Effects of Apolipophorin on Ovarian Development and Lipid Deposition in Locusta migratoria

Lipids are one of the important nutrients required by organisms, which play important physiological functions, including diapause, flight, embryonic development and energy regulation in insects. Apolipophorins (apoLps) are the main components of insect lipophorin particles, which are involved in the transport of lipids among different tissues.

The objective of this study is to investigate the function of apolipophorins (LmapoLp-II/I and LmapoLp-III) by RNA interference (RNAi) in ovarian lipid transport in Locusta migratoria, and to provide a new molecular target for pest control.

RNAi was performed to silence two apolipophorin genes (LmapoLp-II/I and LmapoLp-III) at 1 day post adult eclosion (1 PAE), respectively. dsGFP was used as control, 15 μg dsRNA was injected into each insect. The ovaries at 4, 6 and 8 PAE were dissected and observed after dsRNA injection. The silencing efficiency of LmapoLps in the ovaries at 8 PAE was analyzed by reverse-transcription quantitative PCR (RT-qPCR), and EF1α was used as internal reference gene. Lipidomics technique was used to determine and analyze the differences of lipid metabolites in the ovaries between dsGFP- and dsLmapoLp-II/I-treated groups. The approach combining the fold change, the P value and the VIP value of the OPLS-DA model was adopted to screen for differential abundance of lipids. The contents of neutral lipids and total triglycerides were determined by Bodipy staining and triglyceride assay kit.

After injection of dsLmapoLp-II/I and dsLmapoLp-III, the expression level of target genes could be significantly silenced by 80.84% and 92.89%, respectively. RNAi-mediated silencing of LmapoLp-II/I led to a retarded ovarian development, with significantly decreased neutral lipid content and triglyceride content, while the ovaries of L. migratoria injected with dsLmapoLp-III were the same as those in the control group, which could develop normally and gradually grow larger, with the color gradually changing from white to yellow. After LmapoLp-II/I silencing, a total of 1 166 up-regulated metabolites and 1 384 down-regulated metabolites were detected by lipidomics analysis, of which 20 triglycerides were significantly down-regulated.

LmapoLp-II/I is a major apolipophorin gene that affects ovarian development and is involved in the accumulation and transport of ovarian lipids. These research results not only enrich the research content of lipid metabolism in insects, but also help to find new targets for pest control.