The enhancer of trithorax and polycomb corto interacts with cyclin G in Drosophila.
BACKGROUND
Polycomb (PcG) and trithorax (trxG) genes encode proteins involved in the maintenance of gene expression patterns, notably Hox genes, throughout development. PcG proteins are required for long-term gene repression whereas TrxG proteins are positive regulators that counteract PcG action. PcG and TrxG proteins form large complexes that bind chromatin at overlapping sites called Polycomb and Trithorax Response Elements (PRE/TRE). A third class of proteins, so-called "Enhancers of Trithorax and Polycomb" (ETP), interacts with either complexes, behaving sometimes as repressors and sometimes as activators. The role of ETP proteins is largely unknown.


RESULTS
In a two-hybrid screen, we identified Cyclin G (CycG) as a partner of the Drosophila ETP Corto. Inactivation of CycG by RNA interference highlights its essential role during development. We show here that Corto and CycG directly interact and bind to each other in embryos and S2 cells. Moreover, CycG is targeted to polytene chromosomes where it co-localizes at multiple sites with Corto and with the PcG factor Polyhomeotic (PH). We observed that corto is involved in maintaining Abd-B repression outside its normal expression domain in embryos. This could be achieved by association between Corto and CycG since both proteins bind the regulatory element iab-7 PRE and the promoter of the Abd-B gene.


CONCLUSIONS
Our results suggest that CycG could regulate the activity of Corto at chromatin and thus be involved in changing Corto from an Enhancer of TrxG into an Enhancer of PcG.
Salvaing
Juliette
J
Laboratoire de Biologie du Développement, UMR 7622, Centre National de la Recherche Scientifique (CNRS), Université Pierre et Marie Curie-Paris 6, Paris, France.
Nagel
Anja C
AC
Mouchel-Vielh
Emmanuèle
E
Bloyer
Sébastien
S
Maier
Dieter
D
Preiss
Anette
A
Peronnet
Frédérique
F
D000818:Animals; D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone / Q000502:physiology*; D056746:Cyclin G; D016213:Cyclins / Q000378:metabolism / Q000502:physiology*; D004268:DNA-Binding Proteins / Q000378:metabolism / Q000502:physiology*; D029721:Drosophila Proteins / Q000378:metabolism / Q000502:physiology*; D004625:Embryo, Nonmammalian; D005786:Gene Expression Regulation; D063150:Polycomb Repressive Complex 1; D011485:Protein Binding; D020218:Response Elements; D020798:Two-Hybrid System Techniques
D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D056746:Cyclin G; D016213:Cyclins; D004268:DNA-Binding Proteins; D029721:Drosophila Proteins; C066770:Pc protein, Drosophila; C110988:corto protein, Drosophila; C512571:trx protein, Drosophila; D063150:Polycomb Repressive Complex 1