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Development > Zebrafish > Flashcards

Zebrafish Flashcards

1
Q

Why is zebrafish a good model organism?

A
  1. Development is rapid
  2. It is transparent
  3. Good for genetic modification
  4. Easy to manipulate
  5. Many genes have conserved functions
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2
Q

What is the purpose of the yolk cell?

A

The larvae rely on it for nutrients until they are able to feed.

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3
Q

How many hours after fertilisation does the embryo begin to move?

A

16-18 hours.

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4
Q

What kind of cleavage does zebrafish undergo?

A

Discoidal meroblastic cleavage.

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5
Q

What is discoidal cleavage?

A

Only the cytoplasm of the blastodisc forms the embryo proper.

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6
Q

What does meroblastic mean?

A

The cleavage furrows do not completely divide the egg.

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7
Q

In what part of the egg does cleavage occur?

A

Only in the blastodisc.

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8
Q

Define the blastodisc.

A

A thin region of yolk-free cytoplasm at the animal pole.

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9
Q

What is the majority of the egg made from at the start of blastulation?

A

Yolk.

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10
Q

The egg becomes pear-shaped at the start of blastulation. Why is this? Give 3 steps.

A
  1. Calcium is released at fertilisation
  2. Calcium causes the actin cytoskeleton to contract
  3. This squeezes all non-yolk cytoplasm into the animal cap
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11
Q

Divisions are rapid. How long does each division take?

A

Approx. 15 mins.

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12
Q

How many divisions are synchronous?

A

The first 12.

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13
Q

What do the first 12 synchronous divisions form?

A

A mound of cells at the animal pole of the yolk cell - this will become the blastoderm.

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14
Q

What is the mid-blastula transition?

A

A switch from the transcription of maternal to zygotic genes.

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15
Q

When does the mid-blastula transition occur?

A

Approx. 10 divisions in.

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16
Q

There are 3 distinct cell populations at the mid-blastula transition. What are they?

A
  1. The YSL
  2. The EVL
  3. The deep cells
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17
Q

What is the YSL?

A

The yolk syncytial layer, formed from vegetal cells fused the to underlying yolk cell. This complex contains syncytial nuclei.

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18
Q

What is the EVL?

A

The enveloping layer, this becomes the periderm (protective layer that is shed).

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19
Q

What are the deep cells?

A

They give rise to the embryo proper.

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20
Q

Where are the deep cells found?

A

Between the YSL (inside) and EVL (outside).

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21
Q

Are the fates of the 3 distinct cell lineages determined at blastulation?

A

No.

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22
Q

When do cell fates become specified?

A

At the start of gastrulation.

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23
Q

What is epiboly?

A

Cellular movements that allow dramatic physical restructuring.

24
Q

When does epiboly occur?

A

At the start of gastrulation.

25
Q

What does epiboly occur?

A

The autonomous expansion of the YSL over the yolk cell. The YSL drags the deep cells and EVL with it.

26
Q

What happens to the yolk at the end of gastrulation?

A

It becomes completely engulfed by the cells.

27
Q

What happens to the blastoderm at the end of gastrulation?

A

It becomes completely internalised.

28
Q

The YSL and EVL are tightly bound (with the deep cells in the middle). What happens if this connection is severed?

A

During epiboly the YSL expands on its own and the EVL and deep cells stay on top of the yolk.

29
Q

How does the autonomous expansion of the YSL rely on?

A

A network of microtubules composed primarily of tubulin.

30
Q

Involution occurs at 50% epiboly - what does this mean?

A

When 50% of the yolk is covered by the migrating YSL/EVL.

31
Q

What is formed during involution?

A

The germ layers

32
Q

What is the germ ring and what is it made of?

A

A thickening that occurs at the start of involution. It is made of 2 cell types; the epiblast and hypoblast.

33
Q

Where does involution begin?

A

On the future dorsal side of the embryo.

34
Q

What is the embryonic shield?

A

A thickening composed of intercalated epi and hypoblast cells.

35
Q

The embryonic shield can organise a secondary axis in transplant experiments, meaning it is homologous to which structure in amphibians?

A

The dorsal blastopore lip.

36
Q

What is the chordamesoderm and how is it formed?

A

A precursor to the notochord, formed from the convergent extension of the hypoblast.

37
Q

In which direction does convergent extension of the hypoblast occur?

A

Anteriorward.

38
Q

What is the paraxial mesoderm?

A

Cells next to the notochord that give rise to the somites.

39
Q

What does the epiblast do?

A

It convergently extends to form the neural keel along the dorsal midline.

40
Q

What is the neural keel?

A

A structure that eventually develops into the neural tube.

41
Q

Where is the notochord?

A

Extends from the base of the head to the tail on the dorsal side.

42
Q

What is the purpose of labelling cell nuclei?

A

To build fate-maps/trace cell lineages.

43
Q

What is SPIM and what is it used for?

A

Selective Plane Illumination Microscopy, used to illuminate live specimens from the side.

44
Q

Give 3 advantages of SPIM.

A
  1. High resolution
  2. High speed
  3. Non-invasive
45
Q

Random mutagenesis is a forward genetic screen. What does this mean?

A

Random mutations are generated in individuals, these individuals then breed and mutations in the phenotype of the offspring are observed.

46
Q

How are mutations generated in random mutagenesis? Give 3 methods.

A

With radiation, chemicals or by gene insertion.

47
Q

Some phenotypic mutations are easily observed. Give an example.

A

Cyclopia.

48
Q

How does random mutagenesis help us to understand zebrafish development?

A

When offspring are mutants can look at which genes have been disrupted and thus deduce function.

49
Q

How many mutants has forward genetic screening by random mutagenesis found?

A

Approx. 10,000

50
Q

What is the basic principle of genetic mapping?

A

Assesses how close 2 gene markers are by determining the recombination frequency at meiosis.

51
Q

What are the 2 markers in genetic mapping?

A

A mutation and an identifiable genetic marker like an SSLP

52
Q

What is an SSLP?

A

A simple sequence length polymorphism (also called microsatellites).

53
Q

When can homozygosity mapping identify a mutation?

A

In a small, closed population.

54
Q

What is the candidate gene approach?

A

Whereby a list of candidate genes is derived and tested to see whether they cause a mutation.

55
Q

What 5 things must be considered in a candidate gene approach to mutation?

A
  1. Is the gene expressed in the mutant phenotype
  2. Is there in fact linkage to another mutated gene
  3. Is the gene mutated?
  4. Can wild-type RNA rescue the mutant phenotype?

Development (18 decks)

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