# Dilp8 requires the neuronal relaxin receptor Lgr3 to couple growth to developmental timing

## TL;DR

This study identifies a new role for the Lgr3 receptor in Drosophila, linking organ growth to developmental timing through a neuroendocrine pathway involving Dilp8.

## Contribution

The paper reveals that Lgr3 is a functional relaxin receptor required for Dilp8 signaling in coordinating growth and developmental timing.

## Key findings

- Mutating Lgr3 causes body asymmetries similar to dilp8 mutants, indicating a shared pathway.
- Lgr3 activity is localized to specific CNS neurons that respond to Dilp8 by increasing cAMP signaling.
- Lgr3 is essential for the developmental delay caused by growth perturbations or Dilp8 overexpression.

## Abstract

How different organs in the body sense growth perturbations in distant tissues to coordinate their size during development is poorly understood. Here we mutate an invertebrate orphan relaxin receptor gene, the Drosophila Leucine-rich repeat-containing G protein-coupled receptor 3 (Lgr3), and find body asymmetries similar to those found in insulin-like peptide 8 (dilp8) mutants, which fail to coordinate growth with developmental timing. Indeed, mutation or RNA intereference (RNAi) against Lgr3 suppresses the delay in pupariation induced by imaginal disc growth perturbation or ectopic Dilp8 expression. By tagging endogenous Lgr3 and performing cell type-specific RNAi, we map this Lgr3 activity to a new subset of CNS neurons, four of which are a pair of bilateral pars intercerebralis Lgr3-positive (PIL) neurons that respond specifically to ectopic Dilp8 by increasing cAMP-dependent signalling. Our work sheds new light on the function and evolution of relaxin receptors and reveals a novel neuroendocrine circuit responsive to growth aberrations.

The orphan ligand Dilp8 has been shown to coordinate growth and developmental timing in Drosophila. Here, using Gal4 drivers and CRISPR/Cas9 approaches, Garelli et al. identify a role for relaxin-like receptor Lgr3 in regulating the Dilp8 developmental delay pathway.