BEYOND THE INHERITANCE

ENVIRONMENTAL ENRICHMENT GENERATES CHEMICAL CHANGES IN DNA

Researchers from the laboratory of Biology performed an experiment showing that the effects of the exposure to an enriched environment are recorded as chemical changes in the DNA and how these modifications favor the experience-dependent learning process.

This recently published work is part of the debate aimed to establish if our characteristics are genetically determined or if these are acquired from our environment depending on our experiences. In this context, the research team led by Dr. Bredford Kerr, from CECs Biology Lab, investigated how the information is acquired from the environment and how these characteristics manage to intrude into the intimacy of our genome and become part of our biology. To this end, mice were exposed to an enriched environment with toys, mazes and objects that were daily changed, and were compared to mice kept in a standard environment. The results from these experiments were recently published in Frontiers in Molecular Neuroscience.

Left: A model representing our observations. Enriched environment (EE) exposition increases DNA methylation at the RyR3 gene promoter region (red circles). The methylated cytosine binding protein 2 (MeCP2) binds to the RyR3 promoter directing its transcriptional activation and augmenting RyR3 messenger RNA (mRNA) levels. TSS, Transcription Start Site. Right: Dendrites structural modification in mice exposed to enriched environment. RyR3 transcriptional activation drives a synaptogenic pathway that augments the dendritic spine density in the hippocampus of mice exposed to the enriched environment relative to that of mice kept in standard conditions.

"We were able to observe that in mice exposed to an enriched environment, this information was recorded in the DNA, directing the expression of genes that allow neurons to generate a higher number of connections. Mice unable of reading the information registered in their DNA, were not able to create new connections”, stated Dr. Rodrigo Torres, first author of the paper. DNA is the molecule containing the information that determines the composition and functioning of our cells. However, our observations demonstrate that DNA also “records” information acquired from our experiences, suggesting that our genetics is not indifferent to our environment and experiences”, he added.

“Until a few years ago, it was believed that the chemical changes in DNA were only associated with gene silencing related to cellular differentiation during development. However, many chemical changes in DNA activate gene expression and far from being permanent, they are dynamic and occur throughout the entire life of an individual”, states Dr. Bredford Kerr. “The postnatal neurodevelopment is a process that depends on the correct interaction between environmental factors and the genome. The result of this interaction are chemical changes in DNA that control the chromatin structure and affects gene expression”.

It is worthy to note that this recently published work is part of the Doctoral Thesis of Dr. Torres, who was enrolled in the Ph.D program of the Faculty of Science of the University of Chile.

Dr. Kerr states “we have demonstrated that the correct interaction between environmental factors and the genome generates chemical changes (cytosine methylation) in the Ryr3 promoter that drive the expression of this gene. Ryr3 is an important gene for the formation of connections between neurons and the stabilization of these connections, an essential event in memory formation process and learning. Furthermore, we have observed that the changes in the Ryr3 promoter methylation are not permanent in time, and they decrease as age advances. However, the exposure to a physical, social and cognitive stimuli in an enriched environment, prevents the changes associated with time and maturity”.

Ref.: Mecp2 Mediates Experience-Dependent Transcriptional Upregulation of Ryanodine Receptor Type-3 Front. Mol. Neurosci., 13 June 2017 | https://doi.org/10.3389/fnmol.2017.00188