00:00:24.06 in the molecular details. 00:08:27.05 it's present near the posterior end 00:17:30.05 but with a lot of help with our friends, 00:15:35.01 Now, we notice, however, 00:15:05.27 as a nation or as a religious group, 00:21:29.09 But it doesn't affect the nervous system in hemichordates, 00:11:19.15 And people noticed, back in the late 19th century, 00:21:52.23 we really don't know this happened, 00:24:22.25 it's just to my mind a little bit of a jump, anyways, 00:03:35.20 but the signaling system that was flipped.
The Origin of Vertebrates, Hemichordates, and How Chordates - iBiology 00:09:08.22 as we have the phenotype 00:18:57.19 and I think everybody just sort of felt 00:31:05.22 that vertebrates have, 00:02:09.19 just after Darwin had finished his work, 00:10:25.19 I mean they have this five-fold symmetry, The tail contains skeletal elements and muscles, which provide a source of locomotion in aquatic species, such as fishes. In addition to containing vertebrate classes, the phylum Chordata contains two clades of invertebrates: Urochordata (tunicates) and Cephalochordata (lancelets). 00:10:28.01 And internally also, you can see 00:29:00.02 which is present in vertebrates, 00:27:54.10 the way they are in vertebrates. 00:06:22.05 they're just expressed in totally different patterns. 00:14:02.06 where it had a dorsal heart, { "28.5A:_Phylum_Echinodermata" : "property get [Map MindTouch.Deki.Logic.ExtensionProcessorQueryProvider+<>c__DisplayClass230_0.
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The notochord, on the other hand, is absent in the postnatal stage of vertebrates; this has been . B.) 00:17:01.18 for making this all possible. 00:16:46.19 Well, there are two answers to this question. 00:08:02.20 that's fundamental to dorsal-ventral patterning, 00:16:05.23 into the notochord and endomesoderm 00:06:20.08 Now, we can find all these genes, 00:04:07.15 First of all, they occupy different environments, 00:12:57.17 because they are independent. 00:11:49.10 is now completely around the animal. 00:26:16.05 which has no brain, 00:08:39.11 and there may be some significance to that, I'm not quite sure, In chordates, it is located dorsally to the notochord. 00:18:18.23 was just to get a list of genes 00:18:50.07 Mark Tersaki and Rachael Norris and Michelle Roux. 00:10:55.16 you know, the detailed underlying patterning genes. 00:03:06.19 was that that tissue might or might not 00:18:13.11 And then, to do this molecular analysis, 00:25:58.04 Now, but nodal is on the right side The dorsal hollow nerve cord derives from ectoderm that rolls into a hollow tube during development. 00:14:47.28 you can see the gill slit, that hole on the side, 00:16:06.18 was T.H. 00:08:12.22 and many other unusual phyla live in this group, 00:11:34.16 For example, netrin, 00:21:57.19 but the procedures are utterly conventional 00:10:49.28 In the A-P dimension, 00:09:21.03 The vertebrate organizer is in reality This organism seems to be an intermediate form between cephalochordates and vertebrates. 00:09:49.25 The vertebrate organizer is very complex 00:11:14.10 but now the gill slit goes all the way around the animal, 00:01:13.20 And so whether that's true or not I don't know, 00:13:27.19 Well, it may have had a centralized nervous system, 00:16:30.14 to work on this organism. 00:03:25.11 including a central nervous systems, 00:25:32.27 So, in vertebrates, In chordates, what is the long supporting rod that runs through the body called? 00:11:44.08 when you knock down BMP. A project created by ISKME. 00:05:10.14 and we've looked for all these characteristic genes 00:06:59.21 The first question we could ask, The characteristic features of the phylum Chordata are a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. 