Early Drosophila Development

Question 1

How many Nobel Prizes have been awarded for groundbreaking drosophila work?

Answer 1

6

Question 2

How many scientists have been awarded Nobel Prizes for their ground-breaking work in Drosophila?

Answer 2

10

Question 3

List the scientists that have won Nobel Prizes for their work on Drosophila.

10

Answer 3

Axel
Hall
Hoffmann
Lewis
Morgan
Muller
Nusslein-Volhard
Roshbash
Weischaus
Young

Question 4

What establishes the adult body plan of Drosophila?

Answer 4

Patterning in the early embryo.

Question 5

Outline the life cycle of Drosophila.

7

Answer 5

Embryo
1st instar larva
2nd instar larva
3rd instar larva
Prepupa
Pupa
Adult

Question 6

How long is the fruit fly life cycle?

Answer 6

10 days

Question 7

Which sex is bigger in Drosophila?

Answer 7

Female

Question 8

What segment of the drosophila embryo becomes the prothorax?

Answer 8

T1

Question 9

What segment of the drosophila embryo becomes the mesothorax?

Answer 9

T2

Question 10

What segment of the drosophila embryo becomes the metathorax?

Answer 10

T3

Question 11

What segments of the drosophila embryo becomes the abdomen?

Answer 11

A1-A8

Question 12

Describe what is meant by the syncitial embryo in Drosophila.

Answer 12

In the fruit fly, nuclei initially divide without cellularization, forming the syncitial embryo.

Question 13

When does cellularization begin in Drosophila and what does this lead to?

Answer 13

13 nuclear division
Forms the blastomeres

Question 14

Where are pole cells segregated in Drosophila?

Answer 14

Posterior end of embryo

Question 15

What do the pole cells become?

Answer 15

Germ cells

Question 16

What does the syncytial embryo allow for and how?

Answer 16

Allows for direct A-P patterning by RNA/DNA binding proteins.

Question 17

Describe how syncytial specification is accomplished in Drosophila.

Answer 17

Localized bicoid and nanos mRNAs are deposited at the anterior and posterior ends of the oocyte by the mother.
Upon fertilization of the egg the mRNAs are translated, which leads to their protein products diffusing away from the poles to form morphogen gradients.
bicoid and nanos mRNAs encode for RNA-binding proteins that regulate the translation of downstream TFs that pattern the embryo.

Question 18

What is a morphogen?

Answer 18

Diffusible biochemical molecule that can determine the fate of a cell by its concentration.

Question 19

What type of molecules are typically morphogens? Give examples.

Answer 19

Usually paracrine signalling molecules
Ex. TGF-Beta, Wnt, FGF

Question 20

How do morphogen concentrations determine cell fate?

Answer 20

Cells can sense the [morphogen] in their environment and activate/repress genes in response.

Question 21

What type of molecules act as morphogens in the early Drosophila embryo and why?

Answer 21

They are DNA/RNA binding proteins because the embryo is syncytial!

Question 22

What type of morphogen gradient is formed by the Bicoid protein?

Answer 22

Anterior to posterior gradient

Question 23

What happens to bicoid mutants?

Answer 23

Anterior structures are replaced by posterior structures.

Question 24

What does the bicoid gene encode for in Drosophila?

Answer 24

The morphogen responsible for head structures.

Question 25

What happens once the initial Bicoid and Nanos gradients are formed?

Answer 25

Additional morphogen gradients of transcription factors form in response.

Question 26

What morphogenic gradients appear in response to those of Bicoid and Nanos? Where?

Answer 26

Hunchback in anterior Caudal in posterior

Question 27

List the three types of segment gap mutations in *Drosophila*.

Answer 27

Gap mutants Pair-rule mutants Segment polarity mutants

Question 28

What is a gap mutant?

Answer 28

Lack large regions of the body over several contiguous segments.

Question 29

What is a pair-rule mutant?

Answer 29

Lack portions of every other segment.

Question 30

What is a segment polarity mutant?

Answer 30

Show defects in every segment.

Question 31

What are gap genes?

Answer 31

Zygotic genes that are activated or repressed by the maternal effect genes.

Question 32

In how many broad domains are gap genes expressed?

Answer 32

1 to 3

Question 33

What does the expression pattern of gap genes correlate with?

Answer 33

Correlates with the region that is missing in the mutant embryo.

Question 34

List the major gap genes and what the encode. | 4

Answer 34

*hunchback* *giant Kruppel knirps* All encode transcription factors.

Question 35

What can combined expression of gap genes do?

Answer 35

Can give each nucleus in the A-P axis a specific identity.

Question 36

What converts gradients into compartments?

Answer 36

Repression between overlapping gap genes

Question 37

Explain the process of gradient conversion.

