QUICK SEARCH:   [advanced] Author: Keyword(s):
Home     Help     Feedback     Subscriptions     Archive     Search     Table of Contents

First published online 31 March 2004
doi: 10.1242/dev.01084

This Article Summary Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Sengupta, A. K. Articles by Müller, J. Search for Related Content PubMed PubMed Citation Articles by Sengupta, A. K. Articles by Müller, J.

General transcriptional silencing by a Polycomb response element in Drosophila

Aditya K. Sengupta^1,2,*, Antje Kuhrs^1,* and Jürg Müller^1,2,

¹ EMBL, Gene Expression Programme, Meyerhofstrasse 1, 69117, Heidelberg, Germany
² Max-Planck-Institute für Entwicklungsbiologie, Spemannstrasse 35/III, 72076 Tübingen, Germany

View larger version (82K): [in a new window]   Fig. 3. Silencing by PRE depends on PcG gene function. X-gal stainings of wing imaginal discs from wt and Su(z)12 mutant larvae carrying the indicated reporter genes. Note that silencing of both reporter genes is lost in Su(z)122/Su(z)123 transheterozygous larvae. The Su(z)12 mutant wing discs are smaller than wt wing discs, presumably as they are partially transformed into haltere discs due to misexpression of Hox genes (see Birve et al., 2001).

View larger version (78K): [in a new window]   Fig. 1. The Ubx PRE indiscriminately silences reporter genes that contain an enhancer and a TATA box minimal promoter. (Left) Schematic drawing of the reporter constructs that contain the 1.6 kb Ubx PRE fragment (hatched rectangle) flanked by FRT sequences upstream of either the vgQE, vgBE or dppWE enhancer (black rectangle) linked to hsp70 TATA box minimal promoter (white circle) followed by hsp70 5' UTR (thin line) and lacZ gene (white box). A transgene derivative that lacks the PRE (below) can be created by flp-mediated excision of the PRE fragment. (Right) X-gal staining of wing imaginal discs from transformant lines carrying the indicated reporter gene construct with (left column) and without (right column) the PRE fragment. In each case, the disc on the left is from the original transformant line and the disc on the right is from its derivative line, obtained after excision of the PRE in the germline. In the absence of the PRE fragment, the vgQE, dppWE and vgBE enhancer each direct lacZ expression in the pattern previously described (Williams et al., 1994; Kim et al., 1996; Müller and Basler, 2000). The pattern directed by the vgBE enhancer depends on its relative orientation to the TATA box promoter; in this orientation it activates expression primarily in the hinge and notum region (Williams et al., 1994). Note that in the presence of the PRE fragment, all three reporter genes are completely silenced.

View larger version (66K): [in a new window]   Fig. 2. The Ubx PRE indiscriminately silences reporter genes that contain an enhancer and the Ubx proximal promoter. (Left) The reporter genes are very similar to those shown in Fig. 1 but the TATA box minimal promoter is replaced by a 4.1 kb fragment that contains the proximal Ubx promoter and 5' UTR (thin line, transcription start site marked by arrow). (Right) X-gal staining of wing imaginal discs from transformant lines carrying the indicated reporter gene construct with (left column) and without (right column) the PRE fragment; in each case, the disc on the left is from the original transformant line and the disc on the right is from its derivative line, obtained after excision of the PRE in the germline. Note that in the presence of the PRE fragment all three reporter genes are completely silenced. In the derivative lines lacking PRE, the intensity of X-gal staining suggests that the vgQE enhancer directs higher expression levels from the Ubx promoter than from the TATA box promoter; conversely, the dppWE enhancer activates expression more potently from the TATA box promoter than from the Ubx promoter (compare with Fig. 1).

View larger version (55K): [in a new window]   Fig. 4. Long-term silencing by PRE requires its continuous presence in the transgene. X-gal stainings of wing imaginal discs from larvae that carry the transgenes indicated on the left. Larvae were either not heat-shocked (no hs) or were heat-shocked for 1 hour to induce flp expression and then allowed to develop for the indicated number of hours before analysis (hs + xy hours). Note the loss of expression after flp-mediated excision of the PRE fragment during larval development. (Bottom) Time-course experiment; no X-gal signal is detected 8 hours after flp induction but robust X-gal staining is observed 12 hours after flp induction. Note that flp-mediated excision only occurs in a fraction of the cells, and that the number of X-gal positive cells increases over time due to cell division.