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BMS242 Developmental Biology > L9 - Neural tube Induction and Pattering > Flashcards

L9 - Neural tube Induction and Pattering Flashcards

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1
Q

What aspects of NS formation is common to both vertebrates and invertebrates

A

Neurogenic region found next to the skin This migrates down then goes inside

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2
Q

What feature of NS formation is found only n invertebrates

A

Delamination forming the neruoblast cells

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3
Q

What feature of NS formation is found only in vertebrates

A

Inc cell cell adhestion contactEither side the neural plate is bound by ectoderm, this then fuses above the neural plate

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4
Q

What would happen if all of the cells took their default state

A

All would become skin

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5
Q

Define differentiation

A

Process by which cells are able to become different and acquire specialised properties

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6
Q

What is cell differentiation governed by

A

Changes in gene expression which influences the repertoire of proteins expressed in a cell

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7
Q

Over time what happens to specialisation and pluripotency

A

Spec inc P.P dec

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8
Q

Is BMP found is vertebrates of invertebrates Give an example of an organism it is found in

A

Vertebrtes Xenopus

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9
Q

Is Dpp found in vertebrates or invertebrates Give an example of an organism it is found in

A

Invertebrates Drosophila

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10
Q

BMP7 homologue in drosophila

A

Screw

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11
Q

What does BMP stand for

A

Bone morphogenic protein

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12
Q

What does dpp stand for

A

Decapentaplegic

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13
Q

BMP1 homologue is drosophila

A

Tolloid

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14
Q

BMP4 homologue is drosophila

A

Dpp

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15
Q

Chordin homologue is drosophila

A

Short gastrulation (SOG)

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16
Q

Screw homologue in xenopus

A

BMP7

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17
Q

Dpp homologue in xenopus

A

BMP4

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18
Q

Tolloid homologue in xenopus

A

BMP1

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19
Q

SOG homologue in xenopus

A

Chordin

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20
Q

Normal function of Chordin/SOG

A

Inhibition of BMP/dpp signalling

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21
Q

What is the normal function of BMP4 and dpp

A

The activation of non-neural homeobox genes

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22
Q

Describe the BMP signalling when BMP has bound to the receptor

A

Phosphorylation of the receptor Phosphorylation of R-SMADCombines with SMAD4 Enters the nucelus via the nuclear pore Trancriptional complex Dephosphorylation and it leaves the nucleus

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23
Q

What are the 3(4) components of the SMAD transcriptional complex

A

PHOSPHORYLATED R-SMADSMAD4 Co factor

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24
Q

What two antagonists inhibit BMP signalling

A

Noggin and chordin

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25
Q

What is the function of noggin

A

Causes the inactivation of SMAD4

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26
Q

What are BMP and chordin examples of

A

Genes that have been conserved throughout evolution

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27
Q

What are the two mechanisms by which chordin and sog act as antagonists of the BMP/dpp signalling pathwat

A

Act as a sponge moping up dpp/bmp (binding to and inactivating)Competitively bind at receptors preventing binding of dpp/bmp

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28
Q

What does Dpp and SOG broadly dictate

A

The dorsal and ventral axis

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29
Q

What genes are expressed on the dorsal side of the embryo (insect)

A

Dpp, tld, tsg and SV-2

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30
Q

Describe the activity of the dpp pathway on the dorsal side of the embryo (insect)

A

No inhibition of the dpp pathway

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31
Q

What cell fate is taken by cells on the dorsal side of the embryo (insect)

A

Epidermal

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32
Q

What genes are expressed on the ventral side of the insect embryo

A

Sog and screw

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33
Q

What is the action of SOG

A

Inhibition of dpp binding to its receptor

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34
Q

What fate is taken by cells on the ventral side of the cell

A

Neural cell fate - neurogenic region is formed

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35
Q

What side is the NS found in insects

A

Ventral

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36
Q

What side is the NS found in vertebrates

A

Dorsal

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37
Q

Why is there a difference between the sides which the NS is found in vertebrates and invertebrates

