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Week 4 Notes

by: Natasha Hede

Week 4 Notes BIOL 4384

Natasha Hede
GPA 3.2
Developmental Biology
Amy Sater

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About this Document

Notes covering Vertebrate Axis Determination – Xenopus (read alongside the powerpoint!)
Developmental Biology
Amy Sater
Class Notes
xenopus, developmental biology, amy sater
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This 5 page Class Notes was uploaded by Natasha Hede on Friday February 20, 2015. The Class Notes belongs to BIOL 4384 at University of Houston taught by Amy Sater in Winter2015. Since its upload, it has received 122 views. For similar materials see Developmental Biology in Biology at University of Houston.

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Date Created: 02/20/15
February 17th and 19th 2015 Developmental Biology Notes Vertebrate Axis Determination Xenopus read alongside the powerpoint 1 4 Axis Determination in Xenopus I Cortical rotation leads to dorsal localization of the Disheveled 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 Role of WnT pathway proteins in dorsal ventral axis specification notice how on the ventral side there is a lack of nuclei this correlates with a lack of b catenin 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 belly piecequot d Begs the question what is the importance of the dorsal region 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 Smad 2 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 Chordin Noggin and Goosecoid f Goosecoid is only expressed in the dorsal lip 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 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 TGF B signals are su icient 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 specific region of high level b catenin and TGFB that can induce the mesoderm niewkoop center Bcatenin TGFB signal Dorsal Bcatcnin accumulation Y J Overlap Nieuwkoop center e 2000 Shane Associates Inc f See Slide 10 7 Vegetal Induction of Mesoderm Slide 11 a Diagram B Stage 8 bottom half creates VgI because RNA is already there maternally expressed There s an overlap the yellow dots blue area of b catenin and VgI region which induces the organizer genes and the second round of TGFB signaling b Diagram C Stage 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 Diagram D Stage 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 d 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 e Remember VgI encodes transcription factors whereas VgT encodes transcription factors 8 Mesoderm specification Slide 14 a Nodal encodes eomes which is a transcription factor b 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 c VgI leads to WnT inhibition Feedforward loop Animal Dorsal 3e 4 DEVELOPMENTAL BIOLOGY 10e Figure 814 d 2014 Sinauer Associates Inc 9 VgT CONTRIBUTES TO MESODERM BUT IS REQUIRED FOR ENDODERM FORMATION a lack of VgT the endoderm becomes and ectoderm 10 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 c BMP4 exists outside the organizer ventralizes the mesoderm It s a paracrine factor that is highly dense in ventral nonnodal regions d Induction of ventral mesoderm low an BMP is created here e Ventralization of lateral mesoderm BMP4 diffuses out laterally diffusion is necessary to create an intermediate balance of the mesoderms f BMP4 has a major role in ectoderm g Cells are very sensitive to BMP4 and can read increments of amounts of it this is important for establishing the gradient h This model goes through the stages of gastrulation due to BMP antagonists in the organizer which neutralize BMP proteins noggin and chordin i FGF fibroblast growth factors and IGF insulin like growth factors both which are tyrosine kinase pathways block SMAD1 j this all allows for the creation of somitesmesoderm 11 Dorsal Ventral Patterning and Mesoderm Induction a Slide A induction of dorsal ventral mesoderm b Slide B BMP acting but organizer is sending inhibitors c Slide C quotgradientquot of derms is established 12 Organizer a makes BMP inhibitors chordinnogginfollistratin b inhibits BMP in ectoderm which is necessary for neural tissue development it makes the epidermis 13 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 lip are enough to create the secondary body development and are necessary 14 Regional Specificity of Induction a 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 b Take home message mesoderm knows after gastrulation where it is on the anterior posterior axis and adjusts its signaling to tissues accordingly 15 Temporal Specificity of induction same idea but shows that timing is important 16 Paracrine factor antagonists a Inhibiting wnt is necessary to develop the anterior parts too much blocks the head region b prechordal plate mesodermquot head region expresses wnt and BMP antagonists also expresses IGF c 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 d KNOW THIS SLIDE Slide 25 see that prechordal has both BMP and wnt antagonists 17 Slide 29 General map that specifies ectodermendodermmesoderm a Ectodermin blocks T GFB signaling intracellularly is heavily expressed in the animal section prevents mesoderm formation b Fox11e 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 BMP antagonist 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 Left Right Asymmetry a cdx a transcription factor for trunk posterior development b retinoic acid involved in establishing posterior identity in mesoderm and neural tissue trunk 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 ctXZ on the left side and represses snail a repressor of pitu As a result pitu is expressed on the right side


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