Paola Cognigni

Enteric Neurons and Systemic Signals Couple Nutritional and Reproductive Status with Intestinal Homeostasis

Summary The gastrointestinal tract is emerging as a key regulator of appetite and metabolism, but daunting neuroanatomical complexity has hampered identification of the relevant signals. Invertebrate models could provide a simple and genetically amenable alternative, but their autonomic nervous system and its visceral functions remain largely unexplored. Here we develop a quantitative method based on defecation behavior to uncover a central role for the Drosophila intestine in the regulation of nutrient intake, fluid, and ion balance. We then identify a key homeostatic role for autonomic neurons and hormones, including a brain-gut circuit of insulin-producing neurons modulating appetite, a vasopressin-like system essential for fluid homeostasis, and enteric neurons mediating sex peptide-induced changes in intestinal physiology. These conserved mechanisms of visceral control, analogous to those found in the enteric nervous system and hypothalamic/pituitary axis, enable the study of autonomic control in a model organism that has proved instrumental in understanding sensory and motor systems.

Endocrine remodelling of the adult intestine sustains reproduction in Drosophila

The production of offspring is energetically costly and relies on incompletely understood mechanisms that generate a positive energy balance. In mothers of many species, changes in key energy-associated internal organs are common yet poorly characterised functionally and mechanistically. In this study, we show that, in adult Drosophila females, the midgut is dramatically remodelled to enhance reproductive output. In contrast to extant models, organ remodelling does not occur in response to increased nutrient intake and/or offspring demands, but rather precedes them. With spatially and temporally directed manipulations, we identify juvenile hormone (JH) as an anticipatory endocrine signal released after mating. Acting through intestinal bHLH-PAS domain proteins Methoprene-tolerant (Met) and Germ cell-expressed (Gce), JH signals directly to intestinal progenitors to yield a larger organ, and adjusts gene expression and sterol regulatory element-binding protein (SREBP) activity in enterocytes to support increased lipid metabolism. Our findings identify a metabolically significant paradigm of adult somatic organ remodelling linking hormonal signals, epithelial plasticity, and reproductive output. DOI: http://dx.doi.org/10.7554/eLife.06930.001

Allatostatin A Signalling in Drosophila Regulates Feeding and Sleep and Is Modulated by PDF

Feeding and sleep are fundamental behaviours with significant interconnections and cross-modulations. The circadian system and peptidergic signals are important components of this modulation, but still little is known about the mechanisms and networks by which they interact to regulate feeding and sleep. We show that specific thermogenetic activation of peptidergic Allatostatin A (AstA)-expressing PLP neurons and enteroendocrine cells reduces feeding and promotes sleep in the fruit fly Drosophila. The effects of AstA cell activation are mediated by AstA peptides with receptors homolog to galanin receptors subserving similar and apparently conserved functions in vertebrates. We further identify the PLP neurons as a downstream target of the neuropeptide pigment-dispersing factor (PDF), an output factor of the circadian clock. PLP neurons are contacted by PDF-expressing clock neurons, and express a functional PDF receptor demonstrated by cAMP imaging. Silencing of AstA signalling and continuous input to AstA cells by tethered PDF changes the sleep/activity ratio in opposite directions but does not affect rhythmicity. Taken together, our results suggest that pleiotropic AstA signalling by a distinct neuronal and enteroendocrine AstA cell subset adapts the fly to a digestive energy-saving state which can be modulated by PDF.

Re-evaluation of learned information in Drosophila

Animals constantly assess the reliability of learned information to optimize their behaviour. On retrieval, consolidated long-term memory can be neutralized by extinction if the learned prediction was inaccurate. Alternatively, retrieved memory can be maintained, following a period of reconsolidation during which it is labile. Although extinction and reconsolidation provide opportunities to alleviate problematic human memories, we lack a detailed mechanistic understanding of memory updating. Here we identify neural operations underpinning the re-evaluation of memory in Drosophila. Reactivation of reward-reinforced olfactory memory can lead to either extinction or reconsolidation, depending on prediction accuracy. Each process recruits activity in specific parts of the mushroom body output network and distinct subsets of reinforcing dopaminergic neurons. Memory extinction requires output neurons with dendrites in the α and α′ lobes of the mushroom body, which drive negatively reinforcing dopaminergic neurons that innervate neighbouring zones. The aversive valence of these new extinction memories neutralizes previously learned odour preference. Memory reconsolidation requires the γ2α′1 mushroom body output neurons. This pathway recruits negatively reinforcing dopaminergic neurons innervating the same compartment and re-engages positively reinforcing dopaminergic neurons to reconsolidate the original reward memory. These data establish that recurrent and hierarchical connectivity between mushroom body output neurons and dopaminergic neurons enables memory re-evaluation driven by reward-prediction error.

Do the right thing: neural network mechanisms of memory formation, expression and update in Drosophila.

