An in vivo requirement for the mediator subunit med14 in the maintenance of stem cell populations.
Bottom Line: In planarians, RNAi knockdown demonstrated a requirement for med14 and many other Mediator components in adult stem cell maintenance and regeneration.Multiple stem/progenitor cell populations were observed to be reduced or absent in zebrafish med14 mutant embryos.Taken together, our results show a critical, evolutionarily conserved, in vivo function for Med14 (and Mediator) in stem cell maintenance, distinct from a general role in transcription.
Affiliation: Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Program in Developmental and Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 0A4, Canada.Show MeSH
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Mentions: A novel (s231) allele of the logelei (log) mutant was previously isolated in a screen for mutations affecting cardiovascular development (Jin et al., 2007). At 1-day post-fertilization (dpf), log mutant hearts appeared completely normal (Figure 1A). Cardiac defects first became apparent in log mutants by 2 dpf, with a failure of heart looping (Figures 1B and 1C). By RNA in situ hybridization (ISH), expression of the chamber-specific markers myh6/amhc (atrium) and vmhc (ventricle) was normal in log mutants (Figures 1D–1I). The first observable log phenotype, a defect in brain ventricle inflation (Schier et al., 1996), was apparent by 36-hr post-fertilization (hpf). Following this, a developmental delay became apparent in log mutants from 48–96 hpf, including absence of pectoral fin elongation and semi-circular canals of the otic vesicle (Figures 1J–1M, arrowheads). Head-trunk angle, a measure of developmental progression (Kimmel et al., 1995), was largely fixed in log mutants by 48 hpf (Figure 1N). Despite this arrest in development, there was not an apparent increase in apoptosis or overt proliferative defect (Figure S1).
Affiliation: Department of Molecular Genetics, University of Toronto, Toronto, ON M5S 1A8, Canada; Program in Developmental and Stem Cell Biology, The Hospital for Sick Children, Toronto, ON M5G 0A4, Canada.