00:05:55.15 and yet, 00:14:41.27 That becomes clearer as it gets a little older here. 00:01:20.21 I wanna deal with the fundamental patterning mechanism 00:05:22.20 it has in fact a 00:10:43.25 not only in the hemichordate, In most vertebrates, it is replaced developmentally by the vertebral column. 00:20:38.19 everything is the same. 00:17:23.03 like flies. 00:29:33.01 but we also have some very conserved features of 00:20:11.02 And so by just essentially Show Answer The dorsal hollow nerve cord is derived from ectoderm that rolls into a hollow tube during development. 00:02:47.13 Now, I would then wanna talk about the nervous system of vertebrates, Chordates - Biology 00:03:17.02 But the result was very striking: 00:11:31.12 the secreted Frizzled-related proteins shown in pink, 00:05:54.14 It's some unique features of that organization. 00:09:31.10 And finally, there's a new phylum, up here, 00:13:36.11 it's related to patterning of many, many other elements 00:11:53.27 And pitx, which is found also on this ventral margin, 00:14:52.05 it'll make maybe up to 80 pairs of gill slits in an adult. 00:13:53.13 So this BMP, 00:03:52.08 And on the ventral side of the fly, 00:02:23.20 and they get sucked into the mouth 00:16:53.07 at Woods Hole, Massachusetts, Like tunicates, they are suspension feeders. 00:05:46.03 and the Spemann organizer, as we said, GCSE Biology/Classification of Organisms. 00:16:08.03 to form an organizer. 00:09:05.02 which include not only the vertebrates 00:12:05.12 from what I'm going to tell you about, 00:09:39.05 is not associated with that same structure. 00:03:38.07 arose from tissues 00:26:57.27 For example, in this case we have six3 00:00:34.16 which is a sister phylum to the chordates, 00:12:38.10 which it uses to burrow. 00:19:28.16 the gill slits coming up on the dorsal side. 00:00:07.18 on how the chordate got its chord. 00:05:15.09 chordin, which I've talked a lot about, 00:22:46.09 530 million years ago, The best videos and questions to learn about Invertebrates vs. Vertebrates. 00:02:47.27 and it's involved in dorsal-ventral patterning 00:01:30.19 we began to look at an organism 00:07:05.04 And of course there are other features as well, 00:14:28.14 of burrows in the mud 00:06:30.09 that even though the stomochord is not a notochord, 00:08:22.26 as the first orifice that forms 00:10:40.28 of this radialized animal. 00:16:20.19 we have myself, 00:10:04.17 and you can do that very easily just by 00:19:55.16 because underneath the cilia were nerves, 00:07:52.17 which must have given rise to all the major animal phyla. Describe the invertebrate clade of chordates, Cephalochordata. The anus empties into the excurrent siphon, which expels wastes and water. 00:06:21.02 these genes, which are involved in signaling, 00:10:02.18 in more primitive bilateral organisms. 00:10:57.02 So for example, 00:10:32.22 indentation that occurs on the ventral side, 00:01:04.10 maybe like these kids on the bottom here, 00:21:43.03 since you don't have an inversion of 00:12:03.15 Now, as it turns out, Get smarter on Socratic. 00:07:06.05 from the top by BMP and 00:10:14.09 so now the head doesn't have a mouth anymore, 00:10:30.24 whereas in the control here you see that 00:24:16.17 made up of neurons 00:00:10.26 I'm a professor at the Department of Systems Biology 00:11:41.19 is now found completely around the animal 00:01:44.16 but it is organized in a dorsal and ventral way. 00:03:31.06 And then finally, 00:03:30.02 and all those things 00:22:48.03 and try to recreate their basic organization, 00:17:18.14 how chordates arose, 00:00:36.02 The way this project emerged was that 00:18:54.13 that's superficially similar 00:04:57.29 a right side and a left side, 00:01:54.21 was still valid today. 00:12:21.09 than those that are patterned in vertebrates. 00:18:39.02 in making libraries. 