Worm Breeder's Gazette 16(5): 24 (February 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.
Department of Biology, University College London, NW1 2HE, UK
Genetic variation among different laboratory lines of N2 affects fertility and lifespan. A previous study found that median lifespans of different lines ranged from 12.0±0.8 to 17.0±0.6 days (20oC)(1). To attempt to establish which of these best resembles the original N2 isolate, the lifespans of F1 hybrids between N2 variants, and those of seven C. elegans wild isolates, were examined (1). The results suggested that the N2 male stock currently distributed by the CGC (here designated CGCM), is most similar to the original N2 isolate. This strain is the longest-lived N2 variant.
An alternative approach to establish which variant best resembles wild type is to examine an N2 stock frozen at an early date. One such stock is N2 (ancestral), which is only 6 generations removed from a stock frozen in the Brenner lab in 1968. We compared the fertility and lifespan of N2 (ancestral) with 3 N2 variant lines: CGCM, CGCH (slightly short-lived) and JW (very short-lived). Our expectation was that it would most closely resemble CGCM.
Table 1: Longevity and fertility of N2 (ancestral) and other N2 lines
Strain | Median lifespan (days) | Maximum lifespan (days) | N* | Mean brood size | N* |
N2 CGCM | 20.5 ± 1.0 | 24.4 ± 0.7 | 5 (127) | 292 ±11 | 1 (18) |
N2 CGCH | 18.3 ± 0.8 | 21.9 ± 0.7 | 7 (136) | 270 ± 9 | 1 (18) |
N2 JW | 13.4 ± 1.0 | 23.1 ± 1.0 | 8 (194) | 213 ± 9 | 1 (15) |
N2 (ancestral) | 13.6 ± 0.7 | 21.2 ± 1.0 | 10 (243) | 260 ± 7 | 1 (19) |
N2 CGCM/N2 (ancestral) | 19.7 ± 0.3 | 25.7 ± 0.7 | 3 (53) | ND | - |
N2 JW/N2 (ancestral) | 15.0 ± 3.0 | 22.0 ± 0.0 | 2 (46) | ND | - |
± Standard error. *Number of trials (number of animals scored).
To our surprise, the lifespan of N2 (ancestral) was significantly shorter than CGCM and CGCH (median 20oC lifespan, p < 0.001 in each case)(Student's t test) (Table 1), yet indistinguishable from JW (p > 0.1). Furthermore, its fertility was significantly lower than that of CGCM (p < 0.02) but not CGCH (p > 0.1), but higher than that of JW (p < 0.001).
Does this mean that the longer-lived line CGCM is a mutant variant after all? We favour an alternative explanation: that as early as 1968 there existed a number of genetic variants of N2 in the Brenner lab (Cambridge), and N2 (ancestral) is a short-lived one. In 1975, when Don Riddle moved from Cambridge to Missouri, he took with him CGCH, CGCM and JW (obtained from John White), and froze them upon arrival. These three strains have different lifespans (1). Thus, by 1975 a number of variants certainly did exist.
One possibility is that N2 (ancestral) and JW are related. To test this, the lifespans of F1 hybrid hermaphrodites issuing from crosses between CGCM, JW and N2 (ancestral) were examined. The lifespan of CGCM/N2 (ancestral) was indistinguishable from that of CGCM, and significantly longer than that of N2 (ancestral) (p < 0.001). A reduction in median lifespan was seen in JW/N2 (ancestral) hybrids relative to CGCM/N2 (ancestral) hybrids, but due to the large standard error this did not reach significance. However, the maximum lifespan of JW/N2 (ancestral) was significantly reduced (p < 0.02). These preliminary results support the view that N2 (ancestral) and JW are related, short-lived mutant variants, and that the mutations concerned are recessive.
N2 (ancestral) thus appears to be another short-lived N2 variant, related to JW. We therefore advise that N2 (ancestral) not be used as wild type; instead, we recommend CGCM.
(1) D. Gems & D.L. Riddle (2000) Defining wild-type life span in Caenorhabditis elegans. J. Gerontol. 55A: B215-B219.