Abstract

The sensory and physiological inputs which govern the larval-pupal transition in Drosophila, and the neuronal circuity that integrates them, are complex. Previous work from our laboratory identified a dosage-sensitive genetic interaction between the genes encoding the Rho-GEF Trio and the zinc-finger transcription factor Sequoia that interfered with the larval-pupal transition. Specifically, we reported heterozygous mutations in sequoia (seq) dominantly exacerbated the trio mutant phenotype, and this seq-enhanced trio mutant genotype blocked the transition of third instar larvae from foragers to wanderers, a requisite behavioral transition prior to pupation. In this work, we use the GAL4-UAS system to rescue this phenotype by tissue-specific trio expression. We find that expressing trio in the class IV dendritic arborization (da) sensory neurons rescues the larval-pupal transition, demonstrating the reliance of the larval-pupal transition on the integrity of these sensory neurons. As nociceptive responses also rely on the functionality of the class IV da neurons, we test mechanical nociceptive responses in our mutant and rescued larvae and find that mechanical nociception is separable from the ability to undergo the larval-pupal transition. This demonstrates for the first time that the roles of the class IV da neurons in governing two critical larval behaviors, the larval-pupal transition and mechanical nociception, are functionally separable from each other.

Highlights

  • Understanding the molecular basis of behavior is a broad, overarching goal in neurobiology

  • Driving trio in the class IV da sensory neurons with the GAL4-ppk1.9 driver in this seq-enhanced trio mutant background rescued pupation (49.9±2.2% expected pupae; Fig 1), the magnitude of this rescue was statistically lower than that achieved by pan-neural trio expression

  • Rescue of pupation by driving trio with the GAL4-ppk1.9 driver (Fig 1) shows the perturbation of the larval-pupal transition is due to a correctable defect within the larval class IV da sensory neurons

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Summary

Introduction

Understanding the molecular basis of behavior is a broad, overarching goal in neurobiology. In the Drosophila model system, the mechanisms governing the transition from larvae to pupae have been investigated on multiple levels. Numerous physiological mechanisms have been identified as having a role in the larval-pupal transition by directly or indirectly regulating ecdysone production [1,2,3,4,5,6]. Neuronal mechanisms regulating the larval-pupal transition have been defined. Jayakumar et al identified a key neural circuit that detects external nutrient levels that in turn drive ecdysone production [7]. Wu et al showed that down-regulation of neuropeptide F regulates the food aversion of larvae just prior to pupation [8] as they transition from feeding forager larvae to non-feeding wander larvae [9]

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