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The Journal of Neuroscience, November 30, 2005, 25(48):11210-11217; doi:10.1523/JNEUROSCI.2596-05.2005
Previous Article
Development/Plasticity/Repair
Functional Organization of a Schwann Cell Enhancer
Eric Denarier,1
Reza Forghani,1
Hooman F. Farhadi,1
Samar Dib,1
Nancy Dionne,1
Hana C. Friedman,1
Pierre Lepage,2
Thomas J. Hudson,2
Régen Drouin,3 and
Alan Peterson1
1Laboratory of Developmental Biology, Molecular Oncology Group H-5, McGill University Health Centre, Montreal, Quebec, Canada H3A 1A1, 2McGill University and Genome Quebec Innovation Centre, Montreal, Quebec, Canada H3A 1A4, and 3Service de Génétique Médicale, Département de Pédiatrie, Centre Hospitalier Universitaire de Sherbrooke, Hôpital Fleurimont, Sherbrooke, Québec, Canada J1H 5N4
Myelin basic protein (MBP) gene expression is conferred in oligodendrocytes and Schwann cells by different upstream enhancers. In Schwann cells, expression is controlled by a 422 bp enhancer lying -9 kb from the gene. We show here that it contains 22 mammalian conserved motifs 6 bp. To investigate their functional significance, different combinations of wild-type or mutated motifs were introduced into reporter constructs that were inserted in single copy at a common hypoxanthine phosphoribosyltransferase docking site in embryonic stem cells. Lines of transgenic mice were derived, and the subsequent qualitative and quantitative expression phenotypes were compared at different stages of maturation. In the enhancer core, seven contiguous motifs cooperate to confer Schwann cell specificity while different combinations of flanking motifs engage, at different stages of Schwann cell maturation, to modulate expression level. Mutation of a Krox-20 binding site reduces the level of reporter expression, whereas mutation of a potential Sox element silences reporter expression. This potential Sox motif was also found conserved in other Schwann cell enhancers, suggesting that it contributes widely to regulatory function. These results demonstrate a close relationship between phylogenetic footprints and regulatory function and suggest a general model of enhancer organization. Finally, this investigation demonstrates that in vivo functional analysis, supported by controlled transgenesis, can be a robust complement to molecular and bioinformatics approaches to regulatory mechanisms.
Key words: myelin basic protein; Schwann cell; enhancer; phylogenetic footprint; transgenesis; HPRT
Received June 23, 2005;
revised September 15, 2005;
accepted October 22, 2005.
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