Building Brains 5 - Vertebrates

Question 1

Describe what happens between fertilization and formation of the blastocyst in the early vertebrate embryo. (2)

Answer 1

• Cells proliferate
• Cells compact

Question 2

Name the two structures present in the blastocyst stage of the early vertebrate embryo. (2)

Answer 2

• Trophoectoderm
• Inner cell mass

Question 3

In the blastocyst of the early vertebrate embryo, what structure/s are formed by the trophoectoderm? (1)

Answer 3

Extraembryonic tissue, eg. placenta

Question 4

Name the two layers which form from the inner cell mass of the early vertebrate embryo.

What does each layer form? (2)

Answer 4

• Epiblast (forms adult cells)
• Hypoblast (forms extraembryonic tissue, eg. yolk sac)

Question 5

Complete the sentence regarding the development of the early vertebrate embryo. (2)

The two layers of the inner cell mass, the epiblast and hypoblast, detach from the trophoectoderm to develop as a disk. This structure is now called the ………………………… The entire embryo is now called a ………………………

Answer 5

• Blastodisc
• Gastrula

Question 6

Name the process by which the three germ layers are formed in the early vertebrate embryo. (1)

Answer 6

Gastrulation

Question 7

Describe the order in which gastrulation occurs in the early vertebrate embryo. (1)

Answer 7

From posterior to anterior

Question 8

Describe the structure, location, and role of the primitive streak in the early vertebrate embryo. (3)

Answer 8

Groove

in the dorsal embryonic midline

which is the site of gastrulation.

Question 9

Describe the process of gastrulation in the early vertebrate embryo. (4)

Answer 9

Cells from the surface of the epiblast migrate towards primitive streak

then move down and out

first integrating into the hypoblast layer to form the endoderm

then sitting between the endoderm and ectoderm to form the mesoderm.

Question 10

True or false? (1)

In the early vertebrate embryo, the primitive streak establishes the anterior-posterior axis.

Answer 10

True - however this may not apply to humans

Question 11

In the early vertebrate embryo, the primitive streak establishes the anterior-posterior axis.

Name two other ways that the axis may be determined in the embryo. (2)

Answer 11

• Gravity
• Point of sperm entry into egg

Question 12

Describe the ‘movement’ of the primitive streak throughout development in the early vertebrate embryo. (3)

Answer 12

• The primitive streak extends towards the head
• Then regresses posteriorly after reaching full extension
• Then disappears
• As the primitive streak regresses it leaves the notochord in its wake

Question 13

Describe the migration of the cells during gastrulation, which end up forming the notochord in the early vertebrate embryo. (1)

Answer 13

The notochord is formed by the cells which have passed through the node

at the anterior end of the primitive streak.

They are the last cells to migrate.

Question 14

Name the process which forms the neural tube in the early vertebrate embryo. (1)

Answer 14

Neurulation

Question 15

Describe where neurulation begins in the embryo and how it progresses. (1)

Answer 15

Begins anteriorly and progresses posteriorly.

Question 16

True or false? (1)

When looking at the embryonic nervous system at a single point in time, the posterior part will always be more developed than the anterior part.

Answer 16

False - the cranial nervous system develops before the caudal nervous system, so the anterior part will be more developed

Question 17

Describe the stages of neurulation in the early vertebrate embryo. (4)

Answer 17

• Neural plate thickens
• Neural plate bends in dorsal midline
• Two ends of neural plate join at neural plate borders to form a tube
• As tube closes the neural crest disconnects from epidermis

Question 18

Where does the notochord sit in relation to the neural tube in the early vertebrate embryo? (1)

Answer 18

Directly underneath it (ventrally)

Question 19

The notochord is classed as part of which germ layer in the early vertebrate embryo? (1)

Answer 19

Mesoderm

Question 20

True or false? (1)

In the early vertebrate embryo, the whole of the eye is developed from the neuroectoderm.

Answer 20

False - the retina develops from the forebrain part of the neuroectoderm, but the lens develops from the surface ectoderm.

