Fig. 7. Comparison of Notch-dependent and Notch-independent gliogenic lineages. Schematic representations of five gliogenic lineages in the CNS (C) and PNS (A,B,D,E). The cells in which Notch is likely to be active are shown in blue. This assignment is based on the expression of the Su(H)-reporter gene (this work), and the mutant phenotypes of Notch and sanpodo embryos. The cells that receive Numb protein upon division, or those whose fate requires numb function, are shown in red. The gcm/repo-positive cell is boxed in yellow. Nubbin expression is shown in orange. (A-C) Three independent lineages in which Notch activates glial fate (this work) (Udolph et al., 2001). In all three lineages Nubbin is expressed in the presumptive glial cell before gcm expression initiates in that cell. (D) Chordotonal organ lineage (Orgogozo et al., 2001). In the chordotonal lineage, the ligament cell neither expresses Su(H)-reporter nor requires Notch activity for its fate specification. It expresses Nubbin only after REPO expression is observed in this cell, contrasting with the situation in three lineages shown in A-C. Whether there is a requirement or localization of Numb in IIIb, the ligament cell and the neuron is not known. (E) Lineage in which Notch represses glial fate (Van De Bor and Giangrande, 2001). Whether Nubbin is expressed in this lineage is unknown. SOP, sensory organ precursor cell; IP, intermediate precursor; IIa, IIb, secondary precursor cells; IIIb, tertiary precursor cell; g, glial cell; n, neuron; C, cap cell; e, ectodermal cell; S, scolopale cell; lig, ligament cell; To, tormogen cell; Tr, trichogen cell; Th, thecogen cell.