Wisconsin Public Television University Place  Bad Cell Division Doesn't Always Lead To Cancer  Mark Burkard  3/6/13 UP845  cc >> Welcome, everyone, to Wednesday Nite at the Lab. I'm Tom Zinnen. I work here at the UW Madison Biotechnology Center. I also work for UW Extension Cooperative Extension, and on behalf of those folks and our other sponsors, Wisconsin Public Television, the Wisconsin Alumni Association, and the UW Madison Science Alliance, thanks again for coming to Wednesday Nite at the Lab. We do this every Wednesday night, 50 times a year, and it's your chance to experience science as exploring the unknown here within this community of researchers. Tonight, it's my pleasure to introduce to you Mark Burkard. He is both and MD and a PhD. He is an Assistant Professor of Medicine here at the UW Madison. He's a physician scientist with a clinical interest in medical treatment of breast cancer. He directs a lab in the UW Carbone Cancer Center focused on mechanisms of human cell division and anti-mitotic therapies. 

Mitosis is not good, so we're going to be against mitosis. Mark completed his MD and his PhD training in chemistry at the University of Rochester and postgraduate medical training at the New York Hospital/Cornell and at Memorial Sloan-Kettering Cancer Center. He joined the faculty of UW Madison in 2008 and is currently co-leader of the Breast Cancer Working Group and the Associate director of the Medical Scientist Training Program. He grew up in Buffalo. I think he knows something about snow. Probably a little bit more than we do. And tonight he's got this great title: Bad Cell Division Doesn't Always Lead to Cancer, and we get to hear about his team's discovery of a new type of cell division called klerokinesis. Please join me in welcoming Mark to Wednesday Nite at the Lab. [APPLAUSE]  >> Thank you. It's a pleasure to be here tonight, and it's true, I know snow. 

About a hundred inches worth a year in Buffalo. So about twice as much as here, typically. I want to welcome all of you and thank you for coming out, alumni, public, and I also have the added pressure of teaching a class from UW Platteville Biotechnology, welcome. And today, what I'd like to do is tell you a story of something surprising to us that came up in the lab. And this is the fun part about working in lab, that sometimes you find things you didn't expect to find because you looked, and that's what this story is about today. So, the parts of my talk I'm going to cover today are, number one, a little bit about cells and cell division. Number two, what that has anything to do with cancer itself. And, three, I'm going to tell you the story of how my lab uncovered this unusual form of human cell division called klerokinesis and what we think it means. To start with, we have to recall that what we learn today in the lab is possible because we have the knowledge and the tools that have been developed by those who've come before. I want to cover a little of the material from people that have come before. 

But I just want to dwell on that topic a little bit, and this is an old idea. John of Salisbury wrote in the Metalogicon, we don't give books such colorful names anymore, but he wrote, "We are like dwarfs on the shoulders of giants, so that we can see more than they, and things at a greater distance, not by virtue of any sharpness of sight on our part, or by physical distinction, but because we are carried high and raised up on their giant size." And this is often used as a metaphor to understand how the advances of the science of the past has led to the advances that are discovered now. And so to go cover some of these giants of science and history relevant to our talk today, let's go back to the 17th century. This gentlemen is Robert Hooke. He lived in the day when English scientists were called natural philosophers and had a lot of interests. And his interests were very diverse, from gravitation to astronomy, and a little bit he got into biology. And the reason he got into that is because he lived at a time when people were finally putting lenses together for telescopes, and if you reverse them in just the right way, instead of making something far and big seem near, you could make something small and close look large. And that's what he did. And he wrote a monograph called Micrographia. And in this monograph, he detailed what he first described as cells. 

These are these structures within that he saw under the microscope within living things. The reason he called them cells is because this reminded him of the little rooms that monks lived in. So that's why we call them cells today. Well, one natural question that came later was, well, where do these cells come from? If cells are the building blocks of life, they have to come from somewhere. And there were a lot of thoughts that went around in the 19th century. There were a lot of twists and turns in science as it turns out. And one thought was that cells just appear. And now most of you would think, well, why would anyone think such a thing? But imagine this very simple experiment: you take a broth of any sort, put it in a cup, put it on your counter, and each day you take a little sample of that broth, put it under the microscope, and look what's there. And at first you might see nothing, but over five or six or seven days as that broth goes rancid, you see all the sudden a bunch of cells that show up. And so, naturally, you conclude that cells appear from nowhere. 

