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← Bdelloid rotifers: a new biological model? | Karine Van Doninck | TEDxUNamur

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Showing Revision 19 created 09/20/2019 by Peter van de Ven.

  1. Good evening.
  2. Here you see a little petri dish
    that we use in the lab
  3. with a dry leaf, completely dry,
  4. and on there, there are females.
  5. Why do I say females?
  6. Because that's their way of life:
    They live and evolve without males;
  7. they got rid of males.
  8. And also, they are dry.
  9. They can dry up,
    and we can wait for years,
  10. put them in the freezer,
    and get them back.
  11. Tonight we will do a live experiment
    with one of my scientists, Boris,
  12. to resurrect these animals for you,
  13. these females.
  14. Thanks, Boris.
  15. So look around you.
  16. There is an amazing diversity
    of living organisms on this planet,
  17. from bacteria to fungi to plants
    to animals to human -
  18. nothing looks alike.
  19. But do you know that all this diversity
    arose once from a universal ancestor
  20. around 3.5 billion years ago?
  21. And this ancestor of all living organisms
    was a single simple cell,
  22. something like a bacterium.
  23. But how do we know that all life
    has evolved from a single cell?
  24. We know this because we all
    share the same alphabet;
  25. we have the same DNA code.
  26. DNA is a magical molecule of life.
  27. And DNA is only made up
    of four chemical building blocks:
  28. cytosine, guanine, adenine, thymine.
  29. So only four letters
    that make the whole alphabet of life.
  30. So yes, from bacteria to human,
    we only need four letters,
  31. but then, what's our DNA
    instruction book looking like?
  32. In each of our cells, we have
    around three billion of those letters,
  33. organized on 23 pairs of chromosomes.
  34. So you see here,
  35. it's a compaction of these four letters.
  36. But what makes you different from me
    is that these letters change.
  37. These letters change
    between all these individuals.
  38. So if we all have the same genetic code,
    it means we are all related.
  39. Yes, we are.
  40. We are all cousins from each other.
  41. But then, you may wonder:
  42. How did we evolve to so many complex forms
  43. from such a single cell a long time ago?
  44. And that's when I want you to remember
    the card game we have been playing.
  45. What's essential for evolution
    is genetic variation,
  46. its changes in these letters.
  47. So these letters change randomly.
  48. And most of these changes are neutral,
  49. they have no effect
    on the fitness of the individual,
  50. but if a change is an advantage,
    it can be selected.
  51. Remember?
  52. We select if a positive mutation appears.
  53. Why is it selected?
  54. Because the individual gets an advantage
  55. and it might reproduce
    more than the others
  56. so the mutation is transmitted.
  57. And we know
  58. that natural selection is cumulative,
  59. that we can accumulate
    this positive mutation,
  60. which is important
    for adaptation and evolution.
  61. So as I said, during the card game,
  62. there is nothing of intelligence
    or a creator out there
  63. for evolution.
  64. And look at cancer development.
  65. Cancer development
    is also an evolutionary process;
  66. it follows this same mechanism.
  67. Each of our cells accumulate
    randomly these changes, these mutations,
  68. but if one of these normal cells
    suddenly gets a growth advantage -
  69. a mutation that gives it a growth
    advantage compared to the other cells -
  70. it will start to grow quicker -
  71. an uncontrolled proliferation -
  72. and cancer can occur.
  73. And of course, it's a problem to human.
  74. We know it.
  75. But you know, animals also get cancer.
  76. But do all of them get cancer?
  77. There are a few mysterious species
    that don't develop cancer.
  78. What are they?
  79. The most notorious one
    is this naked mole rat.
  80. Very cute animal, no?
  81. (Laughter)
  82. For scientists,
    it's a very interesting animal.
  83. It's very small. It's like a mouse.
  84. But it lives for 30 years,
    and a mouse lives for four years.
  85. What's also interesting is
  86. if you inject the cancer cell
    in this animal,
  87. it will not develop.
  88. And why?
  89. Scientists have searched
    for this for years
  90. and found that they
    have this kind of molecule -
  91. a high molecular mass, hyaluronan;
  92. it's a kind of super sugar -
  93. that is secreted around
    the cells of these animals,
  94. and it makes their tissue very elastic.
  95. And why is it important?
  96. Because these animals dig into the soil,
    they make these burrows,
  97. and so their tissue
    needs to be very elastic.
