Glia development in the embryonic CNS of Drosophila

Essential genes for astroglial development and axon pathfinding during zebrafish embryogenesis

The formation of the central nervous system depends on the coordinated development of neural and glial cell types that arise from a common precursor. Using an existing group of zebrafish mutants generated by viral insertion, we performed a "shelf-screen" to identify genes necessary for astroglial development and axon scaffold formation. We screened 274 of 315 viral insertion lines using antibodies that label axons (anti-Acetylated Tubulin) and astroglia (anti-Gfap) and identified 25 mutants with defects in gliogenesis, glial patterning, neurogenesis, and axon guidance. We also identified a novel class of mutants affecting radial glial cell numbers. Defects in astroglial patterning were always associated with axon defects, supporting an important role for axon-glial interactions during axon scaffold development. The genes disrupted in these viral lines have all been identified, providing a powerful new resource for the study of axon guidance, glio- and neurogenesis, and neuron-glial interactions during development of the vertebrate CNS.

Asymmetric Prospero localization is required to generate mixed neuronal/glial lineages in the Drosophila CNS

In many organisms, single neural stem cells can generate both neurons and glia. How are these different cell types produced from a common precursor? In Drosophila, glial cells missing (gcm) is necessary and sufficient to induce glial development in the CNS. gcm mRNA has been reported to be asymmetrically localized to daughter cells during precursor cell division, allowing the daughter cell to produce glia while precursor cell generates neurons. We show that (1) gcm mRNA is uniformly distributed during precursor cell divisions; (2) the Prospero transcription factor is asymmetrically localized into the glial-producing daughter cell; (3) Prospero is required to upregulate gcm expression and induce glial development; and (4) mislocalization of Prospero to the precursor cell leads to ectopic gcm expression and the production of extra glia. We propose a novel model for the separation of glia and neuron fates in mixed lineages in which the asymmetric localization of Prospero results in upregulation of gcm expression and initiation of glial development in only precursor daughter cells.