Question 21

Describe briefly and simply how the eye is formed in the early vertebrate embryo. (4)

Answer 21

• Optic vesicle (neuroectoderm) makes contact with ectoderm
• Ectoderm invaginates to form lens placode
• Placode keeps invaginating to form cup-like structure (lens vesicle)
• Optic cup (neuroectoderm) and lens vesicle (ectoderm) develop into eye

Question 22

Describe briefly and simply how the ear is formed in the early vertebrate embryo. (4)

Answer 22

• Invagination of ectoderm to form otic placode
• Formation of otic cup,
• then otic vesicle.
• Collection of cells breaks away from otic epithelium to form acoustic-vestibular ganglion

Question 23

Describe what is meant by ‘the organiser’ when referring to early vertebrate embryos. (2)

Answer 23

The part of the embryo which can induce nearby cells

to become parts of the nervous system and other dorsal fates.

Question 24

True or false? (1)

The organiser in an early vertebrate embryo is only able to cause neural induction - further determination and differentiation require further signalling.

Answer 24

True

Question 25

True or false? (1) In the early vertebrate embryo, the organiser is always located at the cranial end of the primitive streak.

Answer 25

False - in amphibians it is not

Question 26

Name the organiser in an early chick embryo. (1)

Answer 26

Hensen's node

Question 27

Name the organiser in an early mammal embryo. (1)

Answer 27

Node

Question 28

Name the organiser in the early amphibian embryo. (1)

Answer 28

Blastopore (dorsal) lip

Question 29

True or false? (1) The organiser (Hensen's Node, etc) is the first part of the embryo to have its fate determined.

Answer 29

True

Question 30

Describe the structure, location, and movement of the node/Hensen's node during development of the early vertebrate embryo. (3)

Answer 30

- Enlarged group of cells - Anterior end of primitive streak - Location of the node moves anteriorly then posteriorly as the primitive streak extends and retracts

Question 31

Describe the cells which form the notochord, and how the node/Hensen's node is involved in producing the notochord. (2)

Answer 31

The cells which migrate last during gastrulation form the notochord. These cells migrate through the node.

Question 32

Name two structures in the early vertebrate embryo which possess neural inducing activity. (2)

Answer 32

- Notochord - (Hensen's) Node

Question 33

As well as signals produced by (Hensen's) node in the early vertebrate embryo, describe the other requirement for neural induction. (1)

Answer 33

Ectoderm must have intrinsic competence (the ability to respond to signals).

Question 34

Give the three criteria required for a molecule to be a signalling molecule and play a role in embryonic development. (3)

Answer 34

- Necessary - Sufficient - Expressed at correct time

Question 35

Describe simply how the notochord and node are able to induce neural competence in the early vertebrate embryo. Name the molecules involved. (4)

Answer 35

Release of: - Follistatin - Noggin - Chordin

Question 36

How do the molecules released by the notochord and node in the early vertebrate embryo help to induce neural fate? (1)

Answer 36

They are BMP antagonists

Question 37

What is the role of bone morphogenic proteins (BMPs) in determining fate in the early vertebrate embryo? (1)

Answer 37

Promotes epidermal state, inhibits neural state

Question 38

Describe the signalling pathway by which BMPs influence cell fate in the early vertebrate embryo. (4)

Answer 38

- BMP binds to cell surface receptor - Triggers SMAD phosphorylation - SMAD activated - SMAD inhibits neural genes and activates epidermal genes

Question 39

What types of molecules are BMPs in the early vertebrate embryo? (1)

Answer 39

Extracellular signalling molecules

Question 40

What types of molecules are chordin, follistatin, and noggin in the early vertebrate embryo? (1)

Answer 40

Extracellular signalling molecules

Question 41

What type of molecule is SMAD in the early vertebrate embryo? (1)

Answer 41

Transcription factor

Question 42

Describe how FGF inhibits the BMP signalling pathway in the early vertebrate embryo. (3)

Answer 42

- FGF binds to cell surface receptor - phosphorylation of smad - at a different site to that which is phosphorylated by BMP

Question 42

Apart from BMPs and BMP antagonists, name another molecule which is required to confer neural competence in the early vertebrate embryo. (1)

Answer 42

FGF (fibroblast growth factor)

Question 42

Give two roles of FGF in neural induction in the early vertebrate embryo. (2)

Answer 42

- Sox3 expression - Inhibits BMP pathway

Question 43

How is FGF produced in the early vertebrate embryo? When in development does this occur? (2)

Answer 43

Expressed by (Hensen's) node later in development.

