Nutritional and reproductive signaling revealed by comparative gene expression analysis in Chrysopa pallens (Rambur) at different nutritional statuses

July Nutritional and reproductive signaling revealed by comparative gene expression analysis in Chrysopa pallens (Rambur) at different nutritional statuses Benfeng Han 0 1 Shen Zhang 0 1 Fanrong Zeng 0 1 Jianjun Mao 0 1 0 Key Laboratory for Biology of Plant Diseases and Insect Pests, Ministry of Agriculture, Institute of Plant Protection, Chinese Academy of Agricultural Sciences , Beijing , China 1 Editor: Kyung-Jin Min, Inha University , REPUBLIC OF KOREA The green lacewing, Chrysopa pallens Rambur, is one of the most important natural predators because of its extensive spectrum of prey and wide distribution. However, what we know about the nutritional and reproductive physiology of this species is very scarce. - Competing interests: The authors have declared that no competing interests exist. Background Results By cDNA amplification and Illumina short-read sequencing, we analyzed transcriptomes of C. pallens female adult under starved and fed conditions. In total, 71236 unigenes were obtained with an average length of 833 bp. Four vitellogenins, three insulin-like peptides and two insulin receptors were annotated. Comparison of gene expression profiles suggested that totally 1501 genes were differentially expressed between the two nutritional statuses. KEGG orthology classification showed that these differentially expression genes (DEGs) were mapped to 241 pathways. In turn, the top 4 are ribosome, protein processing in endoplasmic reticulum, biosynthesis of amino acids and carbon metabolism, indicating a distinct difference in nutritional and reproductive signaling between the two feeding conditions. Conclusions Our study yielded large-scale molecular information relevant to C. pallens nutritional and reproductive signaling, which will contribute to mass rearing and commercial use of this predaceous insect species. Introduction In recent years, there has been increasing interest in mass production and commercial use of predatory and parasitic natural enemies in biological control of arthropod pests. The green lacewing Crysopa pallens is one of the most important natural predators of aphids, coccids, thrips, mites and caterpillars [1±3]. However, very little is known about the nutritional and reproductive signaling in this natural enemy insect. Vitellogenin (Vg) is the main source of nutrition for the embryo development and is crucial for reproduction of oviparous animals, such as insects [ 4 ]. Several hormones, like juvenile hormone (JH), ecdysone and neuropeptides, are involved in regulation of Vg gene expression [5± 8]. All these endocrine hormones function through certain conserved signaling pathways. There are mainly two pathways involved in conveying of insect nutritional signals, the target of rapamycin (ToR) pathway and the insulin-like peptides (ILPs) pathway [ 5,9 ]. ILPs in insects are analogously to both insulin and IGF in vertebrates. So far, genes encoding ILPs have been cloned in species from different insect orders, including Orthoptera, Diptera, Lepidoptera and Hymenoptera [ 5,10 ]. Genetic studies revealed that insect ILPs act through a conserved insulin signaling pathway and regulate development, longevity, metabolism, diapause and reproduction [11±19]. The ILP/ToR pathways sense nutrient level and play crucial roles in determining the tradeoff between survival and reproduction [ 7 ]. To date, the main elements involved in the ILP/ ToR pathways have been identified. When insect reached a nutritional status suitable for inducing reproductive processes, the ILPs are secreted in response to the high nutritional level. Binding of ILPs with the insulin receptor (InR) activates expression of phosphatidylinositol 3-kinase (PI3K) and subsequently increases the production of phosphatidylinositol trisphosphate (PIP3). Acting as a second messenger, the PIP3 recruits Akt (serine/threonine-protein kinase) to plasma membrane. After phosphorylation, the Akt in turn phosphorylates a series of downstream targets to realize pathway function [ 20,21 ]. FoxO, the transcription factor forkhead-box, class O, is a pivotal agent relevant to the transcriptional activities of the ILPs pathway [22±24]. In fed condition, FoxO was phosphorylated and exported from nucleus to cytoplasm. In contrast, under starved condition, unphosphorylated FoxO is restricted to the nucleus. Both ILP- and ToR-dependent signals coordinately control the translational effector S6 kinase (S6K) and translation initiation factor 4E-binding protein (4E-BP). In presence of ample nutrients, ILP and ToR signaling become active and lead to phosphorylation of S6K, which promote protein synthesis and growth. In the absence of nutrients, ILP/ToR signaling is attenuated. 4E-BP is hypophosphorylated and associates tightly with eIF4E, leading to reduction of protein synthesis and inhibition of growth [ 21,23,25,26 ]. In recent years, deep sequencing via next-generation high throughput techniques has been widely used t (...truncated)