupae significantly reduced this mortality and no deformed adults then emerged. The expression levels of Ae. aegypti prophenoloxidase (AaPPO) 3 and AaPPO 4 were significantly reduced in the Aacec B knockdown pupae. Exogenous Aacec B peptide significantly enhanced the transcription of AaPPO 3 in pupae. Knockdown of AaPPO 3 in pupae caused effects similar to Aacec B-knockdown. The Aacec B peptide could be detected in both the cytoplasm and nuclei of pupal cells and was able to bind to the TTGG(A/C)A motif in AaPPO 3 DNA both in vitro and in vivo. These findings suggest that Aacec B plays a crucial role in pharate adult cuticle formation via the regulation of AaPPO 3 gene expression in pupae.

Highlights

More than 150 antimicrobial peptides (AMPs) in insects have been identified or been predicted via genome sequencing[1]
We have demonstrated that Aedes aegypti cecropin B (Aacec B) plays a significant role in the pharate adult cuticle formation of Ae. aegypti pupae, a novel function for an AMP
We have found that knockdown of Aacec B in pupae results in high mortality (Fig. 2b), the emergence of deformed adults (Fig. 2d) and an impairment of pharate adult cuticle formation

Summary

Introduction

More than 150 antimicrobial peptides (AMPs) in insects have been identified or been predicted via genome sequencing[1]. Other Bmcec genes, such as Bmcec E, which have the lowest levels of induced expression, have the most limited antimicrobial spectrum and the weakest antimicrobial activity. Based on this they suggested that Bmcec B6 and Bmcec D may play crucial roles in eliminating microbial infection, while the other non-major proteins, such as Bmcec E, may function as backups to the major AMPs. We hypothesize in the present study that those AMPs with no or a low level of induced expression may act as backups to the major AMPs, and may play important roles in some other physiological functions. We demonstrate that Aacec B, which is expressed constitutively in Ae. aegypti adults, and the expression level of which is not affected by bacterial challenge, plays an important role in cuticle formation by the insect’s pupae

Methods

Results

Conclusion