A

Possibly due to a rotation of the head

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38
Q

Genes expressed at the dorsal end of a vertebrate - what fate do these cells then take

A

Chordin and Admp cells take a nerual cell fate

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39
Q

Genes expressed at the ventral end of an invertebrate What fate do these cells take

A

Sog, Screw

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40
Q

Molecular pathway ECTODERM IN PRESSENCE OF BMP SIGNALLING

A

High SMAD1 and low SMAD1Msx1, GATA1, Vent (epidermalising transcription factors) LEF1Epidermal differentiation

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41
Q

Molecular pathway ECTODERM WITHOUT BMP SIGNALLING

A

Low SMAD1 and high SMAD7 Xlpou2, SOXd/B (neuralising transcription factors)NeurogeninNeuroDNeural differentiation

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42
Q

What process results in the formation of the neural tub

A

Neuralation Neural plate rolls up to form the neural tube

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43
Q

What occurs during spinobifia

A

Failure of the neural tube to close properly

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44
Q

What can reduce the chances of spinobifida occuring

A

Folic acid

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45
Q

How do we know there are 3 germ layers found in the embryo

A

Repitore of proteins expressed - use of an antibody stain mRNA being expressed - look at using an in-situ hybridisation

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46
Q

What sets up the polarity of the early embryo

A

Established early on due to gravity and interaction of the placenta (in mammals) different cytoplasmic determinants have sunk to the one part of the egg. Leads to cells of this region becomming different and having a specific set of factors being activated

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47
Q

Which part of the embryo is fated to become the furture CNS

A

Cells immediatly adjacent to the organiser

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48
Q

What signal does the organiser secrete … what does this lead to

A

GSC is expressed this acts to upregulate Chordin , Noggin and Follistatin These secreted molecules act to inhibit BMP signalling

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49
Q

What the result of BMP signalling inhibiton

A

Neural plate induction

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50
Q

What are some antagonists of the BMP signalling pathways

A

Chordin NogginFollistatin

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51
Q

Outline the stages of mesoderm induction and patterning

A

Low level Nodal gives the ventral mesoderm High level Nodal gives the organiser Signals from the organiser acts to inhibit BMPs to dorsalise and pattern adjacent mesoderm Antagonism of BMPs –> Gives a neral identity

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52
Q

What receptors do BMPs bind to

A

TGFb-R

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53
Q

How to BMPs tend to act

A

Locally and diffuse to neigbouring cells

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54
Q

What fate do cells take if BMP signalling is active

A

Cells take an ectodermal cell fate

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55
Q

How do chordin noggin and follistatin act as inhibitors of the BMP signalling pathway

A

Antagonists compete for BMP binding - no longer able to activate receptors and cause activation of the BMP pathway

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56
Q

What is different in the development of chicks and humans

A

flattened into three sheets not a hollow sphere

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57
Q

What do cells in the organiser differentiate into

A

Axail mesendoderm and anteiror endoderm

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58
Q

What makes up the axial mesendoderm

A

Anteior endoderm, precordal mesoderm, notochord

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59
Q

What then happens to the axial mesendoderm

A

Involute, intercalates and undergoes convergent extension so it now lies as a rod underneath the neural plate

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60
Q

Describe invagination

A

Epithelial sheet bends inwards

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61
Q

Describe ingression

A

Where individual cells leave an epithelial sheet and become freely migrating mesenchyme

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62
Q

Describe involution

A

An epithelial sheet bends inward forming an underlying layer

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63
Q

Describe epiboly

A

Sheet of cells which streches by thinning

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64
Q

Describe intercalation

A

Row of cells which moves between one another creating an array of cells that is longer and thinner

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65
Q

Describe convergent extension

A

When rows of cells intercalate but this intercalation is highly directional

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66
Q

What is the anterior endoderm and prechordal mesoderm in close contact with

A

The pahrynx and ventral forebrain

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67
Q

Describe the process of the Organiser Graft exptWho performed it and when

A

Speeman and Mangold - 1920Organiser grafted from newt into a second newt - found that a twinned secondary axis was formed

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68
Q

What are the conclusions from the Organiser Graft expt

A

2nd neural tube was host derived shows that the neural tissue was induced from the ectoderm in response to signalling from the organsier The axial mesoderm (precordal mesoderm and notochord) and anterior endoderm was donor derived and therefore differentiates from the organiser

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69
Q

How were BMP antagonists discovered?

