Yeast, and it’s use in the production of alcohol, has allowed humans to practice biotechnology for hundred of decades. In recent years, it has become an important model organism in genetic research for a multitude of reasons.
Around 23% of yeast genes are homologous with genes in the human genome, meaning that research carried out on yeast is particularly applicable to humans, making it an attractive option for genetic replication studies.
Research is now moving beyond simply replicating genes, and towards how we can create new ones.
Eureka for eukaryotes
Researchers have reached a milestone record by producing a yeast that is comprised of over 50% artificial DNA. This record means potential for unchartered expansion in industries that utilise yeast, such as brewing, baking and medicinal production, but it also has wider implications.
Yeast is the first eukaryote which has been produced with over 50% artificial DNA. Eukaryotes are complex organisms whose DNA is contained in a nucleus – like us. The DNA of the model yeast species, Saccharomyces cerevisiae, is organised into 16 distinct chromosomes, and so has significantly more DNA than previously sequenced organisms such as bacteria.
Instead of replicating the genome directly, the researchers opted to redesign the structure of the yeast, adding new modifications and relocating or removing sections of DNA which were deemed unimportant or destabilizing to the structure of the organism.
The scientists even built a genetic mechanism to randomly alternate the order of genes between chromosomes. High genetic diversity within species is essential for maintaining a healthy population. If an environment arises in which certain genes make their organism susceptible to damage or disease, having a diverse genetic range of organisms within the species allows the population to thrive and reproduce despite susceptibility to damage or disease. Useful genes can then be passed down to future generations of the organisms, even if some of the population dies.
The scientists working on this project hail from all over the world, with work coming together from laboratories throughout Europe, Asia, Oceania and the US.
The team working at the Manchester Institute of Biotechnology (MIB) have created a completely new chromosome – tRNA Neochromosome. This additional chromosome has totalled the number of chromosomes in these yeast genomes into an unusual 17, rather than the typical 16 in Saccharomyces cerevisiae. The neochromosome houses 275 nuclear transfer RNA (tRNA) genes.
tRNA are small non-coding DNA molecules which read DNA sequences and select the matching amino acids. A string of amino acids creates a protein, like muscle. Whilst they are essential for our body, they are particularly susceptible to damage and it is as a result of this that scientists decided to segregate them into their own chromosome, tRNA Neochromosome.
The cells were found to continue to grow successfully on addition of tRNA Neochromosome, albeit slowed slightly; however, its addition ultimately allowed the yeast to be more stable.
Ethics and yeast
The research brings new dimensions when considering the ethical questions of the future of genetic research. There has long been controversy and fear surrounding the research into genetic modification in human populations, but historically the predicted trajectory was that large numbers of embryos would be produced and genetically screened, and parents would choose the one which is most suitable.
Here the question could be asked, what happens when we start, not replicating, but creating human cells from scratch? What would we choose to create? And who would get to choose?
There are plenty of imagined possibilities of the future of genetic modification in science fiction. The novel, and subsequent movie, Never Let Me Go by Kazuo Ishiguro explores a future in which cloning is widely accepted and ‘inhuman’ but genetically identical clones are created for every naturally-born human. The novel explores Ishiguro’s concept that research to produce genetically superior humans was entirely rejected by society, but producing genetically identical clones was acceptable.
The successful creation of an entirely synthetic yeast brings us one step further from Ishiguro’s predictions – perhaps we do have the tools to create new life, rather than alter what we already have. And perhaps we will use it after all.