Biology subjects

Waddell, S.

Publications and source records attributed to Waddell, S..

25 records · Page 2Linked to original sources

bioRxiv2020

Complete connectomic reconstruction of olfactory projection neurons in the fly brain

Nervous systems contain sensory neurons, local neurons, projection neurons and motor neurons. To understand how these building blocks form whole circuits, we must distil these broad classes into neuronal cell types and describe their network connectivity. Using an electron micrograph dataset for an entire Drosophila melanogaster brain, we reconstruct the first complete inventory of olfactory projections connecting the antennal lobe, the insect analogue of the mammalian olfactory bulb, to higher-order brain regions in an adult animal brain. We then connect this inventory to extant data in the literature, providing synaptic-resolution holotypes both for heavily investigated and previously unknown cell types. Projection neurons are approximately twice as numerous as reported by light level studies; cell types are stereotyped, but not identical, in cell and synapse numbers between brain hemispheres. The lateral horn, the insect analogue of the mammalian cortical amygdala, is the main target for this olfactory information and has been shown to guide innate behaviour. Here, we find new connectivity motifs, including: axo-axonic connectivity between projection neurons; feedback and lateral inhibition of these axons by local neurons; and the convergence of different inputs, including non-olfactory inputs and memory-related feedback onto lateral horn neurons. This differs from the configuration of the second most prominent target for olfactory projection neurons: the mushroom body calyx, the insect analogue of the mammalian piriform cortex and a centre for associative memory. Our work provides a complete neuroanatomical platform for future studies of the adult Drosophila olfactory system. HighlightsO_LIFirst complete parts list for second-order neurons of an adult olfactory system C_LIO_LIQuantification of left-right stereotypy in cell and synapse number C_LIO_LIAxo-axonic connections form hierarchical communities in the lateral horn C_LIO_LILocal neurons and memory-related feedback target projection neuron axons C_LI

neuroscience↗

bioRxiv2019

A single-cell transcriptomic atlas of the adult Drosophila ventral nerve cord

The Drosophila ventral nerve cord (VNC) receives and processes descending signals from the brain to produce a variety of coordinated locomotor outputs. It also integrates sensory information from the periphery and sends ascending signals to the brain. We used single-cell transcriptomics to generate an unbiased classification of cellular diversity in the VNC of five-day old adult flies. We produced an atlas of 26,000 high-quality cells, representing more than 100 transcriptionally distinct cell types. The predominant gene signatures defining neuronal cell types reflect shared developmental histories based on the neuroblast from which cells were derived, as well as their birth order. Cells could also be assigned to specific neuromeres using adult Hox gene expression. This single-cell transcriptional atlas of the adult fly VNC will be a valuable resource for future studies of neurodevelopment and behavior.

neuroscience↗

bioRxiv2019

Transposon expression in the Drosophila brain is driven by neighbouring genes and diversifies the neural transcriptome

Somatic transposition in neural tissue could contribute to neuropathology and individuality, but its prevalence is debated. We used single-cell mRNA sequencing to map transposon expression in the Drosophila midbrain. We found that neural transposon expression is driven by cellular genes. Every expressed transposon is resident in at least one cellular gene with a matching expression pattern. A new long-read RNA sequencing approach revealed that coexpression is a physical link in the form of abundant chimeric transposon-gene mRNAs. We identified 148 genes where transposons introduce cryptic splice sites into the nascent transcript and thereby produce many additional mRNAs. Some genes exclusively produce chimeric mRNAs with transposon sequence and on average transposon-gene chimeras account for 20% of the mRNAs produced from a given gene. Transposons therefore significantly expand the neural transcriptome. We propose that chimeric mRNAs produced by splicing into polymorphic transposons may contribute to functional differences between individual cells and animals.

genetics↗

bioRxiv2019

Spaced training forms complementary long-term memories of opposite valence in Drosophila

Forming long-term memory (LTM) in many cases requires repetitive experience spread over time. In Drosophila, aversive olfactory LTM is optimal following spaced training, multiple trials of differential odor conditioning with rest intervals. Studies often compare memory after spaced to that after massed training, same number of trials without interval. Here we show flies acquire additional information after spaced training, forming an aversive memory for the shock-paired odor and a safety-memory for the explicitly unpaired odor. Safety-memory requires repetition, order and spacing of the training trials and relies on specific subsets of rewarding dopaminergic neurons. Co-existence of the aversive and safety memories can be measured as depression of odor-specific responses at different combinations of junctions in the mushroom body output network. Combining two particular outputs appears to signal relative safety. Learning a complementary safety memory thereby augments LTM performance after spaced training by making the odor preference more certain.

neuroscience↗

bioRxiv2017

Cellular diversity in the Drosophila midbrain revealed by single-cell transcriptomics

To understand the brain, molecular details need to be overlaid onto neural wiring diagrams so that synaptic mode, neuromodulation and critical signaling operations can be considered. Single-cell transcriptomics provide a unique opportunity to collect this information. Here we present an initial analysis of thousands of individual cells from Drosophila midbrain, that were acquired using Drop-Seq. A number of approaches permitted the assignment of transcriptional profiles to several major brain regions and cell-types. Expression of biosynthetic enzymes and reuptake mechanisms allows all the neurons to be typed according to the neurotransmitter or neuromodulator that they produce and presumably release. Some neuropeptides are preferentially co-expressed in neurons using a particular fast-acting transmitter, or monoamine. Neuromodulatory and neurotransmitter receptor subunit expression illustrates the potential of these molecules in generating complexity in neural circuit function. This cell atlas dataset provides an important resource to link molecular operations to brain regions and complex neural processes.

neuroscience↗

bioRxiv2017

Single Molecule Fluorescence In Situ Hybridisation For Quantitating Post-Transcriptional Regulation In Drosophila Brains

RNA in situ hybridization can be a powerful method to investigate post-transcriptional regulation, but analysis of intracellular mRNA distributions in thick, complex tissues like the brain poses significant challenges. Here, we describe the application of single-molecule fluorescent in situ hybridization (smFISH) to quantitate primary transcription and post-transcriptional regulation in whole-mount Drosophila larval and adult brains. Combining immunofluorescence and smFISH probes for different regions of a single gene, i.e., exons, 3UTR, and introns, we show examples of a gene that is regulated post-transcriptionally and one that is regulated at the level of transcription. We also show that the method can be used to co-visualise a variety of different transcripts and proteins in neuronal stems cells as well as deep brain structures such as mushroom body neuropils. Finally, we introduce the use of smFISH as asensitivealternative to conventional antibody labelling to mark specific neural stem cell populations in the brain.

neuroscience↗

bioRxiv2017

Rapid Sensing Of Volumetric Neural Activity Through Adaptive Remote Focusing

The ability to record neural activity in the brain of a living organism at cellular resolution is of great importance for defining the neural circuit mechanisms that direct behavior. Here we present an adaptive two-photon microscope optimized for extraction of neural signals over volumes in intact Drosophila brains, even in the presence of specimen motion. High speed volume imaging was made possible through reduction of spatial resolution while maintaining the light collection efficiency of a high resolution, high numerical aperture microscope. This enabled simultaneous recording of odor-evoked calcium transients in a defined volume of mushroom body Kenyon cell bodies in a live fruit fly.

neuroscience↗