Highlights • Recurrent connectivity is anatomically and functionally prevalent in fly memory circuits.• Sustained reverberant activity is necessary for memory consolidation.• Feedforward inhibitory neurons impose state control on memory retrieval and behavior.• Recurrent circuits enable re-evaluation and updating of memory.

Local requirement of the Drosophila insulin binding protein imp-L2 in coordinating developmental progression with nutritional conditions.

In Drosophila, growth takes place during the larval stages until the formation of the pupa. Starvation delays pupariation to allow prolonged feeding, ensuring that the animal reaches an appropriate size to form a fertile adult. Pupariation is induced by a peak of the steroid hormone ecdysone produced by the prothoracic gland (PG) after larvae have reached a certain body mass. Local downregulation of the insulin/insulin-like growth factor signaling (IIS) activity in the PG interferes with ecdysone production, indicating that IIS activity in the PG couples the nutritional state to development. However, the underlying mechanism is not well understood. In this study we show that the secreted Imaginal morphogenesis protein-Late 2 (Imp-L2), a growth inhibitor in Drosophila, is involved in this process. Imp-L2 inhibits the activity of the Drosophila insulin-like peptides by direct binding and is expressed by specific cells in the brain, the ring gland, the gut and the fat body. We demonstrate that Imp-L2 is required to regulate and adapt developmental timing to nutritional conditions by regulating IIS activity in the PG. Increasing Imp-L2 expression at its endogenous sites using an Imp-L2-Gal4 driver delays pupariation, while Imp-L2 mutants exhibit a slight acceleration of development. These effects are strongly enhanced by starvation and are accompanied by massive alterations of ecdysone production resulting most likely from increased Imp-L2 production by neurons directly contacting the PG and not from elevated Imp-L2 levels in the hemolymph. Taken together our results suggest that Imp-L2-expressing neurons sense the nutritional state of Drosophila larvae and coordinate dietary information and ecdysone production to adjust developmental timing under starvation conditions.

Spotting the differences: probing host/microbiota interactions with a dedicated software tool for the analysis of faecal outputs in Drosophila.

The intestinal physiology of Drosophila melanogaster can be monitored in an integrative, non-invasive manner by analysing graphical features of the excreta produced by flies fed on a dye-supplemented diet. This assay has been used by various labs to explore gut function and its regulation. To facilitate its use, we present here a free, stand-alone dedicated software tool for the analysis of fly excreta. The Ultimate Reader of Dung (T.U.R.D.) is designed to offer a flexible environment for a wide range of experimental designs, with special attention to automation and high-throughput processing. This software detects the distinctive changes in acid-base and water balance previously reported to occur in response to dietary challenges and mating. We have used T.U.R.D. to test the contribution of the bacterial environment of the flies to various intestinal parameters including the established diet- and mating-triggered responses. To this end, we have analysed the faecal patterns of flies reared in germ-free conditions, upon re-association with controlled microbiota and subjected to food-borne or systemic, non-lethal bacterial infections. We find that the tested faecal outputs are unchanged in all these conditions, suggesting that the impact of the bacterial environment on the intestinal features highlighted by faecal deposit analysis is minimal.

Why flies? Inexpensive public engagement exercises to explain the value of basic biomedical research on Drosophila melanogaster

Invertebrate model organisms are powerful systems for uncovering conserved principles of animal biology. Despite widespread use in scientific communities, invertebrate research is often severely undervalued by laypeople. Here, we present a set of simple, inexpensive public outreach exercises aimed at explaining to the public why basic research on one particular invertebrate, the insect Drosophila melanogaster, is valuable. First, we designed seven teaching modules that highlight cutting-edge research in Drosophila genetics, metabolism, physiology, and behavior. We then implemented these exercises in a public outreach event that included both children and adults. Quantitative evaluation of participant feedback suggests that these exercises 1) teach principles of animal biology, 2) help laypeople better understand why researchers study fruit flies, and 3) are effective over a wide range of age groups. Overall, this work provides a blueprint for how to use Drosophila as a vehicle for increasing public awareness and appreciation of basic research on genetically tractable insects in particular and invertebrates in general.

Correction: Allatostatin A Signalling in Drosophila Regulates Feeding and Sleep and Is Modulated by PDF

[This corrects the article DOI: 10.1371/journal.pgen.1006346.].

12-P004 Development and function of visceral innervation in Drosophila

and ectopic expression, we demonstrated that Gata2 regulates GABAergic neuron development in the midbrain, but not in the rhombomere1. Without Gata2, all the precursors in the embryonic midbrain fail to activate GABAergic neuron-specific gene expression and switch to a glutamatergic phenotype instead. Surprisingly, this fate switch is also observed throughout the neonatal midbrain, except for the GABAergic neurons located in the ventral dopaminergic nuclei, suggesting a distinct developmental pathway for these neurons. We have further investigated the origin, developmental history and regulatory mechanisms of these GABAergic neurons associated with the ventral dopaminergic nuclei. The presented studies identify Gata2 as an essential postmitotic selector of the GABAergic neurotransmitter identity and demonstrate developmental heterogeneity of the GABAergic neurons in the midbrain.