| 1. |
- Wilson, Sara I, et al.
(författare)
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The status of Wnt signalling regulates neural and epidermal fates in the chick embryo.
- 2001
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 411:6835, s. 325-30
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Tidskriftsartikel (refereegranskat)abstract
- The acquisition of neural fate by embryonic ectodermal cells is a fundamental step in the formation of the vertebrate nervous system. Neural induction seems to involve signalling by fibroblast growth factors (FGFs) and attenuation of the activity of bone morphogenetic protein (BMP). But FGFs, either alone or in combination with BMP antagonists, are not sufficient to induce neural fate in prospective epidermal ectoderm of amniote embryos. These findings suggest that additional signals are involved in the specification of neural fate. Here we show that the state of Wnt signalling is a critical determinant of neural and epidermal fates in the chick embryo. Continual Wnt signalling blocks the response of epiblast cells to FGF signals, permitting the expression and signalling of BMP to direct an epidermal fate. Conversely, a lack of exposure of epiblast cells to Wnt signals permits FGFs to induce a neural fate.
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| 2. |
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| 3. |
- Muhr, J, et al.
(författare)
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Convergent inductive signals specify midbrain, hindbrain, and spinal cord identity in gastrula stage chick embryos.
- 1999
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Ingår i: Neuron. - 0896-6273 .- 1097-4199. ; 23:4, s. 689-702
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Tidskriftsartikel (refereegranskat)abstract
- In the chick embryo, neural cells acquire midbrain, hindbrain, and spinal cord character over a approximately 6 hr period during gastrulation. The convergent actions of four signals appear to specify caudal neural character. Fibroblast growth factors (FGFs) and a paraxial mesoderm-caudalizing (PMC) activity are involved, but neither signal is sufficient to induce any single region. FGFs act indirectly by inducing mesoderm that expresses PMC and retinoid activity and also directly on prospective neural cells, in combination with PMC activity and a rostralizing signal, to induce midbrain character. Hindbrain character emerges from cells that possess the potential to acquire midbrain character upon exposure to higher levels of PMC activity. Induction of spinal cord character appears to involve PMC and retinoid activities.
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| 4. |
- Wilson, Sara I, et al.
(författare)
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An early requirement for FGF signalling in the acquisition of neural cell fate in the chick embryo.
- 2000
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Ingår i: Current Biology. - 0960-9822 .- 1879-0445. ; 10:8, s. 421-9
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Tidskriftsartikel (refereegranskat)abstract
- BACKGROUND: In Xenopus embryos, fibroblast growth factors (FGFs) and secreted inhibitors of bone morphogenetic protein (BMP)-mediated signalling have been implicated in neural induction. The precise roles, if any, that these factors play in neural induction in amniotes remains to be established.RESULTS: To monitor the initial steps of neural induction in the chick embryo, we developed an in vitro assay of neural differentiation in epiblast cells. Using this assay, we found evidence that neural cell fate is specified in utero, before the generation of the primitive streak or Hensen's node. Early epiblast cells expressed both Bmp4 and Bmp7, but the expression of both genes was downregulated as cells acquired neural fate. During prestreak and gastrula stages, exposure of epiblast cells to BMP4 activity in vitro was sufficient to block the acquisition of neural fate and to promote the generation of epidermal cells. Fgf3 was also found to be expressed in the early epiblast, and ongoing FGF signalling in epiblast cells was required for acquisition of neural fate and for the suppression of Bmp4 and Bmp7 expression.CONCLUSIONS: The onset of neural differentiation in the chick embryo occurs in utero, before the generation of Hensen's node. Fgf3, Bmp4 and Bmp7 are each expressed in prospective neural cells, and FGF signalling appears to be required for the repression of Bmp expression and for the acquisition of neural fate. Subsequent exposure of epiblast cells to BMPs, however, can prevent the generation of neural tissue and induce cells of epidermal character.
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| 5. |
- Gunhaga, Lena, et al.
(författare)
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Sonic hedgehog signaling at gastrula stages specifies ventral telencephalic cells in the chick embryo
- 2000
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Ingår i: Development. - 0950-1991 .- 1477-9129. ; 127:15, s. 3283-3293
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Tidskriftsartikel (refereegranskat)abstract
- A secreted signaling factor, Sonic hedgehog (Shh), has a crucial role in the generation of ventral cell types along the entire rostrocaudal axis of the neural tube. At caudal levels of the neuraxis, Shh is secreted by the notochord and floor plate during the period that ventral cell fates are specified. At anterior prosencephalic levels that give rise to the telencephalon, however, neither the prechordal mesoderm nor the ventral neural tube expresses Shh at the time that the overt ventral character of the telencephalon becomes evident. Thus, the precise role and timing of Shh signaling relevant to the specification of ventral telencephalic identity remains unclear. By analysing neural cell differentiation in chick neural plate explants we provide evidence that neural cells acquire molecular properties characteristic of the ventral telencephalon in response to Shh signals derived from the anterior primitive streak/Hensen's node region at gastrula stages. Exposure of prospective anterior prosencephalic cells to Shh at this early stage is sufficient to initiate a temporal program of differentiation that parallels that of neurons generated normally in the medial ganglionic eminence subdivision of the ventral telencephalon.
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