This blog is a place where I will translate interesting findings in biomedical and basic science research from scientific jargon to plain old English. The bottom line: You don't need a PhD to understand science!

Wednesday, August 26, 2009

Does our DNA make decisions for us?

In this week’s Proceedings from the National Academy of Science, Christina S. Barr and colleagues report that a mutation in the CRH gene is associated with increased stress-induced alcohol consumption in primates. What are the implications of this study and those like it? What does it mean if a DNA mutation can shape behaviors that affect our society?

First, let’s catch up on the basics. The CRH gene is the piece of DNA that encodes instructions to make corticotropin-releasing factor (CRF), a piece of cellular machinery required by our bodies for stress adaptation. Too much CRF activity can lead to increased anxiety or depression-like symptoms.

Barr’s research involves a mutation in a region of the DNA directly before the CRH gene, called the CRH promoter. In a sense, a gene’s promoter is like password protection for the gene. If the cell doesn’t use the proper combination of factors to satisfy the password, the instructions in the gene cannot be accessed. Other times, a faulty promoter will allow access to the gene too often. In the current study, the mutation in the promoter for CRH causes the cell to make too much CRF.

To determine if the CRH mutation affected stress-related behavior, Barr exposed young macaques to peer rearing (as opposed to mother rearing), an environment that is known to induce stress in these young animals. Next, Barr’s team measured the differences in alcohol consumption between normal macaques and those carrying the CRH mutation. After early stress exposure, the macaques with the CRH mutation consumed significantly more alcohol than the controls with a normal CRH gene.

Stop and think about this result for a moment. What does it mean if a gene mutation significantly affects a quantifiable behavior? To what extent does our genetic make-up contribute to the thousands of decisions every individual makes each day. The outcome of most decisions is benign; what one eats for breakfast or wears to work most likely won’t evoke a second thought. Other decisions, however, can have large impacts on society. The choice to consume excessive amounts of alcohol, engage in violent behavior, or disregard accepted social contracts can land a person in jail, if not worse.

Science progresses at an exponential pace. It is not unlikely that ten to twenty years from now, many more genes will be associated with specific behaviors. There will be a time when a jury will need to decide if a crime was committed with criminal intent or if the accused was at his DNA’s will. To properly handle these future scenarios, we as a society need to develop a basic understanding of cellular biology and learn how to assess the possible implications when something has gone amiss at the genetic level.

One hundred years ago, demons and devils were blamed for unacceptable behavior. One hundred years from now, who will be on trial: the perpetrator or his DNA? These are not questions for a science fiction novel or the next blockbuster film. These are relevant issues that warrant discussion based on educated reason.

Reference: Christina S. Barr et al. “Functional CRH variation increases stress-induced alcohol consumption in primates.” PNAS August 25, 2009. DOI: 10.1073/pnas.0902863106

Friday, August 21, 2009

Early to bed, early to rise, makes a man healthy, wealthy, and A MUTANT?!

Your eyes meet. A foggy haze hangs in the air as you lean in for the kiss. Your lips are just about to touch, and the alarm goes off! We all know the feeling. Just ten more minutes!

For some, those ten minutes come after a comfortable seven to eight hours of sleep. For others, only six hours separates the night and the morning. While shorter sleep cycles lead to chronic sleep deprivation in a large percentage of the population, there are certainly individuals who find six hours of sleep sufficient. Why is it that a lucky few require only a fraction of the recommended seven to eight hours of sleep per night?

It looks as though the answer may reside once again in our DNA. In last week’s issue of Science Magazine, Ying He from the University of California at San Francisco reported that a small mutation in the DEC2 gene significantly decreases the length of a night’s sleep. He’s team identified the DEC2 mutation in two related individuals who indicated very early wake up times in a survey, reportedly sleeping nearly two hours less than other family members.

To study the significance of the DEC2 mutation on sleep cycles, He and colleagues generated transgenic mice that expressed the mutated human form of DEC2, called DEC2-P385R. He’s team found that mice expressing DEC2-P385R indeed had longer activity periods paired with shorter sleep phases. While many groups would be happily satisfied with this finding, He’s group took the experiment one step further. They next expressed the mutated mouse form of DEC2, called mDec2P38R, in fruit flies and recorded daily fruit fly activity. Remarkably, He found that mDec2P385R-expressing flies exhibited significantly less sleep-like behavior as measured by the duration of rest periods in light and dark conditions.

