The daf-2 reference allele e1370 is used widely to assess the function of reduced Insulin/IGF-1 receptor signalling in development, metabolism, stress-defence, and aging. The daf-2(e1370) mutants develop into dauers at higher temperatures (25°C) but not at lower temperatures (15°C; (Gems et al. 1998)). Based on this observation, the assumption is that daf-2(e1370) mutants have lower insulin/IGF-1 signalling (IIS) at 25°C and presumably normal or wild-type IIS at 15°C. However, two pieces of evidence argue against this assumption.

  1. At lower temperature (15°C), the daf-2(e1370) mutants are long-lived to the same extent as at higher temperatures (Figure 1). In addition, at lower temperature (15°C) daf-2(e1370) mutants are also stress resistant (Gems et al. 1998).
  2. The transcription factors DAF-16 and SKN-1 that are phosphorylated directly by IIS, and thereby prohibited from entering the nucleus, are nuclear in daf-2(e1370) mutants at 15°C to the same extent as at higher temperatures (Lin et al. 2001 PMID:11381260; Tullet et al. 2008; Ewald et al. 2015).

These findings suggest that IIS is reduced comparably at 15°C and 25°C and argues against the assumption that e1370 is necessarily a temperature-sensitive allele in the classic sense where temperature affects protein folding and activity. Interestingly, about 10% wild-type worms form dauers when grown at 27°C under otherwise standard culturing conditions (ample food and not overcrowded; (Ailion & Thomas 2000 PMID:11063684)). Furthermore, it has been observed that null mutants in other abnormal-DAuer-Formation (daf) genes than daf-2, only show the dauer phenotype at higher temperatures, suggesting that the dauer phenotype itself is temperature sensitive. This observation was published over 30 years ago (Golden & Riddle 1984) and is discussed in (Wood 1988).

We are motivated to write to the WBG community by the assumption that during adulthood daf-2(e1370) mutants improperly reactive phenotypes that are reminiscent of dauer larvae (reduced mobility, reduced brood-size, short body size; (Gems et al. 1998)). Recently, we have shown that daf-2(e1370) mutants form dauers independent of SKN-1/NRF1,2,3 and that SKN-1 is only required for the daf-2(e1370)-longevity phenotype when these dauer-related phenotypes are not activated during adulthood (Ewald et al. 2015). Furthermore, comparing expression profiles of daf-2(e1370) mutants with dauer larvae revealed that they share only a common overlap under conditions that reactivate these dauer phenotypes (e.g., daf-2(e1370) at higher but not at lower temperatures; (Ruzanov et al. 2007 PMID:17543485; McElwee et al. 2004 PMID:15308663; Ewald et al. 2015)). Finally, treating wild-type worms with dauer pheromone was sufficient to increase lifespan (Kawano et al. 2005 PMID:16377915; Ewald et al. 2015). This suggests that there might be a dauer program activated in daf-2(e1370) mutants at higher temperatures that masks other underlying mechanisms of reduced IIS on lifespan. Further research is required, however, these findings suggest that reduced IIS can extend lifespan via dauer-dependent and dauer-independent mechanisms and this changes the interpretation of experiments performed with daf-2(e1370) mutants under conditions that promote these dauer-associated phenotypes.