The Organization of the Adult Mushroom Bodies (MBs)
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Figure 1 - The organization of the adult mushroom bodies (MBs) and clonal analysis using MARCM.
(A) Composite confocal images of an adult brain show the morphology of the paired MBs, one in each brain hemisphere. Expression of the mCD8-GFP, driven by the GAL4-OK107, allows for visualization of the whole MBs. seg- supraesophageal ganglion, ol- optic lobe, and sub- subesophageal ganglion.
(B) Close-up view of the right MB in A. Five axonal lobes are grouped into 3 sets, based on a previous proposal (Crittenden et al., 1998). The g lobe is outlined in red; the a' and b' lobes are outlined in green; and the a and b lobes are outlined in blue.
(C) Schematic drawing shows the essence of the MARCM system. Mitotic recombination between two FRT sites (triangles) results in loss of the repressor transgene (tubP-GAL80) in one of the daughter cells, and hence GAL4-dependent expression of the marker transgene (UAS-mCD8-GFP).
(D) Schematic drawing shows how mitotic recombination in a dividing Nb can lead to formation of two mutually exclusive types of marked clones. If the regenerated Nb loses the repressor gene, all post-mitotic neurons generated subsequently in the same lineage will be labeled (upper). In contrast, if the GMC loses the repressor gene, only two neurons derived from this GMC will be labeled in the whole lineage (lower). In addition, mitotic recombination in a dividing GMC can generate a single cell clone independently (lower).
(E) Composite confocal images of an adult MB Nb clone demonstrate five axonal bundles, three projecting medially and two projecting dorsally. This clone was generated by inducing mitotic recombination in a newly hatched larva with the genotype of hs-FLP/Y ; FRTG13,tubP-GAL80/FRTG13,UAS-mCD8-GFP ; GAL4-OK107/+.
(F) Based on the observation that five lobes could be grouped into 3 sets of bundles with characteristic antigen compositions, Davis and his colleagues proposed that there are three types of neurons with different characteristic axonal projections (Crittenden et al., 1998). One type of neurons (red) project their axons only into the g lobe, another type of neurons (green) have branched axons projecting into both the a' and b' lobes, and the third type of neurons (blue) have branched axons projecting into both the a and b lobes. The question is: how are they generated from a single neuroblast?
In this and all subsequent figures, the brain is shown in an oblique configuration so that dorsal-anterior is up. All figures except Fig. 1A have midlines on the right side. The unit in the scale bar is mm in this and all subsequent figures.
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