Question 44

Name two Sox molecules which are important for neural induction in the early vertebrate embryo. (2)

Answer 44

Sox2 Sox3

Question 45

What types of molecules are the Sox proteins? (1)

Answer 45

Transcription factors

Question 46

Describe the expression of sox3 throughout development of the early vertebrate embryo. (2)

Answer 46

First expressed throughout ectoderm before being restricted to neural ectoderm as tissue matures. (also expressed in endoderm)

Question 47

Describe the expression of sox2 throughout development of the early vertebrate embryo. (1)

Answer 47

Only expressed in neural ectoderm

Question 48

When the nervous system starts to develop in the early vertebrate embryo, describe the expected distribution of sox2 in the AP axis. (1)

Answer 48

Expressed in anterior regions but not posterior regions (anterior regions develop first)

Question 49

Describe the order in which FGF and BMP are expressed during neural induction in the early vertebrate embryo. (2)

Answer 49

FGF expressed first to induce neural competence. Then BMPs (and inhibitors) expressed to form neural or epidermal ectoderm.

Question 50

Describe the gene/s expressed in the ectoderm of the early vertebrate embryo once it has been exposed to FGF. (1)

Answer 50

Sox3

Question 51

What type of molecule is FGF in the early vertebrate embryo? (1)

Answer 51

Extracellular signalling molecule

Question 52

Give another name for the organiser in a fish embryo, which is found at the blastopore (dorsal) lip. (1)

Answer 52

The ship

Question 53

Which animal's embryo is the closest model to a human embryo that we can use to study development? (1)

Answer 53

Mouse

Question 54

Describe one difference between mice embryos and other vertebrate embryos relating to the way that they fold in utero. (1)

Answer 54

Mouse embryos bend backwards but other embryos bend forwards.

Question 55

Describe what you would expect to happen if an area of mesoderm from the dorsal lip of the early amphibian embryo is transplanted to a different area of the organism. (2)

Answer 55

- Initiates gastrulation and notochord formation - So the embryo develops two nervous systems

Question 56

Describe what you would expect to happen if the Hensen's nodes from two donor quail embryos were taken and transplanted into a single chick embryo. (1)

Answer 56

Chick would develop 3 nervous systems.

Question 57

What would you expect to happen if a region of undifferentiated ectoderm was left to culture and the cells were... a) left intact b) dissociated c) dissociated and added to BMP4 Explain why these things happen. (6)

Answer 57

a) epidermis formed (intact cells express BMP so inhibit neural fates in each other) b) Neural tissue formed (dissociated cells still express BMP but cells too far away to respond) c) epidermis formed (cells inhibited by BMP)

Question 58

Describe where noggin would be expressed in an early chick embryo. (1)

Answer 58

Dorsal midline

Question 59

Describe where smad phosphorylation would occur in an early chick embryo. (1)

Answer 59

Outside CNS (so around the edge) of embryo

Question 60

foxi1 and gata2 are markers which indicate the epidermal fate in an early vertebrate embryo. Describe the expected distribution/level of expression of these in a wild type zebrafish embryo. How would this change if a) BMP b) noggin are added? (3)

Answer 60

- Outside of normal nervous system a) larger area of expression b) very little expression

Question 61

Describe the expected distribution/level of expression of sox2/3 in a wild type zebrafish embryo. How would this change if a) BMP b) noggin are added? (3)

Answer 61

- Within nervous system a) smaller area of expression b) larger area of expression

Question 62

zic2b is a marker which is expressed in the anterior nervous system of the early vertebrate embryo. Describe the expected distribution/level of expression of zic2b in a wild type zebrafish embryo. How would this change if a) BMP b) noggin are added? (3)

Answer 62

- Mainly expressed in head of embryo a) Smaller area of expression b) Larger area of expression

Question 63

Complete the sentence. (2) Overexpressing BMPs in the early vertebrate embryo results in the expansion of the ......................... fate and repression of the ....................... fate. HINT: both answers are either neural or epidermal

Answer 63

epidermal neural

Question 64

Complete the sentence. (2) Overexpressing BMP antagonists in the early vertebrate embryo results in the expansion of the ......................... fate and repression of the ....................... fate. HINT: both answers are either neural or epidermal

Answer 64

neural epidermal

Question 65

Complete the sentence. (2) Overexpressing the FGF signalling inhibitor, SU5402, in the early vertebrate embryo results in the expansion of the ......................... fate and repression of the ....................... fate. HINT: both answers are either neural or epidermal

Answer 65

epidermal neural

Question 66

How are chick embryos mainly used to research neural development, and why are they suited to this purpose? (2)

Answer 66

Transplantation of responding or signalling tissues. They are generally larger and held in place (tethered on a membrane).

