title: The primitive streak gene Mixl1 is required for efficient haematopoiesis and BMP4-induced ventral mesoderm patterning in differentiating ES cells.
abstract: The homeobox gene Mixl1 is expressed in the primitive streak of the gastrulating embryo, and marks cells destined to form mesoderm and endoderm. The role of Mixl1 in development of haematopoietic mesoderm was investigated by analysing the differentiation of ES cells in which GFP was targeted to one (Mixl1(GFP/w)) or both (Mixl1(GFP/GFP)) alleles of the Mixl1 locus. In either case, GFP was transiently expressed, with over 80% of cells in day 4 embryoid bodies (EBs) being GFP(+). Up to 45% of Mixl1(GFP/w) day 4 EB cells co-expressed GFP and the haemangioblast marker FLK1, and this doubly-positive population was enriched for blast colony forming cells (BL-CFCs). Mixl1-null ES cells, however, displayed a haematopoietic defect characterised by reduced and delayed Flk1 expression and a decrease in the frequency of haematopoietic CFCs. These data indicated that Mixl1 was required for efficient differentiation of cells from the primitive streak stage to blood. Differentiation of ES cells under serum-free conditions demonstrated that induction of Mixl1- and Flk1-expressing haematopoietic mesoderm required medium supplemented with BMP4 or activin A. In conclusion, this study has revealed an important role for Mixl1 in haematopoietic development and demonstrates the utility of the Mixl1(GFP/w) ES cells for evaluating growth factors influencing mesendodermal differentiation.
authors.affiliation: Monash Immunology and Stem Cell Laboratories, Monash University, Clayton, VIC 3800, Australia.
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Ng
authors.forename: Lisa
authors.initials: L
authors.lastname: Azzola
authors.forename: Koula
authors.initials: K
authors.lastname: Sourris
authors.forename: Lorraine
authors.initials: L
authors.lastname: Robb
authors.forename: Edouard G
authors.initials: EG
authors.lastname: Stanley
authors.forename: Andrew G
authors.initials: AG
authors.lastname: Elefanty
mesh_terms: D028341:Activins / Q000378:metabolism; D000483:Alleles; D000818:Animals; D019521:Body Patterning; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins / Q000378:metabolism*; D015820:Cadherins / Q000378:metabolism; D002454:Cell Differentiation; D049109:Cell Proliferation; D016895:Culture Media, Serum-Free / Q000494:pharmacology; D017931:DNA Primers / Q000737:chemistry; D004622:Embryo, Mammalian / Q000166:cytology*; D005434:Flow Cytometry; D018507:Gene Expression Regulation, Developmental; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006410:Hematopoiesis / Q000502:physiology*; D006579:Heterozygote; D018398:Homeodomain Proteins / Q000235:genetics* / Q000502:physiology*; D028322:Inhibin-beta Subunits / Q000378:metabolism; D008648:Mesoderm / Q000378:metabolism*; D051379:Mice; D018345:Mice, Knockout; D008856:Microscopy, Fluorescence; D012313:RNA / Q000378:metabolism; D011995:Recombination, Genetic; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000166:cytology*; D013997:Time Factors
chemical_list: C525810:Bmp4 protein, mouse; D055415:Bone Morphogenetic Protein 4; D019485:Bone Morphogenetic Proteins; D015820:Cadherins; D016895:Culture Media, Serum-Free; D017931:DNA Primers; D018398:Homeodomain Proteins; C464781:Mixl1 protein, mouse; C422405:activin A; D028341:Activins; D049452:Green Fluorescent Proteins; D012313:RNA; D028322:Inhibin-beta Subunits