Answer 37

Bicoid and Caudal activate the Gap genes in a gradient manner Overlap of Gap gene expression is resolved by mutual repression If a cell initially expressed two competing Gap proteins, they will bind to each other's enhancers and repress each other. The Gap gene with the higher expression will win this repressive tug of war and become the only Gap gene expressed.

Question 38

What are pair-rule genes?

Answer 38

Transcription factors that establish segmentation in the embryo.

Question 39

How are pair-rule genes expressed?

Answer 39

Expressed in seven alternating stripes that divide the embryo into 15 units

Question 40

How many pair rule genes are known? Give examples.

Answer 40

8 *Hairy even-skipped runt*

Question 41

What is meant by pair-rule gene enhancers being modular?

Answer 41

Each stripe's expression is controlled by a discrete region of DNA

Question 42

What binds pair-rule gene enhancers?

Answer 42

Gap proteins

Question 43

What determines whether a pair-rule gene is expressed?

Answer 43

Concentrations of Gap TFs

Question 44

Describe the model for the formation of the second stripe from the *even-skipped* gene.

Answer 44

500-bp region that is activated by Bicoid and Hunchback and repressed by Giant and Kruppel Within this region: 5 critical binding sites for B, 1 for H, and 3 each for G and K Nearly every activator is adjacent to a repressor site Thus, region can directly sense concentrations of these proteins and make ON/OFF transcriptional decisions.

Question 45

What are segment polarity genes?

Answer 45

Encode members of the Hedgehog and Wingless signalling pathways.

Question 46

How many stripes are segment polarity genes expressed in?

Answer 46

14

Question 47

How do stripes of segment polarity genes form?

Answer 47

Through cell-to-cell signalling

Question 48

How are the pole cells generated?

Answer 48

DUring the ninth division cycle, ~5 nuclei reach the surface of the posterior pole of the embryo and become enclosed by cell membranes, generating the pole cells.

Question 49

What are maternal effect genes?

Answer 49

Genes that are active in the mother to make products for the early development of offspring.

Question 50

When does zygotic gene transcription begin and when is it enhanced?

Answer 50

Begins around cycle 11 and greatly enhanced at cycle 14.

Question 51

What happened when bicoid mRNA was added the the anterior end of a bicoip mutant embryo?

Answer 51

Normal development of the A-P axis

Question 52

What happened when Bicoid mRNA was added to the middle of a bicoid mutant embryo?

Answer 52

Thorax structures on each side and middle region became the head.

Question 53

What happened when bicoid mRNA was added to the posterior end of a wild-type embryo?

Answer 53

Two heads emerged at either end.

Question 54

What portion of the embryo does *hunchback* pattern? *caudal*?

Answer 54

Hunchback = anterior Caudal = posterior

Question 55

How are hunchback and caudal able to mediate their localized patterning activities if they are ubiquitously expressed?

Answer 55

Their mRNAs are suppressed by the diffusion gradients of Nanos and Bicoid proteins.

Question 56

Describe how Nanos and Bicoid proteins suppress hunchback and caudal DNA.

Answer 56

Bicoid proteins prevent translation of caudal in the anterior region. Nanos protein prevents translation of hunchback in the posterior region.

Question 57

What happens if caudal is made in the anterior region?

Answer 57

The head and thorax do not form properly.

Question 58

What does caudal do?

Answer 58

Activates the genes responsible for the invagination of the hindgut. (i.e., critical in specifying posterior domains of the embryo).

Question 59

What are the two main purposes of Bicoid?

Answer 59

Inhibits translation of caudal Activates transcription of hunchback

Question 60

What does hunchback do?

Answer 60

Activates transcription of anterior genes.

Question 61

What does Nanos do?

Answer 61

Inhibits translation of hunchback.

Question 62

Which maternal effect genes are RNA binding proteins? | 2

Answer 62

Bicoid and Nanos

Question 63

Which maternal effect genes are DNA binding proteins?

Answer 63

Bicoid, Hunchback, Caudal

Question 64

List the four maternal protein gradients in the early Drosophila embryo.

Answer 64

A-P of Bicoid protein A-P of Hunchback protein P-A of Nanos protein P-A of Caudal protein

Question 65

What happens once the maternal protein gradients are established?

Answer 65

Activation of the zygotic genes

Question 66

What do high concentrations of Bicoid produce?

Answer 66

Anterior head structures.

Question 67

What do slightly less concentrations of Bicoid produce?

Answer 67

mouthparts

Question 68

What do moderate concentrations of Bicoid produce?

Answer 68

Thorax

Question 69

What is the abdomen characterised by in terms of Bicoid?

Answer 69

Lack of bicoid is associated with the abdomen.

Question 70

What do Hunchback and Bicoid act synergystically to do?

Answer 70

Upregulate the transcription of head-specific genes.

Question 71

Where is Bicoid-dependent transcription of hunchback seen?

Answer 71

IN the anterior half of the embryo

Question 72

How were segmentation genes originally defined?

Answer 72

By zygotic mutations that disrupted the body plan.