Fly Development Flashcards
What differentiates gastrulation in protostomes from gastrulation in deuterostomes?
Protostomes: gastrulation begins at mouth
Deuterostomes: gastrulation begins at anus
Which has a notochord, protostomes or deuterostomes?
Only deuterostomes, and only those that are chordates.
Describe ametabolous development.
No metamorphosis. Immature stages similar to adults, just smaller and lacking genitalia.
Describe hemimetabolous development.
Incomplete metamorphosis involving nymph stage + molting before mature adult.
Describe Holometabolous development. What is an example of an insect which does this?
dissimilar larval and adult stages. Requires complete metamorphosis + molting (ex: drosophila melanogaster).
How long does fruit fly development take, from egg to mature adult?
~10 days.
Outline the 8 stages of fruit fly development.
- Egg
- Cellular blastoderm
- Embryo
- 1st Instar
- 2nd Instar
- 3rd Instar
- Pupa
- Adult
At what 3 stages during fruit fly development is axis formation and patterning being established?
- Egg
- Cellular blastoderm
- Embryo
What is an “imaginal disc”?
Parts of a fruit fly larva/pupa that develop into the mature body parts.
How did Wigglesworth determine what triggered metamorphosis? What were his findings?
By transplanting the head of a nearly mature stinkbug onto the body of a juvenile. Observed that the head had some factor which caused maturation
What hormone did Wigglesworth identify in the kissing-bug head that was required for maturation? What did this produce?
Prothoracicotropic hormone which produced 20-hydroxyecdysone.
How can Wigglesworth’s experiments with kissing-bugs be applied to other research?
Can use insect-specific promoter to control the timing of gene expression in mouse brain (inducible expression system).
Why could Drosophila melanogaster be a good model organism?
Small, easy to breed/store/maintain. Short generation time. Simple, well-studied genome. High conservation between fly and human molecular pathways.
Why might Drosophila melanogaster not be a good model organism?
Tiny, so tissue manipulation is hard. Not transparent. Body plan less relevant to humans.
What is a “syncytial blastoderm”? What common lab organism demonstrates this?
During development, all nuclei are contained within a single large cytoplasm. Seen in drosophila.
Following the nuclear division stage of drosophila development, how do the nuclei get arranged (stage 9/10)?
They all move to the periphery of the embryo.
What characterizes the “cellular blastoderm” stage of drosophila development (stage 13)?
A large inner yolk surrounded by a single-cell layer.
During drosophila development, at what stage does asynchronous division begin to occur?
Stage 14 (immediately after the cellular blastoderm forms).
Where on the early drosophila embryo does gastrulation begin? What are these cells destined to become?
On the ventral side in the “ventral furrow”. These ~1000 cells will become mesoderm.
After the ventral furrow forms in the drosophila embryo, the pole cells invaginate at the anterior and posterior. What will these invaginations form?
The gut.
What do cytoplasm removal and replacement experiments in drosophila embryos suggest?
That AP axis asymmetry already exists in the fertilized egg.
In drosophila development, when are the AP and DV axes specified? By what genes?
Prior to fertilization by maternal effect genes.
Does the egg transcribe maternal effect genes? Where?
No, they are actually transcribed in the supporting nurse cells.
Which are the 3 “tethered” maternal effect genes? Which is the “free” maternal effect gene?
Tethered: 1. Bicoid 2. Oskar 3. Gurken Free: 1. Nanos
How is RNA moved into the drosophila oocyte from the nurse cells?
Along microtubules, carried by dynein.
Where is bicoid mRNA localized in the drosophila germarium? What about nanos mRNA?
Bicoid mRNA is in the middle, while nanos mRNA is at the posterior end.
In drosophila, what 2 things establish the AP axis?
- Bicoid (anterior)
2. Nanos (posterior)
In drosophila, what causes the DV axis to be established?
The nucleus is dorsally localized. Maternal effect gene gurken also stabilizes a dorsal fate.
In drosophila, what causes the deadenylation of nanos? What prevents this? How?
Smaug and CCR4-NOT deadenylate. Oskar prevents this by stabilizing the 3’ UTR (+ poly A tail).
