BioQuakes

AP Biology class blog for discussing current research in Biology

Tag: offspring

Did You Inherit Stress From Your Mother?

Have you ever wondered why you are so stressed? Maybe because of school, sports, or homework, but have you ever thought you could have inherited from your mother? I bet not. Biologists at the University of Iowa found that roundworm mothers subjected to heat stress passed the stress exposure to their offspring and their offspring’s children. 

C elegans maleStress2a

In a study last year researchers looked at how mother roundworms react when she senses danger, such as a change in temperature. Their results were that the mother ringworms release serotonin when she senses dangers by traveling from her nervous system to warn her unfertilized eggs.  The warning is there “stored”, and then passed to offspring. Genes have “memories” of past environmental conditions that affect their expression even after these conditions have changed. It is still unclear how this “memory” is established, how it persists past fertilization and after the embryo develops into adults because most organisms typically reset any changes that have been made to genes’ past activity. 

The research team turned to the roundworm, a creature regularly studied by scientists, for clues. They exposed mother roundworms to unexpected stresses and found the stress memory was ingrained in the mother’s eggs through the actions of a protein called the heat shock transcription factor, or HSF1. The HSF1 protein is present in all plants and animals and is activated by changes in temperature, salinity, and other stressors. Although protein can be found in both Prokaryotic and Eukaryotic cells, this particular protein is only found in Eukaryotic cells which means that it interacts with numerous things found in these types of cells. HSF1 interacts with mRNA processing, chromatin modification, transcriptional coactivators and corepressors, and DNA and RNA metabolism which are all an array of proteins with diverse cellular functions. As we learned in biology, proteins nearly have every task of cellular life, including receiving signals from outside of the cell and mobilizing intracellular response which explains why the HSF1 protein has many functions.

The team found that HSF1 recruits another protein, an enzyme called a histone 3 lysine 9 (H3K9) methyltransferase. This normally acts during embryogenesis to silence genes and erase the memory of their prior activity. However, the research team observed something else entirely. They found that HSF1 collaborates with the mechanisms that normally act to ‘reset’ the memory of gene expression during embryogenesis to, instead, establish this stress memory. One of these newly silenced genes encodes the insulin receptor, which is central to metabolic changes with diabetes in humans, and which, when silenced, alters an animal’s physiology, metabolism, and stress resilience. Because these silencing marks were found in offspring, their stress-response strategy was switched from one that depended on the ability to be highly responsive to stress, to relying instead on mechanisms that decreased stress responsiveness but provided long-term protection from stressful environments.

What the team concluded was that if the mother was exposed to stress for a short period of time, only its offspring would be subjected to stress in utero, but the offspring’s children would not. If the mothers were exposed to stress for a longer period of time, then the offsprings children would retain this “memory” of  stress.

 

Does Exposure to Toxins In the Environment Affect One’s Offspring’s Immune System?

A study has recently surfaced stating that maternal exposure to industrial pollution may harm the immune system of one’s offspring and that this impairment is then passed from generation to generation, resulting in weak body defenses against viruses.

Paige Lawrence, Ph.D., with the University of Rochester Medical Center’s Department of Environmental Medicine, led the study and conducted research in mice, which have similar immune system functions as humans. Previously, studies have shown that exposure to toxins in the environment can have effects on the respiratory, reproductive, and nervous system function among generations; however, Lawrence’s research is the first study to declare that the immune system is also impacted.

“The old adage ‘you are what you eat’ is a touchstone for many aspects of human health,” said Lawrence. “But in terms of the body’s ability to fights off infections, this study suggests that, to a certain extent, you may also be what your great-grandmother ate.”

“When you are infected or receive a flu vaccine, the immune system ramps up production of specific kinds of white blood cells in response,” said Lawrence. “The larger the response, the larger the army of white blood cells, enhancing the ability of the body to successfully fight off an infection. Having a smaller size army — which we see across multiple generations of mice in this study — means that you’re at risk for not fighting the infection as effectively.”

In the study, researchers exposed pregnant mice to environmentally relevant levels of a chemical called dioxin, which is a common by-product of industrial production and wast incineration, and is also found in some consumer products. These chemicals eventually are consumed by humans as a result of them getting into the food system, mainly found in animal-based food products.

The scientists found the production and function of the mice’s white blood cells was impaired after being infected with the influenza A virus. Researchers observed the immune response in the offspring of the mice whose mothers were exposed to dioxin. Additionally, the immune response was also found in the following generations, as fas as the great-grandchildren (or great- grandmice). It was also found that this immune response was greater in female mice.  This discovery now allows researchers to have more information and evidence to be able to more accurately create a claim about this theory.

As a result of the study, researchers were able to state that the exposure to dioxin alters the transcription of genetic instructions. According to the researchers, the environmental exposure to pollutants does not trigger a genetic mutation. Instead, ones cellular machinery is changed and the immune response is passed down generation to generation. This discovery explains information that was originally unexplainable. It is obviously difficult to just avoid how much toxins you are exposed to in the environment, but it is definitely interesting to see the extent of the immune responses in subsequent generations. We can only hope that this new information, and further discoveries, help people adjust what they release into this world that results in these harmful toxins humans are exposed to, and their offsprings.

 

 

 

Guts or Glory?

According to Aristotle, what separates man from beasts is his ability to reason. Humans have this luxury because of their large brains, but it comes at a price; guts! Scientists have long imagined that big brains come with an evolutionary cost and up until a recent study, it was all theory.

A Swedish team of researchers, led by Niclas Kolm decided to put this theory, known as the “expensive tissue hypothesis”, to the test. The hypothesis basically states that there is a trade-off between the demands of the brain and the demands of other organs. So, to prove this theory, the team selectively bred common guppies to produce bigger (or smaller) brains. They were able to produce brains that were as much as 9.3 percent larger. The bigger brained fish tended to have smaller guts, as well as produce fewer offspring.

The experiment tested 48 guppies using an underwater arithmetic test to see if the guppies (with large brains) possessed greater cerebral capabilities. It worked! The “smart” fish were more successful at learning and recognizing geometric shapes, that were on a door, in order to get to the food on the other side.

Where these “brainy” fish lost ground, was in the gut division. Males were found to have a 20 precent decrease and females an 8 percent decrease in gut size. Brainier fish(females) were found to produce 19 percent less offspring than the smaller brained fish. This evidence implies that larger brains may be the cause of smaller broods.

Even though the evidence pretty clearly supports the “expensive tissue hypothesis”, Kolm and his team have not completely ruled out the “genetic mechanism for the trade-off”. It is not obvious whether small guts or big brains develop first.

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