Worm Breeder's Gazette 17(1): 46 (October 1, 2001)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Arrhythmicity of the defecation oscillator in lin-42 mutants

Fred Kippert, Mark L. Blaxter

Institute of Cell, Animal and Population Biology, University of Edinburgh, f.kippert@ed.ac.uk

Part of the heterochronic gene lin-42 (1) shows significant similarity to the Drosophila and vertebrate per circadian clock genes. This encompasses the PAS domain (and adjacent PAC domain) found in many clock genes. One of most interesting aspect of the Drosophila per gene is that mutations affect not only the circadian clock but also two other timing processes, temperature-dependent development and a temperature-compensated ultradian clock modulating the male's courtship song (2).

The defecation oscillator of C. elegans L4 larvae is characterised by a remarkable regularity of the period under a given set of conditions while being highly dependent on temperature and nutritional status. Because of its regularity, it is possible to distinguish between effects on period length and cycle variability in mutants. For example, the period in the clk-1 (qm30) mutant is 50% longer whereas the regularity remains close to that of the wild type. Since defecation is a permanently recurring process, it may be difficult to decide when a mutant is 'arrhythmic'. However, we found that in a presumptive lin-42 null mutant (mg152 [a gift of Ann Rougvie]), regularity was completely lost, with an increase in the mean coefficient of variation for the 15 cycles of a single L4 from 3.5% to 23.1%. It seems justified to call this arrhythmicity. When we looked at a second lin-42 allele (n1089 [from the CGC]), we found it to be temperature-sensitive for the oscillator phenotype. At 20ºC, period regularity of larvae was close to wild type. At 25ºC, the strain became similar to the null mutant. The LIN-42 protein thus appears to play a crucial role in conferring to the defecation oscillator its remarkable regularity.

We have recently described a circadian clock in C. elegans (3) and our preliminary investigation indicates that the two alleles behave similarly with respect to the circadian clock, i.e. arrhythmicity in the null mutant and the ts strain at 25ºC but close to normal circadian rhythms in the ts strain at 20ºC. Like the Drosophila per gene, lin-42 thus appears to be involved in at least 3 different timing processes on different time scales and with different characteristics. Its role in the ultradian and circadian rhythms is now under closer investigation.

(1) Jeon M et al (1999) Similarity of the C. elegans developmental timing protein LIN-42 to circadian  rhythm proteins.  Science 286:1141-1146. (2) Kyriacou CP & Hall JC (1994) Genetic and molecular analysis of Drosophila behavior. Adv. Genet. 31:139-186. (3) Kippert F, Saunders DS & Blaxter ML (2001) C. elegans has a circadian clock. Curr. Biol., in press

    
Strain
(30 L4 each)
   

Temperature

(°C)


Period

(sec)

Shortest
mean
(sec)

Longest
mean
(sec)

Shortest
cycle
(sec)

Longest
cycle
(sec)

N2 

20°C

49.4

46.2

53.5

44

58

N2 

25°C

38.2

35.9

42.2

34

44

clk-1 (qm30)

20°C

77.5

70.8

86.5

66

92

lin-42 (n1089) 

20°C

52.8

46.7

58.4

43

65

lin-42 (n1089) 

25°C

50.5

36.0

62.5

24

91

lin-42 (mg152) 

20°C

53.3

43.1

71.4

22

118

 

 

 

 

 

 

 

 
Strain
(30 L4 each)      

Temperature

(°C)

Standard
deviation

 

Coefficient
of variation
(%)

Mean of
CVs
(%)

Lowest
CV
(%)

Highest
CV
(%)
   

N2

20°C

2.2

4.5

3.5

1.7

5.5

N2

25°C

1.9

5.0

3.7

2.8

5.6

clk-1 (qm30)

20°C

5.3

6.8

4.6

2.3

6.1

lin-42 (n1089) 

20°C

3.6

6.8

4.2

2.3

7.6

lin-42 (n1089) 

25°C

6.7

13.3

14.1

7.2

27.8

lin-42 (mg152) 

20°C

7.6

14.2

23.1

10.6

46.2