title: Alternate PAX3 and PAX7 C-terminal isoforms in myogenic differentiation and sarcomagenesis.
abstract: OBJECTIVE
  Pax3 and Pax7 are closely related genes that are involved in commitment of cells to a myogenic lineage during skeletal muscle development and regeneration. Several Pax3 and Pax7 transcripts are expressed from the genes, generating different isoforms with potentially distinct DNA binding and transactivation properties. The aim of this study was to investigate the implication of Pax3 and Pax7 C-terminal isoforms during myogenic differentiation and tumorigenesis, since fusions involving these genes are commonly associated with alveolar rhabdomyosarcoma (ARMS).
  
  
  METHODS
  Uncommitted (mouse mesenchymal stem cells, MSCs) and committed (C2C12) myogenic precursor cells were stably transfected with PAX3/FKHR and PAXC7/ FKHR fusion genes. We analysed gene and protein expression comparing the newly generated cells with the parental cells, to determine the functional importance of Pax3 and Pax7 C-terminal isoforms.
  
  
  RESULTS
  We found that the transcript Pax3c was expressed at low levels in undifferentiated C2C12 and MSCs cells, but its expression levels increased considerably at later stages of differentiation. However, expression levels of Pax3d transcript increased only slightly after differentiation. Pax7 transcripts, present before differentiation in committed C2C12 cells, but absent in uncommitted MSCs, increased noticeably in MSCs after differentiation. We also found that the presence of PAX/FKHR fusions prevented both C2C12 and MSC cells from terminal myogenic differentiation and increased the expression of discrete endogenous Pax3/7 transcripts, in particular Pax3d and Pax7B.
  
  
  CONCLUSIONS
  Our results suggest that both Pax3 and Pax7 transcripts are required for commitment of cells to the myogenic lineage, with each transcript having a distinct role. More specifically, the Pax3c isoform may be required for terminal myogenic differentiation whereas the Pax3d isoform may be involved in undifferentiated cell maintenance and/or proliferation.
authors.affiliation: School of Exercise Biomedical and Health Science, Edith Cowan University, Joondalup, Australia.
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Charytonowicz
authors.forename: Igor
authors.initials: I
authors.lastname: Matushansky
authors.forename: Mireia
authors.initials: M
authors.lastname: Castillo-Martin
authors.forename: Todd
authors.initials: T
authors.lastname: Hricik
authors.forename: Carlos
authors.initials: C
authors.lastname: Cordon-Cardo
authors.forename: Mel
authors.initials: M
authors.lastname: Ziman
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002460:Cell Line; D019070:Cell Lineage / Q000502:physiology; D006801:Humans; D007150:Immunohistochemistry; D059630:Mesenchymal Stem Cells / Q000166:cytology; D051379:Mice; D032342:Muscle Cells / Q000166:cytology* / Q000378:metabolism; D000072041:PAX3 Transcription Factor; D051763:PAX7 Transcription Factor / Q000235:genetics* / Q000378:metabolism*; D051761:Paired Box Transcription Factors / Q000235:genetics* / Q000378:metabolism*; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018232:Rhabdomyosarcoma, Alveolar / Q000235:genetics* / Q000378:metabolism; D014162:Transfection
chemical_list: D000072041:PAX3 Transcription Factor; C489409:PAX3 protein, human; D051763:PAX7 Transcription Factor; C497321:PAX7 protein, human; D051761:Paired Box Transcription Factors; C497322:Pax7 protein, mouse; D020033:Protein Isoforms; D011993:Recombinant Fusion Proteins; C068686:Pax3 protein, mouse