Transgenerational rescue of gene defect - Lamarckian style!

Transgenerational Rescue of a Genetic Defect in Long-Term Potentiation and Memory Formation by Juvenile Enrichment
Junko A. Arai, Shaomin Li, Dean M. Hartley, and Larry A. Feig
The Journal of Neuroscience, February 4, 2009, 29(5):1496-1502; doi:10.1523/JNEUROSCI.5057-08.2009
URL: http://www.jneurosci.org/cgi/content/abstract/29/5/1496

In an interesting experiment, scientists at the Tufts University School of Medicine, Boston, and Rush University Medical Center, Chicago, demonstrated that exposure of mice that have a genetically engineered defect in long term memory, to two weeks of an "enriched environment" (that includes exposure to novel objects, elevated social interactions and voluntary exercise) enhances memory not only in these "enriched" mice but also in their future offspring even if the offspring never experience the enriched environment. The transgenerational transmission of this effect occurs from the enriched mother to her offspring during embryogenesis.

What this research article is hinting at is that acquired characteristics - like habits, phobia etc. can be inherited. This was previously believed to be an impossibility. For example, if a parent has a particular learned skill, his offspring cannot be expected to be born with the same skill. This is because the skill is an acquired characteristic and such characteristics are not inheritable. At least that was what was previously accepted and this research challenges that premise. If this phenomenon is indeed true in humans, this would mean that a person's childhood experiences could influence behavior, not only in the same person as he/she grows up, but also in his/her offspring who have never been exposed to such experiences.

So, we ask the question: Are acquired characteristics inheritable?

It has been accepted for some time now that acquired characteristics are not inheritable. Proponents of the theory of inheritance of acquired characteristics, like Lysenko (discussed in last week's post) have been discredited and their research thrashed as "unsound science", if not fraudulent science. The theory of inheritance of acquired characteristics, however, is not Lysenko's creation. It was proposed more than 200 years ago by Jean-Baptiste Lamarck and was once widely accepted. Over the next century, publication of Darwin's, and then Mendel's theories led to the general abandonment of the Lamarckian theory of evolution in biology. However, recently Lamarckian evolution has made a comeback of sorts. \

Lamarckian views of evolution are based on two principles:
1. Use and disuse - Individuals lose characteristics they do not require (or use) and develop characteristics that are useful.
2. Inheritance of acquired traits - Individuals inherit the traits of their ancestors.

These principles could be exemplified in the giraffe. Giraffes, while stretching their necks to reach leaves high in trees, strengthen and gradually lengthen their necks. These giraffes have offspring with slightly longer necks. While this example is appealing in its simplicity, there is no evolutionary evidence for this having happened. The theory gained wide acceptance because Darwin and Mendal put forward their theories only after Lamarck's death in 1829.

In any case, Lamarck's views were not completely dead at any point of time. There were many famous scientists who prescribed to Lamarckism in part or in full. These included William McDougall and Ivan Pavlov. William McDougall was a researcher at Harvard who studied the abilities of rats to solve mazes. He found that offspring of rats that had learned solve the maze solved them faster even though they were not exposed to the maze earlier. McDougall attributed this to some sort of Lamarckian evolutionary process. At around the same time, Ivan Pavlov, who was also a Lamarckist, claimed to have observed similar phenomena in animals being subjected to conditioned reflex experiments. He claimed that with each generation, the animals became easier to condition. The claims of McDougall and Pavlov were never proven to be true.

In the first few months of this year, scientists have published research that has shown that Lamarckian type inheritance of acquired characteristics is possible. The actual mechanism underlying these patterns of inheritance is still mystifying to scientists, but the answers seem to be around the corner as we continue to better understand the phenomenon of Epigenetics. More about epigenetics and neo-Darwinism in my next post.