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Developmental, Stem Cell & Regenerative biology > Lecture 10 - Invertebrate models - sea urchin & C. elegans > Flashcards

Lecture 10 - Invertebrate models - sea urchin & C. elegans Flashcards

1
Q

Why is a sea urchin a good genetic model?

A
  • large number of embryos
  • experimental manipulation
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2
Q

Why are genetic models good?

A
  • bred easily in a lab
  • genes within the genome can be altered to study their effect on development
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3
Q

What are sea urchins?

A

echinoderms

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4
Q

What are echinoderms?

A

deuterostomes

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5
Q

In protostomes, where does the blastopore form from?

A

the mouth

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6
Q

In deuterostomes, where does the blastopore form from?

A

the anus

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7
Q

Why are sea urchin’s embryos useful?

A

transparent embryo, which is large & easily accessible for manipulation

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8
Q

How long does it take for a blastula to develop in a sea urchin?

A

4 hours after cell division - meaning they have a strict order & orientation

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9
Q

When is the primitive gut formed in a sea urchin?

A

during gastrulation movements

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10
Q

How does the extensions on the plateaus larva form?

A

the larva has internal calcareous skeleton that is responsible for the extensions on the plateaus larva

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11
Q

What were the 2 types of development discussed surrounding sea urchins?

A

mosaic model and regulative development

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12
Q

What is the mosaic model (Weissman)?

A

the nucleus of the egg contain determinants that specify different fates to different cells by specific segregation to these cells.

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13
Q

What is the regulative development model?

A

cells are communicating and differences can be generated DE NOVO by cell-to-cell communication

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14
Q

What divisions do sea urchins have in their early stages?

A
  • 2 divisions along the animal-vegetal axis
  • 1 perpendicular to these divisions, separating the animal from the vegetal half
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15
Q

In what way are the first 2 cleavages in the development of a sea urchin made?

A

First 2 cleavages are perpendicular

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16
Q

In what way is the 3rd cleavage cut?

A

Perpendicular - and separates the 4 animal cells from 4 vegetal cells

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17
Q

Where does gastrulation occur?

A

at the vegetal pole

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18
Q

How was the sea urchin’s development suggested to be regulative?

A

if determinants were present, as suggested in the mosaic model, then you wouldn’t get a normal embryo, from a single blastomere

  • separated 2 blastomeres at the 2 cell stages
  • didn’t get 2 half embryos, but rather got 2 smaller complete embryos
19
Q

How was the sea urchin development suggested to be mosaic?

A
  • splitting the embryo at the 4 cell stage indicated that development was regulative.
  • splitting the 8 cell embryo in a ventral & dorsal half showed that there is at least this axis a degree of mosaicism is present.
  • normal embryo not found - instead there was an animalised and vegetalised incomplete larve - meaning there appears to be some form of mosaicism.
  • now known that the localised determinists for this are in the cytoplasm rather than the nucleus.
20
Q

Why do we use genetic model organisms?

A

by looking at what ‘goes wrong’, you can infer the normal role of that gene on development

21
Q

What are the ideal characteristics for ease of genetic analysis?

A
  • small organism (because they need to keep large numbers)
  • large batches of embryos
  • short generation time
  • easy to breed
  • easy scoring of phenotypes of +/-
  • sequenced genome
22
Q

What are the main anatomical parts of C elegans?

A

mainly consists of a gut & reproductive organs. Also has muscles that allow it to move & neurons and sensory cells that can convey information to the animal about the environment is navigating

23
Q

Why are C. elegans good gene model organisms?

A
  • C. elegans develop rapidly
  • hatches from egg within 24 hours at normal temperatures
  • develops as a hermaphrodite (first male, then female) - use its own sperm to fertilise eggs
  • occasionally male only individuals occur - these can mate with females.
  • thus prevents continuous inbreeding, which would be detrimental for their fitness
24
Q

Describe the cleavages of a C. Elegans

A

1st cell division create: AB & P1 cell
- P1 cell - P2 & EMS
- AB cell - ABa & ABp

ABa (anterior)
ABp (posterior)

25
Q

What does the AB cell do?

A

make hypodermis & neurones

26
Q

What does the EMS cell do?

A

make mesoderm & endoderm

27
Q

What do P2 & P3 do?

A

make C & D cells, which somatic tissues

28
Q

What does P4 do?

A

form the germline - it also receives cytoplasmic granules named P-granules

29
Q

What causes the first division to be asymmetrical?

A

Par proteins (par from partitioning) - par genes also found in Drosophila

30
Q

Is cell fate deterministic?

A

lineage is invariant, but cell fate isn’t necessarily absolutely determined
- this can be seen by changing the cell position.
- e.g. ABa & ABp swapped and lineage produced will be according to their NEW position - this would be impossible if they would contain determinants.
- EMS cell is formed by what originally .would’ve been the P2 cell, so there is no fixed determinant for this either

31
Q

What has C. elegans development study contributed to biomedical science?

A
  • apoptosis = cell death
  • RNA interference –> switching off genes
32
Q

How many cells are in C. elegans & what do they do?

A

C. elegans is made up of 1090 cells but precisely 131 cells are programmed to die - apoptosis

33
Q

When does apoptosis occur?

A

this happens during development but is also essential in a variety of biological processes in adult

34
Q

Why is apoptosis essential for proper development?

A
  • formation of reproductive organs: male/female
  • skin between digits
  • immune system maturation
35
Q

Why is apoptosis essential for homeostasis?

A
  • mitosis/apoptosis to maintain constant number of cells
  • removal of damaged cells (DNA damage, viral infections)
36
Q

What diseases can improper regulation of apoptosis can to?

A
  • autoimmune disease
  • cancer
37
Q

What are the 4 factors involved in programmed cell death?

A
  • BID
  • Bcl2
  • APAF1
  • Caspase
38
Q

What is RNA interference (RNAi)?

A

a powerful mechanism to control gene activity:
- double-stranded RNA triggers a biochemical process that degrades identical mRNAs, thus it blocks gene activity AFTER transcription has happened.

39
Q

How was RNA interference (RNAi) found?

A

discovered while studying muscle development in C. elegans

40
Q

How does RNA interference (RNAi) work?

A
  • Double-stranded RNA is taken up by cells & recognised and cut into smaller pieces by an enzyme named Dicer creating short interfering (si) RNAs
  • they are loaded into a protein complex named RISC, which uses the siRNA sequence to find mRNAs that are complementary to the siRNA and causes their degradation
41
Q

Why is it important that short RNAs are used in RNA interference?

A

such oligo can be synthesised chemically

42
Q

How has RNA interference been useful?

A

this has allowed the creation of siRNA libraries that can target every gene in the human and of course also C. elegans genomes.

this is a great tool to find genes that are involved in the process of choice

43
Q

What is the application of RNA interference?

A

3 drugs on the market that are directly based on RNAi.
- aim to downregulate genetic diseases caused by overactivity of a gene

44
Q

What are the 3 drugs based on RNAi?

A
  • hereditary transthyretin-mediated amyloidosis
  • acute hepatic porphyria
  • hyperoxaluria type 1

Developmental, Stem Cell & Regenerative biology (15 decks)

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