But Louis Pasteur didn't quite believe that, and he set out to do an experiment to prove that cells could only come from other cells. And he did that by developing a pretty interesting experiment. So he tested this idea of spontaneous generation of cells by sterilizing a broth and placing it in these flasks with curved necks. Now, the point of the curved neck was it's not easy for bacteria of microorganisms to fall into a broth through such a swan neck. And so what he found over time was that broth remains free of microorganisms. Whereas if he took of that curved neck, over time he could easily find microorganisms growing in the broth. So he concluded, based on this elegant experiment, that microorganisms, or cells, come from other cells and don't appear spontaneously from nowhere. It seems obvious now, but it wasn't. So, if cells come from other cells, the next question, naturally, is, how does one cell become two? Obviously, things grow and proliferate. So, that was answered in part by Walter Fleming. 

Walter Fleming was a German scientist in the 19th century, and like many scientists, he took advantage of some unique tools available to him at the time. And if any of you are familiar with 19th century Germany, what was there is, what was developing at that time was the aniline dye industry. So coal tars were a chemical source that had become widely available, and chemists were using these to derive new chemicals. In some cases, these chemicals had very bright colors that could be used commercially to dye clothes, and they had huge advantages over natural dye in that they were brighter, longer lasting, and could be made in large quantities. So there was great commercial value in making new chemicals out of coal tar. Well, Walter took those chemicals and said, well, I wonder what happens if we stain some living cells. And he did that. And he saw these very interesting structures that hadn't been seen under the microscope before because you needed to stain them to see them. And he drew them in black and white, but he called them chromosomes because they stained brightly in color. And not every cell had these chromosomes that he could see like this, but in many cases, and these are his original drawings, in many cases he could see these chromosomes make these discrete structures and he could imagine them lining up and then, in some cases in some cells, they appeared to be separating into two different groups and as you move down into two different groups. 

And finally, he saw some of them which appeared to be dividing cells. And so, he discovered this process and said this is a mechanism of cell division, and it appears that these chromosomes are being separated in a very orderly fashion into two cells. And, of course, he called this mitosis. He said these things look like threads. Mito is Greek for thread, and so this is the mechanism of cell division. Well, not everyone agreed with that point of view. And just to give you an aside here, but also a taste of science, not everything is so clear-cut in science. Many scientists believed that this was not the only way that animal cells could divide. One such scientist was Charles Manning Child, a very knowledgeable PhD scientist, a National Academy member in the United States, and a professor at the University of Chicago. And what he noticed when he was looking at embryos, a lot of these were done at a biological station on the ocean because a lot of these were from ocean-derived organisms, but what he noticed was often he could find cells that appeared to have multiple nuclei. 

And this is his drawing of a cell with different nuclei in a fertilized egg. And this nucleus looks like it's actually dividing into two actively. And people have seen such things since. If you cut and stain a tissue like a mouse liver, and he called it amitosis, if you cut and stain a structure like a mouse liver, you can see these odd things. And this reinforced this idea of amitosis. You could see, here's a cell from a mouse liver that looks like it has two nuclei that had just split. And here's one that looks like they caught it in the act of splitting. Now, I say this as an aside but, again, this is to give you a taste of the way science works. There are a lot of false leads, and we now know that a lot of these findings were indeed abnormal cells but cells that had gone through mitosis in some abnormal way and ended up with multiple nuclei. And so this is thought not to actually be the case. 

But it was a large controversy at the turn of the century. So, with that, I want to bring you up to a more modern view of an animal cell. So I'm going to jump ahead about a hundred years here and give you a picture of how we see things today. So this is a cut out of an animal cell, like a cell in our own body, and what you see is a nice blue membrane, but then all these structures inside, each of which have their own separate membranes, and those are called organelles, and each one has a different function. And an interesting hypothesis about how these cells came to be is that they came from a bunch of bacteria. Bacteria are cells that don't have all these little pieces inside. But if you imagine one bacterium engulfing another engulfing another engulfing another, you could imagine a whole group of bacteria that are living in a community. And that's thought to be maybe one way that such cells originated. In any case, I want to focus today on the nucleus. The nucleus is, in some ways, the heart or the center of a cell, if you will. 

