The POU Factor Oct-25 Regulates the Xvent-2B Gene and Counteracts Terminal Differentiation in Xenopus Embryos

Cao, Ying; Knöchel, Sigrun; Donow, Cornelia; Miethe, Josef; Kaufmann, Eckhard; Knöchel, Walter

doi:10.1074/jbc.m407544200

Cited by 49 publications

(73 citation statements)

References 45 publications

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“…6A shows RNA in situ hybridization for a number of gastrulation stage markers in XlPouV-depleted embryos. Interestingly, we observed a dramatic loss of Bmp4 and Xom (Xvent2) expression, both genes associated with the inhibition of differentiation (Cao et al, 2004;Constance Lane et al, 2004;Ying et al, 2003). We also observed a loss of Fgf8 and brachyury (Xbra) expression, genes normally expressed in the marginal zone.…”

Section: Xlpouv Protein Depletion Disrupts the Expression Of Genes Asmentioning

confidence: 50%

Conserved roles for Oct4 homologues in maintaining multipotency during early vertebrate development

2006

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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.

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Section: Xlpouv Protein Depletion Disrupts the Expression Of Genes Asmentioning

confidence: 50%

Conserved roles for Oct4 homologues in maintaining multipotency during early vertebrate development

2006

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“…Germline inactivation of Oct4 revealed its requirement for germ cell survival (Kehler et al, 2004), which so far precluded further analysis of Oct4 in early asymmetry of the mammalian egg. However, Xenopus XPou-25, which belongs to the same protein subclass as Pou2 and Oct4, can stimulate transcription of Xvent-2B and prevents differentiation of neuroectodermal and mesodermal tissues when misexpressed (Cao et al, 2004). Although the role of pou2 has been mainly studied by loss-of-function experiments, the Xenopus data are reminiscent of the role of pou2 in activation of ventral-specifying genes, neural patterning and differentiation into endoderm.…”

Section: Pou2 and Oct4 In Early Developmentmentioning

confidence: 97%

Maternal control of vertebrate dorsoventral axis formation and epiboly by the POU domain protein Spg/Pou2/Oct4

2006

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Dorsoventral (DV) axis formation of the vertebrate embryo is controlled by the maternal genome and is subsequently refined zygotically. In the zygote, repression of ventralizing Bmp activity on the dorsal side through chordin and noggin is crucial for establishment of a dorsally located organizer. This interplay generates a zygotic Bmp activity gradient that defines distinct positional values along the DV axis. The maternal processes that control expression of the zygotic genes implicated in DV patterning are largely unknown. spiel-ohne-grenzen (spg/pou2) is a maternally and zygotically expressed zebrafish gene that encodes the POU domain transcription factor Pou2, an ortholog of mammalian Oct4/Pou5f1. We show that embryos that are genetically depleted of both maternal and zygotic pou2 function (MZspg) exhibit extreme DV patterning defects and, independently, a blastoderm-specific arrest of epiboly. Dorsal tissues expand to the ventral side at the expense of ventrolateral tissue in MZspg embryos. Dorsally expressed Bmp-antagonists, such as Chd and Nog1, and Gsc are ectopically activated at ventral levels in MZspg. Lack of ventral specification is apparent very early, suggesting that maternal processes are affected in MZspg. Indeed, maternal pou2 function is necessary to initiate zygotic expression of ventrally expressed genes such as bmp2b and bmp4, and for proper activation of bmp7, vox, vent and eve1. A constitutively active Alk8-TGF␤-receptor can ectopically induce bmp2b and bmp4 and rescues the dorsalization of MZspg. This indicates that pou2 acts upstream of Alk8, a maternally provided receptor implicated in the activation of zygotic bmp2b and bmp4 transcription. Consistent with this possibility, Bmp gene misexpression can rescue MZspg embryos, indicating that TGF␤-mediated signal transduction itself is intact in absence of Pou2. Inhibition of Fgf signaling, another pathway with early dorsalizing activity, can also restore and even ventralize MZspg embryos. The requirement for pou2 to initiate bmp2b expression can therefore be bypassed by releasing the repressive function of Fgf signaling upon bmp2b transcription. In transplantation experiments, we find that dorsalized cells from prospective ventrolateral regions of MZspg embryos are non cellautonomously respecified to a ventral fate within wild-type host embryos. Analysis of pou2 mRNA injected MZspg embryos shows that pou2 is required on the ventral side of cleavage stage embryos. Based on the maternal requirement for pou2 in ventral specification, we propose that ventral specification employs an active, pou2-dependent maternal induction step, rather than a default ventralizing program.

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“…GST Pull-down Assays-Preparation of GST fusion proteins and GST pull-down assays were performed in the same way as described previously (31,32).…”

Section: Methodsmentioning

confidence: 99%

“…Electrophoresis Mobility Shift Assays (EMSA)-EMSAs were carried out essentially as described (31,32).…”

Section: Methodsmentioning

confidence: 99%

Oct25 Represses Transcription of Nodal/Activin Target Genes by Interaction with Signal Transducers during Xenopus Gastrulation

Cao

Siegel

Oswald

et al. 2008

Journal of Biological Chemistry

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The balance between differentiation signals and signals maintaining the undifferentiated state of embryonic cells ensures proper formation of germ layers. The nodal/activin pathway represents one of the major signaling chains responsible for the differentiation of embryonic cells into mesodermal and endodermal germ layers, while Oct4 is one of the major players in the maintenance of an undifferentiated state. Here we show that Oct25, an Oct4 homologue in Xenopus, antagonizes the activity of nodal/activin signaling by inhibiting the transcription of its target genes, Gsc and Mix2. The inhibitory effect is achieved by forming repression complexes on the promoters of Gsc and Mix2 between Oct25 and the signal transducers of the nodal/activin pathway, WBSCR11, FAST1, and Smad2. We have analyzed the significance of the Oct binding site for its inhibitory effect within the Gsc promoter. Albeit VP16-Oct25 fusion protein demonstrated a stimulating effect and EVE-Oct25 revealed a repression effect on an artificial reporter that is composed of eight repeats of Oct binding motifs, both fusions, like wild-type Oct25, inhibited mesendoderm formation and the activity of Gsc and Mix2 promoters. These results suggest that the regulatory effect of Oct25 on the expression of Gsc and Mix2 is mediated by specific protein/protein interactions. Furthermore, we demonstrate that histone deacetylase activities are not required for the inhibitory effect of Oct25. Our results provide a novel view in that Oct25 controls the nodal/activin pathway and thus maintains the undifferentiated state of embryonic cells in preventing them from premature differentiation.

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The POU Factor Oct-25 Regulates the Xvent-2B Gene and Counteracts Terminal Differentiation in Xenopus Embryos

Cited by 49 publications

References 45 publications

Conserved roles for Oct4 homologues in maintaining multipotency during early vertebrate development

Conserved roles for Oct4 homologues in maintaining multipotency during early vertebrate development

Maternal control of vertebrate dorsoventral axis formation and epiboly by the POU domain protein Spg/Pou2/Oct4

Oct25 Represses Transcription of Nodal/Activin Target Genes by Interaction with Signal Transducers during Xenopus Gastrulation

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