Cell type-dependent directional transcription at enhancers

Area of Science:

• Genomics
• Transcriptomics
• Molecular Biology

Background:

• Enhancers are crucial noncoding regulatory genomic regions.
• Previously, enhancers were characterized by bidirectional noncoding RNA expression.
• Balanced bidirectional expression was a key feature for enhancer detection.

Purpose of the Study:

• To re-evaluate enhancer transcription patterns using deep transcriptome datasets.
• To investigate the directionality of enhancer transcription in individual cell types and single cells.

Main Methods:

• Analysis of FANTOM5 and other deep cap analysis gene expression (CAGE) transcriptome datasets.
• Utilizing 5' single-cell RNA sequencing data.
• Employing reporter assays to assess enhancer function.

Main Results:

• Enhancer transcription is preferentially unidirectional within individual cell types.
• The preferred directionality can switch between different cell types.
• Single-cell RNA sequencing confirms almost exclusive unidirectional enhancer expression at the single-cell level.
• Enhancer regulatory function is independent of expression directionality (unidirectional vs. bidirectional).

Conclusions:

• The assumption of balanced bidirectional transcription for enhancer detection may lead to the exclusion of many valid enhancers, especially in single-cell type transcriptome data.
• Rethinking enhancer detection criteria is necessary for accurate identification in diverse cellular contexts.