Efficient retina formation requires suppression of both Activin and BMP signaling pathways in pluripotent cells

Area of Science:

• Developmental biology
• Cell signaling
• Regenerative medicine

Background:

• Retina formation relies on precise spatiotemporal regulation of signaling pathways.
• Noggin, a BMP antagonist, can induce retinal cell fate from pluripotent Xenopus laevis cells.
• The intracellular mechanisms underlying Noggin-induced retinal conversion remain incompletely understood.

Purpose of the Study:

• To elucidate the intracellular molecular events governing Noggin-induced retinal cell conversion in Xenopus.
• To investigate the roles of BMP and Activin signaling pathways in this process.
• To identify key molecular targets and pathways involved in retinal specification.

Main Methods:

• Overexpression of Noggin in pluripotent Xenopus laevis animal cap cells.
• Treatment with dominant-negative receptors and chemical inhibitors (dorsomorphin, SB431542) targeting BMP and Activin pathways.
• Animal Cap Transplant (ACT) assay to assess retinal specification in vivo.
• Analysis of downstream molecular markers (Smad1, Smad2 phosphorylation, xk81, xbra, rax).

Main Results:

• Noggin overexpression suppressed Smad1 and Smad2 phosphorylation, reducing mesodermal and endothelial markers.
• Inhibition of Activin signaling, concurrent with BMP signaling inhibition, efficiently promoted retinal specification.
• Simultaneous inhibition of both BMP and Activin pathways (using dominant-negative Smad1/Smad2 or chemical inhibitors) expanded the eye field marker, rax, in whole embryos.

Conclusions:

• Retinal specification in Xenopus is promoted by the combined inhibition of Activin and BMP signaling pathways.
• This dual inhibition mimics the effect of Noggin treatment, suggesting a conserved mechanism.
• Findings provide a foundation for developing methods to generate retinal cells in culture.