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A membrane-associated β-catenin/Oct4 complex correlates with ground-state pluripotency in mouse embryonic stem cells.

Faunes F, Hayward P, Descalzo SM, Chatterjee SS, Balayo T, Trott J, Christoforou A, Ferrer-Vaquer A, Hadjantonakis AK, Dasgupta R, Arias AM - Development (2013)

Bottom Line: Wnt/β-catenin signaling has emerged as a significant potentiator of pluripotency: increases in the levels of β-catenin regulate the activity of Oct4 and Nanog, and enhance pluripotency.A recent report shows that β-catenin achieves some of these effects by modulating the activity of Tcf3, and that this effect does not require its transcriptional activation domain.Our results establish that β-catenin, but not its transcriptional activity, is central to pluripotency acting through a β-catenin/Oct4 complex.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, University of Cambridge, Cambridge CB2 3EH, UK.

ABSTRACT
The maintenance of pluripotency in mouse embryonic stem cells (mESCs) relies on the activity of a transcriptional network that is fuelled by the activity of three transcription factors (Nanog, Oct4 and Sox2) and balanced by the repressive activity of Tcf3. Extracellular signals modulate the activity of the network and regulate the differentiation capacity of the cells. Wnt/β-catenin signaling has emerged as a significant potentiator of pluripotency: increases in the levels of β-catenin regulate the activity of Oct4 and Nanog, and enhance pluripotency. A recent report shows that β-catenin achieves some of these effects by modulating the activity of Tcf3, and that this effect does not require its transcriptional activation domain. Here, we show that during self-renewal there is negligible transcriptional activity of β-catenin and that this is due to its tight association with membranes, where we find it in a complex with Oct4 and E-cadherin. Differentiation triggers a burst of Wnt/β-catenin transcriptional activity that coincides with the disassembly of the complex. Our results establish that β-catenin, but not its transcriptional activity, is central to pluripotency acting through a β-catenin/Oct4 complex.

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A mechanism for β-catenin-mediated regulation of pluripotency. (A) The level of β-catenin is a major determinant of pluripotency through its role in the assembly of a complex with Oct4 and E-cadherin. In the ground state (enriched in 2i conditions), a membrane-associated complex between Oct4 (pink), β-catenin (blue) and cadherin limits the amount of Oct4 available for interactions with other proteins. Most of the Oct4 is available for interactions with Nanog (green), which is abundant in the ground state; the complex promotes pluripotency. In parallel, a different pool of β-catenin interacts with and inactivates Tcf3 (orange), thus allowing efficient activity of the Oct4:Nanog-driven network. If the levels of β-catenin drop, the amount of Oct4 in the membrane-associated complex is reduced and there is more Oct4 available for interactions with other factors, some of which promote lineage priming. The reduced amount of β-catenin limits its interaction with Tcf3, which is now available to repress pluripotency genes. In this state, as a consequence of looser regulation of Oct4 and Tcf3, cells have a higher probability of differentiating and exhibit a noisier pluripotency network. Red lines indicate protein-protein interactions; blue lines indicate transcriptional regulatory interactions. (B) The interactions and activity of β-catenin in these protein complexes does not involve or require its transcriptional activity (for details see text).
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Figure 8: A mechanism for β-catenin-mediated regulation of pluripotency. (A) The level of β-catenin is a major determinant of pluripotency through its role in the assembly of a complex with Oct4 and E-cadherin. In the ground state (enriched in 2i conditions), a membrane-associated complex between Oct4 (pink), β-catenin (blue) and cadherin limits the amount of Oct4 available for interactions with other proteins. Most of the Oct4 is available for interactions with Nanog (green), which is abundant in the ground state; the complex promotes pluripotency. In parallel, a different pool of β-catenin interacts with and inactivates Tcf3 (orange), thus allowing efficient activity of the Oct4:Nanog-driven network. If the levels of β-catenin drop, the amount of Oct4 in the membrane-associated complex is reduced and there is more Oct4 available for interactions with other factors, some of which promote lineage priming. The reduced amount of β-catenin limits its interaction with Tcf3, which is now available to repress pluripotency genes. In this state, as a consequence of looser regulation of Oct4 and Tcf3, cells have a higher probability of differentiating and exhibit a noisier pluripotency network. Red lines indicate protein-protein interactions; blue lines indicate transcriptional regulatory interactions. (B) The interactions and activity of β-catenin in these protein complexes does not involve or require its transcriptional activity (for details see text).

Mentions: We surmise that the β-catenin/Oct4 complex lies at the core of a protein interaction network whose dynamics govern the activity of the pluripotency TFN. The network is defined through interactions between three complexes - Oct4/β-catenin, Oct4/Nanog and β-catenin/Tcf3 - which compete with each other for their individual shared components (Fig. 8). The output of these interactions might be a steady state ratio of the different complexes and free molecules, which determine the degree of pluripotency of the ES cell population: if Tcf3>Oct4, there is a higher probability of differentiation; if Oct4>Tcf3, there is a higher probability of self-renewal (Fig. 8). We surmise that the impact of β-catenin on the network is twofold. In agreement with previous reports (Wray et al., 2011; Yi et al., 2011), it limits the activity of Tcf3 and delays the exit from pluripotency but it also controls the amount of Oct4 that can be free by promoting its membrane localization to ensure that Oct4 interacts preferentially with Nanog rather than with lineage-priming factors. A prediction of this model is that self-renewal will be characterized by limiting amounts of Oct4 that, once they exceed a threshold value, will promote differentiation through their lineage-priming ability. This is in agreement with the sensitivity of pluripotency to the levels of Oct4 (Niwa et al., 2000).


