Cool and warm ionotropic receptors control multiple thermotaxes in Drosophila larvae

FA2H controls cool temperature sensing through modifying membrane sphingolipids in Drosophila

Animals have evolved the ability to detect ambient temperatures, allowing them to search for optimal living environments. In search of the molecules responsible for cold-sensing, we examined a Gal4 insertion line in the larvae of Drosophila melanogaster from previous screening work, which has a specific expression pattern in the cooling cells (CCs). We identified that the targeted gene, fa2h, which encodes a fatty acid 2-hydroxylase, plays an important role in cool temperature sensing. We found that fa2h mutants exhibit defects in cool avoidance behavior and that this phenotype could be rescued by genetically re-introducing the wild-type version of FA2H in CCs but not the enzymatically disabled point mutation version. Calcium imaging data showed that CCs require fa2h to respond to cool temperature. Lipidomic analysis revealed that the 2-hydroxy sphingolipids content in the cell membranes diminished in fa2h mutants, resulting in increased fluidity of CC neuron membranes. Furthermore, in mammalian systems, we showed that FA2H strongly regulates the function of the TRPV4 channel in response to its agonist treatment and warming. Taken together, our study has uncovered a novel role of FA2H in temperature sensing and has provided new insights into the link between membrane lipid composition and the function of temperature-sensing ion channels.

Temperature sensitivity and temperature response across development in the Drosophila larva

The surrounding thermal environment is highly important for the survival and fitness of animals, and as a result most exhibit behavioral and neural responses to temperature changes. We study signals generated by thermosensory neurons in Drosophila larvae and also the physical and sensory effects of temperature variation on locomotion and navigation. In particular we characterize how sensory neuronal and behavioral responses to temperature variation both change across the development of the larva. Looking at a wide range of non-nociceptive isotropic thermal environments, we characterize the dependence of speed, turning rate, and other behavioral components on temperature, distinguishing the physical effects of temperature from behavior changes based on sensory processing. We also characterize the strategies larvae use to modulate individual behavioral components to produce directed navigation along thermal gradients, and how these strategies change during physical development. Simulations based on modified random walks show where thermotaxis in each developmental stage fits into the larger context of possible navigation strategies. We also investigate cool sensing neurons in the larva's dorsal organ ganglion, characterizing neural response to sine-wave modulation of temperature while performing single-cell-resolution 3D imaging. We determine the sensitivity of these neurons, which produce signals in response to extremely small temperature changes. Combining thermotaxis results with neurophysiology data, we observe, across development, sensitivity to temperature change as low as a few thousandths of a °C per second, or a few hundredths of a °C in absolute temperature change.

Antennal Transcriptome Analysis of Olfactory Genes and Characterization of Odorant Binding Proteins in Odontothrips loti (Thysanoptera: Thripidae)

To identify odors in complex environments accurately, insects have evolved multiple olfactory proteins. In our study, various olfactory proteins of Odontothrips loti Haliday, an oligophagous pest that primarily affects Medicago sativa (alfalfa), were explored. Specifically, 47 putative olfactory candidate genes were identified in the antennae transcriptome of O. loti, including seven odorant-binding proteins (OBPs), nine chemosensory proteins (CSPs), seven sensory neuron membrane proteins (SNMPs), eight odorant receptors (ORs), and sixteen ionotropic receptors (IRs). PCR analysis further confirmed that 43 out of 47 genes existed in O. loti adults, and O.lotOBP1, O.lotOBP4, and O.lotOBP6 were specifically expressed in the antennae with a male-biased expression pattern. In addition, both the fluorescence competitive binding assay and molecular docking showed that p-Menth-8-en-2-one, a component of the volatiles of the host, had strong binding ability to the O.lotOBP6 protein. Behavioral experiments showed that this component has a significant attraction to both female and male adults, indicating that O.lotOBP6 plays a role in host location. Furthermore, molecular docking reveals potential active sites in O.lotOBP6 that interact with most of the tested volatiles. Our results provide insights into the mechanism of O. loti odor-evoked behavior and the development of a highly specific and sustainable approach for thrip management.

TACI: An ImageJ Plugin for 3D Calcium Imaging Analysis

Research in neuroscience has evolved to use complex imaging and computational tools to extract comprehensive information from data sets. Calcium imaging is a widely used technique that requires sophisticated software to obtain reliable results, but many laboratories struggle to adopt computational methods when updating protocols to meet modern standards. Difficulties arise due to a lack of programming knowledge and paywalls for software. In addition, cells of interest display movements in all directions during calcium imaging. Many approaches have been developed to correct the motion in the lateral (x/y) direction. This paper describes a workflow using a new ImageJ plugin, TrackMate Analysis of Calcium Imaging (TACI), to examine motion on the z-axis in 3D calcium imaging. This software identifies the maximum fluorescence value from all the z-positions a neuron appears in and uses it to represent the neuron's intensity at the corresponding t-position. Therefore, this tool can separate neurons overlapping in the lateral (x/y) direction but appearing on distinct z-planes. As an ImageJ plugin, TACI is a user-friendly, open-source computational tool for 3D calcium imaging analysis. We validated this workflow using fly larval thermosensitive neurons that displayed movements in all directions during temperature fluctuation and a 3D calcium imaging dataset acquired from the fly brain.