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Advanced Developmental Biology > Drosophila > Flashcards

Drosophila Flashcards

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1
Q

What are the benefits of using drosophila in an experiment?

A
  • Accessible embryology (lay eggs that develop outside body)
  • V.cheap
  • Fast reproducing
  • no ethical concerns
    -not a vertebrate, kept as live stock
  • Main pathways conserved
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2
Q

What is the drosophila life cycle?

A
  • Drosophila life cycle is 10 days at 25 degrees
  • Live for 60-70 days, after 40 days they don’t lay eggs
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3
Q

How did studying drosophila come about?

A

1910- Morgan studied a drosophila fly with white eys that flew into his lab
1913- First genetic map where genes arranged in linear order
191416- Chromosomes must contain genes
1927- Muller shows X-rays cause mutations and chromosomal rearrangements

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4
Q

Why was the study of drosophila ignored until the 1980s?

A
  • After WW2 the study of drosophila went out
  • IN1980s a genetic screen was undertaken to see genes involved in the development and patterning of the larval cuticle
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5
Q

What did they find after studying the pattern of the larval cuticle?

A
  • Significant number of mutations could effect it
  • Mutations named based on their pheontype e.g. white eye flies named ‘white’ mutation
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6
Q

What technological and methodological advances were made in the 80s,90s and 00s?

A
  • Transgenics
  • Enhancer trap for promoter trapping
  • Gal4/US which is a transcriptional activator in yeast which can be put in drosophila to drive gene expression (can cause homologous recombination, misexpression etc.)
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7
Q

When was the drosophila genome published and has it changed?

A

24th March 2000
Hasnt changed much, just a few extra genes

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8
Q

What information can you take away from lining up drosophila genus genomes and comparing the introns and exons encoding for tyrosine phosphatases?

A
  • A lot of protein coding regions stay the same due to the evolutionary pressure to do so
  • Introns drift and change due to no evolutionary pressure
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9
Q

What are the steps in drosophila courtship?

A
  1. Orientation
  2. Tapping
  3. Wing vibration
  4. licking
  5. Attempted copulation
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10
Q

How do we know that drosophila courtship behaviour is genetically encoded?

A
  • Behaviour is completely reproducible even with virgin females
  • All the steps of the process are the same even if the flies are raised separately
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11
Q

Explain spermatogenesis in drosophila

A
  • Group of germ line stem cells at the tip of the testes in drosophila
  • Adjacent to the ‘hub’ which secreted Unpaired
  • Unpaired activates the Jak/Stat pathway which is important in maintaining a pool of stem cells through self renewal and ensuring differentiation into sperm
  • Cells divide, and cells further away differentiate into sperm
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12
Q

How do male drosophila ensure their genes are passed on to offspring?

A
  • Aim is to prevent female from giving birth to offspring that are not the males due to another male having stronger sperm
  • Sex peptide on the male sperm which is transferred to the female during sex
  • Peptide enters female and binds to receptor in the brain, blocking receptors that would allow it to respond to courtship behaviours from other males
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13
Q

How has evolution allowed the sperm to be bigger than the drosophila itself?

A
  • Female produces more inhibitors of sex peptide through evo
  • Male produces more sex peptides through evo and longer sperm length
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14
Q

Explain Oogenesis in drosophila

A
  • Similar stem cell structure to testes
  • Germline cells divide asymmetrically to produce a cytoblast
  • Cytoblast undergoes 4 rounds of mitotic division but the cells dont completely separate (endo-reduplication)
  • Within this ONE cell becomes the oocyte and the other 15 are nurse cells
  • Nurse cells support oocyte with nutrients, RNA, and organelles through intercellular connections called ring canals
  • Nurse cells undergo ‘Cytoplasmic dumping’ in final stages to make the egg bigger
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15
Q

How is microtubule transport relevant in Oocyte genesis?

A

Microtubule transport ensures correct subcellular localisation of maternal factors (e.g. bicoid at the anterior)

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16
Q

Explain early development of drosophila through nuceli divisions

A
  • Nuclei goes through 14 divisions
  • By the 8th round of the division the nuclei migrate to the outside of the egg, the ones that stay in the middle become the egg yolk
  • The vast majority end up on the outside
  • The nuclei at different places are exposed to diff. Conc. of bicoid.
17
Q

Why are the larvae spiracles on its rear?

A

The head end of the larvae eat and the end has the breathing bit so when it burrows into food it can still breathe

18
Q

How is drosophila segmented?

A
  • 3 thoracic segments
  • 8 abdominal segments
19
Q

How does the larvae egg appear and how long does it take to make?

