A Multicomponent Neuronal Response Encodes the Larval Decision to Pupariate upon Amino Acid Starvation

Abstract

Organisms need to coordinate growth with development, particularly in the context of nutrient availability. Thus, multiple ways have evolved to survive extrinsic nutrient deprivation during development. In Drosophila, growth occurs during larval development. Larvae are thus critically dependent on nutritional inputs; but after critical weight, they pupariate even when starved. How nutrient availability is coupled to the internal metabolic state for the decision to pupariate needs better understanding. We had earlier identified glutamatergic interneurons in the ventral ganglion that regulate pupariation on a protein-deficient diet. Here we report that Drosophila third instar larvae (either sex) sense arginine to evaluate their nutrient environment using an amino acid transporter Slimfast. The glutamatergic interneurons integrate external protein availability with internal metabolic state through neuropeptide signals. IP3-mediated calcium release and store-operated calcium entry are essential in these glutamatergic neurons for such integration and alter neuronal function by reducing the expression of multiple ion channels.SIGNIFICANCE STATEMENT Coordinating growth with development, in the context of nutrient availability is a challenge for all organisms in nature. After attainment of “critical weight,” insect larvae can pupariate, even in the absence of nutrition. Mechanism(s) that stimulate appropriate cellular responses and allow normal development on a nutritionally deficient diet remain to be understood. Here, we demonstrate that nutritional deprivation, in postcritical weight larvae, is sensed by special sensory neurons through an amino acid transporter that detects loss of environmental arginine. This information is integrated by glutamatergic interneurons with the internal metabolic state through neuropeptide signals. These glutamatergic interneurons require calcium-signaling-regulated expression of a host of neuronal channels to generate complex calcium signals essential for pupariation on a protein-deficient diet.

Modulation of flight and feeding behaviours requires presynaptic IP3Rs in dopaminergic neurons

“…IP 3 -mediated calcium release from the IP 3 R in the presence of Itpr DN , was tested on previously characterised glutamatergic interneurons in the larval ventral ganglion known to respond to the muscarinic acetylcholine receptor (mAChR) ligand Carbachol. These neurons can be marked with a GAL4 strain ( vGlut VGN6341 ; Jayakumar et al, 2016 ; Jayakumar et al, 2018 ). Changes in cytosolic calcium were measured by visualising Ca 2+ dependent fluorescence changes of a genetically encoded Ca 2+ sensor GCaMP6m ( Chen et al, 2013 ) in ex vivo preparations.…”

“…The cellular mechanism(s) by which IP 3 /Ca 2+ signals regulate neuronal excitability probably vary among different classes of neurons. In addition to the direct activation of Ca 2+ -dependant enzymes such as CamKII, previous reports have shown that knock-down of the IP 3 R in Drosophila larval neurons alters their expression profile and specifically affects the expression of several membrane localised ion-channels ( Jayakumar et al, 2018 ). Reduced translation of proteins due to IP 3 R knockdown has also been demonstrated in peptidergic neurons ( Megha and Hasan, 2017 ).…”

Growth regulation by amino acid transporters in Drosophila larvae

“…In this regard, during mid-third instar Class IV multidendritic nociceptive ppk peripheral neurons react to the loss of environmental arginine via Slif. Then, they activate glutamatergic neurons in the ventral chord, which in turn stimulate Dilp2 release by IPCs [ 51 , 52 ]. Imaginal discs seem also to be sensitive to the presence of nutrients including amino acids via the activity of the tumor suppressor PTEN (phosphatase and tensin homolog deleted on chromosome 10).…”

Modulation of flight and feeding behaviours requires presynaptic IP3Rs in dopaminergic neurons

“…dependant enzymes such as CamKII, previous reports have shown that knock-down of the IP 3 R in Drosophila larval neurons alters their expression profile and specifically affects the expression of several membrane localised ion-channels (Jayakumar et al, 2018). Reduced translation of proteins due to IP 3 R knockdown has also been demonstrated in peptidergic neurons (Megha & Hasan, 2017).…”