Fig. 3. Notch is necessary, but not sufficient, for tubule cell division. Embryos stained for Cut reveal that the tubules of N mutant embryos (B) are shorter than wild type (A) (arrows). This results from a dramatic reduction in cell division from M17, demonstrated by failure to incorporate BrdU. Compare stained cells in the distal region of dissected tubules from stage 12 wild type (arrowheads in C) with the absence of incorporation in tubules from N mutant embryos of the same age (arrowhead in D). Driving the expression of activated Notch (hs-N^intra) from 5-10.5 hours in the tubules fails to rescue cell division and tubule growth in AS-C^–/– [Df(svr)] embryos (compare arrows in E,F). Ubiquitous expression of an activated EGF receptor (UAS-^top) also fails to rescue the tubule phenotype in either N (arrow in G) or AS-C^–/– embryos (arrow in H). A,B,E-H are stained for Cut.

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