The Intricate Role of Ecdysis Triggering Hormone Signaling in Insect Development and Reproductive Regulation.

Insect growth is interrupted by molts, during which the insect develops a new exoskeleton. The exoskeleton confers protection and undergoes shedding between each developmental stage through an evolutionarily conserved and ordered sequence of behaviors, collectively referred to as ecdysis. Ecdysis is triggered by Ecdysis triggering hormone (ETH) synthesized and secreted from peripheral Inka cells on the tracheal surface and plays a vital role in the orchestration of ecdysis in insects and possibly in other arthropod species. ETH synthesized by Inka cells then binds to ETH receptor (ETHR) present on the peptidergic neurons in the central nervous system (CNS) to facilitate synthesis of various other neuropeptides involved in ecdysis. The mechanism of ETH function on ecdysis has been well investigated in holometabolous insects such as moths Manduca sexta and Bombyx mori, fruit fly Drosophila melanogaster, the yellow fever mosquito Aedes aegypti and beetle Tribolium castaneum etc. In contrast, very little information is available about the role of ETH in sequential and gradual growth and developmental changes associated with ecdysis in hemimetabolous insects. Recent studies have identified ETH precursors and characterized functional and biochemical features of ETH and ETHR in a hemimetabolous insect, desert locust, Schistocerca gregaria. Recently, the role of ETH in Juvenile hormone (JH) mediated courtship short-term memory (STM) retention and long-term courtship memory regulation and retention have also been investigated in adult male Drosophila. Our review provides a novel synthesis of ETH signaling cascades and responses in various insects triggering diverse functions in adults and juvenile insects including their development and reproductive regulation and might allow researchers to develop sustainable pest management strategies by identifying novel compounds and targets.

Bisphenol A acts as developmental agonist in Culex quinquefasciatus Say.

Plastic wastes deposited in canals running through Thiruvananthapuram city have created stagnant waters providing breeding sites for mosquitoes. In the present study, plastic waste-derived bisphenol A (BPA) was quantified from four mosquito breeding sites. During summer rain, the concentration of BPA in the stagnant water samples was found to be between 0.86 and 1.14 mg/L, and hence 1 mg/L BPA was considered as the environmentally relevant concentration. In the present study, the effect of BPA on the life cycle and metamorphosis of filarial vector, Culex quinquefasciatus Say was elucidated by rearing larvae in water added with BPA at and above the environmentally relevant concentration viz., 1, 2, and 4 mg/L. The duration required for adult emergence was reduced from 10 to 8.5 days, when the concentration of BPA was increased from 1 to 4 mg/L respectively. Our study revealed that embryonic and larval developments were shortened by BPA treatment. BPA also caused a dose-dependent advancement of 20-hydroxyecdysone (20-E) peaks; phospholipase A2 induction; and upregulation of ecdysone receptor gene, EcRA, and ecdysone inducible gene E75A, which culminated in early pupation. No significant difference in sanguivory and fecundity was observed in adult mosquitoes treated with 1 mg/L of BPA. Our study reveals that BPA is a developmental agonist of C. quinquefasciatus.

Sesquiterpene action, and morphogenetic signaling through the ortholog of retinoid X receptor, in higher Diptera.

Morphogenetic signaling by small terpenoid hormones is a common feature of both vertebrate and invertebrate development. Most attention on insect developmental signaling by small terpenoids has focused on signaling by juvenile hormone through bHLH-PAS proteins (e.g., the MET protein), especially as that signaling axis intersects with ecdysteroid action through the receptor EcR. However, a series of endocrine and pharmacological studies on pupariation in cyclorrhaphous Diptera have remained persistently refractory to explanation with the above two-axis model. Recently, the terpenoid compound methyl farnesoate has been physicochemically demonstrated to exist in circulation at physiological concentrations, in several mecopterid orders, including Diptera. In addition, it has also been recently demonstrated that the receptor to which methyl farnesoate binds with nanomolar affinity (ultraspiracle, an ortholog of retinoid X receptor) requires a functioning ligand binding pocket to sustain the morphogenetic transition to puparium formation. This review evaluates endocrine and pharmacological evidence for developmental pathways reached by methyl farnesoate action, and assesses the participation of the retinoid X receptor ligand pocket in signal transduction to those developmental endpoints.

Differentially expressed genes in the ovary of the sixth day of pupal "Ming" lethal egg mutant of silkworm, Bombyx mori.

The "Ming" lethal egg mutant (l-em) is a vitelline membrane mutant in silkworm, Bombyx mori. The eggs laid by the l-em mutant lose water, ultimately causing death within an hour. Previous studies have shown that the deletion of BmEP80 is responsible for the l-em mutation in silkworm, B. mori. In the current study, digital gene expression (DGE) was performed to investigate the difference of gene expression in ovaries between wild type and l-em mutant on the sixth day of the pupal stage to obtain a global view of gene expression profiles using the ovaries of three l-em mutants and three wild types. The results showed a total of 3,463,495 and 3,607,936 clean tags in the wild type and the l-em mutant libraries, respectively. Compared with those of wild type, 239 differentially expressed genes were detected in the l-em mutant, wherein 181 genes are up-regulated and 58 genes are down-regulated in the mutant strain. The Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis results showed that no pathway was significantly enriched and three pathways are tightly related to protein synthesis among the five leading pathways. Moreover, the expression profiles of eight important differentially expressed genes related to oogenesis changed. These results provide a comprehensive gene expression analysis of oogenesis and vitellogenesis in B. mori which facilitates understanding of both the specific molecular mechanism of the 1-em mutant and Lepidopteran oogenesis in general.

Effects of cycloheximide on cellular elongation in aManduca sexta cell line.

A clone (GV1) of the CHIManduca sexta cell line responds to 20-hydroxy-ecdysone by changing cellular shape from an epithelial-like form to an elongated fibroblast-like form. We have determined that this morphological response to hormone is prevented by treatment with cycloheximide. The inhibition of the elongation response by cycloheximide may relate to a requirement for the synthesis of specific proteins that play a role in the formation of cytoskeletal structure.