ZFIN ID: ZDB-PUB-130710-40
Pbx and Prdm1a transcription factors differentially regulate subsets of the fast skeletal muscle program in zebrafish
Yao, Z., Farr, G.H., Tapscott, S.J., and Maves, L.
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.
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