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Flashcards in C elegans Deck (25)
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1
Q

What is the breeding time for c elegans?

A

3 days

2
Q

What is the brood size for c elegans?

A

2-300

3
Q

What temperature are c elegans stored at?

A

-70 degrees Celsius

4
Q

What it the size of the c elegans genome?

A

100 million base pairs

5
Q

What are the two sexes of c elegans?

A

males and hermaphrodites; hermaphrodites are self fertilising when kept without males.

6
Q

What is the vulva and what is the cellular structure?

A

A structure through which fertilised eggs exit the body; consists of 8 primary cells, 12 secondary cells, 6 tertiary cells. Primary and secondary form vulva opening while tertiary cells secrete immediately surrounding cuticle. All of these cells descend from 6 vulval precursor cells

7
Q

What is the anchor cell?

A

part of the gonad, if ablated vulva does not form; anchro cells produce signal instructing VPCs to develop as vulva instead of normal hypodermis

8
Q

What are the two phenotypic classifications of vulva mutants?

A

Vul; no vulva (recessive, loss of function)

Muv; multiple vulva (gain of function, generally dominant)

9
Q

What is saturation mutagenesis?

A

Further rounds of mutagenesis stopping mutation generation in new genes because all of the genes which can be mutated to the phenotype under investigation have been hit at least once already

10
Q

What is the rule for interpreting the phenotype of double mutants in signalling pathways?

A

When two mutations at different loci in the same pathway have opposite effects on the phenotype, the phenotype of a double mutant will reflect that of the more downstream acting gene.

11
Q

Which genes are implicated in the vul phenotype?

A

lin-3 let-23 let-60

12
Q

Which gene is implicated in the muv phenotype?

A

let-23D =dominant

13
Q

What is the gene order of the genes involved in vulvagenesis?

A

lin-3 - let-23 - let-60

14
Q

What are the assumptions of epistasis analysis?

A
  • genes act linearly to transduce original signal
  • the pathway determines the final state of single end process, cell type or substance
  • That all mutations act as binary switches commiting the pathway to on or off state
15
Q

How does epistasis analysis in biosynthetic pathways differ from signalling pathways?

A

double mutants exhibit the phenotype of the more upstream locus.

16
Q

How many cells are generated in C elegan development?

A

1090

17
Q

How many are surplus?

A

131; only 959 somatic cells exist in adults. Mutations in genes controlling cell death will result in some of these 131 cells surviving.

18
Q

Which genes are implicated in programmed cell death?

A

ced-3 (recessive) and ced-9 (dominant)
Recessive mutations in ced-9 caused excess cell death in lineages not normally affected. (gain of function not haploinsufficieny)

19
Q

How are transgenic C elegans formed?

A

Through injecting the syncitial gonad with transgene DNA at a relatively high concentration. This forms extrachromosomal arrays.

20
Q

What are the technical differences between vertebrates and c elegans in transgenesis?

A
  • In C elegans transgenesis cannot be used for insertional mutagenesis
  • In vertebrates transgene expression is subjected to positional effect; where DNA has integrated. C elegans is not subjected to positional effect
  • In C elegans transgenesis is relatively inefficient and extrachromosomal transgenes are less stabily inherited.
21
Q

What occurred during the cloning of ced-9?

A

The genomic region of ced-9 was cloned, the genomic region was narrowed down from a 60kb region by linkage mapping by seeing which genomic fragments rescued to ced-9 phenotype when injected.
Fragments with rescuing activity contained a bicistronic gene in which the expression of two coding sequences were driven from the same promoter.
cDNAs were cloned separately and used to make transgenes in which each was expressed under the control of an inducible heat shock promoter; only one of the transgenes was able to protect cells from programmed cell death.

22
Q

Where is CED-9 located?

A

Bound to the surface of mitochondria, in cells that are not about to die they form a complex with CED-4 there.

23
Q

What occurs when cells are about to die.

A

pro-death gene egl-1 is activated and EGL-1 binding to CED-9 caused a conformational change that releases CED-4 allowing it to translocate to the perinuclear membranes. CED-4/6 oligomerise in large complexes. Two CED-3 molecules brought together and undergo autocatalytic cleavage to generate the active form of CED-3 which initiates the nuclear degradation and cell engulfment.

24
Q

How do B cell lymphomas arise?

A

Translocations of the coding sequences of oncogene BCL-2 under the control of a B cell specific promoter cause B cell lymphomas. Rate of cell division is normal, but cells dont die. When BCL-2 is expressed from an inducible heat shock promoter it protects them from death.

25
Q

Which gene does BCL-2 have a similar role to?

A

ced-9; two genes show sequence similarity (24%). Functionally equivalent; heat-shock-BCL-2 transgenes have same death protecting effect in C elegans as heat-shock ced-9 transgene.