A

Extracted all the mRNA from the organiser cells and reverse transcribe to cDNA Each then tested for a gene/protein which mimiced the action of the organisers ability to induce a secondary neural plate

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70
Q

What occurs at the Speeman organiser

A

Gsc upregulated Leads to upregulation of chordin, noggin and follistatin Leads to inhibition of BMP signalling Leads to induction of a nerual cell fate

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71
Q

What are features of neural inducers in the organiser

A

Molecules must be expressed in the organiser Must be secreted and act of adjacent cellsOverexpression in an ectopic site should lead to induction of a secondary axis Inhibition should prevent the formation of any neural tissue - and any formation of the axis

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72
Q

Describe how the neural tube is formed

A

Cells of the nerual plate have apical-basal polarity On the apical side - band of F-actin, when this contracts, the cells are forced to change their shape (constriction at the apical edge of the cell) MANY MOLECULES ARE DIFFERENTIALLY DISTRIBUTED AT THE APICAL AND BASAL EDGES - AND MAY INTERACT WITH F ACTION CAUSING THE CONTRACTION AND SUBSEQUENT SHAPE CHANGE

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73
Q

Describe the role of follate receptors in spinofiida

A

Expressed on the apical domains of cells of the neural plate - when folate (derived from folic acid) When folic acid defficient not enough contraction of the F-actin leads to the neural tube not closing properly

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74
Q

What three systems must be developed

A

ENS PNS CNS

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75
Q

What regions make up the forbrain

A

Lateral ventricleTelencephalon Neural retina Lens3rd ventricle

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76
Q

What regions make up the midbrain

A

Mesencephalon and the cerebral aqueduct

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77
Q

What regions make up the hind brain

A

Metencephalon Myclencephalon 4th ventricle

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78
Q

What layers lie under the posterior end of the neural plate

A

Notochord

79
Q

What layers lie under the anterior end of the neural plate

A

Anterior endoderm Prechordal mesoderm

80
Q

What can be said about the signals from the anterior endoderm and prechordal mesoderm compared to the notochord, what does this cause

A

Slightly different signals Signals from the anterior endoderm and prechordal mesoderm cause the induction of the anterior neural identity

81
Q

What experiemental evidence can be obtained if developement is stopped at the instnant where the prechordal mesoderm has involuted

A

Look at the molecular markers can see that the neural plate expresses makers which are later confined to the forebrain i.e. the early neural plate is anterior in character

82
Q

Describe the activation-transformation model and its relevance to the determination of the posterior and anterior identities

A

Signals from the notochord cause cells at the back end of the neural plate to proliferateAt the same time other signals from the notochord changes these cells from an anterior to posterior identity Anterior TFs are turned OFFPosterior TFs turned ON

83
Q

What is the activation-transformation model the basis for

A

The formation of the anterior forebrain and the posterior hind brain and spinal chord

84
Q

What signals are involved at the anterior end

A

BMP antagonists and WNT antagonists

85
Q

What signals are involved at the posterior end

A

FGFs (in a gdt highest most posteriorly)WNTS (in a gdt highest most posteriorly)RA (in a gdt highest most posteriorly)

86
Q

Describe how RA (what does it stand for) signalling works

A

Retanoic acid Small so able to diffuse into cells where it binds to a cytosolic receptor - complex RA-R able to enter the nucleus where it directly influences gene expression

87
Q

Segmentation occurs as a result of

A

Step wise difference in the gradients of the signalling moleucles

88
Q

What are the two models for segemetation by a morphogen

A

Alan Turing - reaction diffusion Lewis- wolpert Postional infromation (french flag)

89
Q

What does HOX stand for

A

Homeobox containing

90
Q

Describe what the HOX genes are responsible for

A

Selection of a certain body area fate along the AP axis e.g. abdomen and the thorax

