title: The role of Sox6 in zebrafish muscle fiber type specification.
abstract: BACKGROUND
  The transcription factor Sox6 has been implicated in regulating muscle fiber type-specific gene expression in mammals. In zebrafish, loss of function of the transcription factor Prdm1a results in a slow to fast-twitch fiber type transformation presaged by ectopic expression of sox6 in slow-twitch progenitors. Morpholino-mediated Sox6 knockdown can suppress this transformation but causes ectopic expression of only one of three slow-twitch specific genes assayed. Here, we use gain and loss of function analysis to analyse further the role of Sox6 in zebrafish muscle fiber type specification.
  
  
  METHODS
  The GAL4 binary misexpression system was used to express Sox6 ectopically in zebrafish embryos. Cis-regulatory elements were characterized using transgenic fish. Zinc finger nuclease mediated targeted mutagenesis was used to analyse the effects of loss of Sox6 function in embryonic, larval and adult zebrafish. Zebrafish transgenic for the GCaMP3 Calcium reporter were used to assay Ca2+ transients in wild-type and mutant muscle fibres.
  
  
  RESULTS
  Ectopic Sox6 expression is sufficient to downregulate slow-twitch specific gene expression in zebrafish embryos. Cis-regulatory elements upstream of the slow myosin heavy chain 1 (smyhc1) and slow troponin c (tnnc1b) genes contain putative Sox6 binding sites required for repression of the former but not the latter. Embryos homozygous for sox6 null alleles expressed tnnc1b throughout the fast-twitch muscle whereas other slow-specific muscle genes, including smyhc1, were expressed ectopically in only a subset of fast-twitch fibers. Ca2+ transients in sox6 mutant fast-twitch fibers were intermediate in their speed and amplitude between those of wild-type slow- and fast-twitch fibers. sox6 homozygotes survived to adulthood and exhibited continued misexpression of tnnc1b as well as smaller slow-twitch fibers. They also exhibited a striking curvature of the spine.
  
  
  CONCLUSIONS
  The Sox6 transcription factor is a key regulator of fast-twitch muscle fiber differentiation in the zebrafish, a role similar to that ascribed to its murine ortholog.
authors: ASTAR Institute of Molecular and Cell Biology, Proteos, 61 Biopolis Drive, Singapore, 138673 Republic of Singapore ; Bateson Centre, University of Sheffield, Western Bank, Sheffield, S10 2TN UK.
authors: Harriet E
authors: HE
authors: Jackson
authors: ASTAR Institute of Molecular and Cell Biology, Proteos, 61 Biopolis Drive, Singapore, 138673 Republic of Singapore.
authors: Yosuke
authors: Y
authors: Ono
authors: ASTAR Institute of Molecular and Cell Biology, Proteos, 61 Biopolis Drive, Singapore, 138673 Republic of Singapore.
authors: Xingang
authors: X
authors: Wang
authors: Bateson Centre, University of Sheffield, Western Bank, Sheffield, S10 2TN UK.
authors: Stone
authors: S
authors: Elworthy
authors: Bateson Centre, University of Sheffield, Western Bank, Sheffield, S10 2TN UK.
authors: Vincent T
authors: VT
authors: Cunliffe
authors: ASTAR Institute of Molecular and Cell Biology, Proteos, 61 Biopolis Drive, Singapore, 138673 Republic of Singapore ; Lee Kong Chian School of Medicine, Nanyang Technological University, Proteos, 61 Biopolis Drive, Singapore, 138673 Republic of Singapore ; Department of Medicine, Imperial College, South Kensington Campus, London, SW7 2AZ UK.
authors: Philip W
authors: PW
authors: Ingham
keywords: Sox6; fiber type; muscle; myosin; spinal curvature; troponin; zebrafish