Researchers at the J. Craig Venter Institute (JCVI) and the National Institute of Standards and Technologies (NIST) have identified seven genes that are indispensable in order for the "minimal genome" or JCV3.0 cell to divide into two equal daughter cells.
John I. Glass is professor and leader of the synthetic biology group at the JCVI, and the co-corresponding author of the paper reporting the findings, which appeared in the April 1, 2021, online issue of Cell.
The minimal genome is a long-running project of the JCVI, which reported an initial artificial genome, consisting of roughly 900 genes, in 2010.
In 2016, the team followed up with an even more downsized genome, consisting of 437 genes.
However, although JCV3.0 was able to divide, it was not able to do so well.
The cell 3.0 "didn't seem to control how it accumulated membrane," Glass said, and as a result, after any cell division the two resulting daughter cells could differ wildly in their size and shape.
Work on the minimal genome for orderly cell division got a boost, he said, when "we found in a freezer a cell that was developed in the process of making 3.0."
In that cell, which the team named 3a, there were 19 additional genes present, and the cell line was capable of orderly cell division.
The team originally had two genes in their sights as being critical for cell division. However, it turned out that they had to add another five genes, for a total of seven, to achieve their goal.
The functions of five of those genes are unknown, which is surprising to most laypeople, but is in line with previous work on the minimal genome.
"When we published our 2016 paper [on JCV3.0], by our very conservative criteria, of the 437 genes, 149 we didn't know what they did," Glass said, although he noted that for almost half of those genes, "we had a good idea -- we might know that this gene is likely a transporter, for example, but not know what it transports."
Since then, several papers have proposed functions for some of the unknown genes, and Glass and his colleagues are themselves "in the middle of an update of the minimal cell," he said. Altogether, the number of unknown genes is down to somewhere between 85 and 100.
Glass, co-corresponding author Elizabeth Strychalski, and their teams are working on figuring out those functions. Glass also said the Cell publication has already led to first clues.
"Within hours of our paper publishing, I got an email...from a protein structure person, and he had thoughts about one of our five proteins of unknown function," he recounted.
Beyond the identification of the cell division genes, Glass told BioWorld Science, "our work shows the utility of this simple system as a way of solving complicated biological problems."
"I have – as of today – 43 academic groups that are using the minimal cell for one function or another," he said.
Some are studying basic biology, such as metabolic pathways for carbon fixation.
Others are somewhat more practical. Unlike the mycoplasma which it is most directly derived from, the minimal cell cannot infect other cells. Several research groups are adding genes from intracellular pathogens into the minimal cell one at a time to identify the critical pathogenic genes.
And "at least one" biopharma company is now using the minimal cell "as a chassis" to see what happens to cell biology as a result of installing specific pathways into minimal cells.