A group led by Dr. Robert Yolken at Johns Hopkins University has been studying the links between viral infections and brain development. They were analyzing viruses taken from the throats of 33 healthy adults who were participating in a study that involved the assessment of cognitive functioning. Unexpectedly, the researchers discovered genetic sequences from Acanthocystis turfacea chlorella virus 1 (ATCV-1). ATCV-1 is a type of Chlorovirus, which infects green algae. These viruses are common in fresh water, such as lakes and ponds, but weren’t thought to infect humans or animals.
To further investigate, the group teamed with Dr. James Van Etten, an expert on algal viruses at the University of Nebraska-Lincoln. Their work was supported in part by NIH’s National Institute of Mental Health (NIMH) and National Center for Research Resources (NCRR). Results appeared online on October 27, 2014, in Proceedings of the National Academy of Sciences.
A sequence-specific assay detected ATCV-1 in throat samples from 40 of 92 (44%) people in the study. The team next examined the link between ATCV-1 and performance on a battery of cognitive tests. ATCV-1 was associated with decreases on tests of visual processing. There was no difference on tests of general knowledge.
Studies in people can involve many complex factors, so the scientists infected a group of mice with ATCV-1. The exposed mice performed worse than control mice in several cognitive tests, such as navigating mazes. The researchers next studied gene expression in the hippocampus, a brain region essential for learning, memory, and behavior. Exposure to ATCV-1 was associated with significant changes in the regulation of over 1,000 genes.
“People have conducted studies looking for more conventional viruses and bacteria in throat swabs, but the way those studies were done meant that they could have easily missed the ones that we work with,” Van Etten says.
More study will be needed to learn how ATCV-1 may alter cognitive functioning. If confirmed, these findings hint that other yet-unknown viruses may have subtle effects on human health and behavior. So, there are many questions. Does the viral presence cause or follow from brain pathology? If it is a cause, is the sub-minimal cognitive impairment reversible if virus is removed? Is the causative pathophysiology actually invasion of brain as a very low-grade encephalitis, or is the action via a remote toxic effect? Especially, is this organism a newly found cause of the many thousands of cases of unidentified meningoencephalitis and encephalitis seen yearly?
wherrera writes: One of the implications of the current Mendelian synthesis in molecular genetics is the idea that natural selection operates via selecting on random variations in the gene pool, which themselves are not influenced by the environmental experiences of the reproducing organisms. Changes of a given organism's body due to experience, such as conditioning, trauma, and memory, are usually assumed to only affect the gene pool of the next generation by influencing how many progeny are produced and raised by the prior generation. This is, however, not the whole story.
Epigenetics is the study of how gene expression changes during the growth and development of an organism. For example, the fertilized egg will divide and grow, not just into a clump of egg cells, but a fully differentiated organism containing many different kinds of specialized cells and tissues. Most of these calls contain the same genetic information as the original fertilized ovum, but the DNA has been subtly modified to make specialized groups of RNA and thus proteins.
The biology of epigenetics thus explains how the same DNA information produces different effects in different cells. Can such changes be inherited? Certainly in plants, they can be. It can be shown that sprouting root tissue from a tree often produces a differently shaped plant than sprouting a branch from the same tree. One way that this occurs is via methylation of the cytosine of a DNA region to make it into nonfunctional, mutation-promoting 5-methycytosine. When such changes in DNA--either in its cytosine or its associated histones--are passed to offspring, this has been called genetic imprinting.
A future question is how a signal given to the nose can actually change the methylation of DNA in produced sperm. But we may have here an explanation for the rapid development of innate fear of a predator (including man) in the offspring of animals newly exposed to such.