Question 67

How are zebrafish embryos mainly used to research neural development, and why are they suited to this purpose? (2)

Answer 67

Good for treatment with molecule injection (eg. RNA, antisense oligonucleotides, signalling molecules) Zebrafish contain large cells in the early embryo, and as they divide the cells get smaller but the embryo doesn't get any bigger, so anything which has been injected does not become diluted.

Question 68

Follistatin, chordin, and noggin all have orthologues in the invertebrate embryo. What is it called? (1)

Answer 68

Sog

Question 69

Name the invertebrate orthologue of BMPs. (1)

Answer 69

DPP

Question 70

Name the invertebrate orthologue/s of SMAD. (1)

Answer 70

Mad/p-mad

Question 71

Give 2 similarities and 2 differences between neural induction in different vertebrate embryos. (4)

Answer 71

SIMILAR: - Genes and signalling pathways (eg. sox2/3) - All have an organiser which secretes BMP antagonists DIFFERENT: - Different name for the organiser - In some (fish, amphibians) the organiser is static whereas others (birds, mammals) it moves with the primitive streak

Question 72

Complete the sentence. (1) When it is first formed, the neural tube is a ...................... epithelium of proliferating cells.

Answer 72

Pseudostratified

Question 73

Why does the neural tube in the early vertebrate embryo appear as a pseudostratified epithelium? (1)

Answer 73

Due to cytokinetic movements during the cell cycle.

Question 74

Describe the cytokinetic movements of cells in the neural tube of the early vertebrate embryo during the cell cycle. (3)

Answer 74

- Nucleus and cytoplasm moves up (away from lumen of neural tube) - Then they move downwards towards lumen - Then retract processes and divide (connections of processes are reestablished by daughter cells)

Question 75

True or false? (1) In the developing neural tube, a cell which is proliferating cannot differentiate, and a cell which is differentiating can no longer divide.

Answer 75

True

Question 76

Describe in general, where cells of the neural tube move to once they stop dividing and start differentiating. (1)

Answer 76

Cells move outwards from proliferating epithelium and further away from lumen of neural tube.

Question 77

Describe the specific migration of differentiating cells in the spinal cord region of the neural tube. (Older cells vs newer cells, name the gradient). (3)

Answer 77

Newly born cells push existing cells up and sit under them. Oldest cells on outside, newest cells on inside. Outside-in gradient

Question 78

Describe the specific migration of differentiating cells in the cortex region of the neural tube. (Older cells vs newer cells, name the gradient). (3)

Answer 78

Newly born cells climb through the layers of existing cells and sit on top of them. Newest cells on outside, oldest cells on inside Inside-out gradient

Question 79

How do differentiating cells in cortex part of the neural tube climb through layers of existing cells to sit on top of them? (1)

Answer 79

Use the architecture of radial glial cells.

Question 80

Describe why it is important to have a precise balance between cell proliferation and cell differentiation in the neural tube of the early vertebrate embryo. (2)

Answer 80

- If all cells started differentiating the CNS would no longer grow - If all cells continued to proliferate there would be no differentiation

Question 81

True or false? (1) In the neural tube of the early vertebrate embryo, cellular differentiation only starts to occur once all cells have stopped dividing.

Answer 81

False - mature cells are gradually produced while other cells continue dividing and proliferating

Question 82

Describe the change in gene expression throughout the AP axis of the early vertebrate embryo as some neural tube cells begin to stop dividing and differentiate. (2)

Answer 82

- Change from producing FGF8 to Raldh2 - Anterior part starts producing Raldh2 first, while the posterior part continues producing FGF

Question 83

Describe the role of FGF8 in balancing cell division and differentiation in the early vertebrate embryo. (2)

Answer 83

FGF inhibits Pax6 Which is necessary for neural differentiation. (FGF inhibits differentiation)

Question 84

Which part of the early vertebrate embryo produces FGF8 as it plays a role in promoting cellular proliferation in the neural tube? (1)

Answer 84

Presomitic/paraxial mesoderm

Question 85

What is the role of Raldh2 in the early vertebrate embryo? (2)

Answer 85

Produces retinoic acid to promote cellular differentiation.

