[Specification of glial lineage in invertebrates]

Glial cells in invertebrates have been known for a long time, however, a systematic analysis of the development and the role of these cells has been missing. In the last few years, the development of new markers and the identification of genes specifically expressed in glial cells have shed some light on the mechanisms leading to gliogenesis in Drosophila melanogaster. The organisation of glial cells in the central and in the peripheral nervous system has been described and the origin of some of these cells has also been assessed. Lineage studies have shown that glial cells display different mechanisms of differentiation depending on their position in the nervous system. In some cases, glial differentiation seems intimately associated with neurogenesis, as has already been shown in the vertebrate peripheral nervous system. This suggests that similar developmental mechanisms have been conserved during evolution and that Drosophila can be used as a model system to study glial differentiation in vertebrates.