Not only did He’s study identify a sleep-specific behavioral function for the DEC2 gene, He's study also showed the remarkable conservation of DEC2 activity between vastly different species. While many genes are in fact shared between humans, mice, and flies, the amount of function that is retained for many genes is unclear. He and colleagues have now shown that DEC2 retains the ability to control sleep behavior in both the fly on your banana as well as in your neighbor next door.

Although this finding is fascinating, it is not yet a cause for jealousy over our peppy mutant friends. Many genes in our DNA carry out more than one function. Therefore, unknown consequences of the DEC2 mutation may yet remain hidden. Until we fully understand the spectrum of DEC2 actions, I wouldn’t be rushing to take a pill of DEC2-P385R.

The Bottom Line: The next time you’re late for work because you slept in, you can blame it on your DNA!

Reference: He et al. “The transcriptional Repressor DEC2 Regulates Sleep Length in Mammals. Science 14 August 2009: Vol. 325. no. 5942, pp. 866 – 870. DOI: 10.1126/science.1174443

Sunday, August 16, 2009

Obesity-Blocking Neurons Found in Fruit Fly Brains

Obesity is a growing problem around the world, no pun intended. Lean models grace the covers of health and fitness magazines, but they certainly do not represent the average reader. Heaviness once was a symbol of wealth and prosperity. Today, extra weight is associated with laziness, a lack of concern for one’s self, and in some cases poverty. We now seem to be in an eternal struggle to permanently eliminate excess fat.

Weight gain is commonly a symptom of overeating combined with a lack of exercise. In some unfortunate cases, failure in an area of the brain known as the hypothalamus can lead to excess body fat. The hypothalamus responds to hormone signals from the body to regulate both hunger and metabolism. If the hypothalamus is compromised, abnormal eating behaviors as well as inadequate metabolic processing can occur. Due to the current obesity “epidemic,” there is an increased interest in understanding neural control over the factors that affect weight gain.

The ability to test predictions about brain activity and obesity in humans is limited due to the ethical problems generated by inhibiting human neural function. Clearly, another model is needed to study the association of brain performance and fat processing.

Both humans and fruit flies share many aspects of fat storage and metabolism. Each organism absorbs fat in the intestine, contains dedicated tissue for fat storage, and synthesizes new fat in specialized cells. In fact, many of the molecular factors required for each of these biological events is conserved between humans and flies.

Last week, a group of scientists lead by Dr. Bader Al-Anzi of the California Institute of Technology reported one more similarity: as in humans, there are neurons in the fruit fly brain that control eating behavior and fat metabolism.

Al-Anzi’s team adapted a chemical test, called rapid thin layer chromatography, to measure the total fat levels in the adult fruit fly body. The group screened the fat levels in hundreds of flies, each fly containing a brain with different combinations of neurons inhibited. His team successfully identified two populations of neurons, called c673a and fruitless, that when inhibited generated fat flies. Interestingly, when these same neurons were hyper-activated, the flies were significantly leaner!

Upon closer examination, Al-Anzi and colleagues determined that the inhibition of c673a neurons provoked increased food intake and decreased fat metabolism, while the silencing of fruitless neurons only affected metabolic processes. In each case, the group was able to reverse the obesity by removing the neural inhibition.

The authors suggest that a signal with information about energy stores in the body, perhaps from the fat cells, is detected by the c673a and fruitless neurons in the brain. These particular target neurons then process the received information to control feeding behaviors and fat metabolism.

With the identity of fat-regulating neurons established in fruit flies, future research can now utilize this model system to determine how neural networks link together to process signals from the body and to identify the genetic components involved in the development and function of such a tightly regulated system. Because many of the molecules that control fat processing in the body are conserved between flies and humans, insights gained from experiments on the fruit fly brain may one day reveal interesting and useful information about our own noggins.

The bottom line: That old childish taunt “fat-head” might not be so far from the truth.

Reference: Al-Anzi et al. “Obesity-Blocking neurons in Drosophila” Neuron 63, 329–341, August 13, 2009 DOI 10.1016/j.neuron.2009.07.021

Wednesday, August 12, 2009

Can all cells be stem cells?

We all want to live longer, escape disease, and experience life to its fullest. Our newspapers claim that stem cells will solve our medical problems. Michael J Fox pleads for support. Yet, debate surrounds stem cell research. We fear what we do not understand.

The controversial cells in question are known as embryonic stem cells (ES cells). Human ES cells are found in the very early four to five-day-old embryo. Their promise resides in the fact that they can become any cell type in the body. ES cells can transform into beta cells for a diabetic, neurons for a Parkinson’s patient, or heart muscle for an individual with cardiac trauma.