How can you characterize the function of bicoid and nanos in drosophila, using one word?
Morphogen.
Describe the general pathway of gurken signalling in drosophila.
Gurken(only dorsal) –> Torpedo –| Pipe synthesis(in ventral) –> cascade of proteolytic cleavages.
How does dorsal protein act to help induce the DV axis?
Acts as a morphogen. Induces ventral cell fate when translocated to nucleus.
How does a fushi tarazu drosophila mutant differ from the wild-type?
It has half the number of segments (7).
What are 3 classes of zygotic mutations that affect drosophila segmentation (in development order)?
- GAP genes
- Pair rule genes
- Segment polarity genes
What kinds of mutant drosophila morphologies arise from GAP gene mutations?
Organisms which lack large regions of the body.
What are some examples of drosophila GAP genes?
Any of:
- Kruppel
- Knirps
- Hunchback
- Giant
- Tailless
- Huckebein
- Buttonhead
- Empty spiracles
- Orthodenticle
What are 5 examples of ways in which the transcriptional activity of a single TF can be regulated?
- Post-transcriptional modification
- Post-translational modification
- Interaction with other proteins
- Epigenetic modification of target site
- Strength of binding site
Why, among the other drosophila GAP genes, is hunchback so important?
Initiates expression of the other GAP genes.
In drosophila, how does the hunchback mRNA interact with nanos?
Nanos inhibits hunchback protein production, ensuring that hunchback is only expressed in the anterior of the oocyte.
What is the general mechanism which establishes the TF morphogen gradient for GAP genes in drosophila oocytes?
Differential binding site affinity.
In addition to its role as a TF, what other function does drosophila bicoid protein have?
Also acts as an RNA binding protein.
In drosophila, how does hunchback interact with knirps? What about giant and kruppel? What does this cause?
Hunchback and knirps mutually repress each other, same as giant and kruppel. This begins establishing TF boundaries leading to segmentation.
In drosophila, how is expression of the primary pair rule genes dictated? How many bands will this create?
By the overlapping expression of the GAP genes. Gives 7 bands.
In drosophila, what do secondary pair-rule genes do in general? What is an example of this kind of gene?
They increase the number of distinct morphogen bands in the oocyte from 7 to 14. (ex: fushi tarazu)
Do the drosophila pair-rule gene band patterns overlap?
No, they express non-overlapping bands.
What is an example of a segment polarity gene in drosophila? What do these genes do in general?
Engrailed is a segment polarity gene. They form a gradient to determine which side of a segment is anterior and which is posterior.
What is an example of a primary pair-rule gene in drosophila?
Even-skipped.
Outline the 4 steps of the hedgehog signalling pathway.
- Hedgehog binds/inhibits patched protein
- Patched inhibits smoothened
- Smoothened stimulates Ci protein
- Ci protein either stimulates or represses transcription
In the hedgehog signalling pathway, how does cubitus interuptus (Ci) function if it is cleaved? What if it is not cleaved?
Cleaved: represses hedgehog-responsive genes
Whole: activates hedgehog-responsive genes
In drosophila, how is segment polarity defined specifically?
By genes involved in wingless and hedgehog signalling. Hedgehog stimulates wingless and vise-versa.
What transcription factor is expressed on the anterior side of a drosophila segment? What about the posterior side? How are these expressed?
Anterior: hedgehog
Posterior: wingless
Both are establish morphogen gradients.
In drosophila, what determines the positional identity of body segments? What are the 2 major examples of this?
Homeotic selector gene complexes:
- Antennapedia complex
- Bithorax complex
How does the chromosomal order of homeotic selector genes affect drosophila segment identity?
They influence segment development in the order that they are arranged on the chromosomes. They also repress adjacent gene expression.
What do all the drosophila homeotic selector genes share? How is specificity achieved?
A ~60 AA domain which binds to DNA. Specificity comes from the identity of the 9th AA of α-helix #3.
Describe, in general, drosophila leg growth?
Begin with the imaginal disc, and then picture a cinnamon bun being popped out from the middle.
