DEVBIO Study Guide
DEVBIO Study Guide BIOL 4384
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This 7 page Study Guide was uploaded by Natasha Hede on Sunday March 22, 2015. The Study Guide belongs to BIOL 4384 at University of Houston taught by Amy Sater in Winter2015. Since its upload, it has received 140 views. For similar materials see Developmental Biology in Biology at University of Houston.
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Date Created: 03/22/15
Developmental Biology Spring 2015 Vertebrate Axis Formation I Xenopus I how does the dorsalventral axis form Key components 1 B catenin 2 TGFbeta family members Vg1 activin nodals nodalrelated an genes Cortical rotation CR is req for localized accumulation of B catenin on future dorsal side opposite the point of sperm entry experiment 1 centrifugation of fertilized eggs during first cell cycle reverses direction of cortical rotation can also make doubleaxis ie conjoined or Siamese twins by centrifuging twice in opposite directions Cortical rotation leads to movement of disheveled protein also Wnt 11 and Bcatenin into dorsal area B catenin visible and active in nuclei in dorsal region What does B catenin do then enters nuclei binds TCFLEF acts as transcription factor TF in absence of Bcatenin TCF sits on chromatin acts as a transcriptional repressor upon binding of Bcatenin to TCF genes repressed by TCF are now activated BcateninT CF complex activates siamois a gene required for induction of dorsal mesoderm also other genes siamois is also a transcription factor siamois TGFB nodal signaling leads to transcriptional activation of goosecoid required for establishment of the Organizer expression of goosecoid on ventral side leads to 2 axis conjoined twins TGFB type signals originate in the vegetal region Vg1 TGFB family member VegT TF mRNAs localized in vegetal region of egg cause early expression of ans Xenopus NodalRelated genes ans expressed in future endoderm encode secreted signals that induce mesoderm Overlap of high Vg1VegT vegetally amp high bcatenin dorsally high an expression in the Nieuwkoop center Nieuwkoop Center in dorsovegetal region induces formation of the Organizer Organizer overlap of high Bcatenin and high andep transcription Activation of andependent transcription in cells in which siamois is active leads to expression of goosecoid Goosecoid transcription factor expressed in the Organizer Expression of goosecoid on ventral side leads to formation of doubleaxis embryos conjoined twins Key activators of the organizer bcatenin and nodal related proteins also in other vertebrates VegT maternally expressed Transcription factor VegT induces expression of nodalrelated genes VegT required for endoderm devlt Lower levels of an signals lead to induction of ventral mesoderm high BMP4 wnt8 Exp of BMP4 is highest in ventral marginal zone opposite site of Organizer formation BMP4 released by ventralmost cells forms gradient within the marginal zone BMP4 induces neighboring mesoderm cells to adopt a ventral fate Experiment 2 Nieuwkoop isolated animal cap and vegetal base from Xenopus blastulae Animal cap 9 ectoderm epidermis Vegetal base 9 endoderm recombinates of animal cap and vegetal cells formed mesoderm originating in animal cells Vegetal cells produce mesoderminducing signal what is it TGFB family members Vg1 activin nodals 4Signal Model for mesoderm induction and establishment of dorsalventral pattern in the mesoderm 1 Induction of dorsal mesoderm bcatenin high an the future Organizer see below 2 Induction of ventral mesoderm low an 3 Ventralization of lateral mesoderm BMP4 4 Dorsalization of ventralized mesoderm in lateral regions by BMP antagonists eg noggin chordin Organizer key signaling center in gastrulastage vertebrate embryo The Organizer is the Xenopus dorsal lip the Zebrafish Dorsal shield chick Hensen s node and the mammalian Node The Organizer Experiment 3 First identified as a signaling center through classic experiments of Hans Spemann and Hilde Mangold they grafted the dorsal lip of a pigmented embryo onto the ventral side of an unpigmented host Result two body axes doubleaxis embryo The 2 axis resulting from the graft had a pigmented notochord but the somites and nearly all of the neural tube were unpigmented meaning that they originated in the ventral tissues of the host Spemann and Mangold concluded that the ventral tissues had altered their fate in response to inductive signals coming from the grafted dorsal lip later studies showed that signals from the dorsal lip are required for formation of neural tissue and somites In vuvo Key signals from Organizer 1 secreted antagonists of BMPs eg