Question 86

Name the part of the early vertebrate embryo which produces Raldh2 to promote cellular differentiation in the neural tube. (1)

Answer 86

Somitic mesoderm

Question 87

Describe where in the cells of the early vertebrate embryo neural tube the receptors for retinoic acid are located. (1)

Answer 87

In cytoplasm

Question 88

Describe how FGF8 and retinoic acid interact with each other in the early vertebrate embryo to regulate the balance between proliferation and differentiation in the neural tube. (1)

Answer 88

They show mutual inhibition

Question 89

True or false? (1) As retinoic acid acts on cells in the neural tube of the early vertebrate embryo, these cells immediately begin to differentiate and stop proliferating.

Answer 89

False - retinoic acid gives the cells the ability to differentiate, but not all cells go on to differentiate straight away

Question 90

Describe the process by which the mesoderm of the early vertebrate embryo switches from producing FGF8 to inhibit cell differentiation to producing Raldh2 to promote cell differentiation. How is a gradient of cell differentiation established in the embryo? (2)

Answer 90

Mesoderm starts to form somites from anterior to posterior.

Question 91

Give four genes expressed in early neuroblasts in the vertebrate neural tube. Name an additional two which are expressed as these cells begin to differentiate. (6)

Answer 91

- Sox2 - Sox3 - Notch - HES-1 - Delta - Sox4/11

Question 92

In areas of the early vertebrate embryo neural tube where cells are exposed to retinoic acid, the cells are told to stop dividing and start differentiating. However if all cells stopped dividing right away, the nervous system would no longer be able to expand. Describe how some cells are able to 'ignore' this signal and continue proliferating for a while. (1)

Answer 92

Inhibition by notch-delta

Question 93

Describe the pathway by which cells stop proliferating and start differentiating in the early vertebrate embryo when signalled by retinoic acid. (3)

Answer 93

- Transcription of neurogenin - Neurogenin protein activates NeuroD transcription - NeuroD protein promotes neural differentiation

Question 94

Describe how notch-delta signalling in the neural tube of the early vertebrate embryo prevents a subset of cells from differentiating. How does it affect the normal pathway leading to neural differentiation? (4)

Answer 94

- Delta binds to notch - Notch intracellular domain is cleaved (and travels to nucleus) - Notch activates transcription of HES genes - HES is a transcriptional repressor - stops Neurogenin transcription (Neurogenin cannot activate NeuroD to activate differentiation)

Question 95

Describe how the process of lateral inhibition and the expression of delta is able to regulate the balance between cellular proliferation and differentiation in the neural tube of the early vertebrate embryo. (4)

Answer 95

- As cells start differentiating they express delta - Delta provides lateral inhibition of differentiation to neighbours in three dimensions - Neighbours will continue to proliferate - Once a cell differentiates and migrates away the inhibition is removed so a new cell can then begin to differentiate

Question 96

As a differentiating cell migrates away from the neural tube in the early vertebrate embryo, lateral inhibition is removed from neighbouring cells and one is then able to begin differentiating itself. How does the embryo decide which cell should be next to differentiate? (2)

Answer 96

- The next cell to reach the right stage in the cell cycle - and which expresses delta to inhibit neighbours, but is not inhibited itself will be next to differentiate

Question 97

Complete the sentence. (1) In an experiment where researchers are overexpressing HES-1 to test its role in inhibiting neural differentiation in the early vertebrate embryo, they are testing the ...................... of HES-1 to cause an effect. This is a ......................... of function experiment. HINT: answer is either sufficiency or necessity, then either gain or loss

Answer 97

Sufficiency Gain

Question 98

Name a technique which could be used to promote overexpression of HES-1 is embryonic mouse retina and forebrain cells. (1)

Answer 98

Viral vector

Question 99

Describe the expected results of an experiment in which neural tube cells in the early vertebrate embryo are manipulated to overexpress HES-1. (2)

