Un circuito neurohormonal mediado por Dilp8-Lgr3 es necesario para establecer la forma del pupario en Drosophila

ANDRES GARELLI,

Chascomús

Taller; IV Taller de Biología Celular y del Desarrollo; 2018

TBCD

Drosophila larvae undergo a dramatic change in body shape at the end of the larval period when the long, flexible, and transparent cuticle of the larvae is transformed into the short, sclerotized, and tanned puparium. This remodelling is achieved by a series of muscular contractions and structural modifications of the cuticle, both of which are not completely understood at the molecular level. Here, we find that loss-of-function mutations in the genes encoding either the relaxin-like peptide hormone Drosophila insulin-like peptide 8 (Dilp8) or the relaxin-receptor-like Leucine-rich repeat-containing G protein coupled receptor 3 (Lgr3) lead to an aberrantly elongated puparium, implicating the Dilp8-Lgr3 pathway in puparium morphogenesis. We propose that the Dilp8-Lgr3 pathway mediates initial steps in the ecdysone-dependent program that controls puparium morphogenesis. This pathway has been previously shown to regulate developmental stability in Drosophila by coupling the timing of pupariation with the growth status of the imaginal discs (larval precursors of adult appendages). To investigate if these roles can be temporally -and/or spatially-separated, we performed gene expression studies in D. melanogaster and Tephri4dae (fruit fly) Cera44s capitata, two species that shared a last common ancestor between 80-100 mya, and neurogenetic experiments in Drosophila. We observed a conserved 30-60 min peak of ilp8 expression at the end of larval stage and a quick return to basal levels within one hour. This surge in ilp8 takes place right a}er spiracles eversion and simultaneous with a set of stereotyped movements linked to salivary glue extrusion that precedes cuticle hardening. Hence, the Ilp8 hormone, which is critical for normal pupariation, is also strongly expressed during the process. Noteworthy, Dilp8 and Lgr3 mutants fail to perform the glue extrusion behavior and produce an elongated puparium. Lgr3 knock-down by RNA interference in neurons in which Lgr3 is required for developmental stability, does not alter puparium morphogenesis. Instead, we find that Lgr3 is required in a separate population of neurons to transduce the cuticle epidermis-derived Dilp8 signal occurring at pupariation. Hence, the peptide hormone Dilp8 and the GPCR Lgr3 constitute a new neuroendocrine pathway directly contributing to puparium morphogenesis.