A eukaryotic cell is often 5-6 orders of magnitude larger than the molecules that make it up. How is it that these molecules interact to organize the complex structures that constitute a cell?
Dr. Hyman explains how cell division in a C. elegans embryo provides an excellent model for organization of cellular structures and processes and how RNA interference (RNAi) is an extremely useful tool to study this model. He describes how individual proteins can form complexes of varying size and complexity. Complexes can then organize to form compartments, or non-membrane bound organelles such as centrosomes or the cell cortex, and the organization of these compartments drives the cellular organization.
All Course Materials for this Session (Educators only) – Created Tony Hyman
- Duration: 27:57
00:00:01.24 Hello. My name is Tony Hyman.
00:00:03.07 I'm a director of Max Planck Institute in Dresden in Germany,
00:00:06.27 and I'd like to talk to you today about organization of cytoplasm.
00:00:10.14 So, one of the key questions in biology that we're all interested in
00:00:15.15 is the following: How does complexity arise from molecular interactions?
00:00:19.18 The things we're interested in, in terms of cells,
00:00:23.03 are often 5 or 6 orders of magnitude bigger than the molecules that make them up.
00:00:28.25 So, if you have a molecule, over here, on this scale,
00:00:32.15 the cells, for instance, are 10^5... 10^6 orders of magnitude bigger
00:00:38.03 than the molecules that make them up.
00:00:39.24 So, what are the rules by which these molecules can interact
00:00:43.09 to create these very complex structures
00:00:45.13 which are so much bigger than they are themselves?
00:00:47.27 I've worked on this problem for most of my career
00:00:51.00 in a small nematode called C. elegans.
00:00:54.12 And, C. elegans makes embryos about 50 microns long,
00:00:59.23 with a very reproducible cell division.
00:01:02.11 There was a Nobel prize won for the study of various things in C. elegans,
00:01:07.27 in particular cell death in the adult.
00:01:09.28 One of the most important things about working on C. elegans
00:01:13.05 is it's completely invariant.
00:01:14.15 So, the cell lineage of the worm... the way in which one cell
00:01:18.25 goes all the way to the different cells of the adult
00:01:21.25 is completely invariant.
00:01:23.04 But, also, the cell division itself is invariant.
00:01:26.15 I've looked in many, many of these embryos over the years,
00:01:29.21 probably too many to think and calculate
00:01:31.20 But, each one of them looks the same as the one before.
00:01:35.17 So this reproducibility allows us to study problems of organization,
00:01:40.23 of cells after fertilization.
00:01:44.20 What I've got in the background here is a movie
00:01:46.26 of a C. elegans embryo, shortly after fertilization.
00:01:50.06 And what you can see is the cytoplasm of the embryo
00:01:54.16 with its 2 pronuclei, one here and the other one over here.
00:02:00.11 And these are the haploid genomes of the mother and the father
00:02:05.10 which are now in one egg, and I'm going to show you a movie of these 2 pronuclei
00:02:09.08 coming together. And when they come together, they then form a mitotic spindle, and they divide.
00:02:15.08 And this is using a technique known as Nomarski microscopy
00:02:18.04 which is a wide-field, bright-field microscopy technique.
00:02:22.00 So, what you can see now is the two pronuclei coming together
00:02:27.16 in a process known as pronuclear migration.
00:02:29.23 And, boom, they've hit each other, and now they're going to make a mitotic spindle,
00:02:34.24 which you can see in the middle here.
00:02:36.27 And they undergo anaphase. The cell divides into two.
00:02:40.28 Note how one cell is smaller than the other cell.
00:02:44.27 And now you're going to see the second cell divisions.
00:02:48.12 Notice how the divisions now are asynchronous,
00:02:53.19 and the cells are also different sizes, and now you have a 4-cell embryo.
00:02:58.11 Have a look at the timing down here,
00:03:01.11 which is about 30 minutes in this timer on the bottom right.
00:03:05.04 So, about 30 minutes after fertilization.
00:03:09.13 That means the cells are undergoing this very, very complex set of arrangements,
00:03:14.02 and they've built very, very complex structures
00:03:16.07 necessary for their correct cell division.
