Synthia v.3A
A simple synthetic cell normally grows and divides
A few years ago, biologists created a single-celled synthetic organism, which, with only 473 genes, was the simplest living cell among all known to science. However, this bacterial-like organism behaved strangely in the process of growth and division, producing cells of completely different shapes and sizes. Now scientists have identified seven genes that can be added to the genome of a synthetic cell to tame its uncontrollable nature and make it grow normally and divide neatly.
Synthetic organism JCVI-syn1.0 (top image), synthetic organism JCVI-syn3.0 (middle image, cells of different sizes are visible, including those combined into threads) and JCVI-syn3.0 with added genes that should ensure normal division (bottom).
This achievement is the result of the collaboration of the John Craig Venter Institute (JCVI), the National Institute of Standards and Technology (NIST) and the Center for the Study of Particles and Atoms of the Massachusetts Institute of Technology (MIT).
Article by Pelletier et al. Genetic requirements for cell division in a genomically minimal cell is published in the journal Cell.
The identification of these genes is an important step towards the creation of synthetic cells capable of doing something useful: producing food, fuel, recycling waste, detecting disease foci in the body and delivering medicines to them or even producing them on the spot.
But to create a cell that will do what we need, first of all it is useful to understand what cells are made of, what, in detail, their minimal functional parts are, how they work and combine with each other, how the most basic processes are organized, including at the genetic level: nutrition, growth, division. Without this foundation, all of the above will remain dreams.
"We want to understand the fundamental rules of designing life," says Elizabeth Strychalski, co-author of the study and head of the Cell Engineering Group at NIST. "If this cage helps us discover and understand these rules, we will be on a horse."
John Craig Venter and colleagues constructed the first cell with a synthetic genome back in 2010. They didn't build this cage completely from scratch. Instead, they started with cells of a very simple type of bacteria called mycoplasma. They destroyed the DNA in these cells and replaced it with DNA that was developed on a computer and synthesized in a laboratory. It was the first organism in the history of life on Earth to possess a fully synthetic genome. They named it JCVI-syn1.0, or Mycoplasma laboratory.
Since then, scientists have been working to reduce this organism to a minimum of genetic components. The ultra-simple cell, created five years ago and called JCVI-syn3.0, was perhaps too minimalistic. Now the researchers have added 19 genes to the genome of this cell, including seven necessary for normal division, thus creating a new variant, JCVI-syn3A. This variant has less than 500 genes. That's pretty small. For comparison, there are about 4,000 genes in an E. coli escherichia coli cell, about 30,000 in a human cell (by genes here we mean open reading frames, that is, nucleotide sequences capable of encoding a protein).
The work to identify these seven additional genes took years of painstaking efforts by the JCVI Synthetic Biology group, led by a co-author of the work John Glass. One of the leading authors Lijie Sun has constructed dozens of variants of strains, systematically adding and removing genes. The researchers then observed how these genetic changes affected cell growth and division.
The role of NIST was to measure the resulting changes under a microscope. It wasn't easy because the cells had to be alive for observation. Using powerful microscopes to observe dead cells is relatively easy. Visualization of living cells is much more complicated.
Keeping these cells in place under a microscope was especially difficult because they are very small and fragile. There would be a hundred or more of them in one Escherichia coli bacterium. The slightest effort could tear them apart.
To solve this problem, Strychalski and co–authors from the Massachusetts Institute of Technology developed a microfluidic chemostat – a kind of mini-aquarium- in which cells could be kept full and happy under a light microscope. As a result, it was possible to obtain a frame-by-frame image of how synthetic cells grew and divided.
Comparing the results of microscopy of the vital activity of JCVI-syn3.0 cells with a video demonstrating the life cycle of new JCVI-syn3A synthetic cells, the scientists noted that if the former divide into cells of different shapes and sizes, often forming filaments, the latter divide into cells of much more identical shapes and sizes.
This is a great success, but, as Elizabeth Strychalski notes, "life is still a black box": scientists were closer to a detailed understanding of the work of the cell, but they achieved it. So, they fully understand the mechanism of operation of two of the seven genes added to the new synthetic organism, they have yet to understand the functionality of the rest.
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