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abdominal A specifies one cell type in Drosophila by regulating one principal target gene

Véronique Brodu, Philip R. Elstob and Alex P. Gould*

Medical Research Council, National Institute for Medical Research, Mill Hill, London NW7 1AA, UK



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  		Fig. 1. abdA is necessary and sufficient to specify oenocytes. In this and subsequent figures, oenocytes are labelled with anti-Sal unless otherwise stated. (A,B) Anti-ß-galactosidase immunostaining of late embryos carrying svp-lacZ showing oenocyte clusters present in A1-A7 (indicated) in a wild-type background (A) but missing in an exdB108 mutant (B). (C-F) Late embryos homozygous for AntpRW10 (C) or Ubxbxd100 (D) display normal oenocyte clusters whereas those homozygous for abdAM1 (E) do not. Scr4 Antp25 (F) double mutants show a wild type oenocyte pattern. (G,H) Using en-GAL4 to drive UAS-Ubx (G) or UAS-abdA (H) indicates that AbdA but not Ubx can specify oenocytes in T1-T3 (indicated).

 


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  		Fig. 2. AbdA misexpression in the thoracic C1 lineage induces oenocytes. (A,B) Oenocyte precursors strongly express AbdA at stage 11 (A) but not stage 13 (B). (C) C1 (circled here and subsequently), labelled with anti-Rho, transiently expresses AbdA at stage 11. (D) Cartoon representing oenocyte precursors (red), chordotonal organ precursors C1-C3 (green), the tracheal pit (tp, green) and the dorsal Sal domain (pink) (Elstob et al., 2001Go) (E,F) Marking the C1-lineage with anti-Rho, reveals that sal-GAL4 and ato-GAL4 drive complementary expression of UAS-nlslacZ in the dorsal ectoderm including the oenocyte precursors (E) or in the C1 lineage (F) respectively. (G) ato-GAL4 driving UAS-abdA produces Alas-positive oenocytes in the thorax. (H) Numbers of thoracic oenocytes produced by misexpressing AbdA with the drivers indicated. This and subsequent graphs show the mean±1 s.d. for experimental (error bars) and wild-type abdominal counts (grey zone).

 


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  		Fig. 3. rho expression in C1 is regulated by abdA and is sufficient to induce thoracic oenocytes. (A-C) Rho is initiated in all C1 homologues at stage 10 (A) but is maintained at early (B) and late (C) stage 11 only in abdominal C1. (D) Ato is expressed in both thoracic and abdominal C1 at stage 10. (E) Rho fails to be maintained in abdAM1 mutants. (F) Rho is prolonged in the thorax by driving AbdA with ato-GAL4. (G-I) rho-lacZ recapitulates Rho maintenance in abdominal C1 (G) and is ectopically expressed in stage 11 thorax by driving AbdA (H) but not Ubx (I) with ato-GAL4. (J,K) ato-GAL4 driving Rho in either a wild type (J) or Scr4 Antp25 (K) background produces oenocytes in T1-T3. (L) The timing of induction is not altered by prematurely providing sSpi using en-GAL4. (M) Numbers of thoracic oenocytes produced by misexpressing Rho or sSpi with the drivers indicated.

 


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  		Fig. 4. Activating the EGFR pathway rescues the oenocyte deficit in abdA mutants. (A,B) AbdA driven by en-GAL4 (A) or ato-GAL4 (B) rescues oenocyte formation or Rho maintenance respectively in abdAM1 homozygotes. (C-E) sSpi driven by ato-GAL4 (C) or en-GAL4 (D) in an abdAM1 background rescues oenocyte formation. In addition, anti-Futsch/22C10 labelling reveals that a dorsal or lateral array of 5-7 chordotonal organs (arrowheads) is produced with en-GAL4 (E), instead of the dorsal triplet found in abdA mutants (Heuer and Kaufman, 1992Go). (F) The lack of oenocytes in ato1/Df(3R)p13 transheterozygotes (Elstob et al., 2001Go), is rescued by driving Rho with en-GAL4. (G) Providing EGFRACT with sal-GAL4 in an abdAM1 background produces a normal oenocyte pattern. (H) Numbers of oenocytes per abdominal cluster produced with the GAL4-driver/UAS combinations indicated.

 


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  		Fig. 5. Permissive model for oenocyte specification by abdA. At stage 10, Ato activates rho transcription in C1. Rho may or may not (?) process mSpi to sSpi in the Golgi apparatus at this stage, either way the response in the dorsal ectoderm is blocked (cross). By stage 11, the dorsal ectoderm acquires the full oenocyte prepattern and becomes competent for induction. At this time, Ato is no longer present but AbdA and its co-factor Exd maintain rho transcription, thus keeping sSpi available to activate the EGFR and in turn the hierarchy of oenocyte differentiation genes including: pointed (pnt), argos, spalt (sal), seven up (svp), ventral veins lacking (vvl), Hepatocyte nuclear factor 4 (Hnf4) and delta-aminolevulinate synthase (Alas).

 

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© The Company of Biologists Ltd 2002