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Formation of the embryonic organizer is restricted by the competitive influences of Fgf signaling and the SoxB1 transcription factors.

Kuo CL, Lam CM, Hewitt JE, Scotting PJ - PLoS ONE (2013)

Bottom Line: We show that ectopic expression of organizer genes induced solely by the inhibition of SoxB1 function is dependent upon the activation of fgf expression.These data allow us to describe a comprehensive signaling network in which the SoxB1 factors restrict organizer formation by inhibiting Fgf, Nodal and Wnt signaling, as well as independently repressing the targets of that signaling.The organizer therefore forms only where Nodal-induced Fgf signaling overlaps with Wnt signaling and the SoxB1 proteins are absent.

View Article: PubMed Central - PubMed

Affiliation: Centre for Genetics and Genomics, School of Biology, University of Nottingham, QMC, Nottingham, United Kingdom.

ABSTRACT
The organizer is one of the earliest structures to be established during vertebrate development and is crucial to subsequent patterning of the embryo. We have previously shown that the SoxB1 transcription factor, Sox3, plays a central role as a transcriptional repressor of zebrafish organizer gene expression. Recent data suggest that Fgf signaling has a positive influence on organizer formation, but its role remains to be fully elucidated. In order to better understand how Fgf signaling fits into the complex regulatory network that determines when and where the organizer forms, the relationship between the positive effects of Fgf signaling and the repressive effects of the SoxB1 factors must be resolved. This study demonstrates that both fgf3 and fgf8 are required for expression of the organizer genes, gsc and chd, and that SoxB1 factors (Sox3, and the zebrafish specific factors, Sox19a and Sox19b) can repress the expression of both fgf3 and fgf8. However, we also find that these SoxB1 factors inhibit the expression of gsc and chd independently of their repression of fgf expression. We show that ectopic expression of organizer genes induced solely by the inhibition of SoxB1 function is dependent upon the activation of fgf expression. These data allow us to describe a comprehensive signaling network in which the SoxB1 factors restrict organizer formation by inhibiting Fgf, Nodal and Wnt signaling, as well as independently repressing the targets of that signaling. The organizer therefore forms only where Nodal-induced Fgf signaling overlaps with Wnt signaling and the SoxB1 proteins are absent.

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Related in: MedlinePlus

Effects of FGF and Sox3 upon the expression of chd cannot be rescued by Gsc.Injection of different mixtures of sox3 or gsc RNA resulted in a range of expression levels of chd from complete repression to dramatic ‘continuous’ expansion as shown in the right of panel A. The phenotypes seen when combinations of sox3 and gsc were injected, were intermediate between those when sox3 or gsc alone were injected (Shown in bar chart in panel A). Treatment with SU5402 was able to inhibit chd expression (Ba,b) even when 50 pg (Bc,d) or 100 pg (Be,f) gsc RNA was also injected. Shown in bar chart in panel C. The proportion of embryos exhibiting these phenotypes is shown at the bottom right of each panel.
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pone-0057698-g005: Effects of FGF and Sox3 upon the expression of chd cannot be rescued by Gsc.Injection of different mixtures of sox3 or gsc RNA resulted in a range of expression levels of chd from complete repression to dramatic ‘continuous’ expansion as shown in the right of panel A. The phenotypes seen when combinations of sox3 and gsc were injected, were intermediate between those when sox3 or gsc alone were injected (Shown in bar chart in panel A). Treatment with SU5402 was able to inhibit chd expression (Ba,b) even when 50 pg (Bc,d) or 100 pg (Be,f) gsc RNA was also injected. Shown in bar chart in panel C. The proportion of embryos exhibiting these phenotypes is shown at the bottom right of each panel.

Mentions: To date, we have analysed gsc and chd as two of the earliest markers of the organizer. Since gsc encodes a transcription factor and injected gsc RNA has been shown to induce chd expression, albeit in a non-cell autonomous manner [18], [19] we set out to determine if the effects of the Fgfs and the SoxB1 factors on chd are indirectly due to effects on gsc. We first showed that injection of RNA encoding Gsc dramatically expanded the domain of chd expression (Fig. 5). In order to determine if the repression of chd by Sox3 was indirectly through the repression of gsc expression, we next determined whether gsc RNA was able to rescue the repression of chd by Sox3. When gsc and sox3 RNA were injected together, Sox3 appeared to repress chd expression in the patches of cells in which it was expressed (as shown by staining for the HA-tag it carried, data not shown) within a broader domain of chd expression induced (non-cell autonomously) by Gsc (Fig. 5A).