  98. So it's an adaptation to this.
  99. But what's interesting
  100. is that this molecule,
    when it's secreted around the cell,
  101. prevents the cell from dividing
    or proliferating further.
  102. So you immediately see
  103. the interesting application
    of the discovery of such a molecule.
  104. But if you think this is
    the only interesting animal out there,
  105. you’re wrong.
  106. Nature is full of mysterious species,
    where we can discover so much.
  107. Nature has been an inspiration
    to scientists for so many years.
  108. Like Albert Einstein said,
  109. "We know less than one thousandth of 1%
    of what nature has to reveal to us."
  110. And if we start to destroy our nature,
  111. we will not even discover
    everything that's out there.
  112. Look at this gecko.
  113. This gecko, we know,
    can run quickly on vertical glass.
  114. But how?
  115. How can these animals
    adhere so strongly to glass
  116. and then just run on it?
  117. And so, for long,
  118. scientists looked at the molecule:
  119. What kind of molecule is secreted
    that makes them like a glue,
  120. like a strong adhesion?
  121. And in fact, by looking at these fingers,
  122. they found there's nothing
    of a molecule that is secreted,
  123. but it's a structure.
  124. What they discovered
  125. is that underneath these fingers,
    there are these hair-like structures,
  126. millions of them.
  127. And if you look even
    at the nanoscopic level,
  128. you see that at the end
    of all of these hairs,
  129. you have hundreds of these
    spatula-likes structures.
  130. And when these are
    in strong contact with glass,
  131. it creates a strong adhesion
    just through simple Van der Waals forces,
  132. the simple forces
    that make this strong adhesion.
  133. And when they rotate their fingers,
  134. this force releases immediately
    and they can run further.
  135. And of course,
  136. laboratories have now been interested
    to reconstruct these nano-structures
  137. to make strong adhesives.
  138. And that's what I want to show you:
  139. It's so interesting to study biology
    because there's so much to discover,
  140. because there has been
    such a long evolution
  141. of all kinds of specimens
    with all kinds of different adaptations.
  142. And what has puzzled me is reproduction.
  143. You know that for life,
    it's essential to reproduce;
  144. we need to reproduce
    or the species will go extinct.
  145. But do you know that sexual reproduction,
  146. the one we all know,
  147. is the queen of problems
    in evolutionary biology?
  148. For us scientists, it's really a puzzle.
  149. And why?
  150. Think about all the energy you need
    to spend to find a partner,
  151. all the strategies the male's developed
  152. to try to attract a female,
    to try to fertilize her,
  153. to the point that there is
    a battle of sexes.
  154. Believe me -
  155. a man penis is boring
    compared to this insect penis.
  156. This is a penis of a bean weevil,
  157. full of spines,
  158. and the males with the longest spines
    are those that fertilize most of the eggs.
  159. Of course, the female cannot
    reproduce anymore afterwards,
  160. but at least, the male is sure
    he has transmitted his genes.
  161. A look at this fruit fly.
  162. You might have many fruit flies
    in summer around your trash bin.
  163. This fruit fly, Drosophila bifurca,
  164. produces giant sperm,
    20 times its body size.
  165. It's like, you men,
  166. you would have a sperm
    that is twenty times your body size,
  167. like a building of 12 stories.
  168. (Laughter)
  169. Wow!
  170. But at least, when it
    transmits this to the female,
  171. the receptacle of the female is filled,
  172. there is no space for another sperm,
  173. so it's sure to transmit its genes.
  174. But then, why did such a complicated mode
    of reproduction evolve?
  175. And why is it so omnipresent?
  176. Is it not just simpler to clone yourself?
  177. One individual makes a new individual?
  178. So why is sexual reproduction
    so prevalent in nature?
  179. In fact, for us biologists,
  180. sex is just about mixing genetic material
    of one individual with another individual
  181. to create each generation
    of offsprings that are all different.
  182. And that's a force of sexual reproduction:
  183. It creates every generation
    this genetic variability
  184. that is essential for evolution.
  185. So does it mean that animals
    that lose sexual reproduction
  186. or that abandon it
    or have no sexual reproduction
  187. cannot evolve, cannot adapt?
  188. That's what we thought
  189. until we discovered
  190. what has been called
    an evolutionary scandal
  191. or an ancient sexual scandal:
  192. It's a microscopic world of animals,
    the bdelloid rotifers.
  193. These are females cloning themselves;
    never has any male been discovered.
