Body Plans Development

Question 1

What is morphogenesis

Answer 1

Process by which an organism or structure develops into a 3D form (like in embryogenesis)

Question 2

Name the 3 axes of an embryo body plan

Answer 2

Antero posterior - head (anterior) to tail (posterior)

Dorso ventral - dorsal (back) to ventral (belly)

Left- right axis - 2 lateral sides of embryo

Question 3

Where is the neural tube located

Answer 3

At the dorsal side (back)

Question 4

What has to occur for body plans to develop

Answer 4

Cell distance into a blastocyst from an embryo

Question 5

What 2 cells present in blastocysts

Answer 5

Trophoblast - cells for structure support

Embryoblast - cells that form embryo

Question 6

What determines type of signalling and how readily it binds to receptors in cell signalling during development

Answer 6

Genes the embryo possesses

Question 7

What are morphogens

Answer 7

Growth factors that control the position of cell types

They repress or induce gene expression depending on concentration

Question 8

Give major examples of morphogens

Answer 8

SHH (hedgehog signal)

Wnt

RA (retanoic acid)

Question 9

How does morphogens from source to sink change to induce different gene expression

Answer 9

Source = most morphogen and then it diffuses in lower conc. the lower conc areas might have different genes expressed

Question 10

Which protein morphogen in flies is famous for activating transcription of ANTERIOR STRUCTURES

Answer 10

Bicoid protein

Question 11

Which morphogen in flies opposes bicoid in antero posterior polarity by suppressing translation closer to ANTERIOR

Answer 11

Nanos

Question 12

Why is diffusion of morphogens easier in flies

Answer 12

Due to it being one egg and not having to go through cellularised tissue

Question 13

How do homeobox genes use morphogens to switch on genes at different areas

Answer 13

Morphogen concentration eg high could allow gene expression at anterior

At low conc it allows gene expression at posterior

Question 14

Name the 4 ways morphogenic signals pass cellular tissues

Answer 14

1- restricted diffusion model

2- planar transcytosis model

3- lipoprotein transfer model

3- cytoneme model

Question 15

Explain the restricted diffusion model of how morphogens can diffuse

Answer 15

They can bind to carbohydrates on the cell surface when secreted and diffuse along the surfaces of cells

Question 16

Explain planar transcytosis

Answer 16

Morphogens pass directly via cytoplasm of cells across

Question 17

Explain lipoprotein morphogen transfer

Answer 17

When secreted lipoproteins can bind and allow movement across cell surface down gradient

Question 18

Explain cytoneme model of morphogen diffusion

Answer 18

Morphogens using cytonemes (cell extensions) to move long distances

Question 19

Name the 2 sources of morphogens in embryo (where they are high in conc) and what they form

Answer 19

1- AVE: anterior visceral endoderm - morphogens used to produce anterior end

2- the NODE - patterns the whole of the embryo including the anterior in sync with AVE

Question 20

How do the node and the anterior visceral endoderm (AVE) have large conc of morphogens

Answer 20

That’s where the cells that release them are located

Question 21

What can disruption of sources such as the Node have on the embryo (give SHH as example)

Answer 21

Can affect body plan of the embryo due to no gene expression in areas

Eg if disruption to shh the embryo can develop with no eyes or tail

Question 22

What side in left right axis formation undergoes cell signalling through morphogens

Answer 22

Left side

Question 23

How is the node important for left right asymmetry

Answer 23

Node releases morphogens such as RA and SHH which are wafted to left side of body to activate gene expression to form eg organ tissues

Question 24

How are morphogens directed in left right axis formation

Answer 24

Cilia on node cells waft to left side to get more gene expression

Question 25

What are PITX homeobox genes for

Answer 25

Development of organs and skeletal muscle

Question 26

Which morphogen on the left side is activated by node morphogen release on left side

Answer 26

Nodal TGF morphogen

Question 27

What does nodal tgf morphogen do when activated by node morphogens on left side

Answer 27

Activate pitX genes which allow for organ development

Question 28

How does dosage of pitX allow for organ asymmetry in the body

Answer 28

Higher conc areas will have different genes meaning different organs formed to low conc areas

