Elongases of Long-Chain Fatty Acids ELO2 and ELO9 Are Involved in Cuticle Formation and Function in Fecundity in the Yellow Fever Mosquito, Aedes aegypti

SIMPLE SUMMARY: Elongases of long-chain fatty acids (ELOs) play an important role in the function and metabolism of fatty acids of different chain lengths. However, little is known about the expression and biological function of fatty acid ELOs in insects, including in the larvae and adult blood-feeding Ae. aegypti mosquitoes. Therefore, the study of ELOs is necessary to understand the development and reproduction of insects, including mosquitoes. In this study, two novel ELO genes were identified in Ae. aegypti. We used two different RNAi methods (larval-nanoparticle feeding; adult-microinjection) to analyze the functions of AeELO2 and AeELO9 in larvae development and adult fecundity in Aedes aegypti. The results indicated that AeELO2 and AeELO9 play crucial roles in larval development and the adult fecundity of Ae. aegypti. AeELO2 mainly participated in larval molting behavior and growth, and it regulated the flexibility and elasticity of adult mosquito cuticles. AeELO9 affected the cold resistance of larvae and adult mosquitoes. It also regulated the permeability of larvae and adult mosquito cuticles and egg development, therefore affecting the reproductive ability of Ae. aegypti. ABSTRACT: Long-chain fatty acid elongases (ELOs) play important roles in the metabolism of fatty acids in insects. In this study, the genes for two elongases from Aedes aegypti were identified, AeELO2 and AeELO9. Quantitative real time PCR showed that AeELO2 and AeELO9 are expressed at all developmental stages and some body parts, but with different expression patterns. RNAi-mediated knockdown of AeELO2 and AeELO9 was performed to investigate their roles in the development, growth, osmotic balance, and cold tolerance of Ae. aegypti. Knockdown of AeELO2 slowed larval growth and development by causing molting abnormalities. Additionally, 33% ± 3.3% of adults died during oviposition, accompanied by an abnormal extension of cuticles in AeELO2-dsRNA knockdown mosquitos. Knockdown of AeEL09 resulted in abnormal balance of cuticular osmotic pressure and a reduction in egg production. The maximal mRNAs of AeELO2 and AeELO9 were detected in eggs at 72 h after oviposition. Moreover, AeELO2 knockdown reduced the egg hatching rates and AeELO9 knockdown larvae did not develop well. In summary, AeELO2 is involved in larval molting and growth, and its knockdown affects the flexibility and elasticity of adult mosquito cuticles. AeELO9 regulates cold tolerance, osmotic balance, and egg development in Ae. aegypti.