Antagonistic action of Six3 and Prox1 at the gamma-crystallin promoter.
Gamma-crystallin genes are specifically expressed in the eye lens. Their promoters constitute excellent models to analyse tissue-specific gene expression. We investigated murine CRYGE/f promoters of different length in lens epithelial cell lines. The most active fragment extends from position -219 to +37. Computer analysis predicts homeodomain and paired-domain binding sites for all rodent CRYGD/e/f core promoters. As examples, we analysed the effects of Prox1 and Six3, which are considered important transcription factors involved in lens development. Because of endogenous Prox1 expression in N/N1003A cells, a weak stimulation of CRYGE/f promoter activity was found for PROX1. In contrast, PROX1 stimulated the CRYGF promoter 10-fold in CD5A cells without endogenous PROX1. In both cell lines Six3 repressed the CRYGF promoter to 10% of its basal activity. Our cell transfection experiments indicated that CRYG expression increases as Six3 expression decreases. Prox1 and Six3 act antagonistically on regulation of the CRYGD/e/f promoters. Functional assays using randomly mutated gammaF-crystallin promoter fragments define a Six3-responsive element between -101 and -123 and a Prox1-responsive element between -151 and -174. Since Prox1 and Six3 are present at the beginning of lens development, expression of CRYGD/e/f is predicted to remain low at this time. It increases as Six3 expression decreases during ongoing lens development.
Lengler
J
J
GSF-National Research Center for Environment and Health, Institute of Mammalian Genetics, D-85764 Neuherberg, Germany.
Krausz
E
E
Tomarev
S
S
Prescott
A
A
Quinlan
R A
RA
Graw
J
J
D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D001665:Binding Sites / Q000235:genetics; D002460:Cell Line; D016384:Consensus Sequence / Q000235:genetics; D003459:Crystallins / Q000037:antagonists & inhibitors* / Q000235:genetics*; D005136:Eye Proteins / Q000235:genetics / Q000502:physiology; D005786:Gene Expression Regulation / Q000235:genetics; D018398:Homeodomain Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D011401:Promoter Regions, Genetic / Q000235:genetics*; D011817:Rabbits; D051381:Rats; D012097:Repressor Proteins / Q000235:genetics; D016415:Sequence Alignment; D025521:Tumor Suppressor Proteins; D000097607:Homeobox Protein SIX3; D000098551:Prospero-Related Homeobox 1 Protein
D003459:Crystallins; D005136:Eye Proteins; D018398:Homeodomain Proteins; D009419:Nerve Tissue Proteins; D000071841:PAX6 Transcription Factor; D051761:Paired Box Transcription Factors; D012097:Repressor Proteins; D025521:Tumor Suppressor Proteins; D000097607:Homeobox Protein SIX3; D000098551:Prospero-Related Homeobox 1 Protein; C000605730:PAX6 protein, human; C000605732:Pax6 protein, mouse; C000605733:Pax6 protein, rat