00:15:07.19 such as chordin or a chordin-like molecule, 00:08:35.21 The first orifice that appears is the anus, 00:15:08.09 which it uses to hold on with as it extends itself 00:01:15.28 for the work in cell and developmental biology 00:08:58.10 And so we tried to knock down genes 00:19:57.28 and if the cilia move together on the back side of vertebrates 00:15:16.15 a chordate chauvinist, In contrast, the nervous system in protostome animal phyla is characterized by solid nerve cords that are located either ventrally and/or laterally to the gut. 00:05:57.10 Because the Spemann organizer, as I said, 00:18:12.13 is well described, and it has a central nervous system, 00:06:49.08 are gill slits, 00:11:04.12 or pax1/9. 00:09:39.21 these just look like little balls on tops of sticks. 00:10:38.16 which has no ventral side anymore, 00:07:31.24 and pulled in all sorts of directions, 00:05:06.08 Are we reflecting something fundamental, 00:03:43.22 that's away from the mouth side of the fly, 00:13:20.14 which are about three-tenths of a millimeter in diameter. 00:23:43.12 00:23:39.23 They're very highly represented 00:25:00.26 So gill slit markers tell us that 00:21:17.20 The basal nervous system OpenStax College, Biology. 00:05:08.02 independent of the nervous system? 00:17:22.25 And this was done on the cheap, in a sense. . 00:01:39.06 is an anatomical structure 00:02:28.28 and so we're gonna call this ventral and this side dorsal. 00:16:44.24 through really three people 00:26:45.24 and we have this inversion of the axis 00:01:14.26 relative to a conserved body plan. 00:00:59.21 and pick the perfect organism 00:21:54.29 I'm sure you can sit down and say 00:03:17.19 A very important observation was that Have a closed circulatory system with only bilateral body symmetry. Here again, the acorn worm, offers the key comparison, being close enough to us to share some recognizable features, but far enough away to indicate the direction from whence we came. 00:28:42.08 And we can draw a specific correspondence 00:13:43.07 and then it finally has a hole here, it makes a beautiful gastrula. 00:08:13.11 and sometimes completely separate, 00:11:20.22 at the midbrain-hindbrain boundary, 00:31:35.29 cannot be used reliably as markers 00:01:16.29 but we wanna get back to the question of 00:17:51.23 as it must have been in a very early stage, 00:32:58.24 but because the bilateral ancestor Vertebrates do not have more than two pairs of limbs. 00:00:37.03 because the story is not the same Learning Objectives Identify the key features of the chordates Key Takeaways Key Points 00:20:28.11 and it has gill slits on its side, 00:01:41.24 we may not be able to identify dorsal from ventral, 00:05:00.26 and that's similar, mirror images, Note: The above text is excerpted from the . 00:16:34.13 This leads to a very simple model for inversion, 00:25:08.01 when nerves are born. 00:07:59.24 yet every detail of the BMP gradient, Members of Urochordata are also known as tunicates (Figure). 00:12:02.28 and where the proboscis had fallen off. 00:11:17.24 That is, Wnts that are very posterior, Chordates | Boundless Biology | | Course Hero 00:02:36.10 but it is our sister phylum, Some examples of vertebrates are sharks, fish, dinosaurs, and human beings. 00:03:18.27 it produced conjoined twins, 00:12:00.15 of course here we see the proboscis, Key Points The phylum chordata is named for the notochord, a longitudinal, flexible rod between the digestive tube and the nerve cord; in vertebrates, this is the spinal column. 00:14:01.17 this little hook which you might think is a tail, 00:05:31.04 we'll talk about some of the details. 00:00:04.24 Marc Kirschner, 00:09:14.21 So, what can we conclude 00:25:04.16 these really are related structures, In most cases this is the spine or backbone. 00:09:08.09 but include animals such as sea squirts - ascidians, 00:00:18.15 in the course of evolution 00:12:15.01 all those genes that patterned 00:12:57.08 to get a glimpse of what that first bilateral animal 00:18:07.24 So, the nervous system of a human being, for example, 00:13:30.14 but it's not exclusively related 00:07:53.04 or maybe most of the genes, 00:13:52.00 and eventually forming as a direct developer 00:14:32.26 a chordate from a hemichordate? 