00:03:18.17 And, if you look at C. elegans embryos, not only is it interesting to study the cell division itself,
00:03:24.29 but an added nice feature of it is the cell division itself is asymmetric.
00:03:29.14 And what I mean by asymmetric is that the fate of the two cells
00:03:34.15 is different. So, this one cell divides into 2 cells, which are illustrated here.
00:03:39.27 The green cell is the germline, and the red cell is the soma.
00:03:43.22 And those two different cells go on to give cells of very different fates.
00:03:48.09 So that means that you can study, in this 30 minute time period,
00:03:52.11 the division of the cell... the basic cell division processes necessary to divide a cell
00:03:57.04 which are likely common to all cells that are trying to divide.
00:04:01.00 And, in addition, you can ask, how is it the cell division can be asymmetric?
00:04:06.02 Now, when you look at a division like this, one very important thing to realize,
00:04:12.07 of course, is that the fertilized egg comes from the fertilization of the oocyte
00:04:17.03 and the sperm. And the majority of the cytoplasm comes
00:04:23.22 from the oocyte, and it's a gift from the mother.
00:04:27.23 And the sperm comes in, provides some components,
00:04:30.25 but it mainly triggers the fertilization process and adds some of the DNA.
00:04:35.27 And so the cytoplasm is a gift from the mother,
00:04:38.24 and in the C. elegans embryos, the oocyte is relatively undifferentiated.
00:04:44.25 That's not true for oocytes in all organisms,
00:04:48.03 but in our particular nematode, the oocyte itself is relatively undifferentiated.
00:04:52.13 It's in cytoplasm that's a gift from the mother. It's like a bag of cytoplasm components.
00:04:57.26 And then, that gets fertilized, at about half an hour afterwards,
00:05:02.02 you organize this rather undifferentiated bag of cytoplasm
00:05:06.21 into this complex choreographed set of events necessary for cell division.
00:05:11.15 One of the key events in trying to understand the division of this nematode,
00:05:20.10 was the sequencing of the DNA. So, the DNA sequence
00:05:25.11 of C. elegans was the first multi-eukaryotic system in which the DNA was sequenced.
00:05:29.26 And, the sequence of the organism defines the potential catalog
00:05:35.28 of genes required for its life.
00:05:39.00 And C. elegans has, depending on the time of the month,
00:05:43.01 about 20,000 different genes.
00:05:47.29 So, what you can ask then is, "Here are my genes..."
00:05:52.09 So, the yellow represents the chromosome, and the black bars represent
00:05:56.03 distribution of genes along the chromosome.
00:05:59.11 And you can ask which one of these genes here
00:06:03.10 is responsible for cell division?
00:06:06.07 Of these 20,000 genes, which one of those are involved in this process of making the embryos
00:06:13.01 and dividing them?
00:06:15.03 And we decided to look at this problem,
00:06:17.21 because of the development of a process... a technique called RNA interference.
00:06:24.28 And this discovery of RNA interference
00:06:26.21 by Andy Fire and Craig Mello also won the Nobel Prize a few years ago.
00:06:32.26 Now, the key thing you want to do, as I said,
00:06:36.13 is to create a catalog. The genes themselves
00:06:39.13 when you sequence the genome,
00:06:43.09 you want to be able to assign a function to each one of those genes,
00:06:47.27 So let's say you've got 20,000... 25,000 genes.
00:06:51.00 You'd like to go to each one of them and catalog its function.
00:06:54.26 And that has been something that most of biomedical research
00:06:59.14 has been trying to do over the last 20 years
00:07:01.09 since the sequencing of the human genome
00:07:03.14 is trying to assign function to each one of those genes.
00:07:07.00 As I said, the key to step forward in that cataloging process
00:07:13.15 of assigning functions is the development of RNA interference.
00:07:16.00 And here I have a slide which outlines how we think RNA interference works
00:07:20.04 and how we can use it to silence the function of genes.
00:07:23.29 So, the idea is, you want to take each gene, one after the other.
00:07:27.03 You want to silence its function. And you want to ask, after we silence its function,
00:07:31.26 what effect does that have on the development or cell division of the organism?
