The gut microbiome promotes locomotion of Drosophila larvae via octopamine signaling.

The gut microbiome is a key partner of animals, influencing various aspects of their physiology and behaviors. Among the diverse behaviors regulated by the gut microbiome, locomotion is vital for survival and reproduction, although the underlying mechanisms remain unclear. Here, we reveal that the gut microbiome modulates the locomotor behavior of Drosophila larvae via a specific neuronal type in the brain. The crawling speed of germ-free (GF) larvae was significantly reduced compared to the conventionally reared larvae, while feeding and excretion behaviors were unaffected. Recolonization with Acetobacter and Lactobacillus can fully and partially rescue the locomotor defects in GF larvae, respectively, probably due to the highest abundance of Acetobacter as a symbiotic bacterium in the larval gut, followed by Lactobacillus. Moreover, the gut microbiome promoted larval locomotion, not by nutrition, but rather by enhancing the brain levels of tyrosine decarboxylase 2 (Tdc2), which is an enzyme that synthesizes octopamine (OA). Overexpression of Tdc2 rescued locomotion ability in GF larvae. These findings together demonstrate that the gut microbiome specifically modulates larval locomotor behavior through the OA signaling pathway, revealing a new mechanism underlying larval locomotion regulated by the gut microbiome.

Activation of cyclic AMP signaling pathway in dopaminergic neurons rescues locomotion defects in a Drosophila larval model of Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disease showing uncontrollable motor symptoms that are primarily caused by the progressive loss of dopaminergic neurons in the brain. Currently no treatment exists to prevent PD progression. Therefore, discovery of new neuroprotective strategies still has great potential to benefit PD patients. A handful of studies show that activation of cAMP pathways is neuroprotective against PD progression. However, the neuroprotective role of this signaling cascade specifically in DA neurons has not been explored. In this study, fruit fly Drosophila melanogaster was used because of its sophisticated and powerful genetic approaches, especially with related to cAMP signaling pathway. We have investigated molecular mechanisms of neuroprotection in a fly larval model of PD by administering an environmental PD toxin rotenone. Increased cAMP signaling in the dunce mutant fly carrying defects in phosphodiesterase (PDE) gene, is neuroprotective against rotenone-induced locomotion deficits. Furthermore, the neuroprotective role of cAMP signaling specifically in DA neurons has been studied as it has not been explored. By using transgenic flies expressing designer receptors exclusively activated by designer drugs (DREADDs), we have shown that an increase of cAMP levels in DA neurons rescues rotenone-induced locomotion deficits. We also showed that this neuroprotection is mediated by activation of Gαs and PKA-C1 subunits. The results provide novel findings that expand our knowledge of neuroprotective mechanisms in DA neurons affecting PD progression, which could contribute to the development of new therapeutic treatments against PD. An important future study will explore downstream targets of cAMP-PKA signaling.

A Simple Method for Quantifying Larval Locomotion in Drosophila melanogaster.

The fruit fly Drosophila melanogaster is a powerful genetic model that has been used for many decades to study nervous system function, development, and behavior. There are a large number of developmental and behavioral traits that can be measured to provide a broad readout of neurological function. These include patterned motor behaviors, such as larval locomotion, which can be used to assess whether genetic or environmental factors affect nervous system function to provide an entry point for deeper mechanistic studies. Here, we describe a protocol for quantifying larval locomotion using a simple camera setup and a freely available image analysis software. This protocol can be readily applied to human disease models or in toxicology studies, for example, to broadly assess the impact of treatments on neurological function.