Question 29

What in left right axial formation prevents signalling morphogens on right side

Answer 29

SHH sonic hedgehog

Question 30

What would happen if nodal signalling was on the right side

Answer 30

Organs would be reversed

Question 31

What would happen if nodal signalling was on both sides

Answer 31

There would be 2 left sides (left isomerism)

Question 32

What would happen if nodal signalling happened on neither side of body

Answer 32

Right isomerism (2 right sides of the body)

Question 33

How were frogs manipulated to see the effects of left right axis formation and signalling in embryo

Answer 33

Frog was dissected and the part where the node was was taken out and transplanted into another frog It was rotated by 180• and this showed organs reversed in the frog embryo = shows structure and orientation is dependant on nodal signalling

Question 34

Which gene knockout meant that instead of asymmetrical lung lobes, mice had 2 left lobes (left isomerism)

Answer 34

Lefty 1 / SHH gene - important for left side cell signalling (stops signalling on right) as pitX was found on both sides of lungs when it was knocked out = left isomerism

Question 35

Which genes famously are related to antero posterior axial formation

Answer 35

Hox genes / homeobox genes - found laterally across the human body aswell as flies (head to tail)

Question 36

Name the 3 main morphogens which affect homeobox genes in anterior posterior axes

Answer 36

Wnt - specific to anterior gene expression RA(retanoic acid) - mid brain gene expression FGF - caudal / tail region

Question 37

What would happen if hox 6 genes where ribs are were expresssed at the tail for example eg due to disruption on morphogen signalling

Answer 37

Ribs would grow at the tail

Question 38

Which morphogen is in high conc at dorsal region (back)

Answer 38

Wnt

Question 39

Which morphogen is at the ventral region at high conc

Answer 39

SHH

Question 40

What does sHH and wnt polarity in dorsal ventral axial formation cause

Answer 40

Different genes expressed which specify different neurones in the brain By activating different homeobox genes

Question 41

What is the proximal and distal axis in terms of limbs such as the arms

Answer 41

Proximal is shoulder Distal is the digits

Question 42

What is the anterior and posterior axis in the limbs

Answer 42

Anterior is what makes pinky distinct from posterior thumb

Question 43

Apart from proximal and distal and posterior and anterior in limbs, what other 2 axis are there

Answer 43

Front or back of the hand which is distinct Left or right hand axis

Question 44

Which morphogens are important in proximal and distal axis from shoulder to digits

Answer 44

RA and FGF

Question 45

Which place on the limb has the most RA and the least FGF

Answer 45

Most RA = shoulder Least FGF = shoulder (Most FGF in digits)

Question 46

What type of genes do RA and FGF in the limbs affect expression of

Answer 46

Hox genes in the limbs

Question 47

Which centre is important for outgrowth of the limbs

Answer 47

Apical ectodermal ridge (AER)

Question 48

What happens if the apical ectodermal ridge is removed or duplicated

Answer 48

If removed no limb is grown If duplicated it causes limb duplication

Question 49

What doesn’t the apical ectodermal ridge determine

Answer 49

Which limb is grown

Question 50

What is the most important morphogen in limb outgrowth

Answer 50

FGF (highest in the digits)

Question 51

Which morphogen is important in anterior posterior axis of the limbs (pinky to thumb) patterning

Answer 51

SHH

Question 52

Where is shh highest and lowest in the anterior posterior of the limb

Answer 52

Highest in the anterior (pinky) Lowest in the posterior (thumb)

Question 53

Which centre is SHH on at the posterior of the limb

Answer 53

Zone of polarising activity (zpa)

Question 54

How does thalidomide alter the expression of morphogens like FGF and SHH

Answer 54

By disrupting the apical ectodermal ridge And zone of polarising activity (zpa)

Question 55

How else apart form disrupting the AER and ZPA does thalidomide disregulate SHH and FGF signalling

Answer 55

By degradation of the transcription factor called sall4