Microtubule-severing protein Katanin regulates neuromuscular junction development and dendritic elaboration in Drosophila.

Microtubules (MTs) are crucial for diverse biological processes including cell division, cell growth and motility, intracellular transport and the maintenance of cell shape. MT abnormalities are associated with neurodevelopmental and neurodegenerative diseases such as hereditary spastic paraplegia. Among many MT regulators, katanin was the first identified MT-severing protein, but its neuronal functions have not yet been examined in a multicellular organism. Katanin consists of two subunits; the catalytic subunit katanin 60 contains an AAA (ATPases associated with a variety of cellular activities) domain and breaks MT fibers while hydrolyzing ATP, whereas katanin 80 is a targeting and regulatory subunit. To dissect the in vivo functions of Katanin, we generated mutations in Drosophila Katanin 60 and manipulated its expression in a tissue-specific manner. Null mutants of Katanin 60 are pupal lethal, demonstrating that it is essential for viability. Loss-of-function mutants of Katanin 60 showed excess satellite boutons, reduced neurotransmission efficacy, and more enlarged cisternae at neuromuscular junctions. In peripheral sensory neurons, loss of Katanin 60 led to increased elaboration of dendrites, whereas overexpression of Katanin 60 resulted in the opposite. Genetic interaction analyses indicated that increased levels of MT acetylation increase its susceptibility to Katanin-mediated severing in neuronal and non-neuronal systems. Taken together, our results demonstrate for the first time that Katanin 60 is required for the normal development of neuromuscular synapses and dendrites.

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.

The cluster digging behavior of larvae confers trophic benefits to fitness in insects.

Collective behaviors efficiently impart benefits to a diversity of species ranging from bacteria to humans. Fly larvae tend to cluster and form coordinated digging groups under crowded conditions, yet understanding the rules governing this behavior is in its infancy. We primarily took advantage of the Drosophila model to investigate cooperative foraging behavior. Here, we report that Drosophila-related species and the black soldier fly have evolved a conserved strategy of cluster digging in food foraging. Subsequently, we investigated relative factors, including larval stage, population density, and food stiffness and quality, that affect the cluster digging behavior. Remarkably, oxygen supply through the posterior breathing spiracles is necessary for the organization of digging clusters. More importantly, we theoretically devise a mathematical model to accurately calculate how the cluster digging behavior expands food resources by diving depth, cross-section area, and food volume. We found that cluster digging behavior approximately increases 2.2 fold depth, 1.7-fold cross-section area, and 1.9 fold volume than control groups, respectively. Amplification of food sources significantly facilitates survival, larval development, and reproductive success of Drosophila challenged with competition for limited food resources, thereby conferring trophic benefits to fitness in insects. Overall, our findings highlight that the cluster digging behavior is a pivotal behavior for their adaptation to food scarcity, advancing a better understanding of how this cooperative behavior confers fitness benefits in the animal kingdom.

Identification of signaling pathways that specify a subset of migrating enteric neural crest cells at the wavefront in mouse embryos.

During enteric nervous system (ENS) development, pioneering wavefront enteric neural crest cells (ENCCs) initiate gut colonization. However, the molecular mechanisms guiding their specification and niche interaction are not fully understood. We used single-cell RNA sequencing and spatial transcriptomics to map the spatiotemporal dynamics and molecular landscape of wavefront ENCCs in mouse embryos. Our analysis shows a progressive decline in wavefront ENCC potency during migration and identifies transcription factors governing their specification and differentiation. We further delineate key signaling pathways (ephrin-Eph, Wnt-Frizzled, and Sema3a-Nrp1) utilized by wavefront ENCCs to interact with their surrounding cells. Disruptions in these pathways are observed in human Hirschsprung's disease gut tissue, linking them to ENS malformations. Additionally, we observed region-specific and cell-type-specific transcriptional changes in surrounding gut tissues upon wavefront ENCC arrival, suggesting their role in shaping the gut microenvironment. This work offers a roadmap of ENS development, with implications for understanding ENS disorders.

Using Drosophila Larval Neuromuscular Junction and Muscle Cells to Visualize Microtubule Network.