The majority of ES cells are harvested from unused embryos after fertility treatments. After isolation, ES cells can be maintained indefinitely in culture with good hands and rigorous care. Unfortunately, cellular contamination and naturally occurring mutations can affect the normal behavior of stem cells.

In a hotly disputed move, the Bush administration limited stem cell research to existing ES cell cultures. Researchers around the world began to pump laboratory manpower into finding ES cell alternatives.

In 2006, K. Takahashi and S. Yamanaka found that a mere four genes introduced into a differentiated mouse cell could coax adult cells back into a stem cell-state. Subsequently, other groups followed suit and had similar results with adult mouse liver, stomach, blood, and skin-specific cells.

A mature cell that is “re-programmed” into a stem cell is known as an induced pluripotent stem cell (iPS cell). Like embryonic stem cells, the iPS cells harbor the ability to differentiate into any cell type in the body. To prove that iPS cells are comparable to embryonic stem cells, they must pass a battery of tests. Only one test continuously stumped researchers – the tetraploid complementation test.

In tetraploid complementation, a flawed embryo serves as an empty vessel. Stem cell contribution to the faulty embryo enables the growth of an animal. Imagine a flowerpot. A flower will not grow from a pot of soil without planting a seed. In this test, the stem cells are like seeds. For iPS cells to be equivalent to ES cells, they must have the ability to grow into an entire animal when planted.

In what seems to be a tie finish, three independent groups successfully performed tetraploid complementation with iPS cells. Their work was released online in two prominent journals, Nature and Cell Stem Cell, last week.

The three teams, lead by Michael Boland of The Scripps Research Institute, Lan Kang of the Chinese Academy of Medical Sciences, and Xiao-yang Zhao of the Chinese Academy of Sciences Institute of Zoology, used mouse embryonic fibroblasts to generate iPS cells.

Fibroblasts produce the connective tissue between all cells in the body and have the ability to generate other cell types such as bone and smooth muscle. Because fibroblasts are primed for a transition to multiple cell types and grow beautifully in culture, they are an optimal choice for iPS cell studies.

To induce stem cells, the three groups each used a virus to deliver four genes, including Oct4, Sox2, Klf4, and c-Myc, into the embryonic fibroblasts. After a series of steps to verify the fibroblasts exhibited typical stem cell-like properties, the iPS cells were subjected to tetraploid complementation.

For the first time, each group successfully obtained at least one surviving adult mouse from their experiments. Importantly, the surviving mice were shown to be fertile, a critical requirement for the iPS cells to be considered equal to embryonic stem cells in this experiment.

While this is a major breakthrough in revealing induced pluripotent stem cell biology, it remains to be determined if cells isolated from adult tissue can have the same potency as the embryonic fibroblasts and if this same finding would hold true for humans. Indeed, for iPS cells to become a viable treatment for disease, we will need to understand the biology of re-programmed cells that are isolated from the human adult.

Finally, I want to ask my readers a question. If we can take a single cell that has already differentiated into its tissue specific form, activate a small set of genes, and use the induced stem cell to generate an entire animal, does this warrant a new area of bioethics in stem cell biology? If one considers human life to start with the potential to grow into an adult, then do all cells harbor this potential? Think about it. I’m happy to answer any questions and look forward to your comments on this controversial issue.

The bottom line: Stem cells generated from mouse embryonic fibroblasts are equivalent to embryonic stem cells in their ability to grow into a functioning adult mouse.

Zhao, X.-Y. et al. Nature advance online publication doi:10.1038/nature08267 (2009).
Kang, L. et al. Cell Stem Cell doi:10.1016/j.stem.2009.07.001 (2009).
Boland et al. Nature advance online publication doi: 10.1038/nature08310 (2009).

A helpful site on stem cells for additional reading:

Sunday, August 9, 2009

What is a transgenic animal?

After my last post, I realized the term “transgenic” gets thrown around a lot in our media. I’m willing to bet that many readers do not understand what transgenic means, why we’d want to make transgenic animals, or how something is made to be transgenic. Therefore, I’d like to take the time to explain this term here.

Whether we are discussing bacteria, flies, or mammals, the sequence of DNA in the cells controls the development of each organism. Many species have specific sequences of DNA that give that animal a unique trait or ability. In biology research, sometimes a special trait in one species would be advantageous in the animal model being used during experimentation. For example, some genes (genetic units in the DNA) might allow for a color change in a cell. If a scientist wants to utilize that trait, the gene from a host species can be taken from its DNA and incorporated into a recipient species. The newly created animal containing another organism’s DNA is called a transgenic animal.

