The BMP signaling gradient is interpreted through concentration thresholds in dorsal-ventral axial patterning

Area of Science:

• Developmental Biology
• Molecular Biology
• Genetics

Background:

• Bone Morphogenetic Protein (BMP) is crucial for patterning the dorsal-ventral embryonic axis in vertebrates.
• The precise mechanism by which cells interpret BMP gradients to achieve distinct cell fates remains unclear.

Purpose of the Study:

• To elucidate how cells in the zebrafish gastrula interpret BMP signaling gradients.
• To identify genes directly activated by BMP signaling and their spatial expression domains.

Main Methods:

• Identified 57 BMP-directly activated genes.
• Utilized single-cell RNA sequencing (scRNA-seq) and Seurat analysis.
• Quantified phosphorylated Smad5 (pSmad5) levels and analyzed spatial gene expression at single-cell resolution.

Main Results:

• BMP-activated genes were found in at least three distinct dorsal-ventral domains.
• Differential gene expression was not explained by BMP gradient slope or signal duration.
• Cells respond to three distinct levels of BMP signaling activity.

Conclusions:

• Distinct phosphorylated Smad5 (pSmad5) threshold levels determine target gene activation.
• This mechanism precisely positions gene expression to pattern the dorsal-ventral axis.
• Provides a model for BMP morphogen interpretation in vertebrate development.