New yeast strain could shed light on aging

Local scientists have created the world's first strain of yeast with only one chromosome, a breakthrough intended to support research on human cell aging and genetic mutation.
Yang Zhengxing

Dr Qin Zhongjun, a molecular biologist, observes the growth of single-chromosome brewer’s yeast at his laboratory at the Center for Excellence in Molecular Plant Sciences, Shanghai Institute of Plant Physiology and Ecology, of Chinese Academy of Sciences.

Local scientists have created the world’s first strain of yeast with only one chromosome, a breakthrough intended to support research on human cell aging and genetic mutation.

The team behind the new strain was led by Dr Qin Zhongjun, a molecular biologist from a Shanghai-based research center affiliated with the Chinese Academy of Sciences. Dr Qin and his fellow researchers spent four years on the yeast, and conducted 15 rounds of end-to-end fusion to create a single-chromosome strain. 

Other strains of yeast have 16 linear chromosomal pairs.

The team’s results were published yesterday in a paper posted on the website of the journal Nature.

The number of chromosomes differs between species. Humans have 23 chromosome pairs, whereas apes have 24, and the male jack jumper ant has only one.

As Dr Qin explained, organisms are generally divided into two categories — eukaryotes and prokaryotes. Eukaryotes like humans, animals and plants have multiple linear chromosomes; while prokaryotes have only a single, circular chromosome. In their new yeast strain, the team used genetic editing to produce a eukaryote with a single chromosome that contains all of its original genetic material.

Ordinary brewer’s yeast is often used in chromosomal research, as “one third of its genes are homologous to human’s,” said Dr Qin.


Single-chromosome brewer’s yeast

Experts say the new strain can aid research on aging and other conditions related to telomere deterioration. 

“Telomeres are protective caps at the ends of linear chromosomes. With increasing numbers of cell division, the length of the telomere will shorten. When a telomere cannot be shortened anymore, the cell will die.”

Dr Qin said human aging has something to do with the length of telomeres, along with many diseases, including cancer. 

The single-chromosome yeast created by Dr Qin’s team has only two telomeres and so can provide a simplified model for researchers to study the functions of human telomeres and cell aging.

Zhou Jinqiu, deputy head of the Shanghai Institute of Biochemistry and Cell Biology, said telomeres are like the plastic tips at the end of shoelaces. Just as shoelaces will come apart without these tips, Zhou explained that “without telomeres, the chromosomes will lose their genes and after they lose all of them the cells will no longer divide and then human tissue will not grow.”

“That’s the concept of aging,” he added.

From this conclusion, experts theorize that if telomere deterioration can be slowed, so too can the aging process be delayed.

With cancer, the unhealthy division of cancer cells requires telomeres to maintain a certain length, thus making them a necessary factor in cancer cells’ growth and division.

“But so far our study still hasn’t made it very clear how to maintain the length of the telomeres on normal cells, or how to cut cancer cells’ telomeres shorter to make them die,” said Zhou.


Qin introduces his research in Shanghai.

According to the paper, the change to the chromosome count has little impact on gene activity. However, the single-chromosome strain produces fewer spores, which are reproductive cells for non-flowering plants, bacteria, fungi, and algae, in sexual reproduction.

“The survival rate of spores produced by a natural yeast strain is 98 percent, while that of ours is 87.5 percent. The gap is not big,” Qin said.

The paper also said that Jef Boeke, a geneticist at New York University, and his team submitted their outcome for similar research. They condensed the yeast genome into a pair of chromosomes, but could not fuse the pair into one.

One explanation for the difference is that Qin’s team removed 19 repetitive stretches of DNA. Qin suggested these sequences might have interfered with the mechanism that cells use to fuse two chromosomes into one.

The two teams worked independently from each other.

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