Dry Lab 2

Question 1

What is a heterochrony?

Answer 1

• Difference in timing or duration of developmental processing compared to other organisms or ancestors
• genetically controlled difference in the the timing of a developmental process

Question 2

What is a heterochronic gene pathway?

Answer 2

• cascade of regulatory genes that are temporally controlled to specify specific timing of developmental events

Question 3

What occurs when there are mutations in heterochronic genes?

Answer 3

• cause temporal transformations in cell fates in which stage-specific events are omitted or reiterated

Question 4

What is let-7?

Answer 4

• a heterochronic switch gene

Question 5

What does loss of let-7 cause?

Answer 5

• causes reiteration of larval cell fates during the adult stage

Question 6

What does an increase in let-7 cause?

Answer 6

• causes precocious expression of adult fates during larval stages

Question 7

Let-7 temporally regulated 21-nucleotide RNA is complimentary to?

Answer 7

• lin-14, lin-28, lin-41, lin-42, and daf-12

- this indicates that expression of these genes may regulate let-7

Question 8

What is the hypothesis of this study?

Answer 8

• The sequential stage-specific expression of the lin-4 and let-7 regulatory RNAs triggers transitions in the complement of heterochronic regulatory proteins to coordinate developmental timing

Question 9

What does lin-4 do?

Answer 9

• regulatory RNA that negatively regulates lin-14 and lin-28

Question 10

What is n2853?

Answer 10

• a mutation that caused strong retarded heterochronic defects in a lin14(+) and a temperature-sensitive adult lethal phenotype with vulval bursting

Question 11

What is mg279?

Answer 11

• a suppressor mutation that caused weak retarded phenotype

Question 12

What normally happens in C. elegans development?

Answer 12

• hypodermal blast cells divide at each larval stage

- at adult stage they exit the cell cycle and fuse with neighbouring hypodermal seam cells and generate cuticular alae

Question 13

What happens during development in C. elegans with n2853 mutation?

Answer 13

• at L4 to adult moult, they reiterated larval patterns of cell division and failed to generate alae
• then at L5 to adult they returned to normal
• the opposite happened for over-expressing let-7

Question 14

What does let-7 upregulate?

Answer 14

• LIN-29 expression in the hypodermis during L4 stage which specifies adult cell fates

Question 15

Which mutations affect late larval stage development?

Answer 15

• let-7, lin-41 and lin-42
• this means that lin-41 and lin-42 may be negatively regulated by let-7 since the mutations are suppressed by each other

Question 16

Which mutations affect early larval stage development?

Answer 16

• lin-14 and lin-28

- this means that lin-14 and lin-28 may directly affect let-7

Question 17

What other experiments were done?

Answer 17

• transgene complementation, RNA expression analysis and mutant allele sequencing
• evolutionary conservation
• both strongly support that let-7 functions as an RNA molecule