91
Q

Describe the different genes that are involved in the segmentation of the drosophila

A

Gap Pair ruleHomeotic genes Segment polarity genes

92
Q

What are the different segments of the drosophila

A

T1-T3 and A1-A8

93
Q

T1-T3 controlled by

A

UBX

94
Q

A1-A4 controlled by

A

AbdA

95
Q

A5-A8 controlled by

A

AbdB

96
Q

What causes activation of the HOX genes

A

Very specific threshold concentrations of posteriorising factors

97
Q

How many HOX genes in humans Why is this the case

A

4Safety measure incase of mutation

98
Q

What is homeobox DNA

A

Encodes a DNA binding protein of 60 amino acids called the homeodomain

99
Q

What are the different regions of hind brain and spinal cord defined by

A

HOX signature

100
Q

What does the RA gradient induce

A

Different patters of HOX transcript

101
Q

What occurs in a knock out of HOXa1 and HOXb1

A

These genes are required to specify rhombomeres 4 and 5 and nerves that are normally made in this region So double knockout for these genes results in a mouse that will develop without the abducens nerve

102
Q

Where are the midbrain strucutres induced

A

At the interaction between the forebrain and hindbrain boundary

103
Q

What are the three primary brain vesicles

A

Prosencephalon Mesencephalon Rhombencephalon

104
Q

What does the prosencephalon give rise to

A

Telencephalon Diencephalon

105
Q

What does the rhombencephalon give rise to

A

Metencephalon Mycelnecphalon

106
Q

What does the mesencephalon give rise to

A

Midbrain

107
Q

What does the telencephalon give rise to

A

Olfactory bulbs Hippocampus Cerebrum `

108
Q

What does the diencephalon give rise to

A

Retina Epithalamus Thalamus Hypothalamus

109
Q

What does the metencephalon give rise to

A

Cerebellum Pons

110
Q

What does the myclencephalon give rise to

A

Medulla

111
Q

The early ground plan for the mature NS is established by?..

A

Antagonistic signalling centres

112
Q

What is secreted from the node/organiser … give an example of one

A

BMP antagonists e.g. chordin

113
Q

What does the secretion of BMP antagonists cause the induction of

A

Induction of neural plate formation

114
Q

Where there is an INTERMEDIATE level of BMP signalling what is this zone known as

A

Neural plate border Found between the neural plate and the non-neural ectoderm

115
Q

3 crucial points of the neural plate border

A

Crucial for neural crest formation - and the formation of the PNS Crucial for the formation of the root plate cells and the patterning of the dorsal neural tub Crucial for complete closure of the neural tube

116
Q

What does neural crest formation and neural tube patterning happen before

A

The expression of Shh in the notochord

117
Q

STAGE 1] An early _______ established due to the ________ between BMP signalling and antagonism. This _____ ______ _______ then begins to express specific transcritpion factors such as _____

A

Border Balance Neural plate border Msx1

118
Q

At the neural plate border BMP signalling level is

A

Intermediate

119
Q

STAGE 2] Other signals (____ and ____) act together with _____ to turn _____________

A

WNT and FGFs Msx1 Turn on other transcription factors

120
Q

What signals are from the preaxial mesoderms

A

WNTs and FGFs

121
Q

What signalis from the non neural ectoderm

A

WNTs

122
Q

Msx1 acts in a ____________________ and WNTS and FGFS act in a _______________ to cause the activation of ________ and ________

A

Intrinsic - cell autonomousExtrinsic - cell non-autonomous PAX3 and ZIC1

123
Q

STAGE 3] ____ signals acts with the transcription factors of the ________________ to upregulate further TFs - (_____,______,_____) which are characteristic of neural crest cells

A

WNT Neural plate border c-myc, Snail, ID

124
Q

PAX3 and ZIC1 act in a ____________WNTS act in a __________To cause the upregulation of ______ and ______

A

Extrinsic - cell non-autonomous Intrinsic - cell autonomous Snail and FoxD3

125
Q

Snail is responsible for

A

Promoting cell survival Promotion of cells to undergo and epithelial mesenchymal transition

