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Vsx2 in the zebrafish retina: restricted lineages through derepression.

Vitorino M, Jusuf PR, Maurus D, Kimura Y, Higashijima S, Harris WA - Neural Dev (2009)

Bottom Line: Vsx2 is a repressor whose targets include transcription factors such as Vsx1, which is expressed in the progenitors of distinct non-Vsx2 bipolars, and the basic helix-loop-helix transcription factor Ath5, which restricts the fate of progenitors to retinal ganglion cells, horizontal cells, amacrine cells and photoreceptors fates.Foxn4, expressed in the progenitors of amacrine and horizontal cells, is also negatively regulated by Vsx2.Our data thus suggest Vsx2-positive RPCs are fully multipotent retinal progenitors and that when Vsx2 is downregulated, Vsx2-negative progenitors escape Vsx2 repression and so are able to express factors that restrict lineage potential.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3DY, UK. mspdcv2@cam.ac.uk

ABSTRACT

Background: The neurons in the vertebrate retina arise from multipotent retinal progenitor cells (RPCs). It is not clear, however, which progenitors are multipotent or why they are multipotent.

Results: In this study we show that the homeodomain transcription factor Vsx2 is initially expressed throughout the retinal epithelium, but later it is downregulated in all but a minor population of bipolar cells and all Müller glia. The Vsx2-negative daughters of Vsx2-positive RPCs divide and give rise to all other cell types in the retina. Vsx2 is a repressor whose targets include transcription factors such as Vsx1, which is expressed in the progenitors of distinct non-Vsx2 bipolars, and the basic helix-loop-helix transcription factor Ath5, which restricts the fate of progenitors to retinal ganglion cells, horizontal cells, amacrine cells and photoreceptors fates. Foxn4, expressed in the progenitors of amacrine and horizontal cells, is also negatively regulated by Vsx2.

Conclusion: Our data thus suggest Vsx2-positive RPCs are fully multipotent retinal progenitors and that when Vsx2 is downregulated, Vsx2-negative progenitors escape Vsx2 repression and so are able to express factors that restrict lineage potential.

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Some Vsx2 progenitors lose Vsx2 expression and differentiate as presumed photoreceptors, amacrine cells and ganglion cells. Time-lapse images of Additional file 4, showing transplanted cells from a transgenic Tg(vsx2:GFP) embryo that was injected with H2B:RFP RNA to mark all cells transplanted. Initially, all transplanted progenitor cells express Vsx2. Some cells (white arrows) undergo cell division and downregulate Vsx2:GFP expression (marked by white arrows at mitosis and white, blue, green and black spots). The Vsx2-negative daughter cells of these divisions (red outlines) end up in the ONL (presumed photoreceptors), inner INL (presumed amacrine cells) and GCL (presumed ganglion cells). In contrast, cells that upregulate the Vsx2:GFP expression late during development become restricted to the INL only, where they differentiate into Vsx2-positive bipolar or Müller cells (purple dots, white outlines). GCL, ganglion cell layer; INL, inner nuclear layer; ONL, outer nuclear layer. Scale bar: 20 μm.
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Figure 8: Some Vsx2 progenitors lose Vsx2 expression and differentiate as presumed photoreceptors, amacrine cells and ganglion cells. Time-lapse images of Additional file 4, showing transplanted cells from a transgenic Tg(vsx2:GFP) embryo that was injected with H2B:RFP RNA to mark all cells transplanted. Initially, all transplanted progenitor cells express Vsx2. Some cells (white arrows) undergo cell division and downregulate Vsx2:GFP expression (marked by white arrows at mitosis and white, blue, green and black spots). The Vsx2-negative daughter cells of these divisions (red outlines) end up in the ONL (presumed photoreceptors), inner INL (presumed amacrine cells) and GCL (presumed ganglion cells). In contrast, cells that upregulate the Vsx2:GFP expression late during development become restricted to the INL only, where they differentiate into Vsx2-positive bipolar or Müller cells (purple dots, white outlines). GCL, ganglion cell layer; INL, inner nuclear layer; ONL, outer nuclear layer. Scale bar: 20 μm.

Mentions: As Vsx2 appears to be downregulated in most RPCs, we decided to monitor Vsx2 progenitors during retinal differentiation. To see all the descendents of the Vsx2 RPCs, Tg(vsx2:GFP) transgenic embryos were injected with H2B:RFP RNA to label nuclei. Cells from such injected embryos were then transplanted into unlabelled wild-type embryos and imaged every 8 minutes for 40 hours from 30 hpf onwards. In these movies, individual Vsx2:GFP RPCs can be followed. Initially, all the transplanted cells expressed Vsx2:GFP and H2B:RFP. Some of these progenitors are then seen to diminish their GFP while keeping RFP as they go through cell division near the apical surface (Figure 8; Additional file 4). The resulting RFP descendents are also progenitors in that they undergo typical interkinetic nuclear migration and divide apically (Figure 8; Additional file 4). The daughters of these RFP progenitors then become restricted to particular positions in the retina (red outlines in Figure 8). Some of these come to reside in the GCL (presumably becoming ganglion cells), some take up residence in the INL, including the inner part of the INL (possibly amacrine cells), and some come to lie with photoreceptors in the ONL (Figure 8). As the RFP is a nuclear marker, it did not allow us to determine cell type by morphology, but the fact that these nuclei are no longer going through interkinetic migration or dividing leads us to believe that these cells are differentiating into the various cell types other than Vsx2-positive bipolars or Müller cells. In contrast, cells that retain and then upregulate the expression of Vsx2:GFP move to their final position in the INL, where the expected Vsx2-bipolar or Müller cells are found (Figure 8).


Vsx2 in the zebrafish retina: restricted lineages through derepression.

