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essential genes

Red blood cell infected with malaria-causing parasites

Caption: Colorized scanning electron micrograph of a blood cell infected with malaria parasites (blue with dots) surrounded by uninfected cells (red).
Credit: National Institute of Allergy and Infectious Diseases, NIH

As a volunteer physician in a small hospital in Nigeria 30 years ago, I was bitten by lots of mosquitoes and soon came down with headache, chills, fever, and muscle aches. It was malaria. Fortunately, the drug available to me then was effective, but I was pretty sick for a few days. Since that time, malarial drug resistance has become steadily more widespread. In fact, the treatment that cured me would be of little use today. Combination drug therapies including artemisinin have been introduced to take the place of the older drugs [1], but experts are concerned the mosquito-borne parasites that cause malaria are showing signs of drug resistance again.

So, researchers have been searching the genome of Plasmodium falciparum, the most-lethal species of the malaria parasite, for potentially better targets for drug or vaccine development. You wouldn’t think such work would be too tough because the genome of P. falciparum was sequenced more than 15 years ago [2]. Yet it’s proven to be a major challenge because the genetic blueprint of this protozoan parasite has an unusual bias towards two nucleotides (adenine and thymine), which makes it difficult to use standard research tools to study the functions of its genes.

Now, using a creative new spin on an old technique, an NIH-funded research team has solved this difficult problem and, for the first time, completely characterized the genes in the P. falciparum genome [3]. Their work identified 2,680 genes essential to P. falciparum’s growth and survival in red blood cells, where it does the most damage in humans. This gene list will serve as an important guide in the years ahead as researchers seek to identify the equivalent of a malarial Achilles heel, and use that to develop new and better ways to fight this deadly tropical disease.

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Many people probably think of mice as unwanted household pests. But over more than a century, mice have proven to be incredibly valuable in medical research. One of many examples is how studies in mice are now helping researchers understand how mammalian genomes work, including the human genome. Scientists have spent decades inactivating, or “knocking out,” individual genes in laboratory mice to learn which tissues or organs are affected when a specific gene is out of order, providing valuable clues about its function.

More than a decade ago, NIH initiated a project called KOMP—the Knockout Mouse Project [1]. The goal was to use homologous recombination (exchange of similar or identical DNA) in embryonic stem cells from a standard mouse strain to knock out all of the mouse protein-coding genes. That work has led to wide availability of such cell lines to investigators with interest in specific genes, saving time and money. But it’s one thing to have a cell line with the gene knocked out, it’s even more interesting (and challenging) to determine the phenotype, or observable characteristics, of each knockout. To speed up that process in a scientifically rigorous and systematic manner, NIH and other research funding agencies teamed to launch an international research consortium to turn those embryonic stem cells into mice, and ultimately to catalogue the functions of the roughly 20,000 genes that mice and humans share. The consortium has just released an analysis of the phenotypes of the first 1,751 new lines of unique “knockout mice” with much more to come in the months ahead. This initial work confirms that about a third of all protein-coding genes are essential for live birth, helping to fill in a major gap in our understanding of the genome.

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Posted In: Health, Science

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