title: Comparative expression analysis of Pax3 and Pax7 during mouse myogenesis.
abstract: Pax3 and Pax7 are closely related transcription factors involved in the commitment of myogenic precursors in the developing trunk. However, it is not yet clear whether these genes are required for myogenic cell specification in the head and for post-somitic myogensis per se. In part, this uncertainty is due to the scarce information about their normal time course and pattern of expression. Here, we present a systematic immunohistochemical in situ analysis of spatiotemporal characteristics of Pax3 and Pax7 protein expression in comparison to that of MyoD and myogenin in the developing trunk and head muscles. The observed patterns of expression suggest that Pax3 is not involved in myogenesis in the head and its post-somitic expression in the trunk and limb muscles is mostly repressed after stage E13.5. In contrast, Pax7 expression is shared among all striated muscles and exhibits a uniform pattern. Pax7 is expressed only in mononucleated cells that either differentiate into myotubes or later form satellite cells. During development of head muscles, expression of Pax7 follows expression of MyoD and myogenin, implying that Pax7 is not required to induce the initial steps of the myogenic program in the head. In Pax7 homozygous mutants, in which muscle development proceeds normally, expression of Pax3 is indistinguishable from its wild-type pattern (i. e. absent), suggesting that after stage E13.5 myogenesis does not require Pax3 and Pax7. These data challenge the concept that Pax3 and Pax7 determine a persistent lineage of myogenic precursors in pre-natal and post-natal muscle development.
authors.affiliation: Klinik und Poliklinik für pädiatrische Hämatologie/Onkologie, Universitätsklinikum Münster, Germany.
authors.forename: David
authors.initials: D
authors.lastname: Horst
authors.forename: Svetlana
authors.initials: S
authors.lastname: Ustanina
authors.forename: Consolato
authors.initials: C
authors.lastname: Sergi
authors.forename: Gregor
authors.initials: G
authors.lastname: Mikuz
authors.forename: Herbert
authors.initials: H
authors.lastname: Juergens
authors.forename: Thomas
authors.initials: T
authors.lastname: Braun
authors.forename: Eugene
authors.initials: E
authors.lastname: Vorobyov
mesh_terms: D000818:Animals; D019070:Cell Lineage / Q000235:genetics; D018507:Gene Expression Regulation, Developmental; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D024510:Muscle Development / Q000235:genetics* / Q000502:physiology; D018482:Muscle, Skeletal / Q000166:cytology* / Q000502:physiology*; D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor / Q000172:deficiency / Q000235:genetics* / Q000502:physiology; D051761:Paired Box Transcription Factors / Q000096:biosynthesis / Q000235:genetics* / Q000502:physiology; D013234:Stem Cells / Q000166:cytology / Q000502:physiology
chemical_list: D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor; D051761:Paired Box Transcription Factors; C497322:Pax7 protein, mouse; C068686:Pax3 protein, mouse