The role of Sox6 in zebrafish muscle fiber type specification

Abstract

BackgroundThe 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.MethodsThe 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.ResultsEctopic 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.ConclusionsThe 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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13395-014-0026-2) contains supplementary material, which is available to authorized users.

Identification of novel MYO18A interaction partners required for myoblast adhesion and muscle integrity

“…We first determined the expression pattern of the four genes by in situ hybridization both in whole embryos at 24 hpf (hours post-fertilization), and in axial sections to distinguish the localization of these transcripts in slow and fast muscles31. Examination of more than 50 embryos hybridized with each probe from two independent experiments indicated that, in all these embryos, the expression of these genes could be detected in the somites.…”

The transcription factor SOX6 contributes to the developmental origins of obesity by promoting adipogenesis

“…The optical transparency of the zebrafish larva facilitates the visualization of adipocytes by Nile Red staining in whole-mount preparations (Flynn et al, 2009). Loss of Sox6 function in zebrafish has previously been shown to disrupt the differentiation of fast-twitch skeletal muscle fibers, but effects on adipocytes have not been addressed (Jackson et al, 2015). For the current study, control and sox6 homozygous null mutant larvae were stained with Oil Red O (Fig.…”

Nfix Induces a Switch in Sox6 Transcriptional Activity to Regulate MyHC-I Expression in Fetal Muscle

“…As a consequence, Sox6 -null mouse muscle displays increased levels of MyHC-I and a general switch toward a slower phenotype (Hagiwara et al., 2007, An et al., 2011, Quiat et al., 2011). Of note, studies in zebrafish have shown that Sox6 is restricted to fast-twitch fibers during embryonic muscle development and that ectopic Sox6 expression in adaxial cells (the slow muscle progenitors in zebrafish) leads to the silencing of slow-twitch genes (such as the slow MyHC isoform smyhc1 and the transcription factor prox1a ) (von Hofsten et al., 2008, Wang et al., 2011, Jackson et al., 2015). …”