On May 10 ScienceExpress published on-line Craig Venter’s Creation of a Bacterial Cell Controlled by a Chemically Synthesized Genome. A talk by Venter given last year at TED.com is a good introduction to the work.
Venter’s achievement is remarkable and embodies two critical accomplishments–first, the use of a chemically (vs. biologically) synthesized chromosome. Venter’s chromosome had never seen a cell prior to its “booting up” in the new host. Of course, the sequence was based on a known bacterial chromosome, but contained modified genes to distinguish it from the host cell and with “watermarks” (more on that later).
The second accomplishment is that the synthesized chromosome was inserted into a host cell (with different DNA from a different species). The system was engineered so that the original host cell DNA would be destroyed and that the new chemically synthesized chromosome would be preserved. This happened and the cell was transformed to function according to the new “program”, the new synthesized chromosome.
This is a remarkable achievement and paves the way to all sorts of future experiments. In principle, however, this is merely a large-scale and chromosome level version of already existing recombinant DNA technology. Venter calls this a “synthetic cell” and at this point I consider this to be mostly hype. Future experiments may result in something that could be called a “synthetic cell”, but for now this is an already existing cell transformed by a chromosome replacement. Thus, the ethical implications of this seem minimal to me.
The ScienceExpress paper notes:
Phenotypic effects of the recipient cytoplasm are diluted with protein turnover and as cells carrying only the transplanted genome replicate. Following transplantation and replication on a plate to form a colony (>30 divisions or >109 fold dilution), progeny will not contain any protein molecules that were present in the original recipient cell. This was previously demonstrated when we first described genome transplantation. The properties of the cells controlled by the assembled genome are expected to be the same as if the whole cell had been produced synthetically (the DNA software builds its own hardware).
Thus within 30 generations, the proteins of the bacterium have been completely determined by the new chromosome. Presumably this would eventually be true of cellular components synthesized by these proteins.
Starting off with a living bacterial cell (even if the DNA has been destroyed) limits the claim of “synthetic cell.” Again, I’m not in the least trying to minimize Venter’s accomplishment, but he started with a living system and synthesized a chromosome that used the same genetic code as the starting living system. I will wait for “booting” the DNA without a starting living system before I apply the moniker “synthetic cell.” That seems a bit more difficult. Since the entire chromosome is synthesized, why not alter the genetic code, i.e. change the aminoacyl-tRNA synthetases so that there is a completely novel relationship between the DNA and amino acid sequences. At first glance this would require booting from scratch, without the presence of the pre-existing living cell, but accomplishing this would be a convincing proof of concept.
Questions have arisen about such experiments in eukaryotes. Could we regenerate a Neanderthal, or a woolly mammoth, or a Tasmanian wolf (organisms for which the code exists “digitally”)? Epigenetic factors in the fertilized egg into which the synthesized chromosome was “booted” would influence development at first. (Think about the chimp with human DNA in Michael Crichton’s Next). But, if it is true that the original epigenetic factors are diluted after a number of generations as in the bacterial case, then perhaps we would end up with something very close to the organism originally coded for by the synthesized DNA. No control exists, however, so we will never know if we have the real Neanderthal or just something very close.
In the TED video Venter comments on the success of this project as showing that via genome acquisition and incorporation, fast and large-scale evolution is demonstrated. Indeed, Mycoplasma capricolum evolved into Mycoplasma mycoides in one generation (or at most 30 generations).
Venter’s watermark is fascinating, and I think somewhat relevant to the intelligent design debate. Venter’s synthetic chromosome spells out the following “words” in some sections of the coded proteins using the one-letter codes of the amino acids coded for by the synthesized gene:
Without overly simplifying the ID argument, it has often struck me that if God wanted to give us a definitive proof of His hand in Creation he could have done such a thing by writing out a message in English (or whatever language you like) using the one letter amino acid codes. (Think about Sagan’s Contact and the message encoded in the digits of pi.) How does the ID argument fare even here? Are these “watermarks,” which we know are intelligently designed, detectable?