The microtubule network is an essential component of the nervous system. Mutations in many microtubules regulatory proteins are associated with neurodevelopmental disorders and neurological diseases, such as microtubule-associated protein Tau to neurodegenerative diseases, microtubule severing protein Spastin and Katanin 60 cause hereditary spastic paraplegia and neurodevelopmental abnormalities, respectively. Detection of microtubule networks in neurons is advantageous for elucidating the pathogenesis of neurological disorders. However, the small size of neurons and the dense arrangement of axonal microtubule bundles make visualizing the microtubule networks challenging. In this study, we describe a method for dissection of the larval neuromuscular junction and muscle cells, as well as immunostaining of α-tubulin and microtubule-associated protein Futsch to visualize microtubule networks in Drosophila melanogaster. The neuromuscular junction permits us to observe both pre-and post-synaptic microtubules, and the large size of muscle cells in Drosophila larva allows for clear visualization of the microtubule network. Here, by mutating and overexpressing Katanin 60 in Drosophila melanogaster, and then examining the microtubule networks in the neuromuscular junction and muscle cells, we accurately reveal the regulatory role of Katanin 60 in neurodevelopment. Therefore, combined with the powerful genetic tools of Drosophila melanogaster, this protocol greatly facilitates genetic screening and microtubule dynamics analysis for the role of microtubule network regulatory proteins in the nervous system.

α-Tubulin acetylation at lysine 40 regulates dendritic arborization and larval locomotion by promoting microtubule stability in Drosophila.

Posttranslational modification of tubulin increases the dynamic complexity and functional diversity of microtubules. Acetylation of α-tubulin at Lys-40 is a highly conserved posttranslational modification that has been shown to improve the flexibility and resilience of microtubules. Here we studied the in vivo functions of α-tubulin acetylation by knocking-out Atat, the Drosophila α-tubulin acetyltransferase, and by mutating Lys-40 to Arg in α1-tubulin. We found a reduction in the dendritic arborization of larval class I dendritic arborization (da) neurons in both mutants. The dendritic developmental defects in atat mutants could be reversed by enhancing the stability of microtubules either through knocking down the microtubule severing protein Katanin 60 or through overexpressing tubulin-specific chaperone E, suggesting that α-tubulin deacetylation impairsed dendritic morphology by decreasing the stability of microtubules. Using time-lapse recordings, we found that atat and α1-tubulinK40R mutations dramatically increased the number of dendritic protrusions that were likely to be immature dendritic precursors. Finally, we showed that both Atat and α-tubulin acetylation were required in class I da neurons to control larval locomotion. These findings add novel insight into the current knowledge of the role of α-tubulin acetylation in regulating neuronal development and functions.

Increased acetylation of microtubules rescues human tau-induced microtubule defects and neuromuscular junction abnormalities in Drosophila.

Tau normally associates with and stabilizes microtubules (MTs), but is hyperphosphorylated and aggregated into neurofibrillary tangles in Alzheimer's disease and related neurodegenerative diseases, which are collectively known as tauopathies. MTs are regulated by different forms of post-translational modification, including acetylation; acetylated MTs represent a more stable microtubule population. In our previous study, we showed that inhibition of histone deacetylase 6 (HDAC6), which deacetylates tubulin at lysine 40, rescues defects in MTs and in neuromuscular junction growth caused by tau overexpression. However, HDAC6 also acts on other proteins that are involved in distinct biological processes unrelated to tubulins. In order to examine directly the role of increased tubulin acetylation against tau toxicity, we generated a site-directed α-tubulinK40Q mutation by CRISPR/Cas9 technology to mimic the acetylated MTs and found that acetylation-mimicking α-tubulin rescued tau-induced MT defects and neuromuscular junction developmental abnormalities. We also showed that late administration of ACY-1215 and tubastatin A, two potent and selective inhibitors of HDAC6, rescued the tau-induced MT defects after the abnormalities had already become apparent. Overall, our results indicate that increasing MT acetylation by either genetic manipulations or drugs might be used as potential strategies for intervention in tauopathies.