Answer 99

- Cells remain in ventricular zone of neural tube and divide - However they can't migrate and differentiate, so eventually die

Question 100

Complete the sentence. (1) In an experiment where researchers are knocking out HES-1 to test its role in inhibiting neural differentiation in the early vertebrate embryo, they are testing the ...................... of HES-1 to cause an effect. This is a ......................... of function experiment. HINT: answer is either sufficiency or necessity, then either gain or loss

Answer 100

Necessity Loss

Question 101

Describe what you would expect to see in an experiment where HES-1 is knocked out in the forebrain of the early vertebrate embryo. (2)

Answer 101

- Premature differentiation - Proliferation ceases so organism has small/underdeveloped forebrain

Question 102

In experiments where HES-1 is knocked out in the early vertebrate embryo to test its role in inhibiting neural tube cell differentiation, the 'expected' results are only seen in the forebrain regions. Why is this? (2)

Answer 102

- In other areas of the embryo, additional forms of HES are present which will take over and inhibit differentiation - However only HES-1 is present in the forebrain

Question 103

Complete the sentence. (1) In an experiment where researchers are overexpressing delta to test its role in inhibiting neural differentiation in the early vertebrate embryo, they are testing the ...................... of delta to cause an effect. This is a ......................... of function experiment. HINT: answer is either sufficiency or necessity, then either gain or loss

Answer 103

Sufficiency Gain

Question 104

Name a technique which could be used to promote overexpression of delta in embryonic chick retina cells. (1)

Answer 104

Viral vector

Question 105

Describe the results you would expect to see in an experiment where delta is overexpressed in neural tube cells of the early vertebrate embryo. (1)

Answer 105

- Inhibition of differentiation and migration

Question 106

Complete the sentence. (1) In an experiment where researchers are overexpressing a faulty form of delta to test its role in inhibiting neural differentiation in the early vertebrate embryo, they are testing the ...................... of delta to cause an effect. This is a ......................... of function experiment. HINT: answer is either sufficiency or necessity, then either gain or loss

Answer 106

Necessity Loss

Question 107

Dominant-negative delta lacks the delta intracellular domain. Describe how expressing this faulty delta in cells is able to cause loss of function of the notch-delta signalling pathway. (3)

Answer 107

- Faulty delta binds to notch - but does not produce a response. - Faulty delta stops functional delta from binding.

Question 108

In experiments investigating the differentiation and migration of cells in the neural tube of the early vertebrate embryo, name two markers that can be used to identify differentiating neurones. (2)

Answer 108

Islet 1/2 Neurofilament

Question 109

Describe the expected results in an experiment where dominant-negative (faulty) delta is expressed in neural tube cells of the early vertebrate embryo. (1)

Answer 109

Premature differentiation (cessation of proliferation)

Question 110

Describe what BrdU is, and how it can show proliferating or non-proliferating cells in the early vertebrate embryo. (2)

Answer 110

BrdU is a marked nucleotide (thymidine analogue) which gets incorporated into DNA during DNA synthesis. If the label is expressed in a cell, it means that the cell is proliferating (and synthesising new DNA molecules to incorporate BrdU).

Question 111

Briefly describe an experiment which can be performed in the developing embryo which can help to determine whether a cell's fate is determined before or after its birth date. What results would you expect to see for both options? (4)

Answer 111

- Label one proliferating precursor cell - Look at offspring (cells containing label) to see what cells have been produced - If cell fate is determined before birthdate, offspring cells will be identical - If cell fate is determined after birthdate, offspring cells will be varied

Question 112

How are proliferating cells labelled in the early vertebrate embryo when carrying out an experiment to determine whether cells acquire their fate before or after their birth date? (1)

Answer 112

Virus + beta-galactosidase

Question 113

Describe whether neural progenitor cells in the retina of the early vertebrate embryo produce identical or different offspring. What does this mean regarding whether cells acquire their fate before or after their birth date? (2)

Answer 113

Different offspring So cells acquire fate after birth date

Question 114

Describe whether neural progenitor cells in the forebrain of the early vertebrate embryo produce identical or different offspring. What does this mean regarding whether cells acquire their fate before or after their birth date? (2)

Answer 114

Identical offspring Cells may have fate decided before birth date (while still dividing)

Question 115

Define what we mean by a cell's 'birth date' in the early vertebrate embryo. (1)

Answer 115

A cell's birth date is the day when in stops dividing and starts differentiating.