And inside the nucleus of a cell, of course, are these important structures that I talked about: chromosomes. And if you break apart these chromosomes, what you find are these fibers called chromatin. Chromatin is made of both DNA, which makes a double helical structure that you've all heard of, but those chromatin are packed in and around these proteins called nucleosomes, and that's important because if we took a human DNA and lined it end to end, it would be three meters long. But each of that has to pack in this orderly structure into a microscopic cell. So, if I took any one of your billions of cells in your body I could unfold three meters of DNA. Pretty amazing. During the process of mitosis, which I talked about, those chromosomes get even more compact so they're not so intertwined and hard to pull apart. And when they're more compact they form these nice structures that one can visualize under the microscope. In this case, these are chromosomes visualized under an electron microscope. Now, in the 1950s, because it took that long, we finally figured out that there are two sets of 23 chromosomes, or human cells typically have 46 chromosomes in a normal individual. 

And the chromosomes can be divided up and numbered. Basically, people just sorted them out by the size so that the longest ones they called number one, the next, number two and so forth until they got to 22. And the last two chromosomes, the X and Y chromosomes, of course are special because they're called the sex chromosomes, and they determine one's gender. Males have one large chromosome and one small chromosome, or XY, as you see here. Whereas, females have two X chromosomes. And people have developed more modern ways to see these chromosomes and color them so that they could more easily distinguish which chromosomes are which and which might be abnormal. And this is a picture of what's called the spectral karyotype, which is a fancy way of painting each chromosome a unique color to aid in identifying them. I want to talk about some of the modern, at least one more modern giant of the biology community and that's Roger Tsien. Roger Tsien is a Nobel Laureate who works at the University of California-San Diego, and what he chose as his life's work is to study fluorescent proteins. And he started with the fluorescent protein that comes from a jellyfish, shown here. 

And these jellyfish naturally, if you shine any type of ultraviolet light, the proteins in them collect that light and emit another light with a longer wavelength that happens to be green that you can see by eye. And what Roger and his colleagues did was he obtained crystal structures of this protein called green fluorescent protein and discovered this barrel-shaped structure, but he also was able to go ahead and make a whole bunch of derivatives of these proteins and very cleverly was able to pull out mutant versions of the green fluorescent protein of pretty much every color in the rainbow. And you might be asking, well, why is this useful? Well, it's useful because before these proteins were available the only way you could see a protein in a cell was to pretty much kill it, fix it, cut it, and stain it. Just like Walter Fleming did with his chromosomes. But now, with this technology, you could put a fluorescent protein, attach that to your protein of interest, and watch that in real time in living cells. And not only could you do that once, you could pick two or three or four of these proteins and watch them simultaneously because you have a whole rainbow of colors. Now, the folks in Roger's lab were also a little bit creative an artistic, and they found other things to do with these fluorescent proteins. [LAUGHTER] And this was a Petri dish they made, and they had proteins being made in different bacteria and they streaked them out in this pattern and made a very nice scene. So science can be fun too. So now that we have that background, we can talk a little more in the modern sense of how we can watch cells divide in the lab. 

And I told you some of the early biologists worked with marine animals just because it was easy and the cells were readily available. Nowadays there are a lot of human cells that are adapted to the lab and you can grow in a plastic dish and watch in real time. And this is a video I made of some human cells derived from retinal pigment cells, so the cells in the back of an eye, and they grow pretty well in culture. What we did is we took that green fluorescent protein that Roger Tsien had and we stuck that to part of the chromatin proteins. So we could watch, really, where the DNA and chromatin and chromosomes in cells were in real time. And what you see here for the second is a bunch of cells, each with a green appearing nucleus. And most of them have a round appearing nucleus where the chromosome is sort of diffuse throughout, but a few of them, if you look closely, have very bright pockets of chromatin. And those are the ones undergoing mitosis. But I'll let you watch the video and you can see if you can catch a few more.  So with the tools of biology available to us today with microscopy fluorescence, fluorescent proteins, we can get a lot of information that wasn't readily apparent to the biologists who came before us. 

And we could do that pretty quickly and conveniently with some of the automated tools. >> About how fast is that? How long is that? >> This whole thing is, each cell division that you're seeing that appears really quick happens over about an hour. So this is a time lapsed video, and the whole video is about 40 hours. So you're watching a couple days worth of cell proliferation here. So we can watch that a little more closely. And I didn't put time stamps on this, but this video is closer to an hour in its total duration. And what you see here are four different human cells. And the one on your right and the one on your left are the most interesting two because those have already started mitosis. And I'll play this a couple times through, but I'd like you to pay attention to the cell on your right where you can see the bright green chromosomes that are all lined up and ready to split into two daughter cells. So let's have a look. 

