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A network of transcriptional repression specifies muscle fibre type in the zebrafish embryo

ABSTRACT: The zebrafish u-boot (ubo) gene encodes the transcription factor Prdm1, which is essential for the specification of the primary slow twitch muscle fibres that derive from adaxial cells. Here we show that Prdm1 executes this function by acting as a transcriptional repressor. Expression of the slow twitch isoform of the myosin heavy chain in adaxial cells is achieved by Prdm1 mediated repression of the transcriptional repressor Sox6. Using Chromatin immuno precipitation (ChIP) we found that genes encoding fast specific isoforms of sarcomeric proteins are direct targets of Prdm1. These genes are ectopically expressed in the adaxial cells of ubotp39 mutant embryos, suggesting that Prdm1 promotes slow twitch fibre differentiation by acting both as a global repressor of fast fibre specific genes as well as of a repressor of slow specific genes. Keywords: ChIP-chip

ORGANISM(S): Danio rerio

PROVIDER: GSE10883 | GEO | 2008/07/03

SECONDARY ACCESSION(S): PRJNA107277

REPOSITORIES: GEO

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Project description:The zebrafish u-boot (ubo) gene encodes the transcription factor Prdm1, which is essential for the specification of the primary slow twitch muscle fibres that derive from adaxial cells. Here we show that Prdm1 executes this function by acting as a transcriptional repressor. Expression of the slow twitch isoform of the myosin heavy chain in adaxial cells is achieved by Prdm1 mediated repression of the transcriptional repressor Sox6. Using Chromatin immuno precipitation (ChIP) we found that genes encoding fast specific isoforms of sarcomeric proteins are direct targets of Prdm1. These genes are ectopically expressed in the adaxial cells of ubotp39 mutant embryos, suggesting that Prdm1 promotes slow twitch fibre differentiation by acting both as a global repressor of fast fibre specific genes as well as of a repressor of slow specific genes. Keywords: ChIP-chip Genomic array design. Microarrays were designed as described below and manufactured by Agilent Technologies (www.agilent.com). We have previously described the ChIP-chip technique in zebrafish and the design of promoter microarrays which cover a 2kb region around the transcription start sites (TSSs) of 11,512 zebrafish genes based on Zv4 (Wardle et al, 2006. Genome Biology 7:R71). In order to capture additional regulatory information further from the basal promoter region we also designed an expanded set of 60mer probes that cover 9kb upstream and 3kb downstream of the TSS of these genes using the same parameters as for the 2kb microarrays. These probe sequences were re-mapped to Zv6 over the course of the project and the coordinates given are for Zv6. We also incorporated several sets of control probes, both positive and negative. On each array there are 769 negative probes designed against zebrafish gene desert regions and Arabidopsis thaliana genes. In addition we included duplicates of promoter probes for several genes that we anticipated may be bound by factors of interest for this and other studies (tnnt3a, mylz2, myhz2, wnt11, flh, vent, msgn1, myod, fgf8, pcdh8) and these probes are arrayed on both slides slide. Finally on each array there are 1804 controls added by Agilent. The final design contained 352,490 probes divided between two microarray slides. Further information on design and manufacture of the microarrays can be found at the Agilent Technologies website.

Project description:The basic helix-loop-helix factor Myod initiates skeletal muscle differentiation by directly and sequentially activating sets of muscle differentiation genes, including those encoding muscle contractile proteins. We hypothesize that Pbx homeodomain proteins direct Myod to a subset of its transcriptional targets, in particular fast twitch muscle differentiation genes, thereby regulating the competence of muscle precursor cells to differentiate. We have previously shown that Pbx proteins bind with Myod on the promoter of the zebrafish fast muscle gene mylpfa and that Pbx proteins are required for Myod to activate mylpfa expression and the fast-twitch muscle-specific differentiation program in zebrafish embryos. Here we have investigated the interactions of Pbx with another muscle fiber-type regulator, Prdm1a, a SET-domain DNA-binding factor that directly represses mylpfa expression and fast muscle differentiation. The prdm1a mutant phenotype, early and increased fast muscle differentiation, is the opposite of the Pbx-null phenotype, delayed and reduced fast muscle differentiation. To determine whether Pbx and Prdm1a have opposing activities on a common set of genes, we used RNA-seq analysis to globally assess gene expression in zebrafish embryos with single- and double-losses-of-function for Pbx and Prdm1a. We find that the levels of expression of certain fast muscle genes are increased or approximately wild type in pbx2/4-MO;prdm1a-/- embryos, suggesting that Pbx activity normally counters the repressive action of Prdm1a for a subset of the fast muscle program. However, other fast muscle genes require Pbx but are not regulated by Prdm1a. Thus, our findings reveal that subsets of the fast muscle program are differentially regulated by Pbx and Prdm1a. Our findings provide an example of how Pbx homeodomain proteins act in a balance with other transcription factors to regulate subsets of a cellular differentiation program. Total RNA samples were genotyped and pooled for 4 sample types: control-MO;prdm1+/+; control-MO;prdm1-/-; pbx2/4-MO;prdm1+/+; and pbx2/4-MO;prdm1-/- embryos at the 10 somite (s) stage from three independent sets of egg collections/injections.

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A network of transcriptional repression specifies muscle fibre type in the zebrafish embryo

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