Early Drosophila Development Flashcards
How many Nobel Prizes have been awarded for groundbreaking drosophila work?
6
How many scientists have been awarded Nobel Prizes for their ground-breaking work in Drosophila?
10
List the scientists that have won Nobel Prizes for their work on Drosophila.
10
Axel
Hall
Hoffmann
Lewis
Morgan
Muller
Nusslein-Volhard
Roshbash
Weischaus
Young
What establishes the adult body plan of Drosophila?
Patterning in the early embryo.
Outline the life cycle of Drosophila.
7
Embryo
1st instar larva
2nd instar larva
3rd instar larva
Prepupa
Pupa
Adult
How long is the fruit fly life cycle?
10 days
Which sex is bigger in Drosophila?
Female
What segment of the drosophila embryo becomes the prothorax?
T1
What segment of the drosophila embryo becomes the mesothorax?
T2
What segment of the drosophila embryo becomes the metathorax?
T3
What segments of the drosophila embryo becomes the abdomen?
A1-A8
Describe what is meant by the syncitial embryo in Drosophila.
In the fruit fly, nuclei initially divide without cellularization, forming the syncitial embryo.
When does cellularization begin in Drosophila and what does this lead to?
13 nuclear division
Forms the blastomeres
Where are pole cells segregated in Drosophila?
Posterior end of embryo
What do the pole cells become?
Germ cells
What does the syncytial embryo allow for and how?
Allows for direct A-P patterning by RNA/DNA binding proteins.
Describe how syncytial specification is accomplished in Drosophila.
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.
What is a morphogen?
Diffusible biochemical molecule that can determine the fate of a cell by its concentration.
What type of molecules are typically morphogens? Give examples.
Usually paracrine signalling molecules
Ex. TGF-Beta, Wnt, FGF
How do morphogen concentrations determine cell fate?
Cells can sense the [morphogen] in their environment and activate/repress genes in response.
What type of molecules act as morphogens in the early Drosophila embryo and why?
They are DNA/RNA binding proteins because the embryo is syncytial!
What type of morphogen gradient is formed by the Bicoid protein?
Anterior to posterior gradient
What happens to bicoid mutants?
Anterior structures are replaced by posterior structures.
What does the bicoid gene encode for in Drosophila?
The morphogen responsible for head structures.
What happens once the initial Bicoid and Nanos gradients are formed?
Additional morphogen gradients of transcription factors form in response.
What morphogenic gradients appear in response to those of Bicoid and Nanos? Where?
Hunchback in anterior
Caudal in posterior
List the three types of segment gap mutations in Drosophila.
Gap mutants
Pair-rule mutants
Segment polarity mutants
What is a gap mutant?
Lack large regions of the body over several contiguous segments.
What is a pair-rule mutant?
Lack portions of every other segment.
What is a segment polarity mutant?
Show defects in every segment.
What are gap genes?
Zygotic genes that are activated or repressed by the maternal effect genes.
In how many broad domains are gap genes expressed?
1 to 3
What does the expression pattern of gap genes correlate with?
Correlates with the region that is missing in the mutant embryo.
List the major gap genes and what the encode.
4
hunchback
giant
Kruppel
knirps
All encode transcription factors.
What can combined expression of gap genes do?
Can give each nucleus in the A-P axis a specific identity.
What converts gradients into compartments?
Repression between overlapping gap genes
Explain the process of gradient conversion.
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.
What are pair-rule genes?
Transcription factors that establish segmentation in the embryo.
How are pair-rule genes expressed?
Expressed in seven alternating stripes that divide the embryo into 15 units
How many pair rule genes are known? Give examples.
8
Hairy
even-skipped
runt
What is meant by pair-rule gene enhancers being modular?
Each stripe’s expression is controlled by a discrete region of DNA
What binds pair-rule gene enhancers?
Gap proteins
What determines whether a pair-rule gene is expressed?
Concentrations of Gap TFs
Describe the model for the formation of the second stripe from the even-skipped gene.
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.
What are segment polarity genes?
Encode members of the Hedgehog and Wingless signalling pathways.
How many stripes are segment polarity genes expressed in?
14
How do stripes of segment polarity genes form?
Through cell-to-cell signalling
How are the pole cells generated?
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.
What are maternal effect genes?
Genes that are active in the mother to make products for the early development of offspring.
When does zygotic gene transcription begin and when is it enhanced?
Begins around cycle 11 and greatly enhanced at cycle 14.
What happened when bicoid mRNA was added the the anterior end of a bicoip mutant embryo?
Normal development of the A-P axis
What happened when Bicoid mRNA was added to the middle of a bicoid mutant embryo?
Thorax structures on each side and middle region became the head.
What happened when bicoid mRNA was added to the posterior end of a wild-type embryo?
Two heads emerged at either end.
What portion of the embryo does hunchback pattern? caudal?
Hunchback = anterior
Caudal = posterior
How are hunchback and caudal able to mediate their localized patterning activities if they are ubiquitously expressed?
Their mRNAs are suppressed by the diffusion gradients of Nanos and Bicoid proteins.
Describe how Nanos and Bicoid proteins suppress hunchback and caudal DNA.
Bicoid proteins prevent translation of caudal in the anterior region.
Nanos protein prevents translation of hunchback in the posterior region.
What happens if caudal is made in the anterior region?
The head and thorax do not form properly.
What does caudal do?
Activates the genes responsible for the invagination of the hindgut. (i.e., critical in specifying posterior domains of the embryo).
What are the two main purposes of Bicoid?
Inhibits translation of caudal
Activates transcription of hunchback
What does hunchback do?
Activates transcription of anterior genes.
What does Nanos do?
Inhibits translation of hunchback.
Which maternal effect genes are RNA binding proteins?
2
Bicoid and Nanos
Which maternal effect genes are DNA binding proteins?
Bicoid, Hunchback, Caudal
List the four maternal protein gradients in the early Drosophila embryo.
A-P of Bicoid protein
A-P of Hunchback protein
P-A of Nanos protein
P-A of Caudal protein
What happens once the maternal protein gradients are established?
Activation of the zygotic genes
What do high concentrations of Bicoid produce?
Anterior head structures.
What do slightly less concentrations of Bicoid produce?
mouthparts
What do moderate concentrations of Bicoid produce?
Thorax
What is the abdomen characterised by in terms of Bicoid?
Lack of bicoid is associated with the abdomen.
What do Hunchback and Bicoid act synergystically to do?
Upregulate the transcription of head-specific genes.
Where is Bicoid-dependent transcription of hunchback seen?
IN the anterior half of the embryo
How were segmentation genes originally defined?
By zygotic mutations that disrupted the body plan.