Vitorino M, Jusuf PR, Maurus D, Kimura Y, Higashijima S, Harris WA - Neural Dev (2009)

Some Vsx2 progenitors lose Vsx2 expression and differentiate as presumed photoreceptors, amacrine cells and ganglion cells. Time-lapse images of Additional file 4, showing transplanted cells from a transgenic Tg(vsx2:GFP) embryo that was injected with H2B:RFP RNA to mark all cells transplanted. Initially, all transplanted progenitor cells express Vsx2. Some cells (white arrows) undergo cell division and downregulate Vsx2:GFP expression (marked by white arrows at mitosis and white, blue, green and black spots). The Vsx2-negative daughter cells of these divisions (red outlines) end up in the ONL (presumed photoreceptors), inner INL (presumed amacrine cells) and GCL (presumed ganglion cells). In contrast, cells that upregulate the Vsx2:GFP expression late during development become restricted to the INL only, where they differentiate into Vsx2-positive bipolar or Müller cells (purple dots, white outlines). GCL, ganglion cell layer; INL, inner nuclear layer; ONL, outer nuclear layer. Scale bar: 20 μm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 8: Some Vsx2 progenitors lose Vsx2 expression and differentiate as presumed photoreceptors, amacrine cells and ganglion cells. Time-lapse images of Additional file 4, showing transplanted cells from a transgenic Tg(vsx2:GFP) embryo that was injected with H2B:RFP RNA to mark all cells transplanted. Initially, all transplanted progenitor cells express Vsx2. Some cells (white arrows) undergo cell division and downregulate Vsx2:GFP expression (marked by white arrows at mitosis and white, blue, green and black spots). The Vsx2-negative daughter cells of these divisions (red outlines) end up in the ONL (presumed photoreceptors), inner INL (presumed amacrine cells) and GCL (presumed ganglion cells). In contrast, cells that upregulate the Vsx2:GFP expression late during development become restricted to the INL only, where they differentiate into Vsx2-positive bipolar or Müller cells (purple dots, white outlines). GCL, ganglion cell layer; INL, inner nuclear layer; ONL, outer nuclear layer. Scale bar: 20 μm.
Mentions: As Vsx2 appears to be downregulated in most RPCs, we decided to monitor Vsx2 progenitors during retinal differentiation. To see all the descendents of the Vsx2 RPCs, Tg(vsx2:GFP) transgenic embryos were injected with H2B:RFP RNA to label nuclei. Cells from such injected embryos were then transplanted into unlabelled wild-type embryos and imaged every 8 minutes for 40 hours from 30 hpf onwards. In these movies, individual Vsx2:GFP RPCs can be followed. Initially, all the transplanted cells expressed Vsx2:GFP and H2B:RFP. Some of these progenitors are then seen to diminish their GFP while keeping RFP as they go through cell division near the apical surface (Figure 8; Additional file 4). The resulting RFP descendents are also progenitors in that they undergo typical interkinetic nuclear migration and divide apically (Figure 8; Additional file 4). The daughters of these RFP progenitors then become restricted to particular positions in the retina (red outlines in Figure 8). Some of these come to reside in the GCL (presumably becoming ganglion cells), some take up residence in the INL, including the inner part of the INL (possibly amacrine cells), and some come to lie with photoreceptors in the ONL (Figure 8). As the RFP is a nuclear marker, it did not allow us to determine cell type by morphology, but the fact that these nuclei are no longer going through interkinetic migration or dividing leads us to believe that these cells are differentiating into the various cell types other than Vsx2-positive bipolars or Müller cells. In contrast, cells that retain and then upregulate the expression of Vsx2:GFP move to their final position in the INL, where the expected Vsx2-bipolar or Müller cells are found (Figure 8).

Bottom Line: Vsx2 is a repressor whose targets include transcription factors such as Vsx1, which is expressed in the progenitors of distinct non-Vsx2 bipolars, and the basic helix-loop-helix transcription factor Ath5, which restricts the fate of progenitors to retinal ganglion cells, horizontal cells, amacrine cells and photoreceptors fates.Foxn4, expressed in the progenitors of amacrine and horizontal cells, is also negatively regulated by Vsx2.Our data thus suggest Vsx2-positive RPCs are fully multipotent retinal progenitors and that when Vsx2 is downregulated, Vsx2-negative progenitors escape Vsx2 repression and so are able to express factors that restrict lineage potential.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Physiology, Development and Neuroscience, University of Cambridge, Downing Street, Cambridge, CB2 3DY, UK. mspdcv2@cam.ac.uk

ABSTRACT

Background: The neurons in the vertebrate retina arise from multipotent retinal progenitor cells (RPCs). It is not clear, however, which progenitors are multipotent or why they are multipotent.

Results: In this study we show that the homeodomain transcription factor Vsx2 is initially expressed throughout the retinal epithelium, but later it is downregulated in all but a minor population of bipolar cells and all Müller glia. The Vsx2-negative daughters of Vsx2-positive RPCs divide and give rise to all other cell types in the retina. Vsx2 is a repressor whose targets include transcription factors such as Vsx1, which is expressed in the progenitors of distinct non-Vsx2 bipolars, and the basic helix-loop-helix transcription factor Ath5, which restricts the fate of progenitors to retinal ganglion cells, horizontal cells, amacrine cells and photoreceptors fates. Foxn4, expressed in the progenitors of amacrine and horizontal cells, is also negatively regulated by Vsx2.

Conclusion: Our data thus suggest Vsx2-positive RPCs are fully multipotent retinal progenitors and that when Vsx2 is downregulated, Vsx2-negative progenitors escape Vsx2 repression and so are able to express factors that restrict lineage potential.

Show MeSH
Related in: MedlinePlus