Proneural genes influence gliogenesis in Drosophila

Fly glial cells in the wing peripheral nervous system of Drosophila melanogaster originate from underlying epithelial cells. Two findings indicate that gliogenesis is closely associated with neurogenesis. First, it only occurs in regions that also give rise to sensory organs. Second, in mutants that induce the development of ectopic sensory organs glial cells develop at new positions. These findings prompted a genetic analysis to establish whether glial and sensory organ differentiation depend on the same genes. Loss of function mutations of the achaete-scute complex lead to a significant reduction of sensory bristles and glial cells. Genes within the complex affect gliogenesis with different strength and display some functional redundancy. Thus, neurogenesis and gliogenesis share the same genetic pathway. Despite these similarities, however, the mechanism of action of the achaete-scute complex seems to be different in the two processes. Neural precursors express products of the complex, therefore the role of these genes on neurogenesis is direct. However, markers specific to glial cells do not colocalize with products of the achaete-scute complex, showing that the complex affects gliogenesis indirectly. These observations lead to the hypothesis that gliogenesis is induced by the presence of sensory organ cells, either the precursor or its progeny.