Conserved roles for Oct4 homologues in maintaining multipotency during early vertebrate development.
All vertebrate embryos have multipotent cells until gastrulation but, to date, derivation of embryonic stem (ES) cell lines has been achieved only for mouse and primates. ES cells are derived from mammalian inner cell mass (ICM) tissue that express the Class V POU domain (PouV) protein Oct4. Loss of Oct4 in mice results in a failure to maintain ICM and consequently an inability to derive ES cells. Here, we show that Oct4 homologues also function in early amphibian development where they act as suppressors of commitment during germ layer specification. Antisense morpholino mediated PouV knockdown in Xenopus embryos resulted in severe posterior truncations and anterior neural defects. Gastrulation stage embryos showed reduced expression of genes associated with uncommitted marginal zone cells, while the expression of markers associated with more mature cell states was expanded. Importantly, we have tested PouV proteins from a number of vertebrate species for the ability to substitute Oct4 in mouse ES cells. PouV domain proteins from both Xenopus and axolotl could support murine ES cell self-renewal but the only identified zebrafish protein in this family could not. Moreover, we found that PouV proteins regulated similar genes in ES cells and Xenopus embryos, and that PouV proteins capable of supporting ES cell self-renewal could also rescue the Xenopus PouV knockdown phenotype. We conclude that the unique ability of Oct4 to maintain ES cell pluripotency is derived from an ancestral function of this class of proteins to maintain multipotency.
Morrison
Gillian M
GM
Centre Development in Stem Cell Biology, Institute for Stem Cell Research, School of Biological Sciences, University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3JQ, UK.
Brickman
Joshua M
JM
D000595:Amino Acid Sequence; D000818:Animals; D036703:Blastula / Q000166:cytology; D019070:Cell Lineage; D002478:Cells, Cultured; D002999:Clone Cells; D017124:Conserved Sequence; D004625:Embryo, Nonmammalian; D008969:Molecular Sequence Data; D039902:Multipotent Stem Cells / Q000166:cytology / Q000502:physiology*; D050814:Octamer Transcription Factor-3 / Q000737:chemistry / Q000235:genetics* / Q000502:physiology*; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D020539:Sequence Analysis, Protein; D017386:Sequence Homology, Amino Acid; D013234:Stem Cells / Q000166:cytology* / Q000502:physiology; D014981:Xenopus / Q000196:embryology* / Q000378:metabolism
D050814:Octamer Transcription Factor-3; D016376:Oligonucleotides, Antisense