Mechanosensing in the Drosophila nervous system

Molecular regulation of axon termination in mechanosensory neurons

Spatially and temporally accurate termination of axon outgrowth, a process called axon termination, is required for efficient, precise nervous system construction and wiring. The mechanosensory neurons that sense low-threshold mechanical stimulation or gentle touch have proven exceptionally valuable for studying axon termination over the past 40 years. In this Review, we discuss progress made in deciphering the molecular and genetic mechanisms that govern axon termination in touch receptor neurons. Findings across model organisms, including Caenorhabditis elegans, Drosophila, zebrafish and mice, have revealed that complex signaling is required for termination with conserved principles and players beginning to surface. A key emerging theme is that axon termination is mediated by complex signaling networks that include ubiquitin ligase signaling hubs, kinase cascades, transcription factors, guidance/adhesion receptors and growth factors. Here, we begin a discussion about how these signaling networks could represent termination codes that trigger cessation of axon outgrowth in different species and types of mechanosensory neurons.

How larvae feel the world around them

A complete map of the external sense organs shows how fruit fly larvae detect different aspects of their environment.

Mechanical vibration patterns elicit behavioral transitions and habituation in crawling Drosophila larvae

How animals respond to repeatedly applied stimuli, and how animals respond to mechanical stimuli in particular, are important questions in behavioral neuroscience. We study adaptation to repeated mechanical agitation using the Drosophila larva. Vertical vibration stimuli elicit a discrete set of responses in crawling larvae: continuation, pause, turn, and reversal. Through high-throughput larva tracking, we characterize how the likelihood of each response depends on vibration intensity and on the timing of repeated vibration pulses. By examining transitions between behavioral states at the population and individual levels, we investigate how the animals habituate to the stimulus patterns. We identify time constants associated with desensitization to prolonged vibration, with re-sensitization during removal of a stimulus, and additional layers of habituation that operate in the overall response. Known memory-deficient mutants exhibit distinct behavior profiles and habituation time constants. An analogous simple electrical circuit suggests possible neural and molecular processes behind adaptive behavior.

Structural and transcriptional evidence of mechanotransduction in the Drosophila suzukii ovipositor

Drosophila suzukii is an invasive pest that prefers to lay eggs in ripening fruits, whereas most closely related Drosophila species exclusively use rotten fruit as oviposition site. This behaviour is allowed by an enlarged and serrated ovipositor that can pierce intact fruit skin, and by multiple contact sensory systems (mechanosensation and taste) that detect the optimal egg-laying substrates. Here, we tested the hypothesis that bristles present in the D. suzukii ovipositor tip contribute to these sensory modalities. Analysis of the bristle ultrastructure revealed that four different types of cuticular elements (conical pegs type 1 and 2, chaetic and trichoid sensilla) are present on the tip of each ovipositor plate. All of them have a poreless shaft and are innervated at their base by a single neuron that ends in a distal tubular body, thus resembling mechanosensitive structures. Fluorescent labelling in D. suzukii and D. melanogaster revealed that pegs located on the ventral side of the ovipositor tip are innervated by a single neuron in both species. RNA-sequencing profiled gene expression, notably sensory receptor genes of the terminalia of D. suzukii and of three other Drosophila species with changes in their ovipositor structure (from serrated to blunt ovipositor: Drosophila subpulchrella, Drosophila biarmipes and D. melanogaster). Our results revealed few species-specific transcripts and an overlapping expression of candidate mechanosensitive genes as well as the presence of some chemoreceptor transcripts. These experimental evidences suggest a mechanosensitive function for the D. suzukii ovipositor, which might be crucial across Drosophila species independently from ovipositor shape.

Mechanical Regulation Underlies Effects of Exercise on Serotonin-Induced Signaling in the Prefrontal Cortex Neurons

Mechanical forces are known to be involved in various biological processes. However, it remains unclear whether brain functions are mechanically regulated under physiological conditions. Here, we demonstrate that treadmill running and passive head motion (PHM), both of which produce mechanical impact on the head, have similar effects on the hallucinogenic 5-hydroxytryptamine (5-HT) receptor subtype 2A (5-HT_2A) signaling in the prefrontal cortex (PFC) of rodents. PHM generates interstitial fluid movement that is estimated to exert shear stress of a few pascals on cells in the PFC. Fluid shear stress of a relevant magnitude on cultured neuronal cells induces ligand-independent internalization of 5-HT_2A receptor, which is observed in mouse PFC neurons after treadmill running or PHM. Furthermore, inhibition of interstitial fluid movement by introducing polyethylene glycol hydrogel eliminates the effect of PHM on 5-HT_2A receptor signaling in the PFC. Our findings indicate that neuronal cell function can be physiologically regulated by mechanical forces in the brain.

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Mechanical forces regulate brain functions under physiological conditions

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Intracerebral interstitial fluid has mechanical roles in regulating brain functions

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Mechanical impact on the head mediates effects of exercise on the brain

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Fluid shear stress physiologically modulates signaling in nervous cells

Emergence of social cluster by collective pairwise encounters in Drosophila

Many animals exhibit an astonishing ability to form groups of large numbers of individuals. The dynamic properties of such groups have been the subject of intensive investigation. The actual grouping processes and underlying neural mechanisms, however, remain elusive. Here, we established a social clustering paradigm in Drosophila to investigate the principles governing social group formation. Fruit flies spontaneously assembled into a stable cluster mimicking a distributed network. Social clustering was exhibited as a highly dynamic process including all individuals, which participated in stochastic pair-wise encounters mediated by appendage touches. Depriving sensory inputs resulted in abnormal encounter responses and a high failure rate of cluster formation. Furthermore, the social distance of the emergent network was regulated by ppk-specific neurons, which were activated by contact-dependent social grouping. Taken together, these findings revealed the development of an orderly social structure from initially unorganised individuals via collective actions.