noggin chordin folllistatin block BMP activity reverse ventralization of lateral mesoderm Antagonism of BMP signaling is required but not necessarily sufficient for neural fate in vivo FGFMAPK signals will also antagonize BMP signals 2 nodals include nodalrelated genes 3 sonic hedgehog 4 secreted antagonists of wnts eg dickkopf FrzB Cerberus also inhibits BMPs nodals The Organizer has some intrinsic Anteroposterior pattern shown by transplantation experiments of Otto Mangold and Hans Spemann Earlier or more anterior dorsal mesoderm grafts produce 2 axes with more anterior features head eyes Later or more posterior dorsal mesoderm grafts produce 2 axes that lack anterior features but form tails etc Head formation requires inhibition of both BMPS and wnts Wnt signaling during gastrulation is assoc w posterior development Establishment of the three germ layers Mesoderm induced by TGFb signals nodals produced in the vegetal region Endoderm requires nodal signals AND VegT Ectoderm requires ectodermin which downregulates nodal and BMP signals also Foxe1 Vertebrate Axis Determination Xenopus read alongside the powerpoint 1 Axis Determination in Xenopus I Cortical rotation leads to dorsal localization of the Disheveed protein which stabilized b catenin in the dorsal portion of the amphibian egg a Centrioles converge to become an aster push on the dorsal site which leads to a shift of the cortex to about 30 degrees b This moves the b catenin and b catenin protection proteins into the dorsal region which leads to an accumulation of b catenin c If blocked the dorsal development is late if it happens at all d Look at Slide 3 2 Role of WnT pathway proteins in dorsalventral axis speci cation notice how on the ventral side there is a lack of nuclei this correlates with a lack of b catenin 3 Asymmetry in the Amphibian Egg a Grey crescent is the dorsal region b If you take an embryo and divide it on the 1st cleavage plane divide a dorsal plane in half basically you can separate the two halves into two functional tadpoles This is the left hand side of the diagram c If you take an embryo and divide it into the ventral and dorsal region however the dorsal region alone will develop naturally the ventral region develops into a quotbelly piecequot d Begs the question what is the importance of the dorsal region 4 What does b catenin do a Regulates gene regulatory networks b catenin is at the top of the gene transcription factor cascade b b catenin can activate siamosis and twin which are both transcription factors They sit down on other promoters alongside with 5mad2 TGFB paracrine factors to activate the organizer c Look at diagram on slide 8 to get a better picture d On the ventral side the TGFB proteins repress transcription of siamosis and twin e The organizer genes activate proteins called Chordn Noggin and Goosecoid f Goosecoid is only expressed in the dorsal lip 5 Ability of goosecoid mRNA to induce a new axis two axes are developed the shorter axis is on the left and the longer axis is on the right This causes conjoined twins 6 Mesodermal induction induced from vegetal region by TGFB family a Animal ectoderm in proximity to the yolk will be induced to become mesoderm b What does this mean TGFB signals are suf cient to produce mesoderm as well as necessary for all vertebrates c maternally expressed RNA encodes additional TGFB signals that act through the SMAD 23 pathways d speci c region of high level b catenin and TGFB that can induce the mesoderm niewkoop center c5iterlin anquot 39 l r r n 47 39 h l A l 1 3quot 3 ve 39 g 39 391 r 7 1hrquot TGEE Signal Dmsall ame11in accumulation It T J OVEHH Nieuwknnp cesi lter I EDEN Sinauer ssuciates Inc f See Slide 10 7 Vegetal Induction of Mesoderm Slide 11 a Diagram BStage 8 bottom half creates Vgl because RNA is already there maternally expressed There s an overlap the yellow dots blue area of b catenin and Vgl region which induces the organizer genes and the second round of TGFB signaling b Diagram CStage 9 the 1st genes to be expressed are node genes which signal genes upward There are high levels on the dorsal side and low levels on the ventral C e Diagram DStage 10 VgT encodes a transcription factor one inside the cell and one outside the cell The red shows ventral mesoderm before gastrulation and the blue shows the dorsal mesoderm Notice that a gradient is being established this is to create a smooth transition of derms rather than create two distinct mesoderms Important thing to remember this is during midblastula stage where transcription levels are highest However it happens to be so that node genes are actually transcripted before this stage The more you know