Friday, November 23, 2012

Next gen sequencing a lens on bug-driven cancer risk

The bacteria, viruses and fungi living on our skin, up our noses and in our guts have a profound impact on our chances for developing cancer and other inflammatory diseases. Every one of the many millions of individual bacteria in our gut, for instance, contains genes that serve as instructions for the building of proteins. These molecules constantly interact with our own cells, helping to do everything from digest food to mistakenly triggering immune responses linked to cancer risk.

With these interactions in mind, the UAB Comprehensive Cancer Center chose "cancer and the microbiome" as the theme for its recent research retreat. The Mix interviewed several retreat presenters, each a nationally recognized expert in the area, and is featuring the chats as a podcast series over the next few weeks.

Our guest today is Michael Crowley, Ph.D., director of the sequencing operations in the genomics core within UAB's Heflin Center for Genomic Science. Before researchers can understand how our complex microbial communities either help or harm us, Crowley says, they must determine which species are present and what they are up to. Much can be revealed by determining the makeup of microbial genes, which offer clues to the molecules and chemicals they release into our bodies, with the help of high-speed sequencing and genotyping tools.

Show notes for the podcast:  

2:15 Fred Sanger came up with the first technique for determining the sequence of the coding units making up human DNA in 1977, and while it has undergone changes, its chemistry is basically the same today, says Crowley.  The technique reveals the order in which the DNA units, or nucleotides, line up to serve as coded instructions for the building of a human being. Initially, the scientists could sequence just a few nucleotides at a time, and then a few hundred. With advances in next-gen sequencing technologies, researchers can now sequence the entire set of genetic information for a person, three billion coding units, in 10 days for $5,000. In way of contrast, it took the Human Genome Project roughly $3.8 billion and six years to do the same thing 10 years ago.

3:47 Crowley is an expert in next-gen sequencing, which analyzes a great many small pieces of DNA in one area all at once on a glass slide. It's like looking at the night sky, seeing all the stars at once, and keeping track of which stars are changing.

4:36 Crowley's next-gen sequencing operation at the Heflin Center is mostly concerned with analyzing genetic material collected from patient samples. The information currently gives researchers clues to how diseases and medications change the microbiome, but in the future, the data will help clinicians adjust care and treatment.

6:11 The most important tool in microbiome and genome sequencing, says Crowley, comes from a company called Illumina, and is called the Genome Analyzer 2X. This second-generation tool enables the team to sequence 95 billion base pairs of information at one time from hundreds of microbiome samples on a single glass slide.

6:33 The question to be answered by this type of analysis changes with researcher that comes in seeking Crowley's help with a microbiome sequence. Often the question is "how has a patient's microbiome changed as he or she developed a disease, or what changes has chemotherapy made in a person's microbiome?"

7:46 Crowley's lab has assisted researchers conducting genomewide association studies, a type of analysis made possible in recent years by the availability of computing power and high-speed sequencing technologies. Such studies compare the genetic makeup of a patients with and without a disease. They determine the variations present at each spot in the genetic code for each person and the degree to which any variation contributes to disease. Crowley's team can look, in real time, at up to five million of these variations, called single nucleotide polymorphisms, or SNPs, which are different for each individual and can be associated with particular diseases.

8:39 The problem with GWAS studies is that they only show that one trait is somehow linked to a disease, not whether or not one can cause the other. Furthermore, associations from GWAS studies can only account for about 5 to 10 percent of the risk of inheriting many diseases. This has been termed the problem of "missing heritability."

8:59 To find this missing genetic risk, the NIH funded the ENCODE project, which has linked diseases to areas of the genetic code, not just to specific genes. The ENCODE project picked up where the Human Genome Project left off in 2003, seeking to understand which bits of the genome have an active role in human biology despite not being genes. While the 20,000 or genes discovered during the Human Genome Project are a central part of the “blueprint for human biology,” ENCODE has helped to confirm that genes represent less than 2 percent of the genome. Genes, it turns out, are surrounded by vast stretches of code, some of which control when, where and how genes turn on and off. Problems with such regulatory sequences have now been implicated in many diseases.

11:36 Sequencing operations in the genomics core within UAB's Heflin Center for Genomic Science work closely with the UAB Microbiome Core in a model where researchers grounded in many disease areas can gain unfettered access to next-gen sequencing expertise and instruments.

13:10 For those interested in reading more on microbiomic genetics, Crowley recommends the NIH's Human Microbiome Project and the National Human Genome Research Institute websites. He also recommends searching Google, which turns up articles including In Good Health? Thank Your 100 Trillion Bacteria (New York Times, @ginakolata), Finally, A Map Of All The Microbes On Your Body (National Public Radio, @robsteinnews) and Discover the Frenemy Within (Wall Street Journal, @ronwinslow).

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