Drosophila brains contain numerous neurons that form complex circuits. These neurons are derived in stereotyped patterns from a fixed number of progenitors, called neuroblasts, and identifying individual neurons made by a neuroblast facilitates the reconstruction of neural circuits. An improved MARCM (mosaic analysis with a repressible cell marker) technique, called twin-spot MARCM, allows one to label the sister clones derived from a common progenitor simultaneously in different colors. It enables identification of every single neuron in an extended neuronal lineage based on the order of neuron birth. Here we report the first example, to our knowledge, of complete lineage analysis among neurons derived from a common neuroblast that relay olfactory information from the antennal lobe (AL) to higher brain centers. By identifying the sequentially derived neurons, we found that the neuroblast serially makes 40 types of AL projection neurons (PNs). During embryogenesis, one PN with multi-glomerular innervation and 18 uniglomerular PNs targeting 17 glomeruli of the adult AL are born. Many more PNs of 22 additional types, including four types of polyglomerular PNs, derive after the neuroblast resumes dividing in early larvae. Although different offspring are generated in a rather arbitrary sequence, the birth order strictly dictates the fate of each post-mitotic neuron, including the fate of programmed cell death. Notably, the embryonic progenitor has an altered temporal identity following each self-renewing asymmetric cell division. After larval hatching, the same progenitor produces multiple neurons for each cell type, but the number of neurons for each type is tightly regulated. These observations substantiate the origin-dependent specification of neuron types. Sequencing neuronal lineages will not only unravel how a complex brain develops but also permit systematic identification of neuron types for detailed structure and function analysis of the brain.
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"Notably, the MB NBs, as the sole NBs that divide incessantly until fly eclosion (Truman and Bate, 1988), yield only three major classes of MB neurons with no sister fate diversification in the paired neurons made by one GMC (Lee et al., 1999). By contrast, the AL NBs end proliferation around pupation but can generate about 40 neuron types from a single hemilineage as their GMCs make daughter cells with distinct A/B fates due to Notch-mediated binary sister fate decision (Lin et al., 2010; Yu et al., 2010; Lin et al., 2012). Additional offspring diversities arise in the complex type II lineages through the production of variant INP sublineages by each type II NB and the derivation of distinct neuron/glia types from each INP (Wang et al., 2014). "
[Show abstract][Hide abstract]ABSTRACT: A brain consists of numerous distinct neurons arising from a limited number of progenitors, called neuroblasts in Drosophila. Each neuroblast produces a specific neuronal lineage. To unravel the transcriptional networks that underlie the development of distinct neuroblast lineages, we marked and isolated lineage-specific neuroblasts for RNA sequencing. We labeled particular neuroblasts throughout neurogenesis by activating a conditional neuroblast driver in specific lineages using various intersection strategies. The targeted neuroblasts were efficiently recovered using a custom-built device for robotic single-cell picking. Transcriptome analysis of the mushroom body, antennal lobe, and type II neuroblasts compared to non-selective neuroblasts, neurons, and glia revealed a rich repertoire of transcription factors expressed among neuroblasts in diverse patterns. Besides transcription factors that are likely pan-neuroblast, there exist many transcription factors that are selectively enriched or repressed in certain neuroblasts. The unique combinations of transcription factors present in different neuroblasts may govern the diverse lineage-specific neuron fates.
"The Journal of Comparative Neurology | Research in Systems Neuroscience which has been mentioned in two studies (Marin et al., 2005; Yu et al., 2010). However, its limited description to date leads us to assume that this glomerulus has been mislabeled and represents in fact glomerulus DC3. "
[Show abstract][Hide abstract]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, 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 panneuronal 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, namely Orco- and GH146-GAL4. The new in vivo AL atlas will be accessible on-line to the neuroscience community.
Full-text · Article · Feb 2015 · The Journal of Comparative Neurology
"PNs that innervate the adult AL are produced both at embryonic and larval stages (Marin et al., 2005; Jefferis et al., 2001). From a complete lineage analysis among neurons derived from the ad-neuroblast, it was revealed that the ad-neuroblast serially generates 40 types of PNs (Fig. 1D) (Yu et al., 2010). Eighteen types of PNs are born during the embryonic stage, and 22 additional types of PNs are generated in the early larval stage. "
[Show abstract][Hide abstract]ABSTRACT: The antennal lobe (AL) of Drosophila is the first olfactory processing center in which olfactory input and output are spatially organized into distinct channels via glomeruli to form a discrete neural map. In each glomerulus, the axons of a single type of olfactory receptor neurons (ORNs) synapse with the dendrites of a single type of projection neurons (PNs). The AL is an ideal place to study how the wiring specificity between specific types of ORNs and PNs is established during development. During the past two decades, the involvement of diverse molecules in the specification and patterning of ORNs and PNs has been reported. Furthermore, local interneurons-another component of glomeruli-have been recently catalogued and their functions have been gradually dissected. Although there is accumulating knowledge about the involvement of these three cell types in the wiring specificity of the olfactory system, in this review, we focus especially on the development of PN dendrites.
Preview · Article · May 2014 · Genes & Genetic Systems