  194. They exist since millions of years
    and we found them everywhere.
  195. And they are not only interesting
  196. because they can reproduce without males
    and evolve without males,
  197. we can also dry them out.
  198. I showed you:
  199. We can just take them, here in the park,
  200. a piece of lichen, a dry lichen,
    bring it back to the lab,
  201. and what you see -
  202. that's also what you see
    on the microscope -
  203. is this dry lichen
    and then they are introns.
  204. But when we add water,
    they start to live again.
  205. So these animals -
  206. We can dry them out
    at any stage in their life,
  207. and we can keep them dry.
  208. We can put them in the -80 freezer.
  209. We can send them
    to collaborators in the US,
  210. and if they add water, they live again.
  211. And it's not only one species.
  212. You could think, "Yeah,
    but it's just this rare animal."
  213. No, it's more than 400 species
    being described
  214. as having diversified
    into many morphological forms -
  215. all females reproducing without males,
  216. most of them being able to dry out.
  217. And of course this makes the newspaper:
  218. ["Asexual reproduction is possible."]
  219. Yes, it's possible.
  220. But then, of course, you might think,
    "How did these females evolve?"
  221. How do they create variability? -
  222. because we know
    it's essential for evolution.
  223. So, if they just cloned themselves,
    how do they ever evolve and adapt?
  224. And so, as a scientist,
  225. it is important to have
    these hypothesis to think of.
  226. So our hypothesis is -
  227. It's easy to work with this animal.
  228. You take a female in the wild,
    you start to clone it in the lab,
  229. you have millions of identical females,
  230. we dry them up,
  231. and then, our question was,
  232. "Do these females -
  233. What happens to the genetic
    material of these females
  234. when we dry them up?"
  235. We know from bacteria
  236. that drying up breaks
    their genetic material into pieces.
  237. Is this also happening in these animals?
  238. And then, what if they don't
    repair perfectly these pieces,
  239. is this a way to create variability? -
  240. meaning,
  241. if you replace males by drying up,
    you might also evolve.
  242. And so, that's what we tested.
  243. So Boris has designed
    a very nice protocol in the lab
  244. to dry them up
    with a high survival rate.
  245. And what happened to these females
    when they are dried up?
  246. You see, the longer they are dried up,
    the more their DNA is broken.
  247. The simpler the gel
    and the DNA migrates through it,
  248. the smaller the pieces.
  249. And when we hydrate them,
    what you see is that they start to repair.
  250. So they can come out of drying,
    they have their broken DNA -
  251. but they can survive
    with broken DNA apparently -
  252. and then they start to repair.
  253. And you know,
  254. if you have a cancer cell,
  255. it's known that sometimes
    during a division some DNA breaks,
  256. and it repairs this broken DNA
    but not perfectly,
  257. and you can have an aggressive
    cancer that appears.
  258. What they do in proton therapy is
  259. use proton radiation to completely destroy
    the DNA of cancer cells
  260. so the cells get completely broken DNA,
    and molecules too.
  261. So we thought if we do
    proton radiation to these animals,
  262. what happens?
  263. So we took, again, a female,
  264. we dry it up,
  265. we add proton radiation,
  266. and what happens?
  267. DNA gets completely broken.
  268. And this 800 grays
    of proton radiation are huge doses.
  269. There are no living cells
    that can survive this.
  270. But what's amazing here is -
  271. you really see the DNA
    is completely broken -
  272. when we re-hydrate these females,
    99% of them survive.
  273. So they come out of drying
    with a completely broken DNA,
  274. without a problem,
  275. and then they start to repair.
  276. And of course, the question is,
  277. "Do they really repair perfectly?
  278. Or do they put all the pieces
    of DNA back together
  279. into their 12 chromosomes? -
  280. because we found they had 12 chromosomes -
  281. or is that just creating
    some variability?"
  282. So we have here preliminary results
    that I'm just showing you tonight,
  283. where we did this experiments,
  284. where we dry them up,
  285. we irradiate them,
  286. and then we look at its genomic structure.
  287. Not going too much into detail,
  288. but what you see here is, for example,
  289. pieces of the ridge
    of the genome from a female
  290. before she was radiated or dried up.
  291. Then we dry it up, we irradiate it,
  292. and we look at whether
    these pieces come back.
  293. You see here - everything is destroyed,
    and whether we get these pieces back -
  294. showing it's stitching back
    all these DNA pieces together
  295. into these 12 chromosomes.