00:07:38.14 So, in our particular case, we'd like to ask, after we've silenced the gene,
00:07:41.19 what effect does that have on the cell division?
00:07:44.26 Now, what we do is we make an RNA in the test tube
00:07:50.11 called a trigger double strand RNA.
00:07:52.06 So, we make a double-stranded RNA, and then we introduce it into the mother.
00:07:57.08 And what happens after that is that the Dicer,
00:08:03.07 which is an enzyme, chops up the double stranded RNA
00:08:06.10 into smaller components that I've shown here.
00:08:10.19 They're called little siRNAs. The Dicer chopped them up into 21-25 base pair
00:08:16.19 little pieces. Then what happens
00:08:20.01 is that the RISC complex binds these siRNAs,
00:08:25.07 unwinds them, and individual unwound RNAs
00:08:33.14 are then bound to the endogenous mRNA
00:08:38.02 which is single stranded, and that triggers its cleavage.
00:08:42.19 So, over here, I've shown that the mRNA has been cleaved
00:08:47.05 by the binding of the single stranded siRNA.
00:08:52.14 So, that's a very powerful technique because now what we can do
00:08:55.23 is we can remove the RNA for any gene we're interested in
00:08:59.27 because RNA makes the protein, you therefore don't make any more protein,
00:09:04.22 and that means that you can then study what happens to your organism
00:09:09.26 when you've removed the function of that gene.
00:09:13.14 Now, it's not quite as simple as that, because there's a problem.
00:09:18.19 which is that, of course, RNA interference removes the messenger RNA very quickly.
00:09:23.21 It's a catalytic process that destroys the mRNA.
00:09:26.22 But, the protein levels then decline at a different rate,
00:09:32.01 and that's because once the message has been destroyed,
00:09:35.20 there's no more message to make any more protein,
00:09:39.06 but the protein that was already existing,
00:09:40.26 first of all has to disappear.
00:09:43.15 And that's one of the difficulties of RNA interference
00:09:46.26 is waiting for the protein to disappear.
00:09:49.01 So, what you're normally doing is worrying about what's known to biologists... called a run-down,
00:09:53.20 which is the protein levels are slowing running down,
00:09:56.17 and the difficulty in RNA interference is deciding,
00:09:59.15 what does it mean if I look at cell division when there's this much protein left,
00:10:04.15 and later on, I look at the same cell division with this much protein left.
00:10:07.09 How do I interpret that phenotype?
00:10:09.06 And it turns out that C. elegans,
00:10:11.24 has a particular advantage which allows us to get around that problem.
00:10:16.08 Now, here what I've done is I've shown from the Wormbook and WormAtlas
00:10:21.15 a picture of a C. elegans with its gonad and its gut.
00:10:26.05 And what you can see from this is C. elegans is basically an egg-laying machine.
00:10:30.07 It makes about 200 embryos after its made,
00:10:34.01 and it makes them rapidly and then it goes on and dies.
00:10:37.28 What I've shown here are the gonads, which here is where the cells of the future oocytes
00:10:44.07 are being made. Then, as they come around the arm of the mother,
00:10:47.14 they're made into these different oocytes,
00:10:49.12 and then they go through the spermatheca here,
00:10:51.28 and then they go on to be fertilized eggs.
00:10:55.19 And here I've got a blow-up of the gonad from the Wormbook,
00:10:59.05 where you can see what's happening is the gonad is what's called syncytial here.
00:11:04.12 (In other words, it's got no membranes.)
00:11:07.06 And, as you come around the bend of the gonad, you make oocytes.
00:11:11.02 And the key thing about this process is shown in the next slide,
00:11:15.27 which is, first of all, you inject the double strand RNA, or you can feed it.
00:11:21.26 And then what happens is that the RNA is then degraded.
00:11:27.05 Then, the protein flushes out because the gonad is constantly making oocytes.
00:11:37.01 So, I've shown in the arrow this constant flushing out process of protein
00:11:40.14 as it makes new oocytes.
00:11:42.20 Now, of course, it then makes new protein to make more oocytes,
00:11:46.27 but because the messenger RNA is now missing because you silenced it,
00:11:49.29 it now means you're making these oocytes in the absence of the protein that you're interested in.
