Lecture 13 - patterning the embryo

Question 1

What creates dorsal/ventral polarity?

Answer 1

a gradient of nuclear localisation of the Dorsal protein:
- High on Ventral side
- Low on Dorsal side

Question 2

What do the promoters of important dorsoventral genes require?

Answer 2

different level of Dorsal protein need to be activated

Question 3

Describe the affinity for Dorsal binding sites in the promoters of the snail gene

Answer 3

• Low affinity Dorsal binding sites
• only expressed when a high level of nuclear Dorsal is present
• make MESODERM

Question 4

What has a high affinity Dorsal binding sites in its promoter?

Answer 4

Rhomboid - in addition it is repressed by Snail
- expressed laterally on both sites of mesoderm
- make NERUOECTODERM

Question 5

What is a promoter?

Answer 5

a control region in the DNA that controls expression of a gene - it “promotes” transcription

Question 6

What gene is expressed when there is low levels of nuclear Dorsal?

Answer 6

Rhomboid

Question 7

What gene is expressed when there is highlevels of nuclear Dorsal?

Answer 7

Snail expressed, interferes with with Rhomboid expression

Question 8

In the dorsal ectoderm, what does Decapentapleguc (dpp) do?

Answer 8

sets up a second signalling centre on the dorsal side of the embryo

Question 9

What is the name of the second signal?

Answer 9

Bone morphogenetic protein (BMP)

Question 10

In what is BMP (bone morphogenetic protein) conserved?

Answer 10

vertebrates

Question 11

What genes does the antero/posterior gradients of Bicoid and Nanos lead to activation of?

Answer 11

a number of gene encoding transcription factors which are known as GAP genes

Question 12

What is the primary target of Bicoid & Nanos?

Answer 12

Hunchback gene, which together with Bicoid, sets up the expression of other GAP genes

Question 13

What do GAP genes create?

Answer 13

a ‘combinatory code’, that defines different regions in the embryo

Question 14

What GAP genes are responsible for striped pair-rule expression?

Answer 14

Even skipped (eve)
Fishing tarazu (ftz)

Question 15

What drives the striped expression of the prefigured segments of the embryo?

Answer 15

each stripe is driven by a specific gap gene combination

Question 16

What are the Pair Rule gene expression stripped known as?

Answer 16

Para segments

Question 17

What is the effect of the segmentation genes?

Answer 17

go from 7 stripes in a pair-rule gene to 14, as high levels of Ftz or Eve switch on Engrailed

Question 18

What does high levels of Ftz & Eve lead to?

Answer 18

switches on Engrailed

Question 19

What directly drives the pattern of the cuticle, e.g. the denticles that form the stripy pattern on the larvae?

Answer 19

The “14-striped” expression of Engrailed and some other genes

Question 20

What forms the POSTERIOR boundary of the segment?

Answer 20

the future visible segments are formed with the Engrailed positive cells

Question 21

What has occurred by the time the Posterior boundary of the segment has formed?

Answer 21

the embryo has cellularised - meaning diffusion will not work as no longer a Syncytium.

Question 22

What has to occur due to transcription factors not being to diffuse anymore, as they are individual cells?

Answer 22

cell-to-cell signalling is required, in order to coordinate the pattern formation within one segment

Question 23

In addition to the transcriptional regulator (En), what 2 highly important signalling proteins are expressed in adjacent cells?

Answer 23

• Wingless (Wg)
• Hedgehog (Hh)

Question 24

What are Wingless (Wg) & Hedgehog (Hh) under the influence of?

Answer 24

at first pair-rule genes
- then as a result of a feedback loop, expression of Wg is maintained by Hh, and En+Hh by Wg

Question 25

What can Wingless & Hedgehog do?

Answer 25

Protein signals that act across cell boundaries - they change expression
- they influence transcription in Drosophila
- also important in other multicellular organisms (including human)

Question 26

What can inappropriate activation of Wnt & Hedgehog (Hh)?

Answer 26

basis of many types of cancer:
Wnt - colon cancer
Hh - basal cell carcinoma

Question 27

What specifies the initial 14 segments’ identity?

Answer 27

The homeotic selector genes (HOX genes)
- discovered through mutations is Drosophila
- homeotic mutations, one structure is replaced with another

Question 28

What is the single complex that HOX genes are found in most organisms?

Answer 28

The HOX complex (in Drosophila broken down into 2 pieces

Question 29

What does the HOX genes order in the genome reflect?

Answer 29

spatial and timing of expression

Question 30

What is first 3’ or 5’?

Answer 30

3’ first and most anterior, 5’ last and most posterior (DNA usually shown 5’ on the left)

Question 31

What do HOX genes do?

Answer 31

these genes that give different segments, different fates and modify along the A/P axis, in most organisms.

Question 32

Why is the Drosophila an exception to the HOX complex?

Answer 32

they have 2 HOX complexes

Question 33

How many HOX complexes do most mammals have?

Answer 33

4 HOX complexes

Question 34

What is the bithorax complex responsible for?

Answer 34

diversification of the posterior segments

Question 35

What is the bithorax complex made up of?

Answer 35

Ubx, abd-A & Abd-B

Question 36

What cab incorrect expression of genes lead to?

Answer 36

incorrect development of vertebrate