Lecture 20 Morphogens and Patterning

Question 1

Morphogenesis is

Answer 1

One of three fundamental aspects of developmental biology

others are control of cell growth and differentiation

Question 2

Morphogens are

Answer 2

Signalling molecules

Shape the form of a tissue

Question 3

Morphogenesis is the

Answer 3

Patterning of multicellular organisms during development

Question 4

Establishing of a tissue pattern requires

Answer 4

1. Local production of a morphogen
2. Degradation of the morphogen
3. Diffusion of the morphogen

Question 5

Variation of production, degradation and diffusion of a single morphogen can lead to

Answer 5

The establishment of a variety of patterns

Question 6

Two or more morphogens and their interactions can lead to the formation of

Answer 6

Very complex patterns

Question 7

Wolpert defines cell fate as a function of the

Answer 7

Morphogen concentration
(French flag model)

Question 8

The French flag model

Answer 8

1. Source secretes a morphogen
2. Morphogen forms a concentration gradient in neighbouring tissue
3. Cell fate is determined by the different concentrations

Question 9

Morphogens guide pattern formation:

Answer 9

Level of morphogen concentration determines whether gene A B or C is activated
This leads to the generation of morphologically different cell types
They are arranged in a way that depends on the localisation of the source

Question 10

Butterflies as an example of Turing’s mathematical model of morphogenesis

Answer 10

Number of activated Wnt receptors determine the genes transcriptionally activated
High threshold: white
Moderate threshold: black
Low threshold: yellow

Question 11

Shh in the spinal cord primordium

Answer 11

Shh is a morphogen pattern in the spinal cord
Shh is released from the floorplate and notochord (FP, NC)
Shh binds to Ptch
Shh-Ptch allows Smo signalling to activate Gli
Different interneuronal and motoneuronal population are induced depending on the Shh activation threshold

Question 12

The number of activated Shh receptors determine the

Answer 12

Transcription factors, which lead to the induction of 5 different neuronal populations

Question 13

In addition to Shh what is also secreted from the spinal roof plate?

Answer 13

BMPs/Wnt

Question 14

BMPs/Wnt countergradients induce

Answer 14

Different neuronal identities in the spinal cord
Interneurons V0-V3 and D1-D6
Motorneurons

Question 15

Critical evaluation of the diffusion based model

Answer 15

French flag and turing models based on assumptions:

1. Production and degradation of a morphogen must be linked
2. Transport allows patterning of entire tissue
3. Tissue integrity and size are maintained

Question 16

The inhibitor model (gierer-meinhardt, 1972)

Answer 16

1. Morphogenetic fields control development of tissues
2. Production of morphogen coupled to production of inhibitor
3. Morphogenesis dependent upon speed

Question 17

Gierer-meinhardt suggested the development of tissues is dependent upon

Answer 17

Diffusion speed
Inducer/activator = slow diffusion, short range
Inhibitor = fast diffusion, long range

Question 18

Hydra is studied for

Answer 18

Regeneration
Polar and continuously renews itself (stem cells)
Mechanical dissociation leads to regeneration of entire new body column

Question 19

Induction and maintenance of a morphogenetic field translates into

Answer 19

Tissue polarity and positional information

Question 20

Hydra supports the

Answer 20

French flag model

Morphogen/inhibitor ratio at time of cutting determines whether a head or foot will grow

Question 21

A graft of head tissue onto a hydra foot

Answer 21

Induces a second head

But only induces a head in areas of hydra where inhibitor is low (so can’t induce a second head close to the first)

Question 22

HydraWnt3 induces

Answer 22

The head
Homolog of vertebrate Wnt3a gene
Expressed at the mouth
Paracrine signalling molecule

Question 23

HydraDkk is the

Answer 23

Inhibitor of HyWnt3
Represses head formation
Long range inhibitor

Question 24

Morphogens determine

Answer 24

The pattern in developing tissue

Question 25

Morphogens are substances which are

Answer 25

Locally produced and secreted to influence the development of neighbouring tissue (Alan Turing)

Question 26

Morphogens form a

Answer 26

Gradient

Question 27

Cells determine their fate depending on

Answer 27

Morphogen concentration (Wolpert)

Question 28

A stable gradient is achieved through

Answer 28

Activator - inhibitor interaction (Gierer and Meinhardt)

Question 29

Interplay of activator and inhibitor allows

Answer 29

Pattern formation of tissue development

Question 30

Morphogenetic gradients are required in

Answer 30

Development and regeneration (hydra)