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Fluorescence filters shed light on unconsidered DNA variation

When the human genome was mapped ‘in full’ over a decade ago, it still technically contained some gaps, and scientists are now investigating these unknown areas using fluorescence filters.

Centromeres are the building blocks of chromosomes, holding them together in a distinctive X shape, and each centromere is surrounded by a repetitive sequence of 171 DNA bases, labelled A, C, G and T.

But some chromosomes contain more than one of these 171-base sequences, which means the centromere itself can be found in one of several locations.

Researcher Beth Sullivan from Duke University School of Medicine used visual techniques to look at chromatin fibres from human chromosomes, painting them with fluorescent probes to highlight subtle variations in these centromere sites.

She found that about seven in ten people have very little variation in these places – but for the other three, more distinct variations might ultimately influence the ‘decision’ as to where the centromere is located, or how stable the chromosome is.

“It is immensely fascinating to think that there are so many people walking around who are essentially centromere mosaics,” said Dr Sullivan.

“One of their centromeres, on one of their chromosomes, has the potential to be dangerously unstable, and it could affect their ability to reproduce, or predispose them to cancer.”

Visual assays of these areas with fluorescence filters were combined with molecular assays to detect the presence of the essential proteins that are needed for the finished centromere to function correctly.

Although this is still at the research stage, ultimately similar methods might lead to new diagnostic methods for the three in ten with potentially unstable chromosomes due to this variability.

The sequences could then act as biomarkers, highlighting defective chromosomes and offering an early warning system to predict heightened risk of genetic diseases such as cancer.