Submitted to: Journal of Insect Physiology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/3/2010
Publication Date: 9/7/2010
Citation: Jones, G., Jones, D., Li, X., Tang, L., Ye, L., Teal, P.E., Riddiford, L., Sandifer, C., Borovsky, D., Martin, J. 2010. Activities of natural methyl farnesoids on pupariation and metamorphosis of Drosophila melanogaster. Journal of Insect Physiology. 56:1456-1464. Interpretive Summary: Insect juvenile hormones (JH) regulate development and metamorphosis in insects. There are a suit of these JHs in insects. An important question in insect physiology is which JHs are important to different phases of from development and metamorphosis. Scientists at the University of Kentucky, Lexington KY, Center for Medical, Agricultural and Veterinary Entomology USDA-ARS, Gainesville FL and University of Florida-IFAS, Florida Medical Entomology Laboratory, Vero Beach, Fl conducted studies using various forms of the hormones and discovered that methyl farnesoate and JH III were similarly active, and more active than bisJH III, in lengthening larval development prior to pupariation. However, the order of activity was changed (JH III > bisJH III > MF) with respect to preventing prepupae from eclosing as normal adults. These data were supported by RNA interference studies. The results show that different forms of JH affect different aspects of development.
Technical Abstract: Methyl farnesoate (MF) and juvenile hormone (JH III), which respectively bind to the receptors USP and MET, and bisepoxy JH III (bisJHIII) were assessed for several activities during Drosophila larval development, and during prepupal development to eclosed adults. Dietary MF and JH III were similarly active, and more active than bisJH III, in lengthening larval development prior to pupariation. However, the order of activity was changed (JH III > bisJH III > MF) with respect to preventing prepupae from eclosing as normal adults, whether administered in the larval diet or as topically applied at the white puparium stage. If endogenous production of all three larval methyl farnesoids was suppressed by a strongly driven RNAi against HMGCR in the corpora allata cells, most larvae did not attain pupariation. Provision of dietary farnesol, which presumably rescued the relative production of all three hormones, rescued attainment of pupariation in a dose-dependent manner. A more mild suppression of endogenous farnesoid production enabled larval attainment of pupariation. However, in this background dietary MF had increased activity in preventing puparia from attaining normal adult eclosion. The physiological relevance of using exogenous methyl farnesoids to block prepupal development to normally eclosed adults was tested by, instead, protecting in prepupae the endogenouos titer of methyl farnesoids. JH esterase normally increases during the mid-late prepupal stage, presumably to clear endogenous methyl farnesoids. When JH esterase was inhibited with an RNAi, it prevented attainment of adult eclosion. Cultured adult corpora allata from male and female Aedes aegypti released both MF and JH III, and the Ae. aegypti nuclear receptor USP bound MF with nanomolar affinity. These Ae. aegypti data support the use of Drosophila as a model for mosquitoes of the binding of secreted MF to USP.