 So that's about an hour. And this is the kind of thing that's happening in our bodies every day as we live and breathe. This is happening in our bone marrow as our bodies are producing more bone marrow cells right now. This is happening in our mouth. This is happening in our intestines. In many parts of our body this is a normal and active process. And as you might imagine, if you want every one of your cells to have two sets of 23 chromosomes, this process better be pretty accurate and orderly. You don't necessarily want it to go awry, otherwise those daughter cells will not have the normal set of chromosomes in a normal human genome. One other point I want to make here is that mitosis is a process of dividing DNA and chromosomes into daughter cells, but another biological process is closely related to mitosis, and is in fact coupled to it, and that is this process called cytokinesis. And all that really means is that the cell membranes divide too. 

So, this is an example of a cell obtained with phase contrast microscopy. So this didn't use fluorescent proteins. But what you can see are these dark chromosomes, again lined up to the center of the cell, and then they segregate to two incipient daughter cells. And you also see that between them there's beginning to be this furrow that people call it, meaning there's some cinching or pinching of the cell membranes. And that's the cytokinesis part. And that continues until you get a deep furrow and the cell divides into two. So cytokinesis is termed a separate process, but it's usually coupled right to the end of mitosis. And to give you a sense of the time of this, this is in minutes here from five minutes to 15. So, the process you're seeing here, you could sit on a microscope and watch these human cells do this. It's faster than watching grass grow. 

[LAUGHTER] So, now I'm an oncologist so I like to bring this back to cancer. What does any of this have anything to do with cancer? Well, it turns out it has a fair bit, and we don't understand it all, but we know there's a strong connection. The first evidence of a connection would go back to David von Hansemann, again we're back to the 19th century briefly. But one thing he did was he took skin cancers and looked at them under the microscope, and he saw that these mitoses were not normal. That instead of chromosomes dividing in two different ways, he could often see what he termed a multipolar mitosis, where the chromosomes in this case were split into four different ways. And so he said, well, something's different about these cancer cells. Another guy who comes into play here is Theodor Boveri, and I'm sorry this is dominated by men, but, actually, Theodor Boveri's wife is thought to be under-credited for the work she did in the cell biology in his lab. But any case, he and his wife worked on sea urchins, which again were a very popular model system to study cell division because you could get the cells readily, you could fertilize eggs and watch them in the laboratory. And you they would divide and you could watch this in real time. Well, what Boveri did is he said, well, maybe I can change this system a little bit and see if I can understand something new about biology. 

And the way he changed the system was he took an egg and instead of fertilizing it normally, he provoked the system to get doubly fertilized so that two sperm would enter the egg at once. And what that did was instead of creating a bipolar mitosis, it created, again, a multipolar mitosis, an abnormal cell division where there were often four poles. And this is, again, his actual diagram from one of his publications in which he diagrams and envisioned chromosomes lining up and splitting abnormally. And for simplicity, he imagined four different chromosomes which he labeled A, B, C, and D. And normally these would divide equally and partition equally into two daughter cells, but what he was getting from these abnormal cell divisions was four daughter cells. And when he watched the behavior of these daughter cells, each one had a unique behavior. They were different. And they were different than normal. Most of them would die right away. Some of them were sick and kind of limped along for a little while. 

But the things he noticed were, one, they were sick and, two, the four cells behaved differently. He surmised from that that perhaps each of those cells had inherited a different set of chromosomes and that had caused those differences in behavior. He leaped a little bit further and said, well, maybe that's a cause of cancer. That maybe these abnormal cell divisions give you abnormal chromosome numbers, and maybe those abnormal chromosome numbers cause people to get cancer. That was a little bit of a leap, but he defended it vigorously in his writings back in 1912. But nowadays there's a lot of evidence to support that idea, that abnormal cell divisions can lead to cancer. And I'm not going to cite every piece of evidence supporting that here tonight, but one simple piece of evidence is that if you look at a cancer genome, it's typically abnormal. And this is a spectral karyotype of a cancer cell. It's like the painted chromosomes I've showed you before. And I didn't sort them out for you. 