A

AS A SYNCITIAL BLASTODERM
- appears uniform, a ‘big bag of proteins, RNA etc’
- nuclei that are dividing, lining up around the outside
- No segmentation at this stage
- 2 hours

20
Q

When do the first signs of segmentation start to appear?

A

Between the syncytial blastoderm stage and gastrulation stage
Grooves and indentations form

21
Q

How were the genes involved in controlling segmentation found?

A
  • Saturation mutagenesis= “saturation” refers to the idea of introducing mutations at a level where every possible mutation at each position within the targeted region is represented.
22
Q

What did saturation mutagenesis show?

A
  • 580 mutations derived from 139 genes
  • Basically found every mutation at least 4 times
23
Q

How did they know the 580 mutations were caused by 139 genes in saturation mutagenesis?

A
  • Process called complementation
24
Q

What is complementation?

A

two individuals with different recessive mutations in the same gene produce offspring with a wild-type phenotype
- mutations are located in different copies of the gene (alleles) and can complement each other’s defects, restoring the function of the gene.

25
Q

What are the groups that the scientists grouped the segmentation mutations in to?

A

Knirp gene = gaps in developmental structure, you get a1 and a8 but nothing in between

Paired genes = every second number is wrong (even and odd paired)

Gooseberry = lose half of each segment , segment polarity genes

26
Q

What is the significance of maternal genes?

A

Provides important morphogens such as Bicoid
- If mother is mutant in Bicoid then embryo doesn’t have it and loses its anterior region

27
Q

What is Bicoid?

A

DNA binding transcriptional activator
- Maternally loaded into the developing oocyte, can bind to DNA as nuclei are not in cells, they are just in the ‘cell bag’

28
Q

How can we study the importance and function of Bicoid?

A
  • Put it at ectopic locations e.g. take some of the anterior region with Bicoid ad put it in the middle of the embryo and the head structures in the middle with thoracic segments on either side
  • KO studies
29
Q

What happens to the segmentation structure when there is more Bicoid than the wild-type?

A

the conc. of Bicoid travels further and segmentation is pushed more posterior

30
Q

What is the molecular basis of Bicoid?

A
  • Binds to DNA binding sites within the genome and even weak binding sites are enough to bind bicoid if there’s enough of it
  • Morphogen concept, both strong and weak conc. needed for differentiation
31
Q

Explain the characteristics of Gap genes

A

Streams Maternal genes –> Gap genes –> Paired genes
- Expression of pair rule genes is controlled stripe by stripe , dependent on the interaction of positively and negatively transcriptional regulators
- In each stripe there is lots of different TFs and it is very complex

32
Q

What do Segment Polarity genes do?

A

Defining the difference between the naked cuticle (the white) and denticle belts (black)

33
Q

What is the phenotype regarding segmentation when Hh is removed?

A
  • It is only the denticle hairy cuticle which is why hh is the way it is because it looks spikey
34
Q

How are Wg and Shh connected regarding segmentation?

A
  • The genes are dependent on each other
  • Hh maintains Wg expression which suppresses denticle development
35
Q

What happens when you remove Wg from the segmentation processes?

A
  • Cells that receive high concentrations of Wg differentiate into smooth, naked cuticle cells,
  • Cells that receive low concentrations of Wg adopt the “cell type 5” fate and produce denticles (hairs) on the denticle belts.
  • If Wg is absent, all cells default to the “cell type 5” fate, leading to the production of denticles by all cells.
    Therefore, removing Wg results in all cells becoming hairy, and the naked cuticle regions are lost.
36
Q

What is the role of Hox genes in segmentation?

A

Each segment is different so hox genes provide this differential who am i info
- Hox mutation can lead to antennapedia (antenna turn into legs)

37
Q

What does long/short germ band mean?

A

Long germ band = all segments are defined at once (drosophila)
Short germ band = Segments defined separately at different times (beetes, centipeded)

38
Q

Explain how segmentation occurs in insects such as centipeded and beetles

A
  1. Start with head and thoracic segments and THEN abdominal segments
    - Segments added over time, not all at once
    - Segments bud off as it gets smaller
    - Delta and notch involved in segment addition
39
Q

Explain the segmentation clock

A

Circuitry using delta +notch + repressor called her/hes

  • Causes gene activity where action of the ligand switches on pathway transcription, her is then made into a protein which comes and represses everything
  • As soon as this happens it decays and goes away and it happens again
  • Pattern of activity/lack of causes segments to form

Advanced Developmental Biology (13 decks)

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