Internal sensory neurons regulate stage-specific growth in Drosophila

The gustatory receptor BdorGr43a mediated sucrose preference in the feeding of Bactrocera dorsalis

The feeding behavior of animals is pivotal for their reproductive success and energy acquisition. In our study, we found that the Bactrocera dorsalis had a pronounced preference for sucrose among six plant-derived sugars during feeding. Then, we searched the entire genome of B. dorsalis for the gustatory receptors (Grs) responsible for sucrose sensation. Putative gustatory receptors involved in the detection of sweetness, bitterness, CO2 and other unknown functions. Together with phylogenetic analysis, expression profiling, calcium imaging, and CRISPR/Cas9 mediated mutagenesis, we found that BdorGr43a is the key receptor responding to sucrose. Our study elucidated the molecular mechanism underlying the sucrose preferences in the feeding of B. dorsalis. Meanwhile, our results will serve as a reference for the understanding of gustatory sensing in insect. Furthermore, BdorGr43a may serve as an important target for the development of food attractants against the oriental fruit fly.

A Neuropeptide Signaling Network That Regulates Developmental Timing and Systemic Growth in Drosophila

Animals sense chemical cues such as nutritious and noxious stimuli through the chemosensory system and adapt their behavior, physiology, and developmental schedule to the environment. In the Drosophila central nervous system, chemosensory interneurons that produce neuropeptides called Hugin (Hug) peptides receive signals from gustatory receptor neurons and regulate feeding behavior. Because Hug neurons project their axons to the higher brain region within the protocerebrum where dendrites of multiple neurons producing developmentally important neuropeptides are extended, it has been postulated that Hug neurons regulate development through the neuroendocrine system. In this study, we show that Hug neurons interact with a subset of protocerebrum neurons that produce prothoracicotropic hormone (PTTH) and regulate the onset of metamorphosis and systemic growth. Loss of the hug gene and silencing of Hug neurons caused a delay in larval-to-prepupal transition and an increase in final body size. Furthermore, deletion of Hug receptor-encoding genes also caused developmental delay and body size increase, and the phenotype was restored by expressing Hug receptors in PTTH-producing neurons. These results indicate that Hug neurons regulate developmental timing and body size via PTTH-producing neurons. This study provides a basis for understanding how chemosensation is converted into neuroendocrine signaling to control insect growth and development.

Mechanisms of gas sensing by internal sensory neurons in Drosophila larvae

Internal sensory neurons monitor the chemical and physical state of the body, providing critical information to the central nervous system for maintaining homeostasis and survival. A population of larval Drosophila sensory neurons, tracheal dendrite (td) neurons, elaborate dendrites along respiratory organs and may serve as a model for elucidating the cellular and molecular basis of chemosensation by internal neurons. We find that td neurons respond to decreases in O2 levels and increases in CO2 levels. We assessed the roles of atypical soluble guanylyl cyclases (Gycs) and a gustatory receptor (Gr) in mediating these responses. We found that Gyc88E/Gyc89Db were necessary for responses to hypoxia, and that Gr28b was necessary for responses to CO2. Targeted expression of Gr28b isoform c in td neurons rescued responses to CO2 in mutant larvae and also induced ectopic sensitivity to CO2 in the td network. Gas-sensitive td neurons were activated when larvae burrowed for a prolonged duration, demonstrating a natural-like feeding condition in which td neurons are activated. Together, our work identifies two gaseous stimuli that are detected by partially overlapping subsets of internal sensory neurons, and establishes roles for Gyc88E/Gyc89Db in the detection of hypoxia, and Gr28b in the detection of CO2.