Mushroom Body is a Quadruple Structure - Figure 6
Fig. 6. A single MBNb is sufficient to autonomously generate all of
the MB structures. (partial ablation of MBNbs with hydroxyurea)
We performed partial ablation of the MBNbs and analysed the projection patterns
of cells labelled with GAL4 enhancer trap in animals that have only one
of the four MBNbs. To selectively ablate the MBNbs, newly hatched larvae
were fed medium containing 3 mg/ml of hydroxyurea (HU) for three hours.
Under these conditions, 20-30 % of examined brains had only one (or two)
surviving MBNb(s) in either one or both hemisphere(s).
With all the MB subtype markers examined, the labelled structure of the
surviving clones was essentially identical to the staining pattern of the
intact brain. Considering that the escape from the ablation should occur
randomly, this strongly suggests that a single MBNb, in the absence of the
other MBNbs, can generate all the MB substructures labelled with these markers.
(oblique view from the anterior).
GAL 4 strain Mz 717 crossed to UAS-GFP S65T. This strain labels fibres in
the dense alpha and beta lobes, as well as fibrous gamma and alpha' lobes.
In the intact brain (A), four clusters of cell
bodies are observed.
In the brain that has only one surviving MBNb clone in each hemisphere (B),
only one cluster is seen in the cortex. Although the fibre number is greatly
reduced, the clone forms essentially identical structures in the lobe region
as would four clones in untreated animals. However, we found that the beta
lobes of both sides often fuse together in the HU-treated flies (arrowhead
(C-E) GAL4 strain Mz 984 crossed to UAS-GFP S65T. This strain labels fibres
in the core region of only alpha and beta lobes. In the intact brain (C),
the large round tip of the alpha lobe and the split tips of the beta lobe
(two arrowheads) are labelled. (m bdl: median bundle)
The same characteristic structure can be observed in brains with single
surviving clones (D). Again, the beta lobes of
the HU-treated animals are fused with each other (arrowhead).
In a brain that has only one MB clone (E), the
beta lobe fibres seem to divert after crossing the midline. It is important
to note that only a defined substructure was affected by the HU treatment.
Although the fibres in the upper tip of the beta lobe seem to cross the
midline; the gamma lobe and the lower tip of the beta lobe look intact.
Thus, we think that the fused lobe is a secondary outcome rather than a
direct consequence of the HU-mediated ablation. Except for this fusion,
the lobe and pedunculus structure of the single clones is essentially identical
with that of the intact brain.
Three-dimensional reconstructions were made from about 160 confocal 1-um
optical sections. Bar, 20 um.
Abbreviations: alpha, alpha', beta, gamma: lobes, ped:
pedunculus, sp, spur, m bdl: median bundle
Go to Index | Fig. 1 | Fig. 2 | Fig. 3 | Fig. 4 | Fig. 5 | Fig. 6