126
Q

c-myc is an Upregualtion will causes

A

OncogeneProliferation of cells

127
Q

ID will cause

A

Stem like behaviour of cells (multipotency)

128
Q

STAGE 4a] In response to _______ and ______ genes that control _______ , _______ and ________ are activated

A

c-myc and SOX9Survival, multipotency and survival

129
Q

Cascade of expression and effect of c-myc

A

c-myc –> ID –> Multipotency and proliferation

130
Q

Cascade of expression and effect of SOX9

A

Sox9 –> Snail –/ Cell death (promotes cell survival)

131
Q

Stage 4b] At the same time there is an upregulation of genes which promote ____________. This then causes the _________ of the _______ _______ cells and ____________

A

Epithelial –> Mesenchymal transition Delamination Neural crest Migration away

132
Q

Neural crest cells are often descirbed as

A

The fourth germ layer

133
Q

What sort of cells do the neural crest cells differentiate into

A

PNS Adrenal medulla Melanocytes Facial cartilage Dentin of the teeth

134
Q

What are the different cell types of the neural crest cell formed by

A

Position of origin (due to HOX gene)Time of generation by the cells Migration pathway and the signals they encounter en route or at the target

135
Q

Describe how the dorsal route ganglion is formed

A

NCCs usually at the posterior of the somite and force to move into the anterior of the somite by pissoffin

136
Q

Describe how the sympathetic and parasympathetic NS are formed

A

NCCs reach are beneath the notochord and the aorta

137
Q

Do all NCCs delaminate

A

No, some stay and form the roof plate clls

138
Q

What are the roof plate cells crucial in

A

Through to play a part in the fusion of the two sides of the neural tube

139
Q

What was previously thought to act as a morphogen

A

BMP from the roof plate

140
Q

What is now thought to be the way in which the roof plate signals

A

Different BMPS secreted from the roof plate ==> each BMP induces a different dorsal cell type

141
Q

What are the different progenitors on the dorsal side of the neural tube

A

P1 –> P6

142
Q

What are the cell types which differentiate dorsally

A

Roof plate cells Neural crest cells Different classes of dorsal sensory relay interneurones

143
Q

What is the single cell thick neural plate also referred to as

A

Neuroepithelium

144
Q

When the neural tube forms what occurs to the medial lateral axis

A

Becomes the DV axis

145
Q

Notochord is _______ to the neural tube

A

Ventral

146
Q

Skin ectoderm is _______ to the neural tube

A

Dorsal

147
Q

Neurones develop with ______________ throughout the entire DV axis

A

Bilateral symmetry

148
Q

How can it be tested that the notochord acts as a DV axis organiser

A

Graft the notochord into an ectopic site

149
Q

What occured when the notochord was grafted into an ectopic location

A

Induction of a secondary floor plate with bilateral symmetry of secondary motor neurones

150
Q

What is the Shh homologue in drosophila

A

Hh

151
Q

What does an insitu hybridisation against Shh show

A

That initially expressed in the notochord Induced expression of Shh in the floor plate cells

152
Q

What does an antibody stain show about Shh expression

A

Forms a gradient - highest ventrally and lowest dorsally

153
Q

What does Shh confer

A

Ventral neural tube identities so progenitors will ultimately give rise to cells that differentiate into ventral motor neurones

154
Q

What occurs when a bead soaked in Shh is grafted into an ectopic site

A

Mimics the effect of the notochord and floor plate Induces the secondary floor plate and ventral motor neurones

155
Q

What does Shh cause

A

Set of transcription factors which are a read outs of the Shh gradient

156
Q

Where is the Shh gradient highest

A

Ventrally

157
Q

What occurs as the ventral cells differentiate

A

The move laterally and differentiate into a neurone

158
Q

Shh acts at an ___________ to confer a _______ pattern of TFs on progenitor cells

A

Early stage DV

159
Q

Oncee the single cell neuroepithelium has been formed what is then induced

A

The neural tube

160
Q

What does the mediallateral axis become

A

DV

161
Q

Where does the notochord form

A

On the ventral surface

162
Q

Whaere does the skin ectoderm form

A

On the dorsal surface

163
Q

What is the floor plate closest to?