In the case of the paper I reviewed in the last post (Zhang et al., 2009), the recipient mice were given new DNA sequences that enabled the researchers to cut the presenilin genes out of the DNA upon exposure to specific drugs. In addition, the transgenic mice received DNA that allowed the scientists to visualize the target neurons through a chemical reaction that caused the neurons to turn blue. Without the incorporation of the new DNA, these experiments would not have been possible.

How is a transgenic mouse made?

A transgenic mouse is made using common laboratory techniques. First, an embryo is taken from a pregnant animal. In the embryo, some of the cells that still have the ability to generate an entire animal (embryonic stem cells) are removed from the embryo. They are put into a dish and exposed to the new pieces of DNA (transgenes). Different methods can be employed to force the transgenes into the embryonic stem cell. Common methods include soaking the cells in the DNA solution, using electrical currents, and microinjection directly into the embryo.

Usually, the new DNA incorporated into the cell has a sequence that offers drug resistance. Therefore, the researchers can expose the cells to a drug and select cells that indeed receive and incorporate the transgene of interest. Next, the cells are re-injected into a fresh embryo so that the cells containing the transgene will contribute to the adult animal. These embryos are placed into a surrogate mother to grow.

The first set of animals from this technique will contain two types of cells: 1) cells from the recipient embryo (usually from a light coat mouse) and 2) cells containing the transgene (originally taken from a mouse with a dark coat). Therefore, the mice will look like they have a mixture of coat color, indicating that the mouse is composed of descendents of both cell types.

The hope is that reproductive cells (eggs or sperm) contain the transgene. After a series of crosses (mating mice together), the researchers will select mice with a uniform dark coat color, indicating that the mice are only composed of cells with the transgene. Voila! A transgenic animal!

Saturday, August 8, 2009

Shy neurons in a model of Alzheimer's disease

What exactly is wrong with Grandma’s brain when she can’t remember the day of the week, or maybe even the year? Sensory information is processed in the brain by sending electrochemical signals along a specific cell type called a neuron. If neurons fail to transmit a signal properly, neurodegeneration can result.

The underlying causes of Alzheimer’s disease are still being discovered in an intense laboratory race against the clock. Like all organs, the brain is composed of an assortment of cells that are shaped and controlled by instructions stored in DNA. One contributing factor to familial Alzheimer’s, a form of the disease that can be passed down through family members, is a gene mutation. Genes are segments of DNA that code for a single piece of the cellular machinery. The set of genes in question are called the presenilin genes, of which humans have two normal versions called presenilin-1 and presenilin-2.

Chen Zhang from the Harvard Medical School recently connected another piece of the puzzle by identifying a potential role of presenilin genes in Alzheimer’s pathogenesis. Mutations in the presenilin genes have been thought to cause neurodegeneration by disrupting the function of the synapse (the site where one neuron communicates with another). Zhang’s team sought to determine if mutated presenilin genes created a problem in the synapse by affecting neurons sending a signal or by affecting those receiving a signal. Using transgenic mice, Zhang disrupted presenilin genes in both types of neurons.

Following stimulation of the mutated neurons with a pulse of electricity, the strength of neuron-to-neuron communication was measured. Zhang’s team found that disruption of presenilin in the neuron sending a signal decreased the strength of signal transmission, while no effect was observed when presenilin activity was eliminated in neurons receiving signals.

In stimulated neurons, calcium plays an important role in the neuron’s ability to release chemicals into the synapse. Upon further investigation, Zhang and colleagues found an upset in calcium balance within the neurons upon presenilin elimination. Subsequently, the signal-sending neurons were no longer able to release the proper amount of chemicals to communicate with their down-stream partners.

Prior to this study, a large portion of research had been focused on cellular events in the signal-receiving neurons. It is now clear that disruption in the neurons that send signals may play an equally important role in the propagation of Alzheimer’s disease pathogenesis. Indeed, other neurodegenerative diseases, such as Parkinson’s disease, are also associated with gene mutations that affect the signal-sending neuron. Perhaps a flaw in the signal-sending events during neural information processing is a more general contribution to the pathogenesis of neurodegeneration than previously thought.

The Bottom Line: A mutation in mouse presenilin genes affects a neuron’s capacity to send signals, stemming from an inability to control chemical release during neuron-to-neuron communication.

Zhang et al. “Presenilins are essential for regulating neurotransmitter release.” Nature Vol 460, 30 July 2009, doi: 10.1038/nature08177.

