Figure S2: A few areas <strong>of</strong> SOX7 + <strong>cells</strong> <strong>in</strong> <strong>the</strong> <strong>FGF</strong>4 –/– cell l<strong>in</strong>e after DE-<strong>in</strong>duction. Cells were differentiated for 5days <strong>in</strong> 30 ng/ml activ<strong>in</strong> w/wo 5 ng/ml <strong>FGF</strong>4 and sta<strong>in</strong>ed for SOX17, E-cadher<strong>in</strong>, SOX7 and <strong>the</strong> nuclear sta<strong>in</strong>DAPI. The yellow frame <strong>in</strong>dicates area blown up and shown to <strong>the</strong> right (red signal boosted). Representativeimages are shown for each condition, except for <strong>FGF</strong>4 –/– <strong>cells</strong> <strong>in</strong> activ<strong>in</strong> alone which shows a SOX7 + area <strong>in</strong> <strong>the</strong>culture. White scale bar: 100 µm; yellow scale bar: 50 µm.82
6. General discussionEndoderm <strong>differentiation</strong>Basic culture conditionsOur culture system is based on serum and feeder-free conditions by means <strong>of</strong> gelat<strong>in</strong>e-coatedculture flasks and <strong>the</strong> N2, B27, BMP4 and LIF supplements. Remnants <strong>of</strong> serum and feedershave been removed by grow<strong>in</strong>g <strong>cells</strong> for 3 passages, i.e. 6 days, under <strong>the</strong>se conditions prior toexperimental setup. In <strong>the</strong> presence <strong>of</strong> LIF and BMP4 <strong>cells</strong> do not differentiate, but it is hard todeterm<strong>in</strong>e <strong>the</strong> effect <strong>of</strong> trace amounts <strong>of</strong> BMP4 on <strong>the</strong> very early <strong>differentiation</strong> <strong>in</strong> <strong>the</strong> culture.However, such <strong>differentiation</strong> would most likely be opposed by trace amounts <strong>of</strong> LIF and<strong>the</strong>refore not have any practical effect especially when <strong>cells</strong> are differentiated us<strong>in</strong>g highconcentrations <strong>of</strong> growth factors.A recent study showed that <strong>in</strong>hibition <strong>of</strong> <strong>FGF</strong>Rs, MEK and GSK3 through addition <strong>of</strong> <strong>the</strong> smallmolecule <strong>in</strong>hibitors SU5402, PD184352 and Chir99021 respectively, could ma<strong>in</strong>ta<strong>in</strong> <strong>cells</strong>pluripotent over time (Y<strong>in</strong>g et al. 2008). This protocol was ref<strong>in</strong>ed by us<strong>in</strong>g <strong>the</strong> stronger MEK<strong>in</strong>hibitorPD0325901 <strong>in</strong> comb<strong>in</strong>ation with Chir99021 (Nichols et al. 2009). Thus, LIF andBMP4 are not necessary for ma<strong>in</strong>tenance <strong>of</strong> pluripotency, as <strong>in</strong>hibition <strong>of</strong> <strong>the</strong> MAPK-pathwayand GSK3 is sufficient. This protocol may be preferred <strong>in</strong> <strong>the</strong> future to avoid ma<strong>in</strong>tenance <strong>of</strong><strong>the</strong> pluripotent state through addition <strong>of</strong> e.g. BMP4, a potent <strong>in</strong>ducer <strong>of</strong> mesoderm<strong>differentiation</strong>.‘Mesendoderm’: Does it exist?Nodal and BMP4, both members <strong>of</strong> <strong>the</strong> TGFβ superfamily are expressed <strong>in</strong> <strong>the</strong> PS and ExE,respectively, and act <strong>in</strong> opposite directions to <strong>in</strong>duce DE and mesoderm. These two germ layersderive from <strong>the</strong> same population <strong>of</strong> epiblast <strong>cells</strong> migrat<strong>in</strong>g through <strong>the</strong> PS dur<strong>in</strong>g gastrulation.Cells mov<strong>in</strong>g through <strong>the</strong> PS are bipotent and are collectively termed <strong>the</strong> mesendoderm before<strong>the</strong>y are fur<strong>the</strong>r differentiated <strong>in</strong>to mesoderm and endoderm (Lawson et al. 1991; K<strong>in</strong>der et al.2001; Rodaway and Patient 2001). This mesendoderm population seems much conserved, as itis found from Caenorhabditis elegans (C. elegans) through Xenopus