Using transplantations to visualise presynaptic sites in the CNS

Fig.1 Reproducible neural cell lineages show reproducible patterns of presynaptic sites:

A) Dorsal view of a Drosophila maggot (compare >>>). The red frame indicates the position of figures B-C'. Abbreviations: Br, brain; vNC, ventral nerve core; ant, anterior; post, posterior.
B-C') Two examples of NB6-1 and NB6-2 cell lineages, respectively (compare >>>). Borders of the synaptic neuropile and the midline are indicated by dashed lines (compare A). Neuronal cell bodies (S) and projections (arrow heads, arrows) are shown in magenta, green spots represent presynaptic sites. Same symbols in B,C versus B',C' indicate comparable structures in the two lineage examples, respectively.

Two conclusions can be drawn from Fig.1: 1) The distribution of synaptic sites in particular cell lineages is reproducible; 2) Presynaptic sites (output synapses) are restricted to compartments within neuronal projections; for example, open arrows in B,B' and curved arrows in C,C' point at stretches of neuronal projections without green spots, whereas these neurites harbour synaptic sites at their termination zones (white arrows, asterisks). Therefore, output synapses of these neurons are compartmentalised, i.e. restricted to their termination zones.

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Fig.2 How to generate preparations like those shown in Fig.1

Transplantations are carried out with two different types of embryos (embryos shown from lateral, anterior left). Donor embryos (top) express a cellular marker (e.g. CD8; magenta) in all neurons. Host embryos (bottom) are mutant and lack a particular presynaptic protein (e.g. Synapsin; yellow spots in top embryo). Therefore, only cell lineages transplanted from the donor embryos express the cellular marker and show synaptic spots at later stages.
Transplantations are carried out at early gastrulation (stage 6; indicated in black circle) following previously described techniques (e.g. Reference 3 >>>/PDF, and 'Flymove' @).

After stage 6 a subfraction of cells acquires neural fate (coloured circles), segregates into the interior of the embryo, divides to give rise to neural daughter cells (smaller circles) which make up the CNS; at stage 12 neurons start forming projections (magenta lines) which constitute the neuropile (not shown) where they differentiate their synaptic sites (yellow dots). For further info on developmental stages of Drosophila see 'Flymove' webpage @.

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Source: modified from Löhr, R., Godenschwege, T., Buchner, E., and Prokop, A. (2002). Compartmentalisation of central neurons in Drosophila: a new strategy of mosaic analysis reveals localisation of pre-synaptic sites to specific segments of neurites. J. Neurosci. 22, 10357-10367.