Strategies to visualise neuro-neuronal synapses of Drosophila embryos
In contrast to amenable neuromuscular synapses (>>> illustration), neuro-neuronal synapses are hidden and densely packed in the neuropile (>>> illustration). A) The Gal4/Uas expression system1 can be used to visualise the morphology of only a specific neuronal subpopulation (blue cells) and their synapses (yellow dots; >>> reference 18). B) Generation of primary cell cultures from such embryos allows visualisation of Ga4-positive neurons in isolation (>>> illustration). C) Via transplantation of single precursor cells from ubiquitously labelled donor into unlabelled host embryos (neuroblasts; see >>> illustration) complete neural lineages can be visualised (green and yellow dots; see >>> reference 18). D) Mixing cells from such donor embryos with unlabelled or differently labelled donors in the same primary cell culture can be used to study neuronal interactions at high resolution. In all the above experiments different genetic constellations (i.e. mutations or gene misexpression) can be used in donors or host embryos to combine functional studies with the visualisation strategies. All kinds of combinations or modifications of the above strategies are possible.

1) Duffy, J. B. GAL4 system in Drosophila: a fly geneticist's Swiss army knife. Genesis 34, 1-15 (2002).