A membrane-associated β-catenin/Oct4 complex correlates with ground-state pluripotency in mouse embryonic stem cells.

Faunes F, Hayward P, Descalzo SM, Chatterjee SS, Balayo T, Trott J, Christoforou A, Ferrer-Vaquer A, Hadjantonakis AK, Dasgupta R, Arias AM - Development (2013)

A mechanism for β-catenin-mediated regulation of pluripotency. (A) The level of β-catenin is a major determinant of pluripotency through its role in the assembly of a complex with Oct4 and E-cadherin. In the ground state (enriched in 2i conditions), a membrane-associated complex between Oct4 (pink), β-catenin (blue) and cadherin limits the amount of Oct4 available for interactions with other proteins. Most of the Oct4 is available for interactions with Nanog (green), which is abundant in the ground state; the complex promotes pluripotency. In parallel, a different pool of β-catenin interacts with and inactivates Tcf3 (orange), thus allowing efficient activity of the Oct4:Nanog-driven network. If the levels of β-catenin drop, the amount of Oct4 in the membrane-associated complex is reduced and there is more Oct4 available for interactions with other factors, some of which promote lineage priming. The reduced amount of β-catenin limits its interaction with Tcf3, which is now available to repress pluripotency genes. In this state, as a consequence of looser regulation of Oct4 and Tcf3, cells have a higher probability of differentiating and exhibit a noisier pluripotency network. Red lines indicate protein-protein interactions; blue lines indicate transcriptional regulatory interactions. (B) The interactions and activity of β-catenin in these protein complexes does not involve or require its transcriptional activity (for details see text).
© Copyright Policy - open-access
Related In: Results  -  Collection

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Figure 8: A mechanism for β-catenin-mediated regulation of pluripotency. (A) The level of β-catenin is a major determinant of pluripotency through its role in the assembly of a complex with Oct4 and E-cadherin. In the ground state (enriched in 2i conditions), a membrane-associated complex between Oct4 (pink), β-catenin (blue) and cadherin limits the amount of Oct4 available for interactions with other proteins. Most of the Oct4 is available for interactions with Nanog (green), which is abundant in the ground state; the complex promotes pluripotency. In parallel, a different pool of β-catenin interacts with and inactivates Tcf3 (orange), thus allowing efficient activity of the Oct4:Nanog-driven network. If the levels of β-catenin drop, the amount of Oct4 in the membrane-associated complex is reduced and there is more Oct4 available for interactions with other factors, some of which promote lineage priming. The reduced amount of β-catenin limits its interaction with Tcf3, which is now available to repress pluripotency genes. In this state, as a consequence of looser regulation of Oct4 and Tcf3, cells have a higher probability of differentiating and exhibit a noisier pluripotency network. Red lines indicate protein-protein interactions; blue lines indicate transcriptional regulatory interactions. (B) The interactions and activity of β-catenin in these protein complexes does not involve or require its transcriptional activity (for details see text).
Mentions: We surmise that the β-catenin/Oct4 complex lies at the core of a protein interaction network whose dynamics govern the activity of the pluripotency TFN. The network is defined through interactions between three complexes - Oct4/β-catenin, Oct4/Nanog and β-catenin/Tcf3 - which compete with each other for their individual shared components (Fig. 8). The output of these interactions might be a steady state ratio of the different complexes and free molecules, which determine the degree of pluripotency of the ES cell population: if Tcf3>Oct4, there is a higher probability of differentiation; if Oct4>Tcf3, there is a higher probability of self-renewal (Fig. 8). We surmise that the impact of β-catenin on the network is twofold. In agreement with previous reports (Wray et al., 2011; Yi et al., 2011), it limits the activity of Tcf3 and delays the exit from pluripotency but it also controls the amount of Oct4 that can be free by promoting its membrane localization to ensure that Oct4 interacts preferentially with Nanog rather than with lineage-priming factors. A prediction of this model is that self-renewal will be characterized by limiting amounts of Oct4 that, once they exceed a threshold value, will promote differentiation through their lineage-priming ability. This is in agreement with the sensitivity of pluripotency to the levels of Oct4 (Niwa et al., 2000).

Bottom Line: Wnt/β-catenin signaling has emerged as a significant potentiator of pluripotency: increases in the levels of β-catenin regulate the activity of Oct4 and Nanog, and enhance pluripotency.A recent report shows that β-catenin achieves some of these effects by modulating the activity of Tcf3, and that this effect does not require its transcriptional activation domain.Our results establish that β-catenin, but not its transcriptional activity, is central to pluripotency acting through a β-catenin/Oct4 complex.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics, University of Cambridge, Cambridge CB2 3EH, UK.

ABSTRACT
The maintenance of pluripotency in mouse embryonic stem cells (mESCs) relies on the activity of a transcriptional network that is fuelled by the activity of three transcription factors (Nanog, Oct4 and Sox2) and balanced by the repressive activity of Tcf3. Extracellular signals modulate the activity of the network and regulate the differentiation capacity of the cells. Wnt/β-catenin signaling has emerged as a significant potentiator of pluripotency: increases in the levels of β-catenin regulate the activity of Oct4 and Nanog, and enhance pluripotency. A recent report shows that β-catenin achieves some of these effects by modulating the activity of Tcf3, and that this effect does not require its transcriptional activation domain. Here, we show that during self-renewal there is negligible transcriptional activity of β-catenin and that this is due to its tight association with membranes, where we find it in a complex with Oct4 and E-cadherin. Differentiation triggers a burst of Wnt/β-catenin transcriptional activity that coincides with the disassembly of the complex. Our results establish that β-catenin, but not its transcriptional activity, is central to pluripotency acting through a β-catenin/Oct4 complex.

Show MeSH
Related in: MedlinePlus