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Developmental Biology > L7 - Drosophila Body Plan > Flashcards

L7 - Drosophila Body Plan Flashcards

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1
Q

What is the Drosophila adult segmentation pattern?

A

Pattern of pigmentation on the abdomen and thorax

Each thoracic segment has a pair of legs associated with it

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2
Q

What is the Drosophila embryo segmentation pattern?

A

Denticle belts in embryo

  • Small hairs that emerge from the otherwise naked cuticle
  • Help larva crawl too food
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3
Q

What is the history of segmentation?

A

Segmentation is an ancient and conserved way of building bodies
Go from an unpatterned egg to a patterned egg in 24 hours

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4
Q

What were the results of the 1980 mutagenesis screen carried out by Nusslein-Volhard and Wischaus?

A

Total lines established – 27,000
Lethal mutations – 18,000
Mutations causing embryonic lethality - 4,000
Mutations causing embryonic phenotypes – 600
Complementation groups – 139

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5
Q

Complementation analysis -If AxA = mutant phenotype

If BxB = mutant phenotype

A

AxB if in same gene = mutant phenotype

Fail to complement

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6
Q

Complementation analysis -If BxC = no phenotype

If AxC = no phenotype

A

Complement - if different genes then
B mutant is over a wildtype on the opposite chromosome
C mutant is over a wildtype on the opposite chromosome

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7
Q

What were the results of the complementation analysis?

A

A and B are mutations of same gene

C is different from A and B

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8
Q

What is saturation?

A

Hitting the genome often enough to ensure we are not finding any new mutations

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9
Q

What were the 3 different genes discovered in the mutagenesis experiments?

A

Didn’t find consistent defects – range of phenotypes
Gap genes
Pair rule gene
Segment polarity genes

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10
Q

What are gap genes?

A

E.g. knirps

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11
Q

What are pair rule genes?

A

E.g. paired

Missing the paired segments

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12
Q

What are segment polarity genes?

A

E.g. gooseberry

Lose the naked cuticle in between the hairs

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13
Q

What are maternal genes?

A

Bicoid – anterior

Nanos – posterior

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14
Q

What is the order of the hierarchy of genes that progressively define the egg?

A

Maternal genes define gap genes
Gap genes define pair rule genes
Segment polarity genes control the fine details

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15
Q

What is Bicoid?

A

A DNA binding transcriptional activator

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16
Q

What are the two bicoid binding sites?

A

High affinity binding sites – activated at lower concentrations of bicoid
Low affinity binding sites – activated at high concentrations of bicoid

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17
Q

How does Bicoid enter the embryo?

A

Maternally loaded into developing oocyte

18
Q

What are the characteristics of the bicoid mutant?

A

Lose head structures

Lose thoracic structures

19
Q

What was the first experiment used to identify bicoid mutant?

A

Transplantation of cytoplasm from anterior end into bicoid mutant
- Partial rescue

20
Q

What was the second experiment used to identify bicoid mutant?

A

Took donor cytoplasm and transplanted into middle of bicoid mutant

  • Head like structures in the middle
  • Mirror image thoracic segments
21
Q

What is the expression pattern of pair rule genes in egg with 1 gene copy of bicoid?

A

7 stripes

Equal gaps at posterior and anterior end

22
Q

What is the expression pattern of pair rule genes in egg with 0 gene copies of bicoid?

A

5 stripes

Fairly equal spacing

23
Q

What is the expression pattern of pair rule genes in egg with 4 gene copies of bicoid?

A

7 stripes

Large gap at anterior end

24
Q

How do gap genes show a readout of bicoid gradient? - e.g. Kruppel

A

Bicoid above threshold – Kruppel not on
Bicoid below threshold – Kruppel not on
Bicoid at standard – Kruppel on
You get a stripe effect of gap genes

25
Q

Pair rule genes - transcriptional repressors example

A

Anterior and posterior ends
E.g. Kruppel and giant
Switch off gene expression of target gene

26
Q

Pair rule genes - transcriptional activators example

A

In the middle
E.g. bicoid and hunchback
Switch on gene expression of target gene

27
Q

Overview of pair rule gene control

A

Expression of pair rule genes is controlled stripe by stripe
Dependent on the interaction of positively and negatively acting transcriptional regulators
Many of which are gap genes

28
Q

What are segment polarity genes?

A

Parasegments and segments are half a segment out of place

Parasegments are where the gene expression barriers are

29
Q

Where are Hh and Wg expressed?

A

Hh maintains Wg expression

Wg is expressed in a cell which directly neighbours a cell expressing Hh

30
Q

What is the role of Wg?

A

Forms a morphogen gradient which is asymmetric
- Further anterior than posterior
Wg suppresses denticle development

31
Q

What are selector genes?

A

Hox genes

32
Q

Where are selector genes expressed?

A

Expression of hox genes along A/P body axis occurs in the same order as the genes are within the genome

33
Q

What controls the expression of selector genes?

A

A combination of gap and pair-rule genes

34
Q

What does the homeobox contain?

A

DNA binding transcription factors

35
Q

What is an example of a long germ band insect?

A

Drosophila

  • All 14 segments are defined at once
  • Quick - embryogenesis complete in just 24 hours
  • Complicated - maternal, gap and pair rule genes interact for every segment
36
Q

How do short and intermediate germ band insects develop?

A

Start with head and thoracic segments
- Via an ancestral version of the system Drosophila uses
Abdominal segments added sequentially
- Posterior disc (proctodeum) bud off segments as it gets smaller
Moderate complexity
Not too slow

37
Q

Segment addition in Strigamia maritima

A

Adjacent stripes of Delta and Hes4 set up feedback loop necessary for oscillation

38
Q

Segmentation clock - feedback loops

A

Notch activation causes down regulation of Notch ligand
Time lag in response causes oscillation between strong and weak signalling levels
Propagation of signal between cells causes wave of activation

39
Q

How do Strigamia get their segmentation?

A

Use segmentation clock

40
Q

How do Tribloium get their segmentation?

A

Use segmentation clock and a few gap genes

41
Q

How do Drosophila get their segmentation?

A

Segmentation all occurs at once using many gap genes

42
Q

Segmentation in vertebrates

A

The majority of known candidate pacemaker genes lie in the Notch pathway

Developmental Biology (16 decks)

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