Fig. 7.

A working model of gliogenesis in Drosophila type II lineages. Type II NBs divide asymmetrically to self-renew and give rise to INPs. Each INP also undergoes multiple rounds of asymmetrical division to self-renew and generates ganglion mother cells (GMCs), which divide once to produce two neurons. Although the exact source of glial precursors remains to be determined, Notch signaling is required for gliogenic switch. The glial precursor might initially be positive for Gcm, which then turn on the downstream glial genes, including repo (Jones, 2005; Viktorin et al., 2011). The glial precursor generates both astrocyte-like and ensheathing glia. The expansion of both glial subtypes is Notch dependent. Lineage identity governs multiple stages of glial development, controlling which INPs produce glial precursors, which glial precursors undergo apoptosis before repo is expressed, the expanding potential of glial precursors, the diversity of glial progeny and their final distribution.