Presenting Histones

Bravery is an interesting word. It's one of those words that has many different subtle shades of definition; ranging from altruism to stupidity. The big question is, of course, was it brave or stupid of me to volunteer to do a presentation at the first supervision of term?

To put this more in context, I haven't actually done a scientific presentation since, well, at all. We did some mini ones in our supervision group last year, but they did not go so well. I haven't had to speak in front of a large crowd of people for about three years, not since the upper sixth performance of 'Dracula' where I stumbled on stage for a few minutes to play Translyvanian Peasant With Godawful Accent.

Here is the title and the link (for those who can get it) for what I have to present:
"Rb targets histone H3 methylation and HP1 to promoters"

I'm going to go through the paper now and try to provide a quick summary of what it is about. I have no idea how I'm meant to present it (hopefully there will be a brief meeting at some point to discuss this) but I can't help but feel things will go slightly better if I actually know what the paper is talking about.

okay... a look at the abstract and one brief scribbled diagram later this is what I've got:

Pretty pictures if you follow the links!

There is lots of DNA in the cell, so in order for it to fit into the nucleus it has to be coiled. One method for coiling involves wrapping the DNA around histone proteins (beads on a string) to keep them coiled. As well as keeping the DNA wound up, histones can also signal to transcription factors (proteins that start the complex process of turning DNA into protein) which bits of the DNA they need to read by displaying chemical signals.

One such signal is the methyl group, -CH3. Sticking a methyl group onto the end of a histone signals to the cells that this DNA is in Do Not Disturb mode, and should not be turned into protein. The study the paper was doing focused on a protein that goes around putting up all the nuclear Do Not Disturb signs; SUV39H1 (which shall henceforth be known as SUVy). This methylated the histones at a certain point (lysine 9 of histone H3 for anyone interested) and keeps the DNA associated with them from being expressed. It does this by recruting HP1 which binds to the DNA and, as far as I can work out from this, just sits there and stops it being expressed.

There are two forms that DNA in the nucleus can take: heterochromatin, which is all coiled up and not doing anything, and enchromatin, which is being actively expressed. This paper was getting fairly excited because while it was known that SUVy and HP1 were good at keeping heterochromatin quiet, they found them interacting with euchromatin! What's more they were consorting with Rb, a very well known protein that is involved in all sorts of processes that supress the expression of DNA, particularly in different parts of the cell cycle.

By doing various assays involving pulling out the Rb bound to DNA and then finding what bit of DNA it was bound to, they discovered that it methylated the same H3 on the lycine that HP1 did. Furthermore, Rb can interact with SUVy, due to a 'pocket domain' which SUVy fits into quite well. The end conclusion of all this is that Rb and SUVy interact together, methylate a part of the DNA which people hadn't really known SUVy was methylating, and then HP1 comes and sits on it.

The exciting thing here (alright not that exciting, but fairly interesting at the least) is that they put forward at the end that there may be other euchromatin repressor proteins out there that bind to SUVy and mobilise the DNA repression in euchromatin. Also, as Rb is involved in cell cycle control, it helps to build a bigger picture of just what is going on in the cell cycle (which cancer reseachers tend to like).

And woohoo I get to do a presentation on it. :)