The Drosophila Connectomics group made a strong showing at CNS2024: Sleep, Consciousness & Cognition, an all-day neuroscience symposium on 5 April at Queens’ College in Cambridge. The symposium featured four sessions of talks on neuroscience and philosophy of mind, including a closing plenary by Anil Seth (University of Sussex), author of Being You: A new science of consciousness. Participants dined together afterwards in the beautiful Old Hall, which dates to 1449. There was also an informal lunch with posters, 6 of them from current or former members of our research group; our research assistant Ilina Moitra was selected to advertise hers in a 3-minute data blitz presentation.
The title of Ilina’s presentation was “Complete Drosophila adult CNS connectome allows thorough mapping of ascending neurons involved in locomotor circuits.” Our new MCNS (male whole-CNS) dataset includes both a brain and a connected ventral nerve cord (VNC). The VNC contains locomotor circuits that control movements such as walking, grooming, flying, courtship, and copulation. Communication between the brain and VNC is primarily carried out by descending neurons (DNs) and ascending neurons (ANs). DNs carry motor commands from the brain to the VNC. Conversely, ANs relay information from the VNC to the brain, but their functions remain more elusive. Ilina focused on two sets of ANs identified in MANC (the isolated male adult nerve cord connectome) that receive input in leg neuropils and strongly output onto leg motor neurons (MNs) in the VNC. By identifying the same sets of ANs in the MCNS dataset, she found that most of the DNs they connect to strongly in the brain also innervate the leg neuropils and play a role in the coordination of movement. Therefore, it may be conjectured that these ANs play a role in motor coordination requiring extensive feedback, such as in the execution of complex motor sequences.
Eva Munnelly presented a poster entitled “What’s Your Type? Investigating Insect Connectome Stereotypy” that described preliminary work comparing the recently completed “Flywire” female whole-brain connectome with the male whole-CNS connectome being generated in our current collaboration with Janelia Research Campus. These comparisons were used to investigate stereotypy between the two whole brain datasets and validate our cell typing strategy. Eva focused on neuronal morphology and connectivity in the antennal lobes, a centre for early olfactory processing in insects, and showed that while (as expected) insect brains are highly stereotyped, individual neurons and cell types can vary significantly in morphology and connectivity. The most important take-away was that, given initial seed matches, similar connectivity alone was a better predictor of cell type than connectivity plus morphology.
Ladann Kiassat presented a poster on “Exploring the Circuitry of Visual Projection Neurons that Control Jumping and Backward Walking in Drosophila Using Connectomics.” Visual Projection Neurons (VPNs) contain dendrites in the optic lobe and relay information to the central brain. To transform visual stimuli to locomotion, they would have to connect directly or indirectly to descending neurons (DNs) which carry information from the brain into the ventral nerve cord, the “spinal cord” of the fly. Ladann selected three types of lobular columnar neurons for detailed study: LC4, LC6, and LC16. She found that although activation of either LC4 or LC6 drives jumping, LC4 seems to have more direct connections to DNs than LC6. LC16, which drives backwards walking, outputs mostly onto other LC16 neurons and central neurons instead of DNs. More work is needed to fully understand what information is being integrated into these circuits and how that contributes to behavioural outcomes upon activation.
Holly Whittome presented a poster on “Investigating sexual dimorphism in the front leg circuits downstream of two descending neurons in Drosophila melanogaster.” She focused on two descending neuron types: DNp13, which is sexually dimorphic, and DNp37, which is female-specific. They are primarily involved in reproductive activities (eg. egg laying and abdominal bending). They also have some axons in the T1 VNC neuropil which is involved in front leg movement. Holly analysed the downstream connectivity of DNp13 and DNp37 down to front leg motor neurons to determine whether there are differences in circuitry between the male and female datasets which may be related to their function. Although the input percentages are relatively small, the female neurons appear to contribute overall to straightening of the front legs and forward movement of the fly, while male DNp13 appears to contribute slightly to bending in the front legs.
And last but not least, Yijie Yin (now a PhD student with Albert Cardona’s group in the Department of Physiology, Development, and Neuroscience) presented the poster “Connectome interpreter: a tool for connectomics data interpretation” on the new tool that she is developing to analyse connectomes. Concerted effort from the Drosophila neuroscience community worldwide has produced a full-brain, synapse-level wiring diagram (‘connectome’) for both the larval and adult fly. However, connectomics data is incredibly complex and difficult to wrap our heads around: for instance, over 96% of the neurons in the adult fly central brain has >10 input/output partners. To help neuroscientists better access and think about connectomics data in an unbiased way, Yijie has developed the “connectome interpreter”, available here with example scripts using the larval and adult connectomes and available to run immediately on Google Colab.
