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LSSS 2015-2016

2015LSSS2016

Life Sciences Seminar Series

 

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Pierre Leopold

University of Nice-Sophia Antipolis, Institute of Biology Valrose, Nice, France

Growth control in Drosophila: from developmental regulations to neoplasms

Selected Publications

The Drosophila TNF receptor Grindelwald couples loss of cell polarity and neoplastic growth.Andersen DS, Colombani J, Palmerini V, Chakrabandhu K, Boone E, Röthlisberger M, Toggweiler J, Basler K, Mapelli M, Hueber AO, Léopold P
Nature 2015 Jun 25; 522(7557):482-6

Abstract

Disruption of epithelial polarity is a key event in the acquisition of neoplastic growth. JNK signalling is known to play an important part in driving the malignant progression of many epithelial tumours, although the link between loss of polarity and JNK signalling remains elusive. In a Drosophila genome-wide genetic screen designed to identify molecules implicated in neoplastic growth, we identified grindelwald (grnd), a gene encoding a transmembrane protein with homology to members of the tumour necrosis factor receptor (TNFR) superfamily. Here we show that Grnd mediates the pro-apoptotic functions of Eiger (Egr), the unique Drosophila TNF, and that overexpression of an active form of Grnd lacking the extracellular domain is sufficient to activate JNK signalling in vivo. Grnd also promotes the invasiveness of Ras(V12)/scrib(-/-) tumours through Egr-dependent Matrix metalloprotease-1 (Mmp1) expression. Grnd localizes to the subapical membrane domain with the cell polarity determinant Crumbs (Crb) and couples Crb-induced loss of polarity with JNK activation and neoplastic growth through physical interaction with Veli (also known as Lin-7). Therefore, Grnd represents the first example of a TNFR that integrates signals from both Egr and apical polarity determinants to induce JNK-dependent cell death or tumour growth.

Sensing of amino acids in a dopaminergic circuitry promotes rejection of an incomplete diet in Drosophila.Bjordal M, Arquier N, Kniazeff J, Pin JP, Léopold P
Cell 2014 Jan 30; 156(3):510-21

Abstract

The brain is the central organizer of food intake, matching the quality and quantity of the food sources with organismal needs. To ensure appropriate amino acid balance, many species reject a diet lacking one or several essential amino acids (EAAs) and seek out a better food source. Here, we show that, in Drosophila larvae, this behavior relies on innate sensing of amino acids in dopaminergic (DA) neurons of the brain. We demonstrate that the amino acid sensor GCN2 acts upstream of GABA signaling in DA neurons to promote avoidance of the EAA-deficient diet. Using real-time calcium imaging in larval brains, we show that amino acid imbalance induces a rapid and reversible activation of three DA neurons that are necessary and sufficient for food rejection. Taken together, these data identify a central amino-acid-sensing mechanism operating in specific DA neurons and controlling food intake.

Neuroendocrine control of Drosophila larval light preference.Yamanaka N, Romero NM, Martin FA, Rewitz KF, Sun M, O'Connor MB, Léopold P
Science 2013 Sep 6; 341(6150):1113-6

Abstract

Animal development is coupled with innate behaviors that maximize chances of survival. Here, we show that the prothoracicotropic hormone (PTTH), a neuropeptide that controls the developmental transition from juvenile stage to sexual maturation, also regulates light avoidance in Drosophila melanogaster larvae. PTTH, through its receptor Torso, acts on two light sensors--the Bolwig's organ and the peripheral class IV dendritic arborization neurons--to regulate light avoidance. We found that PTTH concomitantly promotes steroidogenesis and light avoidance at the end of larval stage, driving animals toward a darker environment to initiate the immobile maturation phase. Thus, PTTH controls the decisions of when and where animals undergo metamorphosis, optimizing conditions for adult development.

High sugar-induced insulin resistance in Drosophila relies on the lipocalin Neural Lazarillo.Pasco MY, Léopold P
PLoS ONE 2012; 7(5):e36583

Abstract

In multicellular organisms, insulin/IGF signaling (IIS) plays a central role in matching energy needs with uptake and storage, participating in functions as diverse as metabolic homeostasis, growth, reproduction and ageing. In mammals, this pleiotropy of action relies in part on a dichotomy of action of insulin, IGF-I and their respective membrane-bound receptors. In organisms with simpler IIS, this functional separation is questionable. In Drosophila IIS consists of several insulin-like peptides called Dilps, activating a unique membrane receptor and its downstream signaling cascade. During larval development, IIS is involved in metabolic homeostasis and growth. We have used feeding conditions (high sugar diet, HSD) that induce an important change in metabolic homeostasis to monitor possible effects on growth. Unexpectedly we observed that HSD-fed animals exhibited severe growth inhibition as a consequence of peripheral Dilp resistance. Dilp-resistant animals present several metabolic disorders similar to those observed in type II diabetes (T2D) patients. By exploring the molecular mechanisms involved in Drosophila Dilp resistance, we found a major role for the lipocalin Neural Lazarillo (NLaz), a target of JNK signaling. NLaz expression is strongly increased upon HSD and animals heterozygous for an NLaz null mutation are fully protected from HSD-induced Dilp resistance. NLaz is a secreted protein homologous to the Retinol-Binding Protein 4 involved in the onset of T2D in human and mice. These results indicate that insulin resistance shares common molecular mechanisms in flies and human and that Drosophila could emerge as a powerful genetic system to study some aspects of this complex syndrome.

Secreted peptide Dilp8 coordinates Drosophila tissue growth with developmental timing.Colombani J, Andersen DS, Léopold P
Science 2012 May 4; 336(6081):582-5

Abstract

Little is known about how organ growth is monitored and coordinated with the developmental timing in complex organisms. In insects, impairment of larval tissue growth delays growth and morphogenesis, revealing a coupling mechanism. We carried out a genetic screen in Drosophila to identify molecules expressed by growing tissues participating in this coupling and identified dilp8 as a gene whose silencing rescues the developmental delay induced by abnormally growing tissues. dilp8 is highly induced in conditions where growth impairment produces a developmental delay. dilp8 encodes a peptide for which expression and secretion are sufficient to delay metamorphosis without affecting tissue integrity. We propose that Dilp8 peptide is a secreted signal that coordinates the growth status of tissues with developmental timing.