00:11:56.12 And that's particularly because we can access what's known as the maternal cytoplasm.
00:12:02.00 And therefore, we can ask the embryos to be laid
00:12:05.03 i n almost the complete absence of the protein we're interested in.
00:12:08.19 And that is a great advantage of doing RNA interference in
00:12:11.24 C. elegans and why it's been so successful
00:12:14.07 in looking at particular phenotypes.
00:12:16.19 The genome-wide screen was primarily the work of two people, Pierre Gonczy and Chris Echeverri.
00:12:24.04 Pierre Gonczy and Chris pioneered the techniques for doing this in high throughput.
00:12:31.04 And, they designed the following screen,
00:12:34.22 where you took a genome-wide set of double stranded RNAs,
00:12:37.17 and we synthesized them, microinjected a pair of worms,
00:12:42.05 and we looked for cell division embryonic defects.
00:12:43.21 So, the idea was to try and film the cell division for after RNAi
00:12:51.03 of each one of the genes in the genome.
00:12:53.06 And one of the problems you have, in any experiment like this,
00:12:58.09 is we made about 45,000 different movies of these cell divisions.
00:13:03.05 And how do you quantify this problem?
00:13:05.11 What you want to get away from is this idea of saying,
00:13:09.13 well this seems to have a cell division defect,
00:13:11.08 that may have a defect in dividing the cell in two.
00:13:14.09 You want to be quantitative.
00:13:15.28 By being quantitative, you can then understand a lot more about the particular phenotype.
00:13:20.23 We came up with the following method to do it,
00:13:23.11 which is, we divided the division into 47 different things that we thought
00:13:30.13 could go wrong,
00:13:32.09 and then we looked through the movies manually,
00:13:35.06 and if there was a defect, we gave it a 1, and if there was no defect, we gave it a 0.
00:13:39.13 And then we did each movie 5 times,
00:13:42.17 and then we did 5 movies of each embryo.
00:13:46.16 And then, from that, we were able to get a heat map,
00:13:49.09 where you can see that the colors represent the penetrance of the phenotype.
00:13:53.07 So, like 100% means that every movie that we looked at had a particular phenotype.
00:14:00.27 And so, by doing that for all the movies, we then ended up with what's known
00:14:05.02 as a heatmap here, which is the defect categories on this axis,
00:14:09.02 and the genes on this axis, and then you can see you have clusters of genes
00:14:14.09 with certain phenotypes.
00:14:15.20 So these ones, for instance, are required for chromosomes to form and segregate.
00:14:21.11 What that screen did, is it defined a catalog of genes required for the first cell division
00:14:29.14 of a C. elegans. And for those of you who are interested,
00:14:32.11 we put all the movies online at the website on the bottom of the slide.
00:14:36.22 And, of course, we were also able to divide up the genes into functional categories,
00:14:41.04 of genes that are required for particular, different purposes.
00:14:45.12 But one of the questions that biologists now face
00:14:48.25 is, in this huge amount of information, how do we make sense of it?
00:14:51.17 How do we make sense of this massive complexity...
00:14:54.04 800 genes is an enormous amount of data to work with.
00:14:59.05 How can we make this simpler in a way that we can actually try and study particular problems?
00:15:05.08 Because all we've done here is really created the catalog
00:15:09.04 of genes... what you might call Gene X is required for process Y,
00:15:13.12 and that, of course, is powerful, but it doesn't tell us
00:15:18.05 how the embryo itself is organizing and dividing.
00:15:22.01 And that's the problem that I've always been interested in.
00:15:24.13 Now, one thing to remember... if you think about this question...
00:15:28.23 How is the function of 800 genes coordinated?
00:15:32.05 It's important to remember the following fact,
00:15:34.15 which is cytoplasm is not an undifferentiated soup of genes.
00:15:39.23 You can't think about the cytoplasm as a set of 800 proteins,
00:15:44.02 floating around, and somehow organizing a cell division.
00:15:49.27 That's not how we think about the cell. That would be much too complicated.
