title: Mouse muscle identity: the position-dependent and fast fiber-specific expression of a transgene in limb muscles is methylation-independent and cell-autonomous.
abstract: We previously characterised transgenic mice in which fast-muscle-specific regulatory sequences from the human aldolase A pM promoter drive the chloramphenicol acetyltransferase gene expression. Mutation of a NF1/MEF2 binding site (M2 motif) in this promoter does not affect fibre-type specificity of the transgene but modifies its expression in a subset of fast-twitch fibres at the limb level, preferentially affecting distal limb muscles. We investigated the molecular and cellular bases of this peculiar expression pattern that provided an adequate model to characterise the mechanisms responsible for muscle positional information. By direct electrotransfer of mutated M2 construct in adult muscle, we demonstrate that positional differences in mutated M2 transgene expression are not observed when the transgene is not integrated into chromatin. Also, this transgene expression pattern does not seem to be correlated with the extent of CpG methylation in its promoter sequence. Finally, we show that positional values reflected by CAT levels are maintained in primary cultures established from different adult limb muscles, as well as in heterotopically transplanted muscles. Our results suggest that mutation of the M2 site contributes to reveal a molecular memory of fibre fate that would be set up on pM promoter during development and persist into adulthood possibly through a chromatin imprint maintained in satellite cells associated with various limb muscles.
authors.affiliation: Département de Génétique, Développement et Pathologie Moléculaire, Institut Cochin-INSERM U 567, CNRS UMR 8104, and Université René Descartes Paris V, 24 rue du Faubourg St-Jacques, Paris, France.
authors.forename: Valerie
authors.initials: V
authors.lastname: Ngô-Muller
authors.forename: Anne
authors.initials: A
authors.lastname: Bertrand
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Concordet
authors.forename: Dominique
authors.initials: D
authors.lastname: Daegelen
mesh_terms: D020816:Amino Acid Motifs; D000818:Animals; D002478:Cells, Cultured; D002843:Chromatin / Q000378:metabolism; D018899:CpG Islands; D019175:DNA Methylation; D005121:Extremities / Q000502:physiology; D005260:Female; D005634:Fructose-Bisphosphate Aldolase / Q000378:metabolism; D006614:Hindlimb / Q000378:metabolism; D008745:Methylation; D051379:Mice; D008822:Mice, Transgenic; D018656:Muscle Fibers, Fast-Twitch / Q000502:physiology*; D009132:Muscles / Q000378:metabolism / Q000502:physiology*; D009154:Mutation; D011401:Promoter Regions, Genetic; D016378:Tissue Transplantation; D015533:Transcriptional Activation; D014162:Transfection; D019076:Transgenes
chemical_list: D002843:Chromatin; D005634:Fructose-Bisphosphate Aldolase