Thursday, August 6, 2009

Pass the Orange Juice and Pass the Test

After spending five minutes in a typical grocery store, it is clear that food manufacturers and consumers understand the importance of proper nutrition: Neon blue drinks glow with 100% vitamin C; boxes of chocolate flavored cereal are pumped with iron and folic acid; even yoghurt has fiber added to the extra calcium and vitamin D.

With the mass-marketing of fortified sugar water and the diligent offering of Flintstone chewables, it comes as a bit of a surprise, at least to me, that a significant population of children might be vitamin C deficient. While recorded reports of scurvy in the western world are far and few between, recent studies indicate that vitamin C deficiency might not be as rare as we would like to think. Approximately one-third of young children are measured to have vitamin C deficiency in some populations.

Most people can probably guess that malnutrition can have detrimental effects on growth and development of the world’s youth. Although, how vitamin deficiencies specifically affect brain development and function is not so obvious. Indeed, malnutrition during fetal growth can result in cognitive disabilities of the child. Impaired development of the hippocampus, a brain center responsible for long-term memory, has also been observed.

Last week, Pernille Tveden-Nyborg from the University of Copenhagen reported a critical link between postnatal vitamin C deficiency and memory retention in guinea pigs, an animal model that, like humans, is unable to generate its own vitamin C.

While people envision vitamin C as a glass of orange juice or a small round pill, to the cell, vitamin C is the superhero antioxidant that fends off DNA damaging free radicals. Cells risk severe damage, if not complete obliteration, without a counterbalance to the oxidative injury that occurs to proteins, lipids, and DNA in the presence of dangerously paired oxygen molecules floating around the cell.

Based on a previous finding that the brain of neonatal guinea pigs is particularly vulnerable to oxidative stress during vitamin C deficiency, Tveden-Nyborg hypothesized that sufficient levels of vitamin C are critical for normal brain development. To test this hypothesis, Tveden-Nyborg and colleagues raised guinea pigs that experienced chronic vitamin C deficiency during early postnatal life. Subsequently, two month old vitamin C deficient guinea pigs were compared to nourished controls in the Morris Water Maze, a task designed to test memory and spatial navigation.

The Morris Water Maze consists of a dark pool measuring 1.5 meters in diameter. If four quadrants are imagined in the pool, a small platform is placed at the center of a single quadrant 12 cm below the water’s surface. On day one, each guinea pig is randomly placed in the pool and trained to find the platform, which both nourished and vitamin C deficient guinea pigs do equally well. After four days of no training, the guinea pigs are retested for their ability to remember the location of the platform in the pool. Only this time, the platform is sneakily removed! Measurements are recorded on the length of time it takes each guinea pig to enter the proper quadrant, how long each guinea pig remains in the quadrant, the number of times the guinea pig crosses the previous location of the platform, and the average distance the guinea pig swims from the target site, presumably trying to find the missing island.

Tveden-Nyborg found that the guinea pigs with proper vitamin C supplementation performed significantly better than guinea pigs exhibiting vitamin C deficiency on all measurements, suggesting that early postnatal vitamin C deficiency impaired the guinea pig’s spatial memory later in life.

Both spatial navigation and long-term memory are controlled, in part, by the hippocampus, a distinct compartment found on the side of each brain hemisphere. When Tveden-Nyborg and colleagues studied post-mortem hippocampus preparations, they found a significant decrease in the number of neurons present in sections of the vitamin C deficient brains as compared to the controls. At this time, it is unclear if the decreased neuron number is due to an increase in cell death, a lack of normal cell division, or both.

While the results from these experiments in Guinea Pigs do not directly provide information about human development, they certainly indicate that nutritional requirements for early brain growth and function is an area that warrants further investigation.

So, for those picky-eaters who won’t touch anything that can be grown in the backyard, perhaps some Juicy Juice and a Flintstone vitamin isn’t such a bad idea after all.

Tveden-Nyborg et al. “Vitamin C deficiency in early postnatal life impairs spatial memory and reduces the number of hippocampal neurons in guinea pigs.” Am J Clin Nutr. doi: 10.3945/ajcn.2009.27954.

An Introduction

“The Bottom Line in BioScience” is a blog designed to help all readers learn, appreciate, and respect science (no matter their academic background). I hope to use the knowledge I have gained from my doctoral studies in Molecular, Cell and Developmental Biology to help translate interesting findings in biomedical and basic science research from scientific jargon to plain old English. I will strive to summarize complicated research in an accurate, yet palatable, manner. Questions and comments to my posts are always welcomed (in fact encouraged!) so that we may generate insightful discussions and maybe learn a little something once in a while!

The Bottom Line: I want to bring science to everyone.
Welcome to the new blog! I will be setting up over the next few days, check back!