AP Biology class blog for discussing current research in Biology

Author: sharothymine

Cas9: A Clue Into Making Gene Editing Safer

CRISPR is a revolutionary system that edits the DNA of living organisms with ease. The gene-editing technology offers scientists insight into genetic diseases and is widely used in biotech and agriculture, as well as to treat cancer and viral infections. But the CRISPR system and its mechanisms are not yet fully understood. However, researchers at the Ohio State University have reported that they have figured out the mechanism of how the CRISPR system figures out where and when to cut the DNA strands. This is particularly revolutionary as it provides insight into preventing gene-cutting errors.

Cas9 is an enzyme that is used by the system to target and cut out or insert specific genes. In the second of two paper published in the Journal of the American Chemical Society, the team invalidates the widely-held belief that the enzyme cuts DNA evenly. Professor of chemistry and biochemistry Zucai Suo explains that instead of cutting both sides of the DNA double-helix to the same length, Cas9  actually trims each side to uneven lengths. Ohio State doctoral student Austin Raper and his co-authors determined that the two different parts of the “Cas9 molecule communicate with each other to set the location and timing of a cut”. The first part of the molecule sets forth to cut its respective DNA strand and changes shape and signals to the second part to cut its respective second strand.

Crystal Structure of Cas9 Enzyme

Suo says that he hopes their work allows for scientists to minimize and eventually eliminate gene-editing errors. CRISPR rarely target unintended genes, but gene-editing errors can have very serious consequences. For example, if the system accidentally cut a tumor suppressor gene from a person’s DNA, they would be much more likely to develop cancer. As Raper says, it is important to understand CRISPR and the Cas9 enzyme mechanisms in order to allow CRISPR to advance to its full potential.



New Developments in the Biology of Alzheimer’s Disease

Recent work by Boston University School of Medicine researchers shows developments in a new model for the biology of Alzheimer’s disease, which could lead to entirely new approaches in treating the disease. Alzheimer’s disease disrupts one’s cognitive abilities, including memory, thinking, and behavior. It accounts for 60-80% of all dementia cases. The neurodegenerative disease is caused by clumps and accumulations of 2 proteins –beta-amyloid and tau– which cause nerve cell injury and in turn, dementia.

Comparison of a normal brain (left) and the brain of a person diagnosed with Alzheimer’s (right).

Recent work by the BUSM researchers has shown that the clumping and accumulation of the tau protein are largely due to stress. The accumulation of tau produces “stress granules” (RNA/protein complexes). The brain responds to these stress granules by producing important protective proteins. However, with excessive stress, there is a greater accumulation of stress granules, which in turn leads to greater accumulation of clumped tau, which causes nerve cell injury. In this study, researchers are using this model to show that reducing the level of stress granules could lead to improved nerve cell health. It may be possible to reduce the level of stress granules by genetically decreasing TIA1, a protein required for stress granule formation.

In an experimental model of Alzheimer’s disease, the research team found that reducing the TIA1 protein led to striking improvements in memory and life expectancy. However, although stress granule levels decreased (leading to better protection), the team observed that the clumps of tau became larger. The researchers further looked at the tau pathology and found that the while small clumps of tau (known as tau oligomers) are toxic, larger tau clumps are generally less toxic. According to pharmacology and experimental therapeutics professor Benjamin Wolozin, this discovery would explain why the experimental models experienced better memory and longer life expectancy. The implications and ability of TIA1 protein reduction in order to provide protection may lead to further novel developments in the biology and treatment of Alzheimer’s disease.


Birthday Cakes: the New Bacterial Hangout

Various media outlets have been warning readers about the various unexpected places that germs like cold viruses and bacteria can be found: on a cellphone, the kitchen sink, and a toothbrush. Cake frosting can now find itself on that very list, because according to a study by food safety professor Paul Dawson, blowing out birthday candles can increase bacteria growth on the surface of cake icing by 1,400%.

Dawson conducted the study as a series around common questions regarding food safety. After preliminary tests showed that blowing on nutrient agar (edible sugar-based foods) may be a source of bacterial transfer, Dawson and his Clemson University students conducted a formal study in which the research objective was to “evaluate the level of bacterial transfer to top the of a cake after blowing out the candles”. Rather than using a real cake, they frosted a piece of foil over a cylindrical styrofoam base. In attempt to simulate an authentic birthday party, Dawson and his team had test subjects consume pizza in order to stimulate their salivary glands, then extinguish lit candles by blowing. This process was repeated multiple times Once the icing samples were sterilely recovered, they found that the bioaerosols in human breath led to a definitive increase in bacterial transfer. On average, the amount of bacteria on the frosting increased by 14 times. In one trial, it increased the number of bacteria by more than 120 times.

However, birthday cake lovers should not despair. Dawson says, “It’s not a big health concern in my perspective.” Human saliva is already abundant with bacteria, most of them harmless. If blowing out candles on birthday cakes posed a significant risk in the spread of bacterial diseases, it would be extremely apparent due to the popularity of the tradition. But if need be, especially paranoid germaphobes now have the option of “germ-proofing” birthday cakes with sanitary birthday cake covers especially equipped with holes for candles. So we can have our cake, and eat it too.



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