Lecture 11 Flashcards Preview

BMS237 - Advanced Developmental Biology > Lecture 11 > Flashcards

Flashcards in Lecture 11 Deck (38)
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1
Q

Which axis is the first to be laid down during embryonic development

A

Anterior-posterior axis

2
Q

Explain the results of ectopic grafting of boundary cells

A

Somite boundary cells isolated from one embryo transplanted into another embryo is sufficient to induce the formation of a new boundary. Where you’d expect to see one somite you would now get two. This shows that boundary cells instruct cells that are anterior to it to form a boundary

3
Q

Which mesodermal tissue gives rise to the somites

A

Paraxial mesoderm

4
Q

Which germ layer forms at the primitive streak during gastrulation

A

Mesoderm

5
Q

What five factors must cells in the paraxial mesoderm be able to respond to

A

Positional information, mechanisms that coordinate left and right, anterior and posterior boundary formation and the formation of the cleft

6
Q

What is meant by the determination front

A

Wavefront that travels from the anterior part of the presomitic mesoderm towards the posterior embryo

7
Q

What determines the adoption of different mesodermal fates in the developing embryo

A

Where the cells ingress along the anterior-posterior axis into the primitive streak

8
Q

How do RA and FGF8 interact to regulate expression of transcription factor(s) involved in somite boundary formation

A

RA activates Mesp2 expression whilst FGF8 inhibits it. Mesp2 expression in turn blocks local Notch signalling. Lower Notch signalling on one side of the border results in high notch signalling in adjacent cells on the other side of the boundary.

9
Q

What transcription factor do RA and FGF8 regulate the expression of

A

Mesp2

10
Q

What model describes the periodicity of somite formation and how is this achieved

A

Clock and wavefront model. The clock explains the temporal component whilst the wavefront provides spatial information to drive somite formation. Where cells hit the travelling wavefront an abrupt change of property leads to the decision to form somites

11
Q

The pre-somitic mesoderm is unsegmented, T or F

A

T

12
Q

Describe the rough structure of the somites viewed as a horizontal cross section

A

The somites show a clear metameric structure with a clear repeating pattern and defined anterior and posterior boundaries

13
Q

How do the number of somites relate to segmentation in vertebrates such as humans

A

Somite number dictates the number of vertebrae

14
Q

The axial mesoderm is one of the mesodermal tissues formed by the ingression of cell into the primitive streak, what two subtypes of mesoderm does it give rise to and where

A

Prechordal mesoderm (anteriorly) and the notochord (posteriorly)

15
Q

Cells that ingress posteriorly to the paraxial mesoderm give rise to which tissue

A

Intermediate mesoderm

16
Q

RA and FGF8 agonise eachother, T or F

A

F – they antagonise each other

17
Q

What family of genes were discovered to be expressed at the somite boundaries

A

Notch family genes. They are selectively expressed in the anterior or posterior part of the somite

18
Q

Explain the results of forced lunatic fringe expression in the paraxial mesoderm and the significance of this

A

Lunatic fringe is a gene that blocks notch activity and thus forced expression results in an inhibition of notch signalling. This results in the formation of a new boundary and hence an additional somite

19
Q

The number of somites is fixed for any given species and the timing of somite formation remains constant, T or F

A

F – whilst the number of somites does differ between species, so too does the timing of somite generation

20
Q

Explain how RA and FGF8 interact to dictate determination front positioning

A

High levels of FGF8 result in high levels of Cyp26 which inhibits RA synthesis. High levels of FGF8 also inhibit the production of the Rhald2 enzyme that is normally required for RA synthesis

21
Q

Explain how a molecular oscillator drives mesodermal segmentation in chick embryos

A

In the embryo levels of the helix-loop-helix transcription factor C-hairy was found to fluctuate at different embryonic stages. Later genes were discovered that regulate the timing of this clock oscillation and are members of the notch, wnt or FGF signalling pathways

22
Q

Somites are the earliest evidence of segmentation in vertebrates, T or F

A

T

23
Q

Give an example of a human disease that proves a role of notch signalling in mesodermal segmentation

A

Jarcho Lewin syndrome causes spondylocostal dysplasia due to problems with the segmentation of the axial skeleton. This occurs due to a mutation in the delta 3 ligand that alters notch signalling and problems with somite segmentation

24
Q

List the structures that the paraxial mesoderm give rise to

A

Axial skeleton, heart, somites, cartilage and tendons

25
Q

How many components is the lateral mesoderm divided into and what do these divisions give rise to

A

The lateral mesoderm divides into 3 components, two of which give rise to the circulatory system and the other which contributes to extraembryonic structures and limb bones

26
Q

How does the determination front dictate somitigenesis

A

When the cells of the paraxial mesoderm encounter oscillations from the molecular clock an abrupt change determines their formation of the next somite pair

27
Q

What are the downstream effects of opposing notch signalling in cells either side of the boundary

A

High notch acitivity in one side and low activity in the cells opposite leads to formation of the somite boundary. The boundary itself forms from physical formation of cleft within the mesenchymal tissue. Downstream extensive changes in cell morphology and adhesion leads to creation of this cleft and is mediated by ephs and ephrins

28
Q

What structure separates the left and right somites

A

Spinal cord

29
Q

The formation of somites occurs in a sequential manner on both sides with the size of somites being preserved throughout, T or F

A

T

30
Q

Alike the axial mesoderm, the posterior paraxial mesoderm is also subdivided, what are these subdivisions

A

Unsegmented posterior paraxial mesoderm and the segmented posterior paraxial mesoderm that give rise to somites

31
Q

How many somites are present in humans and how does this relate to their segmentation

A

The human embryo has between 38 and 44 somites, this correlates to the 33 vertebrae which we are born with

32
Q

Explain how the determination front is positioned

A

The determination front is determined at the interface of two opposing gradients. Retinoid acid which is high anteriorly and fibroblast growth factor 8 which is high posteriorly. When these gradients are equal the determination front forms.

33
Q

What structures do the intermediate mesoderm give rise to

A

Kidneys and gonads

34
Q

Where is retinoic acid produced to dictate determination front positioning

A

Somites

35
Q

The more posterior a cell ingresses into the primitive streak, the more posterior the mesoderm it will give rise to will be, T or F

A

F – more posterior ingress, the more lateral the mesoderm

36
Q

Put these different mesodermal tissue types in order from most anterior to most posterior. Intermediate mesoderm, axial mesoderm, lateral mesoderm, paraxial mesoderm

A

Axial mesoderm, paraxial mesoderm, intermediate mesoderm, lateral mesoderm

37
Q

What aspect of the paraxial mesoderm determines somite boundary formation

A

Position of the somite minus II (S-II)

38
Q

What experimental method lead to the identification of the origin of mesodermal tissue development

A

Lineage tracing