Neuronal connectome of a sensory-motor circuit for visual navigation

Abstract

Animals use spatial differences in environmental light levels for visual navigation; however, how light inputs are translated into coordinated motor outputs remains poorly understood. Here we reconstruct the neuronal connectome of a four-eye visual circuit in the larva of the annelid Platynereis using serial-section transmission electron microscopy. In this 71-neuron circuit, photoreceptors connect via three layers of interneurons to motorneurons, which innervate trunk muscles. By combining eye ablations with behavioral experiments, we show that the circuit compares light on either side of the body and stimulates body bending upon left-right light imbalance during visual phototaxis. We also identified an interneuron motif that enhances sensitivity to different light intensity contrasts. The Platynereis eye circuit has the hallmarks of a visual system, including spatial light detection and contrast modulation, illustrating how image-forming eyes may have evolved via intermediate stages contrasting only a light and a dark field during a simple visual task.DOI: http://dx.doi.org/10.7554/eLife.02730.001

Whole-organism cellular gene-expression atlas reveals conserved cell types in the ventral nerve cord of Platynereis dumerilii

“…Because ProSPr can easily be applied to other stages, this will allow tracking cell types through development. Furthermore, the small size of Platynereis larvae and the relatively small overall cell number enable whole-body connectomics (42), and thus the integration of ProSPr and connectomics data into multidimensional, cellular whole-body atlases, which can finally be complemented by functional characterization of key genes and cell types using Crispr-Cas9. The possible transfer of ProSPr to other model species has the potential to boost comparisons between species and phyla, and to thus contribute to unraveling the evolutionary history of cell types.…”

Spectral Tuning of Phototaxis by a Go-Opsin in the Rhabdomeric Eyes of Platynereis

“…Larval phototaxis is mediated by simple eyes that can express various types of light-sensitive G-protein-coupled receptors known as opsins [2][3][4][5][6][7][8]. Since opsins diversified early during metazoan evolution in the marine environment [9], understanding underwater light detection could elucidate this diversification.…”

“…The Go-opsins form an ancient and poorly characterized group retained only in marine invertebrate genomes. Here, we characterize a Go-opsin from the marine annelid Platynereis dumerilii [3][4][5][12][13][14][15]. We found Go-opsin1 coexpressed with two r-opsins in depolarizing rhabdomeric photoreceptor cells in the pigmented eyes of Platynereis larvae.…”

Large-Scale Combinatorial Deorphanization of Platynereis Neuropeptide GPCRs

“…The annelid Platynereis has emerged in recent years as a powerful lophotrochozoan laboratory animal for the study of development, neuronal circuits, and zooplankton behavior (Jé kely et al, 2008;Randel et al, 2014;Tosches et al, 2014;Zantke et al, 2014). Its larval stages represent accessible models for studying the role of neuropeptides in behavior, development, and physiology at the whole-organism level (Conzelmann et al, 2011(Conzelmann et al, , 2013bWilliams et al, 2015).…”