Visualizing DNA folding and RNA in embryos at single-cell resolution

Area of Science:

• Developmental Biology
• Genomics
• Molecular Biology

Background:

• Gene regulation relies on precise interactions between genes and regulatory DNA elements.
• Understanding the 3D organization of chromatin and its role in cell-type specificity is limited.
• Current methods lack the resolution to study these interactions in single cells.

Purpose of the Study:

• To develop a high-resolution method for analyzing 3D chromatin architecture in single cells.
• To investigate how chromatin structure varies across cell types during development.
• To understand the relationship between DNA organization, gene regulation, and developmental outcomes.

Main Methods:

• Optical Reconstruction of Chromatin Architecture (ORCA) was developed to trace DNA paths with nanoscale accuracy and 2-kilobase genomic resolution.
• ORCA was applied to cryosectioned Drosophila embryos.
• Simultaneous labeling of approximately 30 RNA species was performed to correlate DNA structure with gene expression.

Main Results:

• ORCA enabled high-resolution, single-cell DNA domain analysis in vivo.
• Cell-type-specific physical borders between active and Polycomb-repressed DNA were identified.
• Unexpected Polycomb-independent borders were discovered, and their deletion caused developmental defects.

Conclusions:

• ORCA provides a powerful approach for studying 3D chromatin organization at the nanoscale in single cells.
• Chromatin domain structures are dynamic and cell-identity specific.
• Border elements play a crucial role in establishing physical DNA domains and ensuring proper gene regulation during development.