Question 115

When talking about cells in the early vertebrate embryo acquiring their fate before or after their birth date, in what axis are we referring to cell fate? (1)

Answer 115

Medial-lateral axis

Question 116

Describe a method which could be used to study cell birth dates in a vertebrate embryo, and explain how it works. (6)

Answer 116

- Label cells with 3H-Thy or BrdU - These marked nucleotides only get incorporated into cells making DNA and dividing - Wash out label after giving it time to be incorporated - When looking in the future, cells born on the day that the label was injected will still show the label - Cells which were born before label injected do not show label as it was never incorporated into the cell as it was not dividing - Cells born after label was injected do not show label as multiple divisions have taken place since injection and diluted label

Question 117

Describe a way of labelling cells in the entire embryo (not just specific cells) in... a) frog embryo b) mammalian embryo (2)

Answer 117

Frog - add label to water Mammal - inject label into mother

Question 118

True or false? (1) When labelling cells in the early vertebrate embryo to study their birth dates, the label which was injected will still be seen long into the future in cells born on the same day.

Answer 118

True - because cells born on the day that the label was injected stop dividing after incorporating the label, the label is not diluted, and remains in the cells long into the future

Question 119

Describe to what extent a cell's fate is determined in the medial-lateral axis according to birth date. (1)

Answer 119

Determines what layer of cortex the cell will end up in

Question 120

When carrying out an experiment to label cells in the early vertebrate embryo and determine their birth dates and fates, why isn't the label present in any cells if the label was injected during very early stages of gestation? (2)

Answer 120

All cells are still dividing (none are being born yet) so label gets diluted and undetectable in all cells.

Question 121

When carrying out an experiment to label cells in the early vertebrate embryo and determine their birth dates and fates, why isn't the label present in any cells if the label was injected during very late stages of gestation? (2)

Answer 121

Cells are no longer dividing so they do not incorporate the stain in the first place.

Question 122

Describe the position/location of cells in the early vertebrate embryo which were labelled with BrdU and have retained that stain, as cells are just beginning to stop dividing and differentiate. (1)

Answer 122

They will be in layer 6 of the cortex

Question 123

Describe the position/location of cells in the early vertebrate embryo which were labelled with BrdU and have retained that stain, as cells are ending their phase of differentiation in the neural tube. (1)

Answer 123

Layer 1 of the cortex

Question 124

Do cells migrate according to fate, or is cell fate determined by environment in the vertebrate embryo? (in the medial-lateral axis, ie. layers of the cortex)

Answer 124

Cells migrate according to fate (once cells stop dividing they 'know' what cells they are, and then migrate to the right layer)

Question 125

A study was carried out where a cell which is just starting to cease proliferation and begin differentiation/migration on embryonic day 9 is transplanted into an embryo at postnatal day 1. Normally, the E29 cell will migrate to layer 6, and P1 cells would migrate to layer 2/3. To which layer would the E29 cell migrate to in the P1 embryo if it is transplanted after it has completed its last S phase of cell division? (1)

Answer 125

Layer 6 (cell retains fate)

Question 126

A study was carried out where a cell which is just starting to cease proliferation and begin differentiation/migration on embryonic day 9 is transplanted into an embryo at postnatal day 1. Normally, the E29 cell will migrate to layer 6, and P1 cells would migrate to layer 2/3. To which layer would the E29 cell migrate to in the P1 embryo if it is transplanted as it is completing its last S phase of cell division? (1)

Answer 126

Layer 2/3 (cell takes on fate of new embryo)

Question 127

What is the S phase of cell division? (1)

Answer 127

DNA synthesis

Question 128

When exactly during a cell's last cell cycle does it acquire its fate on it's birth date in the vertebrate embryo? (1)

Answer 128

After last S phase (DNA synthesis) but just before it migrates.

Question 129

Describe the hypothesis which describes how a cell which is still proliferating but getting ready to migrate from the neural tube in the vertebrate embryo knows what layer of the cortex it is going to become. (1)

Answer 129

Newly-differentiating and migrating cells send signals back to still-proliferating cells to indicate their fate and therefore the fates of the next cells to migrate.