Development of the DGI (GAL4 strain Mz 423 x UAS-tau)

Original images that appeared in Fig. 5 of:
Kei Ito, Heinz Sass, Joachim Urban, Alois Hofbauer and Stephan Schneuwly (1997)
GAL4-responsive UAS-tau as a tool for studying the anatomy and development of the Drosophila central nervous system
Cell and Tissue Research 290:1-10

Contents:

Another GAL4 strain, Mz 423, revealed the development of a single neurone not described before. Because of its large cell body and its projections confined to the dorsal protocerebrum, we call this neurone as the dorsal giant interneurone (DGI).

Click each thumbnail image to see the original figure. This picture corresponds to Fig. 3B.

The strain Mz 423 labels the following neurones: cells labelled throughout the postembryonic stages #6 the dorsal giant interneurone (DGI) cells labelled only in larvae #7 descending neurone from the larval posterior brain to the ventral nerve cord (VNC) (see fig. B, C) cells labelled only after late pupal stages #8 cells in the pars intercerebralis #9 cells that project to the dorsal branch (d bra) of the DGI #10 large-field "R-neurones" of the ellipsoid body (Fig. 20 of Hanesch et al. 1989) #11 a cluster of translobula-plate neurones (Tlp: Fig. 4 of Fischbach and Dittrich, 1989) #12 a few medulla neurones. Note that not all the labelled cells appear in each photograph, although the depth of focus is considerably enlarged by the digital montage.

(Bar = 50 um)	A: stage-17 embryo Mz 423 labels no neurones in the embryonic brain. (The staining between the brain hemispheres is not inside the CNS.)
B:Brain in the 1st-instar larva (24 hrs after larval hatching, ALH) At the end of the first instar, the first labelled neurones, #6 (DGI) and #7, appear. While the neurone #7 in the posterior cortex extends a long axon that reaches the caudal segments of the ventral nerve cord (VNC), the DGI cell body, which lies close to the anterolateral corner of the brain neuropile, has no fibres. C: Brain in the 3rd-instar larva (72 hrs ALH) The DGI remains fibreless throughtout the larval stages. (Staining in the left hemisphere is not reconstructed in this figure.)

(Bar = 50 um)

Brain in the early pupa (17 hrs after puparium formation: APF) The labelling of the neurone #7 is no longer detectable. The DGI sends a fibre that runs along the outer surface of the lateral horn neuropile (l ho in E) and makes dorsal and ventral branches (d bra and v bra, respectively). The dorsal branch runs anteriorly and the ventral branch medially. The tips of the fibres do not yet cross the midline at this stage. The DGI fibre has no arborisation between the cell body and the first branching point.

Brain in the late pupa (82 hrs APF) The ventral branches of both sides cross the midline to connect with each other. As the lateral horn becomes massive in late pupae, the DGI fibre keeps running along the outer surface of the neuropile. The fibre, therefore, starts to show an acute bend near the cell body. From the late pupal stage onwards, the strain Mz 423 also labels a cluster of translobula-plate neurones (Tlp: Fig. 4 of Fischbach and Dittrich, 1989) in the posterior optic lobe cortex (#11). The cell bodies lie posterior to the lobula plate (lo p), sending fibres through lobula plate to the lobula (lo). The extensive fibril arborisations are observed in the pupal lobula plate.

Brain in the mature adult (10 days after eclosion). More cells become labelled in the adult brain. The dorsal branch (d bra) of the DGI projects to the ipsilateral region of the ellipsoid body (e b), which is innervated by the neurones #10. Neurons #9 innervate the DGI structure. Compared to late pupae (Fig. G) the lobula-plate arborisations of the neurones #11 become simpler in the adult. Accordingly, the lobula plate neuropile becomes more compact in the mature brain (compare Figs. F and H). This may correspond to the situation in the vertebrate CNS, where immature neurones often send out extra fibres that eventually disappear, although the lack of Tau molecule in very fine branches in the adult brain cannot be excluded. The neurones #12, innervate the medulla tangentially. Note that, although the cell bodies of the DGI and #12 lie very close to each other, their fibres project to the opposite directions. In Drosophila, the position of the cell bodies and the area of their arborisations are often uncorelated. This makes it very difficult to predict the area of arborisation when only the position of the cell body is known. The technique to label not only the cell bodies but also the projections, such as the UAS-tau system described here, is very helpful in such a situaiton.

References

• Fischbach KF, Dittrich APM (1989) The optic lobe of Drosophila melanogaster. - I. A golgi analysis of wild-type structure. Cell Tissue Res 258:441-475
• Hanesch U, Fischbach KF, Heisenberg M (1989) Neuronal architecture of the central complex in Drosophila melanogaster. Cell Tissue Res 257:343-366

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