Summary of IUPS 2013 Lecture
This account was posted by a graduate student at the Congress on the same day as the opening ceremony and lecture: 21st July 2013:
“Physiology moves back onto centre stage: a new synthesis with evolutionary biology”
Denis Noble CBE FRS. About: Eminent researcher in cardio-vascular physiology, current president of the IUPS.
Key point: New insights in physiology are exploding the traditional concepts of Neo-Darwinism evolutionary theory, and opening up a new world of hereditary mechanisms.
“If physiology has moved off centre stage, it is coming back with a vengeance”.
“The genome is an organ of the cell, not a dictator. Control is distributed”.
The focus of this lecture was in demonstrating how the classic views of evolutionary theory are being pulled apart by new physiological advances. According to Neo-Darwinism, evolution is primarily gene-centred and occurs through the gradual accumulation of random mutations. According to the Weismann barrier, the germ line is completely isolated from the parent, hence there is no possibility of acquired traits being inherited. Noble first asked “Are genetic mutations actually random”? Current evidence indicates that genetic mutations follow distinctly non-random patterns throughout the genome. An example of this is P elements, DNA transposons in Drosophila fruit flies – demonstrated to hone in on functionally related areas as they jump between parts of the genome. Noble then explored whether evolution only occurs through gradual assemblies of single mutations. Analysis of the draft human genome sequence in 2001 indicated that the evolution of transcription factors and chromatin binding proteins could not have proceeded one amino acid at a time – rather whole areas and domains must have been shuffled to obtain the current conformation, indicating that mechanisms of reconfiguring the genome must exist. This was illustrated by the example of domestication, a process of introducing changes gradually through generations. However this form of selection “has never led to the formation of a new species. It is a purifying force, not a creative force”. Compare this with hybridisation, which involves mixing up two distinct parental genomes.
Noble also described how our very concept of a gene has changed and the classic linear progression of DNA –> phenotype has been abandoned in favour of a three way interaction between DNA, the environment and the phenotype via a biological network. This explains why knocking out genes rarely reveals their function as the network can compensate for their loss. This was demonstrated effectively by Hillenmeyer et al. who showed that approximately 80 % of knock out gene mutations in yeast are silent unless additional environmental constraints are imposed.
Noble then moved on to ask “Why should a physiologist be concerned with evolutionary biology?”. Traditional evolutionary views are gene centred, yet physiological research is demonstrating that organisms can “immune themselves from the genome”. Furthermore, information transmission is not a one-way process as organisms can impose downward control onto DNA through cell signalling, transcription factors and epigenetic modification. An example of this is provided by work on rats showing that regular grooming in early life makes the mature adult less fearful – is grooming time limited in colonies stressed by predation or starvation? Another exciting illustration is the production of cross species fish by placing a carp nucleus into an enucleated cell from a goldfish. In the rare circumstances when this produces an embryo, the skeletal configuration is intermediate between the two, but much more similar to the goldfish. Hence, information cannot be transmitted solely by the DNA but must be influenced by maternal factors in the egg cytoplasm. Work on the nematode worm C. elegans meanwhile, has revealed that epigenetic changes can be incredibly robust. Here the inheritance of antiviral RNA molecules was demonstrated for up to 100 generations, even though the DNA template had been lost; inheritance had been achieved through RNA polymerase amplification in the cytoplasm. Our view of the DNA machinery should echo that of Barbara McClintock, who viewed DNA as a highly sensitive organ that can detect and respond to unexpected events. Noble cited how genome reorganisation may also occur through the lateral acquisition of new DNA material from unrelated cells, such as the ingestion of the prokaryote cells which became reduced to mitochondria and chloroplasts. The central concept of this stimulating lecture was clear: the genome is NOT isolated from the environment and furthermore, acquired characteristics can be inherited. Perhaps Lamarck wasn’t so wrong after all.