Researchers have identified seven essential genes for cell division in a simple synthetic cell, allowing those created in a lab to divide in a manner similar to natural cells.
The study, published March 29 in Cell, brings scientists one step closer to answering a fundamental question in biology: What are the minimum requirements for a living cell?
"A Holy Grail for biology for decades, maybe even 100 years, has been the creation of a minimal cell," said senior author Elizabeth Strychalski, leader of the cellular engineering group at the National Institute of Standards and Technology. "What's the minimal number of functions and components you need for a pile of nonliving stuff to become animate? Our paper is very much a step in this larger narrative."
This narrative got its start in the 1960s, when the first artificial cells were developed by Thomas Chang at McGill University. However, these cells were extremely basic, essentially amounting to a cell-sized nylon capsule capable of letting molecules diffuse in and out.
In 2016, a major leap forward was made in the journey toward a simple, synthetic cell. Researchers from the J. Craig Venter Institute developed a freely reproducing cell with the smallest known genome, only 473 genes, building upon a previous cell they engineered in 2010.
However, this cell demonstrated erratic reproduction, multiplying at random and producing daughter cells at a large range of sizes, suggesting that its genome may have actually been too simple to regulate its growth.
In the present study, researchers at the Venter institute worked to pinpoint the minimum gene requirements for regular division. They accomplished this by reintroducing genes into the cell to tame its wild growth patterns. However, it proved difficult to measure such small changes in its growth and division. This is where Strychalski and her team at NIST came into the picture.
They designed a microfluidic chemostat — essentially a cell-sized aquarium — holding the cell in a closed environment shut off from external forces, allowing the team to observe the effects of different genes on the cell under the microscope.
"The cells are very delicate, something like a soap bubble," said coauthor James Pelletier, a postdoctoral researcher at Massachusetts Institute of Technology. "The cells are held in this very small chamber and provided a steady supply of food that the cells need to grow. The device also [helps remove] any byproduct that the cell produces as it's growing."
This highly controlled environment let the researchers painstakingly add and remove individual genes from the cell, systematically building an understanding of how the genes each contributed to the cell's reproduction, finally developing a variant of the cell that reproduced normally, which they called JCVI-syn3A.
"Our goal is to know the function of every gene so we can develop a complete model of how a cell works," Pelletier said.
While a large motivation for completing this work was to build upon fundamental biological knowledge, the researchers are also optimistic that this knowledge will see real-world applications as scientists become increasingly capable of synthesizing and controlling cells.
"People call this the century of biotechnology. Even without full mastery of the cell, there are still a lot of applications we can support," Strychalski said. "There are therapeutics, environmental applications, food applications and bio manufacturing."
However, there are still puzzles left to solve. Though the team identified seven genes involved in uniform reproduction of the synthetic cell, they were only able to ascertain the function of two of these genes. The other five are still unclear, one of many remaining mysteries in the new frontier of synthetic biology.
"The boundary of the unknown is so proximate," Strychalski said. "When I was coming into my own as a scientist, I was always wondering, 'Well if we know everything, what's left to discover?' But the more you learn, the more you learn what's left to learn."
The study, "Genetic requirements for cell division in a genomically minimal cell," published March 29 in Cell, was authored by James F. Pelletier, Andreas Mershin and Neil Gershenfeld, Massachusetts Institute of Technology; Lijie Sun, Kim S. Wise, Nacyra Assad-Garcia, Ray-Yuan Chuang and John I. Glass, J. Craig Venter Institute; Bogumil J. Karas, The University of Western Ontario; Thomas J. Deerinck and Mark H. Ellisman, University of California-San Diego; and Elizabeth A. Strychalski, National Institute of Standards and Technology.