00:19:39.14 the BMP-chordin gradient, 00:17:40.11 for hemichordates to make their big comeback, 00:03:15.05 on the belly. 00:26:05.15 So let's go through the logic here: 00:30:32.24 that some animals, like fruit flies for example, 00:10:02.06 But if we're too close, 00:18:35.20 so that's what's demonstrated in the blue. 00:13:43.15 which kind of pattern the anterior-posterior axis, What one characteristic distinguishes most vertebrates from the other chordates? 00:04:18.11 and this tissue, this signaling tissue, 00:32:45.24 and then it was then lost in the hemichordate at some point, 00:24:45.24 -- in the proboscis -- 00:01:01.11 and Eddie De Robertis, 00:18:05.21 were graduate students and technicians there 00:10:18.18 are also not very useful. 00:02:03.10 may have revealed to answer some of the questions 00:14:15.01 and a ventral anti-BMP pattern, 00:07:01.19 and work together in the vertebrate embryo. 00:32:36.16 was the ancestral state? 00:05:49.03 so it's not the existence of this kind of organization Invertebrates are any other animal that is classified outside of that class. In Part 1: The origin of the vertebrate nervous system: the Hemichordate perspective, I discuss why vertebrates ended up with a centralized nervous system that is highly organized from head to tail. All vertebrates are unisexual animals. 00:20:16.14 he thought the hemichordate was a pretty good chordate to start with. 00:15:51.03 in the 1880s. 00:28:45.15 between genes that are expressed 00:06:58.09 some of you may not have thought of: 00:11:24.19 Also, if we knock down BMP, 00:30:30.06 because it's becoming clear 00:04:04.08 from the surrounding tissues, 00:23:14.00 in terms of their organization, After hatching, a tunicate larva swims for a few days until it finds a suitable surface on which it can attach, usually in a dark or shaded location. 00:02:02.13 how did we get our chord? 00:15:39.19 We centralized our nervous system to the dorsal side, 00:07:17.13 so it's not even in a place where it can do any of that. 00:26:31.11 That is, as if this thing had a forebrain, 00:16:55.29 with this early bilateral ancestor, 00:09:03.25 And hex, These innovations may be associated with the whole genome duplications that resulted in a quadruplication of the basic chordate genome, including the Hox gene loci that regulate the placement of structures along the three axes of the body. 00:20:29.00 So there's no real axis inversion here going on; 00:30:45.12 And so what's happened in the lineage 00:19:38.19 called the Auricularia Hypothesis, 00:25:25.22 So we, for example, have sox1/2/3, 00:01:44.28 and it organizes them in the course of development, 00:08:10.15 and the mollusks, and the nematodes, A cranium is a bony, cartilaginous, or fibrous structure surrounding the brain, jaw, and facial bones (Figure). 00:06:41.22 one of which is BMP, 00:15:01.13 about them as individuals, How do they obtain their nutrients? 00:16:11.14 And then, more recently, we have Bullock and Colwin, Any opinion, finding, conclusion, or recommendation expressed in these videos are solely those of the speakers and do not necessarily represent the views of the Science Communication Lab/iBiology, the National Science Foundation, the National Institutes of Health, or other Science Communication Lab funders. 00:24:41.27 that the structures really are in fact related. 00:11:36.14 which is just found on the ventral edge of the wildtype embryo, 00:05:29.02 they're just somewhere else. 00:18:27.11 Eric Lander and Nicole Stange-Thorman, at MIT, 00:26:21.06 to the left side in vertebrates, 00:02:00.26 a real mystery, 00:06:59.29 all chordates, and no other animals, 00:07:22.22 that gives rise to very anterior tissues 00:07:49.28 of the vertebrate central nervous system. 