Scientists complete the fruit fly's 166,000-neuron connectome, enabling the first sex-by-sex brain comparison
Researchers at HHMI's Janelia Research Campus and collaborators completed the first full connectome of a fruit fly's central nervous system, mapping more than 166,000 neurons across the brain and nerve cord. Four papers published in Cell trace several hundred sex-specific neuron types, tied to the fruitless and doublesex genes, to differences in courtship behaviour between male and female flies, and place the new male map alongside the 2024 female brain map for direct comparison.
Science··Night
Researchers complete first full connectome of a fruit fly's nervous system
Researchers at HHMI's Janelia Research Campus, working with the Cambridge Connectomics Group and Google Research, published the first complete map of a fruit fly's central nervous system, covering more than 166,000 neurons across the brain and the fly's equivalent of a spinal cord, Live Science and El País reported. Four papers describing the map appeared in the journal Cell on 3 September, and Live Science reported the same dataset also ran in Current Biology. The new map joins the female fruit fly brain map released in 2024, so the two sexes' wiring can now be compared directly; Janelia's Gerry Rubin told Live Science it is the first time researchers can compare both sexes of an animal with complex social behaviour.[1], [2]
Companion paper traces the fly's taste circuits from receptors to feeding
Live Science reported that the male connectome was assembled by the FlyEM team at Janelia together with the Cambridge Connectomics Group and Google Research, using electron microscopy to slice and scan the tissue with machine reconstruction checked by hand. A companion paper led by Carlos Ribeiro of the Champalimaud Foundation in Lisbon traced the fly's taste receptors, on its legs, wings, mouthparts and throat, back into the brain and on to the circuits that drive swallowing and walking. Live Science reported the next targets for the same mapping approach are larval zebrafish and the small fish Danionella.[1]
Sex-specific circuits trace courtship differences to two genes
El País reported that fly connectome mapping advanced in stages over two decades, from a 25,000-neuron half-brain map in 2020 and a complete 3,016-neuron larval brain in 2023 to the first adult brain map, with 140,000 neurons, in 2024, before the new map closed the remaining gap. The papers identified several hundred sex-specific neuron types, making up 4.8% of neurons in the male brain and 2.4% in the female brain, tied to the fruitless and doublesex genes; the researchers said the resulting courtship-behaviour differences between the sexes trace to deep, higher-order processing centres rather than to differences in what the flies perceive. Albert Cardona of the Laboratory of Molecular Biology in Cambridge, who was not involved in the new papers, told El País the fruitless gene is expressed in about 10% of neurons in both sexes but 'in different ways', wiring the sexes' circuits differently.[2]
