Growth Coordination During Drosophila melanogaster Imaginal Disc Regeneration Is Mediated by Signaling Through the Relaxin Receptor Lgr3 in the Prothoracic Gland

Abstract

Damage to Drosophila melanogaster imaginal discs activates a regeneration checkpoint that (1) extends larval development and (2) coordinates the regeneration of the damaged disc with the growth of undamaged discs. These two systemic responses to damage are both mediated by Dilp8, a member of the insulin/insulin-like growth factor/relaxin family of peptide hormones, which is released by regenerating imaginal discs. Growth coordination between regenerating and undamaged imaginal discs is dependent on Dilp8 activation of nitric oxide synthase (NOS) in the prothoracic gland (PG), which slows the growth of undamaged discs by limiting ecdysone synthesis. Here we demonstrate that the Drosophila relaxin receptor homolog Lgr3, a leucine-rich repeat-containing G-protein-coupled receptor, is required for Dilp8-dependent growth coordination and developmental delay during the regeneration checkpoint. Lgr3 regulates these responses to damage via distinct mechanisms in different tissues. Using tissue-specific RNA-interference disruption of Lgr3 expression, we show that Lgr3 functions in the PG upstream of NOS, and is necessary for NOS activation and growth coordination during the regeneration checkpoint. When Lgr3 is depleted from neurons, imaginal disc damage no longer produces either developmental delay or growth inhibition. To reconcile these discrete tissue requirements for Lgr3 during regenerative growth coordination, we demonstrate that Lgr3 activity in both the CNS and PG is necessary for NOS activation in the PG following damage. Together, these results identify new roles for a relaxin receptor in mediating damage signaling to regulate growth and developmental timing. KEYWORDS Lgr3; checkpoint; growth coordination; regeneration G ROWTH rate and developmental time must be regulated in concert to ensure that organs develop to the correct size and proportion. Following damage to imaginal discs, Drosophila larvae activate a regeneration checkpoint that delays development and slows the growth of undamaged imaginal discs. These systemic responses to damage may function to coordinate regeneration with the growth and development of undamaged tissues (Stieper et al. 2008;Halme et al. 2010;Parker and Shingleton 2011;Jaszczak et al. 2015). The peptide Dilp8 is required for both delay and growth coordination and is secreted by regenerating imaginal discs to activate the regeneration checkpoint (Colombani et al. 2012;Garelli et al. 2012). Dilp8 induces developmental delay by inhibiting production of the neuropeptide prothoracicotropic hormone (PTTH) in the central nervous system (CNS) (Halme et al. 2010;Colombani et al. 2012), whereas Dilp8 inhibits growth of the undamaged imaginal discs by reducing biosynthesis of the steroid hormone ecdysone through activation of nitric oxide synthase (NOS) in the prothoracic gland (PG) (Jaszczak et al. 2015).Dilp8 has been classified as a member of the insulin/ insulin-like growth factor/relaxin family of peptide hormones (Garelli et al. 2012). Relaxin receptors in mammals belong to a l...

Imaginal disc regeneration takes flight

“…Expression of Dilp8 is activated by JNK [49, 73], Yki [75] and, indirectly, by the chromatin modifying enzyme Trithorax [76]. Dilp8 binds to a G-protein-coupled receptor, Lgr3 [77–80], that is expressed on a subset of neurons. The Lgr3-expressing neurons synapse with PTTH-secreting neurons which innervate the prothoracic gland (PG) and promote the synthesis of ecdysone, the hormone that promotes metamorphosis.…”

“…In addition, Lgr3 is also expressed in the PG itself, where it activates nitric oxide synthase. NOS activity is necessary to slow the growth of undamaged discs while damaged tissue is being repaired [80, 81]. …”

The Hippo signalling pathway coordinates organ growth and limits developmental variability by controlling dilp8 expression

“…Dilp8 is secreted from abnormally growing organs and acts remotely on the central brain complex to delay entry into metamorphosis67. Dilp8 signals through the Leucine-rich repeat-containing G-protein-coupled receptor 3 (Lgr3) in a pair of bilateral brain (GCL) neurons activating a neuroendocrine circuit that ultimately suppresses synthesis of the moulting hormone ecdysone891011. Interestingly, mutations in the dilp8 and lgr3 loci produce animals that exhibit FA.…”

Des insulines pour orchestrer la croissance

“…Lgr3 est pré-sent dans une sous-population de neurones dont deux seulement sont requis pour l'induction du retard déve-loppemental par Dilp8 (appelés growth coordinating Lgr3-positive neurons ou neurones GCL). Les neurones GCL semblent contrôler les niveaux d'ecdysone par une interaction physique avec des neurones intermédiaires à PTTH (prothoracicotropic hormone) 3 qui projettent leurs axones sur la glande en anneau, le site de production de l'ecdysone [20][21][22][23][24]. 2 Le cycle de vie de la drosophile se divise en quatre phases durant lesquelles les individus prennent des morphologies trè s diffé rentes : l'oeuf (stade embryonnaire), la larve (stade larvaire), la pupe (stade pupal) et l'imago (stade adulte).…”