Repeated DNA sequences that pose health risks when disrupted inside living cells can now be seen with a synthetic instrument
A new synthetic probe offers a safe and straightforward approach to visualize the ends of chromosomes in living cells. Designed by scientists at the Institute for Integrated Cellular Materials Science (iCeMS) and their colleagues at Kyoto University, the probe can advance research into aging and a wide range of diseases, including cancers. Details have been posted at Journal of the American Chemical Society.
“The ends of a chromosome are constantly at risk of degeneration and fusion, so they are protected by structures called telomeres, which are made of long, repetitive DNA sequences and linked proteins,” says Hiroshi Sugiyama, the chemist at iCeMS who led the study. If telomeres malfunction, they will not be able to keep the chromosomes stable, which could lead to diseases such as cancer. Also, telomeres usually shorten with each cell division until they reach their maximum, causing cells to die. “
Visualizing telomeres, and especially their physical arrangements in real time, is important to understanding their relationship to disease and aging. Several visualization techniques exist, but they have drawbacks. For example, some can only observe telomeres in conserved or “fixed” cells. Others are time consuming or involve harsh DNA treatments.
Sugiyama and colleagues overcome these issues by using a synthetic pyrrole-imidazole polyamide (PIP) probe that can accurately deliver a fluorescent compound to telomeres at the ends of chromosomes.
“PIPs are a class of small molecules made of pyrol and imidazole molecules that can be preprogrammed to link specific DNA sequences,” explains Yotaro Tsubono, first author of this study.
The team designed PIP targeting the DNA replication sequence found in telomeres. A fluorescent compound, called silicon-rhodamine, has been attached to the PIP. The SiR-TTet59B labeled probe binds to telomeres in live cells. When low-intensity near-infrared light is shone on cells, silicon and rhodamine fluoresce, and telomeres appear in action.
“Our study on a programmable near-infrared probe creates opportunities for the use of these molecules in biological and medical applications,” says iCeMS Ganesh Pandian Namasivayam, a bioengineer.
The team used their probe to monitor telomere dynamics during different stages of cell division and measure telomere length by measuring fluorescence intensity. The ability to visualize telomere length was surprising and exciting, Namasivayam says, as it could be developed to create an effective and robust approach for detecting acute telomere shortening in diseases, such as age-related retinal degeneration, with low-energy light.
Since PIPs can be designed to target any DNA sequence in the genome by changing their arrangement, scientists expect that the approach can be adapted to make near-infrared fluorescence probes to visualize other important disease-related DNA sequences.
DOI: 10.1021 / jacs.0c04955
About Kyoto University’s Institute for Integrated Cellular Materials Science (iCeMS):
At iCeMS our mission is to explore the secrets of life by creating compounds to control cells, and also on the path to creating materials inspired by life.
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