A

The notochord

164
Q

The roof plate is ______ wherase the floor plate is ______

A

Dorsal Ventral - next to the notochord

165
Q

What occurs at the same time as the neuralation

A

The axial mesoderm (notochord and prechordal mesoderm) forms and comes just beneath the ventral midline of the neural tube

166
Q

What do neurones develop with around the midline throughout the whole DV axis

A

Bilateral symmetry

167
Q

What is secreted by the notochord and the floor plate cells What does this act as

A

Shh Morphogen

168
Q

How can it be tested that the notochord and floorplate secrete a morphogenWhat were the results of this experiement?

A

Grafting the notochord into an ectopic site into a host embryo Induces a secondary floor plate and second set of motor neurones around - these exhibit bilateral symmetry

169
Q

What does an in-situ hybiridisation over time for Shh show

A

Initially expressed in the notochord This is then induced in the floor plate cells

170
Q

What experiment could be used to show that Shh is acting as a morphogen

A

Antibody stain

171
Q

What does an antibody stain for Shh show

A

Forms a concentration gradient (highest ventrally - lowest dorsally)

172
Q

What does Shh cause

A

Expression of a certain set of TFs in the cells that it act on

173
Q

What dose the TFs induced by Shh confer

A

Ventral neural tube identities so progenitors will give rise to cells that differentiate into ventral neurons

174
Q

What is the experimental evidence that it is SHH as a signalling molecule

A

Bead soaked in purified Shh protein is able to mimic the effect of the notochord and floor plate - induces a secondary floor plate and motor neurones

175
Q

In real life the set of TFs are readouts of the

A

Shh gradient

176
Q

Shh is highest

A

Ventrally

177
Q

What occurs to the cells as they differentitate

A

As they divide one cell retained as the mother cell and one moves laterally and differentiates into a neurone

178
Q

Shh acts at an __________ to confer ________ of TF on progenitor cells

A

Shh acts an early stage to confer a DV pattern

179
Q

What is the Shh gradient

A

Highest at the notochord and then the floor plate

180
Q

What is the BMP graient

A

From neural plate border cells and then the roof plate cells

181
Q

BMPs are members of the

A

TGF beta superfamily

182
Q

Progenitor domains made up of bands of proliferating cells are established by …

A

The opposing action of BMPS/WNTS (dorsally) and Shh (ventrally)

183
Q

Which way do cells move as they differentiate

A

Laterally

184
Q

Descibe how hedgehog signalling occurs

A

Hh ligand binds to PtcPtc then unable to inhibit Smo Smo then causes an increase in the ammount of Gli activator

185
Q

Hh signalling creates a balance of

A

Gli activator and repressor

186
Q

What is the Hh signalling in the inactive form

A

No Hh ligand bound to PtcNormal function of Ptc is to inhibit Smo Smo unable to cause increase in Gli activator Smo unable to cause increase in Gli activator ]More gli repressor than gli activators

187
Q

Describe the phenotype of the Shh -/-

A

Multiple dysmorphology No ventralisation of neural tube Holoprosencephaly CyclopiaAbnormal limbs/digits Lack of pituitary

188
Q

What is holoprosencephaly

A

Where there is no separation of the two parts of the brain

189
Q

What does Shh govern

A

Governs ventralisation along the whole rosto-caudal axis

190
Q

How come different neurones are formed at different levels along the A-P axis of the neural tube

A

The DV shh gradient intersects the AP hox gradient - forms a Cartesian grid of information - leads to different types of neurones being formed that are in the same DV position but differ on the AP axis

191
Q

What type of neurones form in the forebrain

A

Hypothalamic neurones

192
Q

What type of neurones form in the midbrain

A

Dopaminegric neurones

193
Q

What type of neurones form in the hindbrain

A

Serotonergic neurones

194
Q

What neurones form elsewhere along the DV axis

A

Motor neurones

BMS242 Developmental Biology (17 decks)

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