Gene-editing technology used to fit entire genome of yeast on a single large chromosome.
Brewer’s yeast (Saccharomyces cerevisiae) normally has 16 chromosomes. In the latest study published in Nature, a group of Chinese scientists successfully fitted all the genetic material on a single large chromosome. This was done along with deletion of some unnecessary genes (19). Other than reduced asexual reproduction no other deleterious effect was witnessed on the new man-made yeast specie.
The single strain chromosome is the result of extreme genetic surgery performed by this group of scientists using CRISPR gene-editing tool. Using the technology scientists first removed the telomeres (caps that protect the end of chromosomes from degrading) and simultaneously removed centromere (button that joins two chromosomes strands together) of one of the two chromosomes. Followed by fusing the chromosomes end to end, one by one. Finally adding all other chromosomes successively in the similar fashion. During the process each addition of chromosome lead to reduction of chromosome number until a single large chromosome was obtained. The super chromosome (one) so produced was identical to the normal yeast chromosomes (16) except of the fact that here all the genetic material was condensed on one long chromosome.
The paper also said that Jef Boeke, a geneticist at New York University, and his team submitted their outcome for similar research. Boeke’s team also used CRISPR to remove telomeres and centromere and relied on yeasts natural DNA repair mechanism. They ended up with a yeast strain that had two extra-long chromosomes, but they could not get the pair to fuse into one. Possible explanation can be removal of 19 repetitive stretches of DNA, by Qin and his team, which might have interfered with the mechanism that cells use to fuse two chromosomes into one.
Both the study suggests the role of DNA-sequence changes in creating new species. As the new single chromosome yeast strain produced shows similar biological function like cell growth, development, assimilation like normal 16 chromosome yeast. Also the new yeast strain can mate with each other but not its parent yeast from which it was made.
Beyond the current finding, the study is also important in understanding the function of telomeres. Earlier research found that the length of telomeres is related to early aging, the formation of tumors, and other diseases. Telomeres shorten as a cell splits, but if telomeres cannot shorten anymore, the cell dies.
Again the study will help in studying fundamental concepts in chromosome biology, including replication, recombination and segregation. Though the discovery gives an insight to some of the answers it also raises fundamental questions like why the number of chromosomes that eukaryotes have varies wildly but seems to have no correlation with the amount of genetic information they possess. Why does every organism has a specific set of chromosomes? In fact why cells have chromosomes at all? With only one chromosome and two telomeres, it will be easier to find the patterns.
The work is also a demonstration how “large-scale genome engineering” can be done to create “new man-made species”.
Would CRISPR technology be a prime in creating man-made species of future?