I'm sorry. But you can notice some things that are out of the ordinary. For example, here's a chromosome where you have two different colors that have become joined together. But also, you can find things like this chromosome. Instead of having two copies, there are four copies in this genome. So something went awry in the process of cell division that led to this cell getting abnormal chromosomes. Now, if we go back to the idea of Theodor Boveri, he said, well, this could arise if you have a failed cell division, and this is what he wrote about. So let's imagine for a minute that you have a normal cell that does mitosis and it separates its chromosomes but somehow fails in the second process, that cytokinesis process that divides the cell into two. And you end up with a cell that has two separate nuclei, each of which harbors a normal set of chromosomes, but those two nuclei are in the same cell now because cytokinesis didn't happen. What Boveri said is, well, when that cell tries to undergo the next division, it's going to be like the doubly fertilized sperm where there are too many chromosomes and there are too many of these poles. 

And so that might divide abnormally and lead to cancer. So, this brings me to my third topic and that's what we've done in the lab because we set out to test that very hypothesis, to test the idea that if you have one cell that doesn't do cytokinesis, would that lead to aneuploidy, would that lead to cancer. And this led us down this path to find something unexpected. So, the idea was just to go back and repeat this experiment. We had human cells, we weren't dealing with sea urchins. We had fluorescent proteins we could use. We had time-lapsed microscopes with video cameras instead of poor Boveri and Ms. Boveri who had to draw each picture of what they were seeing in the microscope. And so we took advantage of those tools and asked what would happen. Would we get these abnormal chromosome sets that are often found in cancer? So, that's what we did. We created cells that had undergone mitosis, but we used a chemical to prevent them from doing cytokinesis. 

So these are human cells, abnormal cell divisions, and we ended up with cells with two nuclei. So each cell in this picture, as the one circled that you can see, have two nuclei instead of one. We said, well, let's just subclone. Subclone is a fancy science term which basically means we take all those cells, we break them apart, and we put them each in their individual wells on a plate, and then we wait and let them grow, give them time, feed them, and see what comes of it. So we waited. And then we started counting, and we figured most of these were going to be pretty sick because Boveri said these cells, if they try to divide, are going to have abnormal divisions, the cells that come from that are going to be sick. And we were surprised to find they weren't as sick as we expected. This is one of the results of the experiment. If we took a cell that had a control cell, so in science we always have to do our control experiment first, so before we get to the results. If we took a cell with a normal cell and plated that into wells, well, only about half the time were those able to grow into a healthy group of cells, a colony that we call it. 

But if we took one of these cells with two nuclei that had failed cell division, one that we expected to be sick, basically, well that still made healthy colonies about 40% of the time. So, we lost a few colonies by doing that, but not as many as we expected. So that was a surprise to us. And we did this with different kinds of cell lines. We said maybe this is something odd about these retinal cells. So we tried it with these other cell lines. The one in the middle is thought to be a normal-like breast epithelial cell from humans, and the one on your far right is a colon cancer cell. But they gave us pretty similar results. They were healthier than expected after failing cytokinesis. So then we said, well, at least did they have abnormal chromosome sets? So we took those cells with two nuclei, and I know it's a little hard to see in this light, but this cell has two little green nuclei with the fluorescent protein. 

So it was alive. We put it in its own well, and we waited. And we got a bunch of cells and when we took those cells out and did the karyotypes, we found, surprisingly, it was normal. We did it again, and that one was normal too. And by this time we were pretty shocked because it's not at all what we expected to get, but most of these cells that we looked at, when we grew those cells that had failed cytokinesis into a colony of cells, they gave us cells that looked indistinguishable from what we started with. And, in fact, we discovered about 90% of all the cells of this type, when we recovered colonies, 90% of them had normal chromosome sets. So that went against some of the ideas that we had and others had in the field. So a natural question is, what is going on? How would these cells that had failed cytokinesis by some process normalize themselves into normal healthy cells? Because the only way that we know that cells could divide, at least human cells, would be to go through mitosis and copy their DNA and go through that process. So we said, well, let's watch. Let's take a microscope. 

Let's watch these cells and make movies. And this movie I have timed for you. We had to watch a while. This is 49 hours. But every once in a while we saw something unusual. And I want you to keep an eye on the cell in the middle here that has two nuclei colored green. Oops. Did you keep your eye on it? It moved fast. All right, let's try again. So, every once in a while we saw that cell kind of stretch and move those nuclei to opposite parts and then break off into two. 

And that, again, was surprising because all cell division in humans, at least previously, has been coupled to mitosis. And, in this case, we didn't see any of the chromosomes condense into neat little structures and separate. None of that happened. The cell just happened to stretch and snap into two. So we were a little surprised by that. I guess it seems possible. It made sense that they kept their normal chromosome number because the nuclei stayed segregated, but it was surprising. And when we looked again and again, we could find many instances of this. Here it is now in the breast epithelial cell line. Here's a cell with two nuclei. 