00:15:53.24 Rather, what we do, as cell biologists,
00:15:56.06 and generally as biologists, is we think about biology as a hierarchy of organization.
00:16:01.01 So, here I've shown you 1 hierarchy of organization,
00:16:05.13 which is, you can see that proteins themselves form protein complexes
00:16:11.14 as an example. And that appears to be one of the first levels of organization
00:16:17.09 under which proteins function in the cell.
00:16:19.29 Most proteins appear to function in protein complexes with other proteins,
00:16:24.23 and in fact, some of the protein complexes are very, very sophisticated
00:16:28.04 with many, many proteins. The ribosome, for instance, has over 100 proteins.
00:16:33.02 And so, here are some crystal structures of ribosomes and nuclear pore complexes.
00:16:40.17 And, molecular machines tend to be protein complexes that are very complex.
00:16:45.19 And that's one way that we can think about how to organize the cytoplasm,
00:16:50.04 which is to say, not what the function of the individual proteins are,
00:16:53.20 but what are the functions of different protein complexes.
00:16:56.28 And, because of the power of that approach,
00:17:00.13 there's been a huge amount of work done using mass spectrometry.
00:17:05.02 Mass spectrometry is a way of defining individual proteins
00:17:09.19 which has been very powerful for working out which proteins are in which protein complexes.
00:17:14.26 And here I have a diagram of how we do these experiments.
00:17:19.19 We take an antibody, and we immunoprecipitate one protein.
00:17:25.00 Now, if the protein is in a protein complex, it brings down not only the protein that you're
00:17:28.23 immunoprecipitating, but also all the other proteins in the complex.
00:17:33.00 So, if there are 10 proteins in the complex, you'll immunoprecipitate 1 member of that complex,
00:17:37.22 and then you'll bring down all the other 9 proteins.
00:17:41.25 Then, what you do, is you take that mixture and you hit it with trypsin.
00:17:47.15 You add trypsin or another proteolytic enzyme,
00:17:51.09 and that cleaves the different proteins into their component peptides.
00:17:56.06 The key thing with mass spectrometry, which has been known for many decades,
00:18:02.11 is that the mass accuracy of the measurements are exquisitely sensitive.
00:18:07.03 I'm not going to go into the details -- there are many places you can read into that problem.
00:18:13.03 But, the key thing to remember is that mass spectrometry can, with exquisite precision,
00:18:19.03 measure the mass of different peptides.
00:18:22.05 And then, what you can do, is you can ask which peptides -- from the masses --
00:18:27.18 are like to be part of different proteins, and that's turned out to be very accurate
00:18:32.05 with modern mass spectrometers, and then that allows you
00:18:35.04 to define the different protein complexes and the proteins in those complexes.
00:18:39.22 And that's what been known as proteomics.
00:18:41.16 And, for instance, here's one study where we can look at the different proteins
00:18:46.01 in the different complexes and define different protein complexes required for different purposes.
00:18:51.05 And, proteomics is a big industry now.
00:18:56.06 Many labs are trying to define the sets of protein complexes
00:19:01.13 involved in various different processes.
00:19:04.05 For instance, we might like to understand not what are the proteins required for cell division,
00:19:07.03 but what are the protein complexes required for the division of a cell.
00:19:11.09 Now, some protein complexes are more interesting in the way they actually function.
00:19:20.11 And I want to show you a couple of examples of those.
00:19:22.23 One of those are polymers.
00:19:24.03 And so, here I'm showing you a microtubule growing and shrinking.
00:19:28.10 And, for instance, there are things like centrioles, which are also very complex structures.
00:19:34.16 They're protein complexes that are also put together in very complex ways.
00:19:40.06 And, in the next parts of my talk today,
00:19:43.04 I'm going to talk to yo more about microtubules and centrioles
00:19:46.21 and how they're put together.
00:19:48.11 If we go back to our scale axis that I introduced at the beginning,
00:19:54.20 If you remember I talked about the fact that we have proteins over here,
00:19:59.07 and how are they organized to make cells,
00:20:02.00 which are many orders of magnitude bigger than the proteins themselves.
