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Tripartite Mushroom Body Architecture
Revealed by Antigenic Markers

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Jill R. Crittenden1*, Efthimios M.C. Skoulakis1, Kyung-An Han1, Daniel Kalderon3 and Ronald L. Davis1,2

1Department of Cell Biology
2Department of Psychiatry and Behavioral Sciences, Baylor College of Medicine, Houston, Texas 77030 USA
3Department of Biology, Columbia University, New York, New York 10027 USA

Originially published in: Crittenden et al., 1998, Learning and Memory, 5: 38-51

*Correspondence: Jill Crittenden jr691194@bcm.tmc.edu


The images are organized as follows: When you click on the small image number, a bigger version of the published plate is loaded. This will be an image map. E.g., when you click on Figure 2A, Figure 2A is loaded at full resolution.


Summary

We have explored the organization of the axonal lobes in Drosphila mushroom bodies by using a panel of immunohistochemical markers. These markers consist of antibodies to eight proteins expressed preferentially in the mushroom bodies: DAMB, DCO, DRK, FASIL, LEO, OAMB, PKA RII, and RUT. Previous to this work, four axonal lobes, two projecting dorsally (alpha and alpha') and two medially (beta and gamma), had been described in Drosphila mushroom bodies. However, our analysis of immunohistochemically stained frontal and sagittal sections of the brain revealed three medially projecting lobes. The newly distinguished lobe, which we term beta', lies along the dorsal surface of beta, just posterior to gamma. In addition to resolving a fifth lobe, our studies revealed that there are specific lobe sets defined by equivalent marker expression levels. These sets are (1) the alpha and beta lobes, (2) the alpha' and beta' lobes, and (3) the gamma lobe and heel (a lateral projection formed by a hairpin turn of some of the peduncle fibers). All of the markers we have examined are consistent with these three sets. Previous Golgi studies demonstrate that each mushroom body cell projects one axon that branches into a dorsal lobe and a medial lobe, or one unbranched axon that projects medially. Taken together with the lobe sets listed above, we propose that there are three major projection configurations of mushroom body cell axons: (1) one branch inthe alpha and one in the beta lobe, (2) one branch inthe alpha' and one in the beta' lobe, and (3) one unbranched axon projecting to the heel and the gamma lobe. The fact that these neuron types exhibit differential expression levels of a number of mushroom body genes suggest that they may have corresponding functional differences. These functions may be conserved in the larvae, as several of these genes were expressed in larval and embryonic mushroom bodies as well. The basic mushroom body structure, including the denritic calyx, peduncle, and lobes, was already visible by the late stages of embryogenesis. With new insights into mushroom body organization, and the characterization of markers for developing mushroom bodies, we are beginning to understand how these structures form and function.


Figure 1 - Cartoon of the Mushroom Body Lobes Depicted from an Anterior View-point


Figure 2 - Cartoon of a Cross-section Through the Peduncle at the Level of the Fan-shaped Body


Figure 3 - Frontal Sections Through the Adult Brain Stained for Mushroom Body Markers


Figure 4 - Sagittal Sections Through the Adult Brain


Figure 5 - Frontal Sections Through the Brain of a Wandering Third Instar Larva Stained with anti-FASII


Figure 6 - Sagittal Sections Through Single Brain Hemispheres of Wandering Third Instar Larvae


Figure 7 - Frontal Section of the Mushroom Body from a Wandering Third Instar Larva Stained for LEO


Figure 8 - Sections of Embryonic Central Nervous System Stained to Detect anti-FASII


Figure 9 - Sagittal Sections of Embryonic Brains Stained for Markers


Figure 10 - Frontal Paraffin Sections Through an Adult Brain Challenged with anti-HRP


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