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Abstract Background Insulin-like signaling (IS) in insects is a conserved pathway that regulates development, reproduction and longevity. Insulin-like peptides (ILPs) activate the IS pathway by binding to the insulin receptor (InR) and trigger the ERK and AKT cascades. A varying number of ILPs were identified in Aedes aegypti mosquito and other insects. Aedes albopictus is an invasive mosquito which transmits dengue and Zika viruses worldwide. Until now, the molecular and expression characteristics of IS pathway in Ae. albopictus have not been investigated. Methods The orthologues of ILP in Ae. albopictus genome assembly was analyzed by using sequence blast. Phylogenetic analysis and molecular characterization were performed to identify the functional domains of ILPs. Quantitative analysis was performed to determine the expression characteristics of ILPs, InR as well as ERK and AKT in mosquito development and different tissues of female adults after blood-feeding. In addition, the knockdown of InR was achieved by feeding larvae with Escherichia coli-producing dsRNA to investigate the impact of IS pathway on mosquito development. Results We identified seven putative ILP genes in Ae. albopictus genome assembly, based on nucleotide similarity to the ILPs of Ae. aegypti and other insects. Bioinformatics and molecular analyses suggested that the ILPs contain the structural motif which is conserved in the insulin superfamily. Expression levels of ILPs, InR as well as ERK and AKT varied in Ae. albopictus development stages and between male and female adults. Quantitative analyses revealed that expression of ILP6, the putative orthologue of the insulin growth factor peptides, was highest in the midgut of female adults after blood-feeding. Knockdown of Ae. albopictus InR induces a significant decrease in the phosphorylation levels of ERK and AKT proteins and results in developmental delays and smaller body sizes. Conclusions The IS pathway of Ae. albopictus mosquito contains ILP1-7, InR and ERK/AKT cascades, which exhibited different developmental and tissue expression characteristics. Feeding Ae. albopictus larvae with E. coli-producing InR dsRNA blocks the ERK and AKT cascades and interferes with the development of mosquito. Our data suggest that IS pathway plays an important role in the metabolism and developmental process and could represent a potential target for controlling mosquito-borne diseases. Graphical Abstract

Hyla annectans is a tree frog living in the southwestern plateau area of China where there is strong ultraviolet radiation and long duration of sunshine. So their naked skin may possess chemical defense components that protect it from acute photo-damage. However, no such peptide or components has been identified till to date. In the current work, two novel peptides (FW-1, FWPLI-NH2 and FW-2, FWPMI-NH2) were identified from the skin of the tree frog. Five copies of FW-1 and four copies of FW-2 are encoded by an identical gene and released from the same protein precursor, which possess 167 amino acid residues. FW-1 and -2 can exert significant anti-inflammatory functions by directly inhibiting Ultraviolet B irradiation (UVB)-induced secretion of inflammatory cytokines such as tumor necrosis factor-α (TNF-α) and interleukin-6 (IL-6). They may achieve this function by modulating the UV-induced stress signaling pathways such as Mitogen-activated protein kinases (MAPK) and Nuclear Factor Kappa B (NF-κB). Besides, FW-1 and -2 showed potential antioxidant effects on epidermis by attenuating the UVB-induced reactive oxygen species (ROS) production through an unknown mechanism. Considering small peptides’ easy production, storage, and potential photo-protective activity, FW-1/2 might be exciting leading compounds or templates for the development of novel pharmacological agents for the suppression of UVB-induced skin inflammation. Moreover, this study might expand our knowledge on skin defensive mechanism of tree frog upon UVB irradiation.