Jumping Genes and Stem Cells

I have always held a fascination for transposons, or jumping genes as they are sometimes called. Part of this interest may be due to my background in Drosophila genetics, where a transposon called a P element has been used extensively for genetic manipulation of flies for years. But also there is the fact that P elements appears to have made the jump into Drosophila melanogaster only recently (with in the past 50 years). From an evolutionary perspective this is fascinating as it allows us to study how a genome (in this case Drosophila) responds to the introduction of a new transposon.

However, On another front, the study of transposons joined forces with the study of stem cells this week. Even though President Obama has reversed the ban on using embryonic stem (ES) cells in research, scientists are still actively pursuing methods of generation stem cell lines. of particular interest are the induced pluripotent stem cells (iPS cells - see "This Isn't Science Fiction Anymore"). iPS cells are adult stem cells that have been convinced to revert back to a more generalized (less specialized) state. Although iPS cells have only been around for a few years, they have created a definite interest in the scientific community. If a method of making iPS cells was simplified - then it may be possible to make stem cells out of almost any human cell type. This would practically eliminate the need for embryonic (ES) stem cells and open up new avenues for genetic research.

One of the main problems with the generation of iPS lines has been the genetic vector used to alter the cells. For the past few years this has focused almost exclusively on the use of viruses. The main problem with viruses has been the fact that they are very disruptive to genomes. When a virus integrates itself into the genome it has the potential to disrupt important genes or their regulatory regions. But there is now another way and it involves the use of transposons. Once of the benefits of the transposon is that it carries a gene called transposase, which is what promotes the movement of the transposon in the genome. It also means that the location of the transposon is transient - it can move in and then move back out again. Like viruses, transposons can be genetically engineered to contain other genes, in this case the genes to make a cell pluripotent. One of the transposons that has been selected to do this is appropriately named piggyBac. piggyBac is a rather large transposon (around 2,400 base pairs in length) that has been used in the past to perform genetic transformation in fruit flies and other insects.

What is now possible, at least in mouse trials, is to deliver a genetically engineered transposon containing genes for pluripotency into a cell. Then, once the genes have been expressed, and the cell has undergone a transformation into a stem cell, the transposon can be activated and the genes removed. Thus, if the transposon inadvertently inactivated a gene of importance, it may be removed from the gene with very little consequence. By doing this geneticists hope to greatly increase the potential of using iPS cells in research.

What is LRRK2?

The recent announcement that Sergey Brin, the multibillionaire co-founder of Google, has discovered that he possesses a genetic mutation that predisposes him to a form of Parkinson's disease has resulted in multiple stories in the news on the "genetic basis" of Parkinson's and the candidate gene LRRK2.

But what exactly is LRRK2? The fact that we now have names for so many of these genes signifies one of the true advances in modern medicine - the fact that we actually know the location, but not necessarily the function, of most genes in humans. But we often forget that these genes themselves are very interesting. LRRK2 stands for leucine-rich repeat kinase 2, which means about nothing to most people. This means that the gene encodes for a protein that has within it a leucine-rich regions, and some sort of kinase function. Still mean nothing? Well, leucine-rich regions tend to be associated with proteins that interact with one another. This is common in many metabolic pathways. In fact, we know that the dardarin protein (the protein encoded for by LRRK2) is actively involved in the mitochondria of the cell - the energy powerhouses that burn carbohydrate fuel to produce energy. And the term kinase indicates that this protein is basically a form of cellular "on-off' switch. Kinases add phosphates to other molecules, effectively turning them on or off. So dardarin turns on and off other proteins.

So what does this tell us? Well, by dissecting the name we can see that this gene, and its gene product (the dardarin protein) are most likely a component of a much larger, protein activation pathway. From a cellular perspective, these pathways can be, and usually are, very complex, with defects at many locations possible. Any of these defects may cause Parkinson's. The disease may also be caused by mutations in genes that have nothing to do with dardarin or LRRK2. So, it is unlikely that the discovery of Mr Brin's mutation will be the silver bullet in the fight against Parkinson's disease. Mutations in this gene account for only a small percentage of Parkinson's cases. However, Mr Brin's announcement will serve to increase awareness, and hopefully funding, of research to better understand the chemical pathways that LRRK2 is part of. But we can add dardarin to the diseasome, or those proteins that are known to cause disease. And once we understand the function, we may be able to start talking about gene therapy and drug development.

