C elegans

Question 1

What is the breeding time for c elegans?

Answer 1

3 days

Question 2

What is the brood size for c elegans?

Answer 2

2-300

Question 3

What temperature are c elegans stored at?

Answer 3

-70 degrees Celsius

Question 4

What it the size of the c elegans genome?

Answer 4

100 million base pairs

Question 5

What are the two sexes of c elegans?

Answer 5

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

Question 6

What is the vulva and what is the cellular structure?

Answer 6

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

Question 7

What is the anchor cell?

Answer 7

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

Question 8

What are the two phenotypic classifications of vulva mutants?

Answer 8

Vul; no vulva (recessive, loss of function)

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

Question 9

What is saturation mutagenesis?

Answer 9

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

Question 10

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

Answer 10

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.

Question 11

Which genes are implicated in the vul phenotype?

Answer 11

lin-3 let-23 let-60

Question 12

Which gene is implicated in the muv phenotype?

Answer 12

let-23D =dominant

Question 13

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

Answer 13

lin-3 - let-23 - let-60

Question 14

What are the assumptions of epistasis analysis?

Answer 14

• 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

Question 15

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

Answer 15

double mutants exhibit the phenotype of the more upstream locus.

Question 16

How many cells are generated in C elegan development?

Answer 16

1090

Question 17

How many are surplus?

Answer 17

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

Question 18

Which genes are implicated in programmed cell death?

Answer 18

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)

Question 19

How are transgenic C elegans formed?

Answer 19

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

Question 20

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

Answer 20

• 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.

Question 21

What occurred during the cloning of ced-9?

Answer 21

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.

Question 22

Where is CED-9 located?

Answer 22

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

Question 23

What occurs when cells are about to die.

Answer 23

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.

Question 24

How do B cell lymphomas arise?

Answer 24

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.

Question 25

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

Answer 25

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.