Progression Through Pupariation Behaviors Requires Dilp8-Lgr3 Signaling Between the Cuticle Epidermis and Thoracic CNS Neurons

ANDRÉS GARELLI; YANEL A VOLONTE; PEREIRINHA, JOANA; ALISSON M GONTIJO; HEREDIA, FABIANA; CASIMIRO, ANDREA

Lausanne

Congreso; 26th European Drosophila Research Conference; 2019

Holometabolan insects have evolved different behaviors and processes that promote survival during metamorphosis. Cyclorraphous flies, such as Drosophila, for instance, metamorphose within a puparium, a protective capsule consisting of the reshaped and hardened ecdysed cuticle of the last larval instar. Puparium formation (pupariation) is associated with additional survival-promoting behaviors, including the selection of a favorable pupariation site, extrusion of anterior spiracles for efficient gas exchange, and attachment of the puparium to the substrate via extrusion of a salivary-gland-derived ?glue?. Proper survival through metamorphosis therefore requires tight coordination between these associated behavioral programs and the morphogenetic processes of pupariation: a set of body-reshaping motor programs and a cuticle sclerotization program that fixes the achieved morphological changes. Although the whole pupariation process is known to be triggered by the Ecdysone hormone, the downstream programs are thought to be mediated by specific neuroendocrine signals and circuits, most of which remain to be characterized. Here, we show that proper progression through a cascade of morphogenetic and behavioural pupariation programs, including a previously undescribed one that promotes glue spreading on the ventral body surface, requires transient relaxin-like Dilp8-Lgr3 signaling between the cuticle epidermis and six thoracic interneurons. This new role of the Dilp8-Lgr3 pathway is spatially and temporally independent of its known role in controlling the timing of the onset of pupariation in third instar larvae carrying abnormally growing imaginal discs. Detection of strong ilp8 expression in the cuticle of pupariating Tephritidae larvae suggests this new pupariation-facilitating interorgan signaling event is conserved in cyclorraphous flies.