It’s not just organisms that change as they grow old—individual cells age too. Among myriad changes during cellular aging is the gradual shortening of telomeres, the protective ends of gene-containing chromosomes. To study telomeres, their regulation, and their associations with health and disease, biologists have largely relied on collections of cells to measure average telomere length. Older groups of cells have, on average, shorter telomeres than younger groups of cells. Now, a team of researchers has developed a way to measure the telomeres in one individual cell at a time. The method, published in a PNAS Early Edition paper this week, can be used to uncover telomere heterogeneity between similar cells and to better understand the regulation and consequences of telomere length.
Older methods used to measure telomere length in cells were costly and time consuming, says Sherman Weissman, a Yale University School of Medicine genetics researcher who spearheaded the new work. But the new technique, he says, “is very robust and quick and inexpensive.”
The biggest drawback to previous techniques is that, to measure telomeres, they required more DNA than a single cell contains. So cells had to be combined into groups to get large enough samples. To get around this problem, Weissman and his collaborators developed a method that, instead of measuring only the telomeres, compares the length of telomeres to the length of other
genes that are more stable in length. One cell’s worth of DNA is sufficient for this comparison.
To perform the measurements, the researchers used quantitative real-time PCR (qPCR), an established method that determines the amount of DNA in a sample. They’ve dubbed their new approach single-cell telomere qPCR, or SCT-pqPCR. To illustrate its usefulness, the team measured telomere length in a variety of human cells, as well as mouse embryos.
“We discovered that during repeated cell divisions, telomeres not only become shorter, but also become more heterogenic,” says Xinghua Pan, a Yale genetics researcher who collaborated with Weissman.
It will take more work to understand the significance of this heterogeneity, and uncover molecular differences that impact it. To help speed up the experiments required to answer such questions, the team wants to develop a high-throughput version of SCT-pqPCR so that they can get many single-cell measurements at once. But they expect the current version of the method to gain popularity even without these improvements—being able to measure single-cell telomere lengths will be a boon to researchers studying human fertility, stem cells, and cancers, Weissman says. And the method is easily adoptable by any lab that already performs other qPCR experiments.
And now that they can measure the telomeres of individual cells, Weissman’s team has set their sights even higher: “We would like to be able to measure the telomere length of individual chromosomes now,” Weismann says. Heterogeneity likely doesn’t end with at the cellular level, he says, and it’s important to know which chromosomes are wearing down the fastest and how this affects cells.