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Antagonism between Smad1 and Smad2 signaling determines the site of distal visceral endoderm formation in the mouse embryo.

Yamamoto M, Beppu H, Takaoka K, Meno C, Li E, Miyazono K, Hamada H - J. Cell Biol. (2009)

Bottom Line: A Smad2-activating factor such as Activin also contributes to DVE formation by generating a region of VE positive for the Smad2 signal and negative for Smad1 signal.DVE is thus formed at the distal end of the embryo, the only region of VE negative for the Smad1 signal and positive for Smad2 signal.An inverse relation between the level of phosphorylated Smad1 and that of phosphorylated Smad2 in VE suggests an involvement of antagonism between Smad1- and Smad2-mediated signaling.

View Article: PubMed Central - PubMed

Affiliation: Developmental Genetics Group, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan. myamamoto@fbs.osaka-u.ac.jp

ABSTRACT
The anterior-posterior axis of the mouse embryo is established by formation of distal visceral endoderm (DVE) and its subsequent migration. The precise mechanism of DVE formation has remained unknown, however. Here we show that bone morphogenetic protein (BMP) signaling plays dual roles in DVE formation. BMP signaling is required at an early stage for differentiation of the primitive endoderm into the embryonic visceral endoderm (VE), whereas it inhibits DVE formation, restricting it to the distal region, at a later stage. A Smad2-activating factor such as Activin also contributes to DVE formation by generating a region of VE positive for the Smad2 signal and negative for Smad1 signal. DVE is thus formed at the distal end of the embryo, the only region of VE negative for the Smad1 signal and positive for Smad2 signal. An inverse relation between the level of phosphorylated Smad1 and that of phosphorylated Smad2 in VE suggests an involvement of antagonism between Smad1- and Smad2-mediated signaling.

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A limited level of type II Activin receptors is responsible for antagonistic balance between Smad1 and Smad2 signaling in the mouse embryo. (A) Experimental strategy. An effector gene, together with a GFP expression vector, was introduced into epiblast cells on the distal side of E5.2 mouse embryos. The embryos were cultured for 12 h and were examined for the distribution of p-Smad1 by immunohistofluorescence staining. (B–E) Localization of p-Smad1 (pS1; green) and merged images of p-Smad1 with GFP-positive cells (GFP; red). Arrowhead indicates the GFP-positive cell. S4, Smad4; Actr2, Actr2a plus Actr2b. Bars, 50 µm.
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fig8: A limited level of type II Activin receptors is responsible for antagonistic balance between Smad1 and Smad2 signaling in the mouse embryo. (A) Experimental strategy. An effector gene, together with a GFP expression vector, was introduced into epiblast cells on the distal side of E5.2 mouse embryos. The embryos were cultured for 12 h and were examined for the distribution of p-Smad1 by immunohistofluorescence staining. (B–E) Localization of p-Smad1 (pS1; green) and merged images of p-Smad1 with GFP-positive cells (GFP; red). Arrowhead indicates the GFP-positive cell. S4, Smad4; Actr2, Actr2a plus Actr2b. Bars, 50 µm.

Mentions: We next examined the molecular basis of the antagonism between BMP and Activin–Nodal signaling. Activin–Nodal and BMP share common signaling components, extracellular components such as ActR2A and ActR2B as well as intracellular components including Smad4. If the amount of a common component is limited, an increase in one signal would result in a decrease in the other. To test this possibility, we introduced a Smad4 or Actr2a+Actr2b expression vector into a p-Smad1–positive cell in the distal region of E5.2 embryo and examined if such cells would maintain or lose p-Smad1 12 h later (equivalent to E5.7; Fig. 8). Normally, such p-Smad1–positive cells at E5.2 (Fig. 2 B) lose p-Smad1 by E5.5 (Fig. 2 C). However, if a limiting factor commonly used for both signaling is overexpressed into such a cell, it would prevent the antagonism and the cell would remain positive for p-Smad1 at E5.5. This is what we observed when Actr2 was overexpressed (Fig. 8 A).


Antagonism between Smad1 and Smad2 signaling determines the site of distal visceral endoderm formation in the mouse embryo.