My Friend, E. coli

While as a geneticist my vote would go to Drosophila melanogaster as the greatest organism of all time, I do recognize that Escherichia coli is probably one of the most beloved organisms of the biomedical research community. This versatile little microbe can be found in teaching and research labs from high schools to research institutions and large biomedical facilities. We probably know more about E. coli than almost any other organism on the planet, including ourselves. Many of the advances in medicine and drug development would probably not be possible if it were not for this wonderfully versatile little bacteria. But, as we are all aware, E. coli has a dark side.

The March 24 issue of New Scientist features an article ("Mystery Food Poisoning Traced to Salads") which presents statistics on the increase in the rate of food poisoning associated with salad greens. While the article does not specifically mention E. coli, if you asked the common person on the street what was causing the food poisoning in spinach and lettuce, most would guess this bacterium. In fact, E. coli is probably the only microbe, or any other organism for that matter, that most people know by its scientific name! Unfortunately, that recognition is not a good one. From baby diapers and water parks in the 1990s to ground beef and salad greens in this decade, E. coli has earned a reputation as a menace.

I have found that most students are surprised to find out that their intestines contain more bacterial cells than there are human cells in their bodies. Most are disgusted by the thought, and some actually pale when I mention that one of the leading organisms is E. coli. I have even had a few ask if they can get antibiotics from the campus health clinic to rid them of these "parasites."

After a brief discussion of why these little creatures are present in our system, and the benefits that they provide us by protecting us from harmful bacteria, synthesizing necessary vitamins, and stabilizing our blood glucose levels, most of the students develop a real appreciation for E. coli. From that point we can proceed to discussions on how important it is to keep your intestinal bacteria content by reducing unnecessary use of antibiotics and consuming plenty of fiber. It is then relatively easy to understand why probiotics, such as yogurt and Acidophilus pills, work as supplements. With a little public relations work, E. coli is transformed from the villain to a misunderstood hero.

Why is any of this important? In the March 1 edition of Science News, science writer Janet Raloff ("Nurturing Our Microbes") presents an intriguing possibility that someday it may be possible to reprogram our natural flora of microbes to combat disease. She first discusses how probiotic supplements may be used to increase the efficiency of intestinal bacteria in enhancing our immune system, by increasing the absorption of nutrients such as calcium and by regulating weight. Raloff then presents comments by Jeremy Nicholson of the Imperial College in London, who said that future drug therapies might one day be directed at the bacterial inhabitants of the intestinal system.

As a researcher, I think that is an important advance for medicine. We all know of the problems that have plagued large-scale implementation of gene therapy. Given the number of bacteria in the lumen of the gut, it should be possible to achieve a higher rate of transformation than is experienced in in vivo eukaryotic cells. Furthermore, by having the bacteria produce the drug of interest, it may be easier to get the drug directly into the bloodstream than traditional oral routes that need to navigate the hostile environment of the stomach.

And since this is an election year, and at least some of the focus appears to be on health care, the use of genetically modified E. coli may reduce the cost of certain medicines, since once transformed the individual would have a constant, renewable source of the drug.

However, before we proceed with the development of drug-producing recombinant bacteria, I would like to make a suggestion. If the drug companies state that they are ready to produce a genetically altered bacterium, especially one named E. coli, the general public is going to have a revolt.

Movies such as I Am Legend have not presented a pretty picture of genetically engineered organisms. Recent public responses to cloned meat, and once again to certain forms of immunizations, reveal that the general public is not convinced that we know what we are doing.

So my suggestion is this — start a public relations campaign on behalf of E. coli. Get E. coli, or its agent, on The Daily Show and Good Morning America. Start thinking about how to spin the benefits of E. coli to an increasingly research-phobic public. Work the media, begin ad campaigns, and most importantly, get the message out to the science teachers to incorporate it into their curriculum. For if we don't, this promising medical advance may be a tremendous waste of money.

Note: this article first appeared in the April 10, 2008 issue of BioWorld Perspectives, and is reproduced here by permission of AHC Media, LLC