00:19:21.24 on our back. 00:04:53.13 he argued that 00:07:54.18 So, okay, Amniotes are animals whose eggs are adapted for terrestrial living, and this group includes mammals, reptiles, and birds. In contrast, other animal phyla are characterized by solid nerve cords that are located either ventrally or laterally. Lancelets are only a few centimeters long and are usually found buried in sand at the bottom of warm temperate and tropical seas. 00:26:55.08 but in hemichordates we have chordin on the ventral side. 00:19:11.00 Now, if the hemichordates 00:23:01.11 some structure that arose by convergence? 00:23:54.11 This is from a paper published about in 2001, 00:10:43.17 the sea urchins, the sea cucumbers 00:28:06.09 These are the hox genes that are not present in insects. The notochord is prevalent in vertebrates in embryonic developmental stages, where it stimulates neural tube formation and acts as a framework for the growing embryonic structure. 00:11:01.13 which we have very good evidence for, 00:26:05.29 around the back to front of the animal, 00:29:42.13 is organized in this animal in absolutely complete terms, 00:04:00.08 it really is special in 00:04:43.25 The crux of Bateson's argument 00:06:08.27 The situation as we look to the patterning 00:15:18.15 it has this antagonism here, 00:25:53.26 then nodal is expressed on the left side. 00:11:34.24 which is the most characteristic structure of chordates, How many bones are there in a giraffe's neck? 00:03:48.23 which is in fact a TGF--like molecule. 00:02:06.26 which is cylindrically symmetrical in this animal, 00:21:08.26 but has been given a lot of support by some molecular evidence, 00:08:21.29 if we look at brachyury, which is the classic trunk organizer, 00:19:34.03 began to change a few things. 00:17:46.11 that even though its been 120 years, Members of the subphylum Urochordata, commonly called tunicates, belong to the deepest-branching lineage of chordates. 00:28:16.03 and these also have it, 00:04:27.02 and how these features specific to this phylum arose. 00:05:57.29 So let's look at what makes us special: 00:03:05.10 and to compare that organization. 00:16:16.09 to the chordin side, which is the dorsal side, 00:16:27.01 and John Gerhart, and myself, 00:20:03.19 they would have formed a central nervous system. 00:00:13.17 where we're gonna tell you all the little features 00:19:23.13 And so how did these two things arise in the first place? Lancelets are suspension feeders that feed on phytoplankton and other microorganisms. A muscular, postanal tail which extends posterior to the anus. 00:25:35.12 a gene called nodal, The majority of chordates belong to a group called Vertebrata. 00:14:34.21 and that may have been 00:01:49.16 as I pointed out, 00:32:53.29 So these are still questions 00:08:33.19 in the whole course of development. 00:08:26.09 maybe we shouldn't be even talking about it. 00:28:50.24 and genes that are expressed in the neural plate of vertebrates, a notochord, a dorsal hollow nerve cord, pharyngeal slits, and a post-anal tail. Most tunicates live a sessile existence on the ocean floor and are suspension feeders. 00:30:05.28 And this hemichordate, 00:09:41.19 And either it came apart or, 00:19:19.19 and we have a centralized nervous system 00:25:49.07 that is if we stand up here like this, 00:11:28.12 that we can see in the hemichordates. 00:25:37.03 they go all the around the body of the animal. 00:04:59.23 and he based it on the fact that the structure, 00:16:47.07 who got together for an intense month of work 00:05:34.12 and BMP is on the dorsal side, 00:01:51.15 and it seemed to us the rationale of 120 years ago 00:16:38.25 And I'd like to talk a little, for a moment, 00:23:23.04 and the right should be left? 00:05:20.02 just like vertebrates, 00:23:26.14 imagine the ancestry of these animals, What distinguishes craniates from all other chordates?
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