Yamamoto M, Beppu H, Takaoka K, Meno C, Li E, Miyazono K, Hamada H - J. Cell Biol. (2009)

A limited level of type II Activin receptors is responsible for antagonistic balance between Smad1 and Smad2 signaling in the mouse embryo. (A) Experimental strategy. An effector gene, together with a GFP expression vector, was introduced into epiblast cells on the distal side of E5.2 mouse embryos. The embryos were cultured for 12 h and were examined for the distribution of p-Smad1 by immunohistofluorescence staining. (B–E) Localization of p-Smad1 (pS1; green) and merged images of p-Smad1 with GFP-positive cells (GFP; red). Arrowhead indicates the GFP-positive cell. S4, Smad4; Actr2, Actr2a plus Actr2b. Bars, 50 µm.
© Copyright Policy - openaccess
Related In: Results  -  Collection

License 1 - License 2
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getmorefigures.php?uid=PMC2654303&req=5

fig8: A limited level of type II Activin receptors is responsible for antagonistic balance between Smad1 and Smad2 signaling in the mouse embryo. (A) Experimental strategy. An effector gene, together with a GFP expression vector, was introduced into epiblast cells on the distal side of E5.2 mouse embryos. The embryos were cultured for 12 h and were examined for the distribution of p-Smad1 by immunohistofluorescence staining. (B–E) Localization of p-Smad1 (pS1; green) and merged images of p-Smad1 with GFP-positive cells (GFP; red). Arrowhead indicates the GFP-positive cell. S4, Smad4; Actr2, Actr2a plus Actr2b. Bars, 50 µm.
Mentions: We next examined the molecular basis of the antagonism between BMP and Activin–Nodal signaling. Activin–Nodal and BMP share common signaling components, extracellular components such as ActR2A and ActR2B as well as intracellular components including Smad4. If the amount of a common component is limited, an increase in one signal would result in a decrease in the other. To test this possibility, we introduced a Smad4 or Actr2a+Actr2b expression vector into a p-Smad1–positive cell in the distal region of E5.2 embryo and examined if such cells would maintain or lose p-Smad1 12 h later (equivalent to E5.7; Fig. 8). Normally, such p-Smad1–positive cells at E5.2 (Fig. 2 B) lose p-Smad1 by E5.5 (Fig. 2 C). However, if a limiting factor commonly used for both signaling is overexpressed into such a cell, it would prevent the antagonism and the cell would remain positive for p-Smad1 at E5.5. This is what we observed when Actr2 was overexpressed (Fig. 8 A).

Bottom Line: A Smad2-activating factor such as Activin also contributes to DVE formation by generating a region of VE positive for the Smad2 signal and negative for Smad1 signal.DVE is thus formed at the distal end of the embryo, the only region of VE negative for the Smad1 signal and positive for Smad2 signal.An inverse relation between the level of phosphorylated Smad1 and that of phosphorylated Smad2 in VE suggests an involvement of antagonism between Smad1- and Smad2-mediated signaling.

View Article: PubMed Central - PubMed

Affiliation: Developmental Genetics Group, Graduate School of Frontier Biosciences, Osaka University, Osaka, Japan. myamamoto@fbs.osaka-u.ac.jp

ABSTRACT
The anterior-posterior axis of the mouse embryo is established by formation of distal visceral endoderm (DVE) and its subsequent migration. The precise mechanism of DVE formation has remained unknown, however. Here we show that bone morphogenetic protein (BMP) signaling plays dual roles in DVE formation. BMP signaling is required at an early stage for differentiation of the primitive endoderm into the embryonic visceral endoderm (VE), whereas it inhibits DVE formation, restricting it to the distal region, at a later stage. A Smad2-activating factor such as Activin also contributes to DVE formation by generating a region of VE positive for the Smad2 signal and negative for Smad1 signal. DVE is thus formed at the distal end of the embryo, the only region of VE negative for the Smad1 signal and positive for Smad2 signal. An inverse relation between the level of phosphorylated Smad1 and that of phosphorylated Smad2 in VE suggests an involvement of antagonism between Smad1- and Smad2-mediated signaling.

Show MeSH