Speaker: Martin Howard
Department: John Innes Center
Subject: Dissecting the fundamentals of transcriptional regulation
Location: TU Delft
On the 12th of January, there was a bionanoscience seminar given by Martin Howard. He was trained as a physicist, but he has since then moved into the field of biology as currently does research on epigenetic memory.
The presentation was started of by the question: when is transcription regulated in an on/off manner and when is it regulated in a continuous manner? In addition he asked whether the process is noisy/bursty or not. The rest of the seminar mainly concerned itself with the first question, because there was too little time to go into the second question.
Epigenetic inheritance means the inheritance of phenotype not based on the DNA sequence. Martin Howard studies epigenetics by zooming in on one locus. The system that he studies is called Arabidopsis, in particular flowering locus C (FLC). This locus is involved with aligning plant development with the seasons. The switch to flowering in a plant is repressed by FLC. FLC is in turn repressed by vernalization.
The level of FLC throughout the year.
Correct timing is very important for the FLC is very important because plants cannot flower too early or too late. In the graph above it is visible that the level of expression on return to the warm period depends on the length of the cold period. The Arabidopsis model is very slow, which can be difficult in experiments but also allows a very quantitative study.
After an explanation of the model, the speaker went on to explain about epigenetic memory. This memory can be stored in a trans way and in a cis way. Trans means that it is stored in diffusible factors and is uniformly distributed, cis means that it is stored in chromatin based histone modifications and is locally stored. There is still an active debate in biology as to how the memory is stored.
Systems for digital cell autonomous epigenetic memory is bi-stable. For an individual cell, it is all or nothing. With this knowledge, it can be concluded that the quantitative quality (shown in the graph above) must come from the fraction of cells. The final part of the presentation concerned an experiment with which Martin Howard showed that there is a favour for the cis memory.
I found this seminar very interesting because it largely concerned ecology, a subject which is not often discussed during these seminars. I found the model quite interesting and it was nice to hear that a lot of field research was done for the discussed experiments as well. The final part of the presentation was quite difficult to understand but the rest was fairly easy to follow in my opinion. In addition, I liked that Martin Howard has a very ‘physicist’ way to explore biology, he focussed on a single locus which made it quite easy to explain epigenetics.