Quantitative analysis of genomic element interactions by molecular colony technique

Area of Science:

• Genomics
• Molecular Biology
• Cell Biology

Background:

• Distant genomic elements interact within the folded eukaryotic genome.
• Chromosome conformation capture (3C) has limitations in quantifying interaction frequency and multiple simultaneous interactions.

Purpose of the Study:

• To introduce a novel technique, in-gel replication of interacting DNA segments, for analyzing genomic interactions.
• To overcome the limitations of 3C by determining the percentage of cells with interactions and detecting simultaneous interactions of multiple genomic elements.

Main Methods:

• Formaldehyde-cross-linked chromatin fragments are isolated and embedded in a polyacrylamide gel.
• Multiplex polymerase chain reaction (PCR) is performed directly within the gel to amplify interacting DNA segments.
• Multi- and monocomponent molecular colonies are distinguished and counted to quantify interactions.

Main Results:

• In mouse erythroid cells, the majority of fragments containing active β-globin gene promoters and remote enhancers did not form stable complexes.
• These complexes were not stable enough to withstand sodium dodecyl sulfate extraction and sonication.
• The study quantified the frequency of DNA interactions within a cellular context.

Conclusions:

• The findings suggest that active β-globin gene promoters and enhancers may not interact directly in the majority of cells at a specific time.
• Alternatively, the DNA-protein complexes formed may not be stabilized by formaldehyde cross-linking.
• The in-gel replication technique provides a new approach for studying genome organization and DNA interactions.