Remember Vgl encodes transcription factors whereas VgT encodes transcription factors 8 Mesoderm speci cation Slide 14 10 a b c d Nodal encodes eomes which is a transcription factor Basically take away message from this slide is the feed forward loop nodal activates VgT and eomes which also activates VgT The whole purpose of this is to create a system that has increased resistance against disruption Vgl leads to WnT inhibition Feedfo rward loop An i m all lDorsall Vegetal DEVELOPMENTAL BiOlO GY We Figure 814 2014 Sinauer Associates Inc 9 VgT CONTRIBUTES TO MESODERM BUT IS REQUIRED FOR ENDODERM FORMATION a lack of VgT the endoderm becomes and ectoderm Four Signal Model a TGFB nodal goes through the SMAD 2 and 3 pathways b BMP bone morphogenic protein goes through SMAD 1 pathway Is strongly expressed in oogocytematernal formation BMP4 exists outside the organizer ventralizes the mesoderm It s a paracrine factor that is highly dense in ventral nonnodal regions Induction of ventral mesoderm low an BMP is created here Ventralization of lateral mesoderm BMP4 diffuses out laterally diffusion is necessary to create an intermediatebalance of the mesoderms BMP4 has a major role in ectoderm 11 a b c 12 a b 13 Cells are very sensitive to BMP4 and can read increments of amounts of it this is important for establishing the gradient This model goes through the stages of gastrulation due to BMP antagonists in the organizer which neutralize BMP proteins noggin and chordn FGF broblast growth factors and IGF insulin like growth factors both which are tyrosine kinase pathways block SMAD1 this all allows for the creation of somitesmesoderm Dorsal Ventral Patterning and Mesoderm Induction Slide A induction of dorsalventral mesoderm Slide B BMP acting but organizer is sending inhibitors Slide C gradient of derms is established Organizer makes BMP inhibitors chordinnogginfollistratin inhibits BMP in ectoderm which is necessary for neural tissue development it makes the epidermis Organization of secondary axis this experiment takes a stained graft from developing embryo and grafts it to another it shows that signals from the dorsal ip are enough to create the secondary body development and are necessary Regional Speci city of Induction This slide shows that by cutting out anterior parts of the mesoderm and sticking it on other parts ventraldorsal of a developing gastrulating embryo it forms different things Take home message mesoderm knows after gastrulation where it is on the anteriorposterior axis and adjusts its signaling to tissues accordingly Temporal Speci city of induction same idea but shows that timing is important 14 a b 15 16 a b c d 17 Paracrine factor antagonists Inhibiting wntis necessary to develop the anterior parts too much blocks the head region quotprechordal plate mesodermquot head region expresses wntand BMP antagonists also expresses IGF Cerberus is a gene transcription factor the mutation causes multiple heads Its role is to inhibit BMP and wnt signals has binding sites to nodals establishes head formation KNOW THIS SLIDE Slide 25 see that prechordal has both BMPand wnt antagonists Slide 29 General map that speci es ectodermendodermmesoderm a Ectodermin blocks TGFB signaling intracellularly is heavily expressed in the animal section prevents mesoderm formation b Fox1e is inhibited by the nodal creates the ectoderm 18 Slides 2931 know them well be able to tell how everything relates to the other 19 Know the chick s role in the dorsoventral axis on Slide 32 20 Slides 1419 on Part II are about the relationship of frogzebrafishchickmouse embryo developments to one another Be able to gain a general understanding of the similarities and differences 21 BMP Signaling and inhibition through chick gastrulation notice that BMPantagonist focuses exclusively on Hensen s node and the primary streak As a result BMP expression is in the posterior part but not the anterior or dorsal sideSMAD1 which is necessary for BMP signaling is also blocked in those areas 22 Slide 33 is very important 23 LeftRight Asymmetry a cdx a transcription factor for trunk posterior development b retinoic acid involved in establishing posterior identity in mesoderm and neural tissuetrunk formation c Asymmetry begins through the node that creates a cascade d Slide 37 sonic the hedgehog is expressed only on the left side which indirectly leads to the left only expression of nodal which then does two things activates ctX2 on the left side and represses snail a repressor of pitu As a result pitu is expressed on the right side March 339 March 5th March 10thMarch 12th February 24th 26th
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