Our contemporaries in Behavioural genomics and Neurobiology are suggesting that epigenetics may be the key to understanding how the environment interacts with genes to produce obesity, longevity, sterility, mental illness, and maybe even cancer. But what is epigenetics? And, why is it important to Neuroanthropology?
Epigenetic processes provide a way for environmental factors to affect gene activity. These processes involve the chemical modification of the genome resulting in an alteration of gene expression. While the underlying DNA sequence remains unchanged, the activity of particular genes can be turned on or off. Nutrition, exposure to toxins and other exogenetic mechanisms can all be potentially involved in epigenetic activity. These environmental influences can act upon RNA transcripts, cellular structures, DNA methylation/chromatin remodeling, and even prions. For example, smoking can effect your epigenome which is believed to result in some forms of cancer.
Human research into epigenetics can be fraught with ethical dilemmas, and can take a number of generations before sufficient data is produced. But, this is where anthropologists come in. Behavioural and environmental data coupled with social statistics from communities across the world can provide scientists with useful data for analyzing long-term mental and physical health in relation to the environment and corresponding socio-cultural behaviours. Such data is particularly useful when collected from communities exposed to biological disasters or specific nutritional limitations.
To study epigenetics inside the very cells of our body, where most anthropologists are not able to venture, there is another option. Now, for the first time in an insect species, epigenetic modification has been identified and functionally implicated. The recent sequencing of the honey bee genome in 2006 has allowed scientists to discover genes that mediate epigenetic effects.
A queen bee is genetically identical to her workers, and yet she is fertile and can live for several years while worker bees are sterile, much smaller and have a life-span of only several weeks. The difference between the Queen bee and her workers is attributed to a difference in diet. A baby bee lucky enough to feed exclusively on a diet of royal jelly is destined to become a queen. Eating the royal jelly appears to modify a bee larvae’s DNA so that the activity of the gene coding for the enzyme DNA methyltransferase (Dnmt3) is suppressed. This process is called DNA methylation; the attaching of a methyl group to particular genes so as to suppress their expression.
Kurchaski, Maleszka, Foret and Maleszka (2008) tested what happens when the Dnmt3 gene is silenced in bee larvae. When the Dnmt3 gene is active, most larvae turn into workers. If, however, the Dnmt3 gene is silenced, most larvae turn into queens. By comparing the pattern of gene expression in larvae whose Dnmt gene was silenced with that of larvae fed royal jelly in the hive, Kurchaski et al. (2008) have been able to conclude that DNA methylation has the same effect as eating royal jelly. While Royal Jelly may act through a different biochemical pathway than laboratory induced suppression of the Dnmt gene, this experiment clearly demonstrates that DNA methylation is involved in determining phenotype. Kucharski et al. (2008) suspect that this epigenetic process could also be influencing the way bee’s brains develop, and thus also have an affect on behaviour and social organisation.
At certain basic levels of biological processes, epigenetics accounts for cellular differentiation. Indeed, epigenetic modification is a requirement of dynamic variability to cellular function and phenotype. Epigenetics is believed to contribute to congenital disorders such as Angelman syndrome and Prader-Willi syndrome. The role of epigenetic inheritance, not discussed here, will also be an interesting point of study for future research. Epigenetic inheritance involves changes in the phenotype which persist for generally only a few generations. With the accumulating data for epigenetic processes, one thing is for sure, we may as researchers need to reassess the validity and application of Lamarckism in sociobiological theory.
As a researcher interested in neuroanthropology, I have always been fascinated by the question, “Does the culture we grow up in act as an environmental factor that influences the very biology of our brain? If so, should we be speaking about epineural processes and should we leave the door open for the possibility that our culture-influenced behaviour, when propagated over time, acts through epigenetic pathways to alter the gene expression of our brains?”
R Kucharski, J Maleszka, S Foret, R Maleszka. Nutritional Control of Reproductive Status in Honeybees via DNA Methylation. Science. 2008 Mar 13.
Abstract: Fertile queens and sterile workers are alternative forms of the adult female honey bee that develop from genetically identical larvae following differential feeding with royal jelly. We now show that silencing the expression of DNA methyltransferase Dnmt3, a key driver of epigenetic global reprogramming, in newly hatched larvae, leads to a stunning royal jelly-like effect on the larval developmental trajectory; the majority of Dnmt3 siRNA-treated individuals now emerge as queens with fully developed ovaries. Our results suggest that; DNA methylation in Apis is utilized for storing epigenetic information; that the utilization of that information can be differentially altered by nutritional input, and that the flexibility of epigenetic modifications underpin profound shifts in developmental fates with massive implications for reproductive and behavioural status.