Digital in vivo 3D atlas of the antennal lobe of Drosophila melanogaster

Abstract

As a model for primary olfactory perception, the antennal lobe (AL) of Drosophila melanogaster is among the most thoroughly investigated and well-understood neuronal structures. Most studies investigating the functional properties and neuronal wiring of the AL are conducted in vivo, although so far the AL morphology has been mainly analyzed in vitro. Identifying the morphological subunits of the AL-the olfactory glomeruli-is usually done using in vitro AL atlases. However, the dissection and fixation procedure causes not only strong volumetric but also geometrical modifications; the result is unpredictable dislocation and a distortion of the AL glomeruli between the in vitro and in vivo brains. Hence, to characterize these artifacts, which are caused by in vitro processing, and to reliably identify glomeruli for in vivo applications, we generated a transgenic fly that expresses the red fluorescent protein DsRed directly fused to the presynaptic protein n-synaptobrevin, under the control of the pan-neuronal promotor elav to label the neuropil in the live animal. Using this fly line, we generated a digital 3D atlas of the live Drosophila AL; this atlas, the first of its kind, provides an excellent geometric match for in vivo studies. We verified the identity of 63% of AL glomeruli by mapping the projections of 34 GAL4-lines of individual chemosensory receptor genes. Moreover, we characterized the innervation patterns of the two most frequently used GAL4-lines in olfactory research: Orco- and GH146-GAL4. The new in vivo AL atlas will be accessible online to the neuroscience community.

Morphological characterization of the antennal lobes in the Mediterranean fruit fly Ceratitis capitata

“…The number of 53 glomeruli is very close to the 54 present in the closely related species D. melanogaster (Grabe et al 2015). Other aspects of the glomerular arrangement that we found in C. capitata are also reminiscent of D. melanogaster: presence of glomeruli innervated by the palps, contralateral innervation from the antennal nerve, and glomerular size (glomeruli range in size from 500 to 5000 μm 3 , Grabe et al 2015).…”

“…Other aspects of the glomerular arrangement that we found in C. capitata are also reminiscent of D. melanogaster: presence of glomeruli innervated by the palps, contralateral innervation from the antennal nerve, and glomerular size (glomeruli range in size from 500 to 5000 μm 3 , Grabe et al 2015). However, the comparison with D. melanogaster should also serve as a cautionary one: from the first studies of the full glomerular complement (Stocker et al 1983;Laissue et al 1999) to the later ones (Couto et al 2005;Endo et al 2007;Silbering et al 2011;Tanaka et al 2012;Grabe et al 2015) there have been numerous changes in glomerular number, glomerular identity, and information about innervated neurons, some of which needed genetic tools to be solved. Therefore, our atlas of C. capitata should be used as a tool representing the current knowledge of this species-better staining techniques, in particular genetic ones, will most likely refine our understanding of the glomerular arrangement in this species.…”

“…So far, 3D reconstructions of the ALs have been made in several insects, among which other Diptera (e.g. Laissue et al 1999;Ignell et al 2005;Ghaninia et al 2007;Poddighe et al 2010;Grabe et al 2015), but also Hymenoptera (e.g. Galizia et al 1999;Smid et al 2003), Lepidoptera (e.g.…”

“…Galizia et al 1999;Smid et al 2003), Lepidoptera (e.g. Berg et al 2002;Greiner et al 2004;Huetteroth and Schachtner 2005;Couton et al 2009;Varela et al 2009;Montgomery and Ott 2015;Grabe et al 2015) and Coleoptera (e.g. Dreyer et al 2010;Hu et al 2011).…”

Scintillate: An open-source graphical viewer for time-series calcium imaging evaluation and pre-processing

“…Performing in-vivo imaging in a fruitfly requires considerable dissection care. Preparations, however good, are likely to be variable in quality (Grabe et al, 2014).…”