And I'm sorry if it's hard to see in the light in this room, but I'll show it to you anyway. And we saw these cells move around, and every once in a while they would decide to go in opposite directions, like they were schizophrenic. And the cells would stretch and stretch, and pop into two. So we surmised that we were observing a new process of cell division that allowed these cells to maintain their normal chromosome number. And here's some pictures of the frames of that movie and some of the other movies that we saw. And, basically, we saw this again and again where if we looked at different frames the cells stretch and each daughter cell ended up with one nucleus with a normal set of chromosomes. Here's a third one I didn't show you the movie for. And it's a slow process. It's not as fast as mitosis. So this one started at 67 hours and took until 83 hours. 

It was a rather slow process. And one of the reasons that we think not a lot of people have seen this before is we had to be very patient to see this. When we counted cells very carefully, this happened in about every 24 hours, if we watched a hundred cells, we would see it once. Sometimes twice. So, it seemed pretty rare by that calculation, but if you think about the process of slow divisions that can happen and slow recovery over days, this could quite easily become a third of the number of cells recovering this way. Well, I can't say this is completely novel, and our reviewers like to point out that such things have been seen before in biology. And one place it's been seen are in these interesting organisms called slime molds. And I picked this one as one of my favorite pictures of a slime mold. Every once in a while if you go walking in the woods and you carefully look around, you'll see something like this that is colorfully called dog vomit slime mold because of what it looks like. But these slime molds are these interesting fungi-like organisms. 

They're not plants. They don't do photosynthesis. But every once in a while these slime molds can make one big cell with many nuclei. Oh, sometimes they're more colorful than that dog vomit one. But they can make cells with many nuclei. For example, this cell diagrammed here on the upper right has many of these little black circles which are diagrams for nuclei, and people observed these pinching off into little daughter cells. So, some divisions of this sort have been observed in slime mold, but it's a different organism. So, this leaves us with where we are today, which is a little bit surprised with this model. And the model is this, that many times our bodies have cells that are dividing all the time. And when our cells are dividing, every once in a while something may go awry. 

If what goes awry is a cytokinesis failure, we'll end up with a cell with two nuclei. If that decides to go through the mitosis route, that can lead to aneuploidy in cancer. But, at least in the system we were looking at, we saw this process that we call klerokinesis that happened more commonly, and more commonly than this other process. It was slow, but this process was slower. And so, in most cases, the cells recovered. So we think that maybe this was a very primordial process that was present in lower organisms that's also true in human biology. We don't know how this is controlled. If there's a way to control this, maybe we could bias the system towards the recovery process that might avoid cancer. So, it's a big idea, but maybe this has something to do with cancer prevention. So that leads me pretty much near the end of my story, and I'm going to leave you with some take-home points. 

And those points are abnormal cell divisions, when they go bad, they can lead to abnormal chromosome number called aneuploidy. And aneuploidy is bad because aneuploidy can promote the development of cancer. It's thought to be one cause, important cause of cancer. This process, klerokinesis, these abnormal cell divisions, can prevent aneuploidy after a failed cytokinesis event. One question that's important is, does this operate in humans? What we've done is we've done the experiments largely in cell culture systems. So we know there's an apparent process by which human cells can do this, and we've seen this in multiple cell types. But a harder question is, is this something that's actually happening in us when a cell division goes bad? And I don't know the answer to that yet. Well, I think that leaves us with some thoughts. I just want to acknowledge some of the people who did the work. I have an active research group, and the one who did the most work on this project and did quite a lot of it was -- shown here. 

But other people in my group have done a lot of other related work on cell division and cancer. Sara Holmstrom, Melissa Martowicz, Amber, Amy Fothergill, Yin Jun, --. We've collaborated with other labs. Beth Weaver's lab is interested in cell division and cancer, and Dave Beebe is an engineer who we work with. Kim -- and Jennifer Laffin helped us do karyotypes. One of the most fun things I've done since I've joined the university was, one day I picked up the phone and called William Brockliss. William Brockliss is a professor of the classics department, and all these biology terms were named after Greek roots, and he's a Greek expert. And so we sat down and had some coffee and talked about what to call this process. And he came up with klero, which is the Greek root for allotted inheritance. And we thought that was fitting because each of the cells was allotted a normal chromosome set. 

And I want acknowledge my funding. None of this research happens in a vacuum. And thank all of you for coming today. [APPLAUSE]