00:20:05.01 What you can see of course is that one of the ways that we think about that
00:20:09.00 is how the proteins are organized into these complexes.
00:20:12.24 And you can see that helps to bridge the scale gap.
00:20:17.05 But what about this big area here?
00:20:20.01 It turns out, in this area, there are also a lot of complexes,
00:20:23.09 about which we understand very little. And these are called compartments, or else organelles.
00:20:28.20 And, how protein complexes organize into compartments is much less well understood
00:20:35.21 than how proteins are organized into protein complexes.
00:20:38.23 And, these various different structures are things like centrosomes,
00:20:43.27 kinetochores, proteins, nuclear bodies
00:20:48.23 and these are large, non-membrane-bound compartments,
00:20:53.22 where many, many different protein complexes live together
00:20:56.18 and undergo particular aspects of cell physiology.
00:21:01.14 So, for instance, there are centrosomes, shown here.
00:21:04.29 And here I have kinetochores, illustrated by electron microscopy.
00:21:09.16 And these are all large, non-membrane-bound complexes...
00:21:14.03 compartments, which contain many, many different protein complexes.
00:21:19.15 And, let me show you movies... some other ones, such as the cortex,
00:21:24.05 which is the outside layer of the cell.
00:21:26.06 That, as an example, is also a compartment.
00:21:31.18 A very interesting compartment.
00:21:34.06 Then, for instance, we can look at centrosomes and chromosomes.
00:21:38.13 These are other compartments in the cells.
00:21:39.28 And, you can see here, a movie of mitosis,
00:21:45.10 where we've labeled the centrosomes and the chromosomes with GFP,
00:21:48.26 and you can see them going through mitosis.
00:21:51.13 These are also large compartments,
00:21:53.21 which are organized from many, many different protein complexes.
00:21:56.28 The key thing about these compartments is, first, they have no obvious structure,
00:22:05.16 when you look by electron microscopy.
00:22:07.13 A second important thing about these compartments
00:22:10.22 is they turn over quickly.
00:22:13.07 So, in other words, if you do a photobleaching experiment,
00:22:15.21 then the components in these compartments will exchange with the cytoplasm very quickly.
00:22:22.08 And, I'll show you some examples of that in subsequent slides.
00:22:25.12 But, the protein complexes that make up these compartments tend to turn over very slowly --
00:22:30.18 on the order of hours.
00:22:32.00 So, the protein complexes I discussed with you earlier in this segment are very, very stable.
00:22:37.26 You can isolate them in test tubes. Some of them you can just leave sitting around in a test tube
00:22:41.18 for many, many days, and they'll be stable.
00:22:45.18 So, they don't turn over very fast.
00:22:47.18 But, the protein complexes in these compartments exchange very, very rapidly.
00:22:53.02 Just to give you an example of that, let's come back to our favorite topic, the centrosome.
00:23:00.05 What I'm showing you here is the centrosome by electron microscopy.
00:23:03.16 You can see very little because it's a very fuzzy, electron dense material,
00:23:08.07 with no obvious structure. What you can see is the centriole in the middle of the centrosome.
00:23:12.07 Now, let's take a component of the centrosome, the gamma-tubulin,
00:23:17.26 and we label it with GFP. Now gamma-tubulin is a big complex of proteins.
00:23:22.08 It depends, but it varies between 3 and 8 proteins in different systems.
00:23:26.17 If we label one of those components,
00:23:28.19 we're not labeling or following the activity of the whole complex.
00:23:32.07 If we photobleach that particular GFP... in other words, we hit it with very bright laser light
00:23:40.28 so that the fluorescence of the complexes in the centrosome is now bleached,
00:23:46.05 we can look at the recovery of fluorescence.
00:23:48.22 And the fluorescence can only recover by new gamma-tubulin complexes
00:23:53.20 diffusing in from the cytoplasm and into the centrosome.
00:23:56.28 So that gives you an idea of the turnover of these complexes at the centrosome.
00:24:01.29 If we do that, we find that they recover very quickly.
00:24:06.11 So, if you notice in that movie, I photobleached the centrosome,
00:24:10.24 and within 60 seconds, the fluorescence is already beginning to recover,
00:24:14.11 where the gamma-tubulin complex itself turns over very slowly.