  296. So they can do this:
  297. They reconstruct their genome as before,
  298. or at least, that's what
    it seems to look like.
  299. And even the descendants
    have that same structure
  300. as a parent’s alignment.
  301. So is there no genetic
    scrambling going on?
  302. That's possible.
  303. Maybe they don't, indeed,
    make a completely new genome;
  304. they keep their genome.
  305. But what we then ask ourselves is:
  306. "How can you survive
    when you are irradiated,
  307. because not only your DNA is broken,
    but also your molecules must be broken?"
  308. But they must keep
    their molecules somehow intact
  309. because you need these molecules
    to repair your DNA.
  310. So what do they have?
  311. What's their secret?
  312. What did we find
    by sequencing the first genome,
  313. really sequencing the entire
    alphabet of this animal?
  314. We found that they have
    a huge amount of antioxidants.
  315. Antioxidants are essential
  316. to protect yourself
    from these damaged cells.
  317. We all have antioxidants.
  318. That's because our cells
    accumulate damages,
  319. a kind of what we call oxidative stress,
  320. and your proteins, your DNA -
    everything gets damages.
  321. That's why we get older.
  322. And that's why you put all these creams on
    that are full of antioxidants,
  323. to try to prevent the aging of your cells,
  324. but it will not.
  325. But here, these animals
    have a huge amount of these antioxidants.
  326. So next time, think about it,
  327. don't buy all these expensive creams
    full of antioxidants,
  328. just drink some rotifers.
  329. You find them in the nature
    and they might help.
  330. (Laughter)
  331. But of course,
  332. these are all things we discovered,
  333. but as a scientist,
  334. when you discover things,
    you have even more questions.
  335. And so recently,
  336. I obtained a grant
    from the European Research Council
  337. to really try to demystify
    all these mysteries we found.
  338. We found they have
    this huge amount of antioxidants,
  339. but are they really effective?
  340. How do they repair this broken genome?
  341. What are the molecules,
    the mechanism they have
  342. to repair such a broken genome
    to survive drying, freezing?
  343. Then one last thing we discovered is
  344. by sequencing their genome,
    we found, among their genetic material,
  345. genetic material
    from bacteria, plants, fungi -
  346. so they seem to integrate DNA
    from their environment.
  347. And that's of course puzzling.
  348. But we also thought,
  349. If they can integrate this foreign DNA,
  350. can they also integrate DNA
    from other females out there,
  351. other rotifers that also dry up?
  352. And the first results we got on this
  353. is that we found some signatures
    of DNA exchange between these females,
  354. and we think it's not conventional sex,
    because we never found males,
  355. so they are not using the strategy
    that all animals do -
  356. a sperm and an ovocyte
    to exchange DNA.
  357. So what is the strategy? We have no idea.
  358. We call it sapphomixis -
  359. it's a mixing of genetic
    material between females.
  360. And you immediately see here
    why it's so beautiful to be a scientist -
  361. you discover a lot,
    but you have even more questions.
  362. But what's for sure
  363. is that we have a very interesting
    model organism here to understand,
  364. "How can they evolve without males?
  365. How does sapphomixis happen?
  366. And how can they survive
    such extreme conditions
  367. as drying up, freezing,
    and high doses of radiation?"
  368. There's so much still to discover there.
  369. And one of our next challenges
    is to send them to space.
  370. We got a grant from
    the European Space Agency
  371. to send, in 2019, rotifers to space, RISE.
  372. Why? Because space is also
    an extreme environment.
  373. We have no idea at the moment
  374. what this extreme environment has
  375. as pressure on astronauts
    or any living animal.
  376. This is a very interesting
    model organism to send out there
  377. and to understand much better
    what space is like.
  378. And of course,
  379. I cannot end this presentation
    without thanking all the funding
  380. but especially all the people
    in my lab - many are here.
  381. This work is never done by one person.
  382. A lab is really a group
    of persons working,
  383. tackling these questions.
  384. A lot of frustrations.
  385. They know it better than me right now.
  386. And then, I would like to thank
    the rotifer and Boris
  387. with the whole experiment
  388. because thanks to these rotifers,
  389. I'm really happy to go every day,
    or almost every day, to my work.
  390. At least, when I know I can do science
    and I can work with rotifers,
  391. I'm a happy person.
  392. Thank you.
  393. (Applause)