Characters are inherited... Are memories inherited too?

It has been understood from ages past that characters are passed on parents to offspring. From the time of Mendel till today we strive to understand what it is that makes this inheritance possible. Just when the scientific world exulted over understanding the basis of process of inheritance, another challenge presented itself - the challenge of trying to understand how behavioural responses and even more strangely, environmental effects on life span were inherited. The then current theories of DNA based inheritance could not explain this and to answer these questions researchers have had to fall back to the theory that not only DNA but some other proteins and sometimes even RNA can act as a genetic vehicle. This so called “extra DNA inheritance” is now called epigenetics and is a field of science in its own right. The best known, least understood and often romanticised example of this is the inheritance of behavioural characteristics. The fact that behaviour is greatly affected by stress has been observed in all living creatures. Stress is a major evolutionary force and the positive adaptations to stress give organisms a lead over the competition. Short-term intensive stress – till now thought to be non-heritable – is damaging as it forces unnatural behavioural responses which may affect offspring through non-genetic mechanisms such as social interaction. However, recent studies have shown that epigenetic transmission of stress induced behavioural patterns is possible.
This article deals with a case of epigenetic transmission of behavioural responses that was observed in chickens. Researchers from Europe (Norway and Sweden) carried out a study to observe if learning impairment caused by stress is transmitted from stressed parents to normal offspring. The study was carried out in two different species in chickens – one wild {Red Jungle Fowl – RJF} and one domesticated {White Leghorn – WL}. The chickens were subjected to mild chronic stress for an extended period of time and its effects on them were checked via a spatial ability and learning test. As expected, the stressed chickens underperformed in the tests. However, the RJF performed better than the WL in the tests. Surprisingly, it was seen that the offspring of the stressed parents preformed badly at the same tests though they were brought up under unstressed conditions. This generational transfer of behavioural changes due to environmental stress was found to be epigenetic in nature. When gene expression tests were run on the brain tissue, similar up- or down-regulated gene expression patterns – for 31 genes – were noticed in the hypothalamus of the stressed parents and their offspring. Also, it was noticed that the offspring of the stressed WL were more competitive than those of the unstressed. The most important observation was that the epigenetic transmission was seen clearly in the WL when compared to the RJF – i.e. domestication seemed to favour epigenetic inheritance. However the mechanism through which this was achieved remains to be understood. This leaves us with many questions to ponder on – What types of memories or behavioural patterns are passed down generations? Does what we do today affect our children? These are the questions that epigenetics soon hopes to answer.

MANOJ PRAJWAL BHATTARAM
41921555

Paper referred to
Transmission of Stress-Induced Learning Impairment and Associated Brain Gene Expression from Parents to Offspring in Chickens
Christina Lindqvist, Andrew M. Janczak, Daniel Natt, Isabella Baranowska, Niclas Lindqvist, Anette Wichman, Joakim Lundberg, Johan Lindberg, Peter A Torjesen, Per Jensen


For further reading :

• Transgeneration memory of stress in plants
Jean Molinier, Gerhard Ries, Cyril Zipfel & Barbara Hohn

• Sex-specific, male-line transgenerational responses in humans
Marcus E Pembrey, Lars Olov Bygren, Gunnar Kaati, Sören Edvinsson, Kate Northstone, Michael Sjöströ , Jean Golding and The ALSPAC Study Team

• HIV integration site selection: Analysis by massively parallel pyrosequencing reveals association with epigenetic modifications
Gary P. Wang, Angela Ciuffi, Jeremy Leipzig, Charles C. Berry, and Frederic D. Bushman