Quantitative neuroanatomy for connectomics in Drosophila

Abstract

Neuronal circuit mapping using electron microscopy demands laborious proofreading or reconciliation of multiple independent reconstructions. Here, we describe new methods to apply quantitative arbor and network context to iteratively proofread and reconstruct circuits and create anatomicallyenriched wiring diagrams. We measured the morphological underpinnings of connectivity in new and existing reconstructions of Drosophila sensorimotor (larva) and visual (adult) systems. Synaptic inputs were preferentially located on numerous small, microtubule-free "twigs" which branch off a single microtubule-containing "backbone". Omission of individual twigs accounted for 96% of errors.However, the synapses of highly connected neurons were distributed across multiple twigs. Thus the robustness of a strong connection to detailed twig anatomy was associated with robustness to reconstruction error. By comparing iterative reconstruction to the consensus of multiple reconstructions, we show that our method overcomes the need for redundant effort through the discovery and application of relationships between cellular neuroanatomy and synaptic connectivity.

Volume scanning electron microscopy for imaging biological ultrastructure

“…tracing morphology to capture cellular and subcellular structures), visualisation and annotation. Besides commercial software such as Amira or Imaris, free tools are available, for example KNOSSOS (Helmstaedter et al., ), TrakEM2 (Cardona et al., ), CATMAID (Saalfeld et al., ; Schneider‐Mizell et al., ), ilastik (Sommer et al., ), Microscopy Image Browser (Belevich et al., ) or VAST (Kasthuri et al., ). A literature survey of volume EM data processing tools has recently been conducted (Borrett and Hughes, ); a more comprehensive list of software tools can be found there.…”

Divergent Connectivity of Homologous Command-like Neurons Mediates Segment-Specific Touch Responses in Drosophila

“…To understand how Wave neurons might receive the touch sensation on the head and induce backward locomotion, we mapped synapse-level circuits from a nanometer-scale EM volume of the whole CNS by using CATMAID software (Saalfeld et al, 2009;Schneider-Mizell et al, 2016). We started by reconstructing a pair of Wave neurons in the A1 neuromere to identify all the arbors and synaptic sites.…”

Drosophila glia: Few cell types and many conserved functions

“…The combination of extensive Gal4 driver collections, opto‐ and thermogenetics and the complete TEM based reconstruction of the larval nervous system will allow to decipher neuronal circuits to be deciphered in great detail. Together with easy genome engineering using CRISPR based knockout or knockin approaches or the MiMIC technology this holds great promises for future work on glial cells (Diao et al, ; Li et al, ; Ohyama et al, ; Schneider‐Mizell et al, ; Venken et al, ).…”