Formation of the embryonic organizer is restricted by the competitive influences of Fgf signaling and the SoxB1 transcription factors.

Kuo CL, Lam CM, Hewitt JE, Scotting PJ - PLoS ONE (2013)

Effects of FGF and Sox3 upon the expression of chd cannot be rescued by Gsc.Injection of different mixtures of sox3 or gsc RNA resulted in a range of expression levels of chd from complete repression to dramatic ‘continuous’ expansion as shown in the right of panel A. The phenotypes seen when combinations of sox3 and gsc were injected, were intermediate between those when sox3 or gsc alone were injected (Shown in bar chart in panel A). Treatment with SU5402 was able to inhibit chd expression (Ba,b) even when 50 pg (Bc,d) or 100 pg (Be,f) gsc RNA was also injected. Shown in bar chart in panel C. The proportion of embryos exhibiting these phenotypes is shown at the bottom right of each panel.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3585176&req=5

pone-0057698-g005: Effects of FGF and Sox3 upon the expression of chd cannot be rescued by Gsc.Injection of different mixtures of sox3 or gsc RNA resulted in a range of expression levels of chd from complete repression to dramatic ‘continuous’ expansion as shown in the right of panel A. The phenotypes seen when combinations of sox3 and gsc were injected, were intermediate between those when sox3 or gsc alone were injected (Shown in bar chart in panel A). Treatment with SU5402 was able to inhibit chd expression (Ba,b) even when 50 pg (Bc,d) or 100 pg (Be,f) gsc RNA was also injected. Shown in bar chart in panel C. The proportion of embryos exhibiting these phenotypes is shown at the bottom right of each panel.
Mentions: To date, we have analysed gsc and chd as two of the earliest markers of the organizer. Since gsc encodes a transcription factor and injected gsc RNA has been shown to induce chd expression, albeit in a non-cell autonomous manner [18], [19] we set out to determine if the effects of the Fgfs and the SoxB1 factors on chd are indirectly due to effects on gsc. We first showed that injection of RNA encoding Gsc dramatically expanded the domain of chd expression (Fig. 5). In order to determine if the repression of chd by Sox3 was indirectly through the repression of gsc expression, we next determined whether gsc RNA was able to rescue the repression of chd by Sox3. When gsc and sox3 RNA were injected together, Sox3 appeared to repress chd expression in the patches of cells in which it was expressed (as shown by staining for the HA-tag it carried, data not shown) within a broader domain of chd expression induced (non-cell autonomously) by Gsc (Fig. 5A).

Bottom Line: We show that ectopic expression of organizer genes induced solely by the inhibition of SoxB1 function is dependent upon the activation of fgf expression.These data allow us to describe a comprehensive signaling network in which the SoxB1 factors restrict organizer formation by inhibiting Fgf, Nodal and Wnt signaling, as well as independently repressing the targets of that signaling.The organizer therefore forms only where Nodal-induced Fgf signaling overlaps with Wnt signaling and the SoxB1 proteins are absent.

View Article: PubMed Central - PubMed

Affiliation: Centre for Genetics and Genomics, School of Biology, University of Nottingham, QMC, Nottingham, United Kingdom.

ABSTRACT
The organizer is one of the earliest structures to be established during vertebrate development and is crucial to subsequent patterning of the embryo. We have previously shown that the SoxB1 transcription factor, Sox3, plays a central role as a transcriptional repressor of zebrafish organizer gene expression. Recent data suggest that Fgf signaling has a positive influence on organizer formation, but its role remains to be fully elucidated. In order to better understand how Fgf signaling fits into the complex regulatory network that determines when and where the organizer forms, the relationship between the positive effects of Fgf signaling and the repressive effects of the SoxB1 factors must be resolved. This study demonstrates that both fgf3 and fgf8 are required for expression of the organizer genes, gsc and chd, and that SoxB1 factors (Sox3, and the zebrafish specific factors, Sox19a and Sox19b) can repress the expression of both fgf3 and fgf8. However, we also find that these SoxB1 factors inhibit the expression of gsc and chd independently of their repression of fgf expression. We show that ectopic expression of organizer genes induced solely by the inhibition of SoxB1 function is dependent upon the activation of fgf expression. These data allow us to describe a comprehensive signaling network in which the SoxB1 factors restrict organizer formation by inhibiting Fgf, Nodal and Wnt signaling, as well as independently repressing the targets of that signaling. The organizer therefore forms only where Nodal-induced Fgf signaling overlaps with Wnt signaling and the SoxB1 proteins are absent.

Show MeSH
Related in: MedlinePlus