Myoinhibiting peptide signaling via sex peptide receptor is critical for proper glue expulsion and spreading behavior during drosophila development

Abstract

Drosophila pupariation consists of a series of innate behaviors and morphogenetic changes that reduce predation and desiccation during metamorphosis via the formation of a compacted and hardened pupal case (puparium) from the larval cuticle and its firm attachment to a substrate. The latter is achieved by a rapid and highly-stereotyped behavior, glue expulsion and spreading behavior (GSB), which is preceded by strong body-remodelling contractions, termed pre-GSB. These behaviors must be executed in order and precede cuticle hardening to ensure proper pupariation. The steroid hormone ecdysone coordinates the whole pupariation process, inducing initiation of pre-GSB by an unknown mechanism and its progression to stronger contractions and ultimately to GSB by inducing a cuticle epidermis-to-CNS neuron relaxin-like Dilp8-Lgr3 signaling event. The factors, if any, that induce GSB and post-GSB behaviors downstream of ecdysone remain to be defined. Here we use neuronal-specific RNA interference against a series of neuropeptides to identify Myoinhibiting peptide (MIP) as a critical peptide required for proper GSB. Behavioral monitoring using a muscle calcium reporter (GCamp) shows that the execution of GSB is abnormal in the absence of MIP. Epistasis assays show that MIP acts spatially and temporally downstream of the Dilp8-Lgr3 pathway. Cell type-specific MIP RNAi showed that MIP is required in a single bilateral brain neuron for proper GSB. Further experiments show that MIP acts on neurons expressing Sex-peptide receptor (SPR), which is also critical for proper GSB. We propose that MIP is a key modulator of motor circuits during pupariation. Our results significantly advance our molecular and cellular understanding of pupariation control, and contributes to the understanding of how multi-step innate behaviors are coordinated in time