Session 1 - Molecular and cellular memory
For our Science and Society meeting at EMBL this year we will pursue how the past is inscribed and encoded in the biology of living organisms. In the opening session we will have three talks demonstrating, how memory works at the molecular and cellular level.
DNA can be said to remember, and it can also forget. The haemoglobin mutant HbS that causes sickle cell anemia in the black population of the USA is a memorial to the fact that the ancestors of its present carriers were selected for resistance to malaria in their original West African home. DNA remembers dynamically through generations by repeated copying using the complementarity principle inherent in the double helix. But given time, the HbS allele will vanish in the USA and this mark of African history will have been forgotten.
DNA can also remember because, like the Rosetta Stone, it is made of a robust material. The extraordinary chemical stability of DNA means that, given the exquisite techniques used by our first speaker, Eske Willeslev, we can read the genes of our ancient ancestors, their plant and animal companions, and their parasites. These memories also get lost through the depredations of time, but enough survive, like the Rosetta Stone, to tell us about long lost civilisations.
Memories of our infections persist in the cells of the immune system and last no longer than our short lifetimes. This is the memory of a specific set of DNA sequences encoding protein receptors, created during our lifetime in lymphocytes that recognise antigens on pathogens. As Adrian Hill will tell us, however, immunological memory sometimes doesn’t last long enough, making efforts to extend memory a challenge for global health.
On much shorter timescales, during development cells acquire the distinctive properties of eg neurones or muscles. They all carry the same DNA, so the memory of a cell's differentiated state is not carried in the DNA sequence. But DNA also allows for a different kind of modification, reversible and therefore transient, in which the genetic material becomes decorated in specific positions with chemical modifications, either, like methylation, directly on the DNA helix itself, or on the nucleosome proteins that fold and pack the DNA in the nucleus. These decorations, chemical marks, which define short-term states of cellular behaviour, short-term cellular memories, will be the target of Hannah Landecker's lecture.