00:24:18.29 Many hundreds of hours, probably.
00:24:21.15 So, that is a conundrum which we don't really understand, which is,
00:24:28.08 what are the rules by which the protein complexes, which themselves are so stable,
00:24:32.21 interact together in things such as a centrosome or the kinetochore,
00:24:37.03 or other things such as the nuclear body to organize themselves?
00:24:41.29 Just to give you another example of the cortex, which is the outside layer of the cell.
00:24:48.16 I've shown you that's divided into 2 different domains,
00:24:51.21 a posterior and an anterior domain,
00:24:54.17 and those domains are defined by different protein complexes.
00:24:57.25 And, I've shown you an example of one complex over here, the so-called anterior PAR complex.
00:25:03.00 Now, that, of course, is a relatively stable protein complex.
00:25:07.16 But, let's photobleach a component of the other compartment here
00:25:11.01 and watch it's recovery rate.
00:25:12.29 And see how fast it... BAM!
00:25:15.14 We've photobleached it, and look, a few seconds later, it's almost completely recovered.
00:25:19.06 So, that's exactly the same sort of problem,
00:25:21.03 which is what are the rules which keep these protein complexes in these compartments,
00:25:27.03 despite the fact they're turning over so quickly.
00:25:29.10 So, we come back then, to our scale here. What I've done to introduce this problem
00:25:39.12 is to show you how we can go from the proteins all the way to the cells
00:25:46.06 and bridge that scale by understanding the organization of different compartments.
00:25:52.29 And, one of the ways we think about that is emergent properties,
00:25:58.08 which is something you may have been hearing about,
00:26:00.28 which is emergent properties of collections of individuals.
00:26:04.22 So, the proteins themselves are individuals,
00:26:07.21 and the collective is an example of protein complexes.
00:26:10.20 So we can try and understand what properties of protein complexes emerge
00:26:14.10 from the collection of proteins that make up those protein complexes.
00:26:18.21 The same we can answer with protein complexes. We take all those protein complexes,
00:26:23.15 we put them together in like a centrosome or a nuclear body and can ask
00:26:26.27 what activities emerge from the combined activity of all those protein complexes?
00:26:32.08 And we can go further, of course, to ask, now we have all the compartments,
00:26:36.13 and we've put them together in a cell.
00:26:38.05 How does the property of the cell emerge from the organization of those compartments?
00:26:42.28 How do they actually work together?
00:26:44.10 And then, of course, we could ask the same thing in tissues.
00:26:47.17 Cells collectively work together to make tissues.
00:26:52.04 And the important thing about this is that at each level, at each scale,
00:26:56.08 we have to use different ways to think about it.
00:26:58.10 We need different microscopy, we need different theory
00:27:02.26 to understand each one of these different scales.
00:27:06.08 And that's what's made biology so interesting is that each one of these scales,
00:27:09.29 we had to think of new ways to do it,
00:27:11.24 and try and develop new microscopy techniques,
00:27:13.22 and try and pick up new theoretical ways
00:27:16.24 to think about how these different organizational structures work.
00:27:21.05 And, in the other sections of my talk,
00:27:23.22 what I'm going to come back to is talk about some of these levels of organization
00:27:28.22 in a bit more detail...
00:27:30.18 microtubules, centrioles, and something called p-granules,
00:27:34.13 and illustrate from these talks the different sorts of microscopy
00:27:38.10 and the different sorts of problems that occur
00:27:40.27 in trying to understand how these complexes are made up.
In his talk, Dr. Hyman discusses two methods: RNA interference and Mass Spectrometry (following immunoprecipitation).
Compare the type of information that each of these methods can produce when it comes to analyzing:
- A given protein’s function
- A given protein’s contribution to a particular protein complex
Tony Hyman received his BSc in Zoology from University College, London and his PhD from the Laboratory of Molecular Biology in Cambridge. He then moved to the University of California, San Francisco to pursue postdoctoral research. Hyman returned to Europe in 1993 when he joined the EMBL in Heidelberg as a young faculty member. After… Continue Reading