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. 2011 Dec 15;25(24):2644–2658. doi: 10.1101/gad.171959.111

Figure 2.

Figure 2.

N signaling promotes cell growth and dedifferentiation of IPs into ectopic NBs. (A) Ectopic NBs (Dpn+, Pros−; yellow arrowheads) in ada mutant clones. From this panel on, yellow arrowheads mark ectopic NBs. (B) Ectopic NBs in ada mutant clones contain enlarged nucleoli compared with IPs in wild-type clones (white arrowheads). (C) Quantification of nucleolar/cellular volume ratio in normal or ectopic NBs within ada mutant or N overactivation clones. (*) P < 0.0001; n = 8–10. (D) CldU pulse and chase revealed a cell cycle delay of ectopic NBs in ada mutant clones. After a 20-h chase, CldU was undetectable in the primary NBs (bracket) within wild-type or ada mutant clones. The only cells retaining the CldU label (white arrowheads) in wild-type clones were terminally differentiated neurons furthest from the primary NB. In contrast, CldU was detectable in some ectopic NBs within ada mutant clones (bigger nucleoli; yellow arrowheads). (Green) CldU; (red) fibrillarin; (blue) GFP. (E) Cell lineage tracing showing that mature IPs of ada mutants could dedifferentiate back into type II NBs (yellow bracket; identified by the expression of NB marker Mira and the absence of mature IP and GMC marker Ase), while wild-type mature IPs only generate GMCs or neurons (closed arrowhead; Mira−). Note that Ase is specifically expressed in type I but not type II NBs. A type I NB (Ase+Mira+) is shown in the left panel. (F) A schematic model summarizing cell lineage tracing data shown in E. (Green) Mira labeling NBs, immature IPs, and mature IPs; (red) lacZ; (blue) Ase. In ada mutants, immature and mature IPs can dedifferentiate into type II NBs (purple arrows). (G) Ectopic NBs induced by N overactivation specifically in mature IPs (driven by Erm-GAL4) contain larger nucleoli (yellow arrowheads) than control IPs (white arrowhead). (H) A working model proposing that when N signaling is overactivated (N↑), immature IPs (or mature IPs, not shown) gradually increase cellular and nucleolar sizes and dedifferentiate into a stem cell. Bar, 10 μm.

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