TRANSCRIPTOME 2002: From Functional Genomics to Systems
Downstream of MyoD: An in vivo 27-time Point Temporal Series, Defining Novel Gene Transcriptional Pathways in Muscle
Po Zhao1, Simona Iezzi2, Ethan Carver3, Devin Dressman1, Thomas Gridley3, Vittorio Sartorelli2, and Eric P Hoffman1, 1Children’s National Medical Center, George Washington University, Washington DC, 2NIAMS, National Institutes of Health, Bethesda, MD, 3The Jackson Laboratory, Bar Harbor, ME
Temporal expression profiling was utilized to define transcriptional regulatory pathways in vivo in a mouse muscle regeneration model. Potential downstream targets of MyoD were identified by temporal expression in a 6 time point cardiotoxin (CTX) degeneration/regeneration series in mouse muscle in vivo. Nucleated clusters with known downstream targets were further queried by promoter database mining, and gel shift and supershift assays; Slug, calpain6, Peg3, Sox11 and nectin3 were all identified as novel MyoD targets. Slug, a member of the snail/slug family of zinc finger transcriptional repressors critical for mesoderm/ectoderm development, was further shown as a downstream target by promoter/reporter constructs, and demonstration of defective muscle regeneration in Slug null mice. The E box consensus identified in genes regulated by MyoD in vivo was found to be considerably more stringent (CACAG[G/C]TGT) than the in vitro consensus (CAnnTG). We then continued the temporal expression profiling approach with expression profiling of 27 time points to more finely define temporally regulated gene clusters. In addition, we defined potential downstream targets of Slug by expression profiling muscle regeneration in Slug null mice. The results reported here demonstrate that transcriptional pathways can be defined in vivo in vertebrates, not only for genes downstream of well characterized transcription factors (e.g. MyoD), but also for less well-characterized transcription factors (e.g. Slug).
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