Clonal analysis ofDrosophilaantennal lobe neurons: diverse neuronal architectures in the lateral neuroblast lineage

Abstract

The antennal lobe (AL) is the primary structure in the Drosophila brain that relays odor information from the antennae to higher brain centers. The characterization of uniglomerular projection neurons (PNs) and some local interneurons has facilitated our understanding of olfaction; however, many other AL neurons remain unidentified. Because neuron types are mostly specified by lineage and temporal origins, we use the MARCM techniques with a set of enhancer-trap GAL4 lines to perform systematical lineage analysis to characterize neuron morphologies, lineage origin and birth timing in the three AL neuron lineages that contain GAL4-GH146-positive PNs: anterodorsal, lateral and ventral lineages. The results show that the anterodorsal lineage is composed of pure uniglomerular PNs that project through the inner antennocerebral tract. The ventral lineage produces uniglomerular and multiglomerular PNs that project through the middle antennocerebral tract. The lateral lineage generates multiple types of neurons, including uniglomeurlar PNs, diverse atypical PNs, various types of AL local interneurons and the neurons that make no connection within the ALs. Specific neuron types in all three lineages are produced in specific time windows, although multiple neuron types in the lateral lineage are made simultaneously. These systematic cell lineage analyses have not only filled gaps in the olfactory map, but have also exemplified additional strategies used in the brain to increase neuronal diversity.

DrosophilaPQBP1 Regulates Learning Acquisition at Projection Neurons in Aversive Olfactory Conditioning

“…The UAS-dPQBP1 transgenic fly, carrying a 0.7 kb full-length cDNA of CG11820 on the second chromosome was developed from w1118 parental strain. GH146-LexA::GAD (LG-GH146) and LexAop-GFP fly stocks were previously described (Lai et al, 2008).…”

Genetic Control of Wiring Specificity in the Fly Olfactory System

“…In addition to the processes of 1300 ORNs and 200 PNs, the antennal lobe also contains neurites from 200 local interneurons (LNs) (Das et al 2008;Lai et al 2008;Okada et al 2009;Chou et al 2010a). LNs make connections with both ORN axons and PN dendrites and play important roles in ORN-to-PN information transformation (Wilson 2013).…”

Development of olfactory projection neuron dendrites that contribute to wiring specificity of the <i>Drosophila</i> olfactory circuit

“…Thus Acj6 and Drifter are required for the specification of dendrite targeting of ad-and l-PNs, respectively. However, recent findings revealed that Acj6 is also expressed in some atypical PNs in l-lineage (Lai et al, 2008;Lin et al, 2012), suggesting that the targeting specification by Acj6 is limited inside uniglomerular PNs. Inside lineages, the birth order strictly dictates the fate of each postmitotic neuron.…”

“…Thus the fate of individual neurons in the ad-PN lineage is tightly regulated on the basis of the time window of their birth. Another study showed that the birth order is also important in l-and v-lineages that produce not only PNs but also other types of neurons, such as LNs (Lai et al, 2008;Lin et al, 2012). To ensure the temporal specification of the types of neurons, various transcription factors can also be sequentially and transiently expressed in neuroblasts that produce PNs, since the transcription factor cascade (early to late: Hunchback → Krüppel → Pdm → Castor) is known to specify the first several neurons across neuroblast lineages in the embryonic ventral nerve cord (Isshiki et al, 2001).…”

“…Axons of ORNs expressing the same type of OR or IR gene converge to a single glomerulus. To receive the direct input from one ORN type, most of the PNs send dendrites into a single glomerulus (uniglomerular PNs) and the other PNs with diverse morphologies send dendrites to multiple glomeruli (atypical multiglomerular PNs) (Lai et al, 2008;Lin et al, 2012). The cell bodies of 150-200 PNs are arranged in 4 distinct clusters around the AL (Ito et al, 2013;Yu et al, 2010;Lin et al, 2012).…”