laevis (Xenopus) tozebrafish (Rodaway et al. 1999; Rodaway and Patient 2001). A bipotent mesendoderm cellpopulation has also been shown <strong>in</strong> m<strong>ES</strong> cell work where a pool <strong>of</strong> <strong>cells</strong> express<strong>in</strong>g T orGSC/FOXA2/PDGFRα, i.e. a mesendoderm population, had <strong>the</strong> potential to form bothmesoderm and endoderm dependent on <strong>the</strong> growth factors presented (Kubo et al. 2004; Tada etal. 2005). Indeed, we found that by us<strong>in</strong>g GFP-reporter cell l<strong>in</strong>es for <strong>the</strong> PS markers T, Gsc andMixl1, we could analyse <strong>the</strong> effect <strong>of</strong> anterioris<strong>in</strong>g and posterioris<strong>in</strong>g TGFβ- and WNT<strong>signall<strong>in</strong>g</strong><strong>in</strong> <strong>the</strong> early <strong>differentiation</strong> steps.Although <strong>the</strong> mesendoderm cell population is well-established from C. elegans to <strong>mouse</strong>development, it is challenged by a recent study. By use <strong>of</strong> s<strong>in</strong>gle-cell l<strong>in</strong>eage trac<strong>in</strong>g, <strong>the</strong>authors claim that endoderm and surface ectoderm segregate dur<strong>in</strong>g gastrulation, whereas apool <strong>of</strong> bipotent neuromesoderm persists through all stages <strong>of</strong> axis elongation (Tzouanacou etal. 2009). If <strong>the</strong>se observations hold true, it has implication for <strong>ES</strong> cell <strong>differentiation</strong> <strong>towards</strong><strong>cells</strong> <strong>of</strong> <strong>the</strong> DE l<strong>in</strong>eage, as it will <strong>the</strong>n be better to obta<strong>in</strong> a pool <strong>of</strong> <strong>cells</strong> express<strong>in</strong>g DE markersonly, and not a comb<strong>in</strong>ation <strong>of</strong> DE and mesoderm markers at early stages.O<strong>the</strong>r groups and we have shown derivation <strong>of</strong> DE <strong>cells</strong> from a population <strong>of</strong> <strong>cells</strong> express<strong>in</strong>gapp. 40 – 70% mesendoderm markers (Tada et al. 2005). Whe<strong>the</strong>r <strong>the</strong>se DE <strong>cells</strong> derive from amesendoderm population or ra<strong>the</strong>r from an endoderm population directly, is difficult toestablish without <strong>the</strong> use <strong>of</strong> l<strong>in</strong>eage trac<strong>in</strong>g dur<strong>in</strong>g <strong>differentiation</strong>. Also, any contribution <strong>of</strong>signals from randomly differentiated <strong>cells</strong> to <strong>the</strong> form<strong>in</strong>g DE may prove important, but are asyet not studied <strong>in</strong> depth. All <strong>in</strong> all this mesendoderm population may prove not to have apractical limitation to <strong>ES</strong> cell <strong>differentiation</strong> <strong>in</strong> vitro as long as <strong>the</strong> DE is properly established.83
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PhD thesisCand.scient. Janny Marie
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ResuméSukkersyge er en sygdom der
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Table of contents1
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ICMinner cell massIdInhibitor of di
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cell mass regenerates probably thro
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Figure 1-1: Early embryo developmen
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Figure 1-3: Regional expression of
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The pluripotent stateThe pluripoten
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There are four membrane-bound FGFRs
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2. AimsThe aim of this study was to
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Developmental Biology 330 (2009) 28
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- Page 96: AcknowledgementsThe work presented
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