Tissue-Specific Coupling between Insulin/IGF and TORC1 Signaling via PRAS40 in Drosophila

PRAS40 has recently been identified as a protein that couples insulin/IGF signaling (IIS) to TORC1 activation in cell culture; however, the physiological function of PRAS40 is not known. In this study, we investigate flies lacking PRAS40. Surprisingly, we find both biochemically and genetically that PRAS40 couples IIS to TORC1 activation in a tissue-specific manner, regulating TORC1 activity in ovaries but not in other tissues of the animal. PRAS40 thereby regulates fertility but not growth of the fly, allowing distinct physiological functions of TORC1 to be uncoupled. We also show that the main function of PRAS40 in vivo is to regulate TORC1 activity, and not to act as a downstream target and effector of TORC1. Finally, this work sheds some light on the question of whether TORC1 activity is coupled to IIS in vivo

Desensitisation of Notch signalling through dynamic adaptation in the nucleus

During embryonic development, signalling pathways orchestrate organogenesis by controlling tissue‐specific gene expression programmes and differentiation. Although the molecular components of many common developmental signalling systems are known, our current understanding of how signalling inputs are translated into gene expression outputs in real‐time is limited. Here we employ optogenetics to control the activation of Notch signalling during Drosophila embryogenesis with minute accuracy and follow target gene expression by quantitative live imaging. Light‐induced nuclear translocation of the Notch Intracellular Domain (NICD) causes a rapid activation of target mRNA expression. However, target gene transcription gradually decays over time despite continuous photo‐activation and nuclear NICD accumulation, indicating dynamic adaptation to the signalling input. Using mathematical modelling and molecular perturbations, we show that this adaptive transcriptional response fits to known motifs capable of generating near‐perfect adaptation and can be best explained by state‐dependent inactivation at the target cis‐regulatory region. Taken together, our results reveal dynamic nuclear adaptation as a novel mechanism controlling Notch signalling output during tissue differentiation

Ovary ecdysteroidogenic hormone functions independently of the insulin receptor in the yellow fever mosquito, Aedes aegypti

Most mosquito species must feed on the blood of a vertebrate host to produce eggs. In the yellow fever mosquito, Aedes aegypti, blood feeding triggers medial neurosecretory cells in the brain to release insulin-like peptides (ILPs) and ovary ecdysteroidogenic hormone (OEH). Theses hormones thereafter directly induce the ovaries to produce ecdysteroid hormone (ECD), which activates the synthesis of yolk proteins in the fat body for uptake by oocytes. ILP3 stimulates ECD production by binding to the mosquito insulin receptor (MIR). In contrast, little is known about the mode of action of OEH, which is a member of a neuropeptide family called neuroparsin. Here we report that OEH is the only neuroparsin family member present in the Ae. aegypti genome and that other mosquitoes also encode only one neuroparsin gene. Immunoblotting experiments suggested that the full-length form of the peptide, which we call long OEH (lOEH), is processed into short OEH (sOEH). The importance of processing, however, remained unclear because a recombinant form of lOEH (rlOEH) and synthetic sOEH exhibited very similar biological activity. A series of experiments indicated that neither rlOEH nor sOEH bound to ILP3 or the MIR. Signaling studies further showed that ILP3 activated the MIR but rlOEH did not, yet both neuropeptides activated Akt, which is a marker for insulin pathway signaling. Our results also indicated that activation of TOR signaling in the ovaries required co-stimulation by amino acids and either ILP3 or rlOEH. Overall, we conclude that OEH activates the insulin signaling pathway independently of the MIR, and that insulin and TOR signaling in the ovaries is coupled