Extended Data Figure 3. Tyramine-deficient animals are resistant to environmental stress.

a, Tyramine and octopamine biosynthesis pathway. Tyramine is synthesized from tyrosine by tyrosine decarboxylase (TDC-1) in the RIM and RIC neurons; octopamine is synthesized from tyramine by tyramine β-hydroxylase (TBH-1) in the RIC neurons¹³While tdc-1 null mutants are deficient in both tyramine and octopamine, tbh-1 null mutants are deficient only in octopamine. b-c, Survival percentages of wild-type, tyramine/octopamine deficient (tdc-1), octopamine deficient (tbh-1) and tyramine receptor (tyra-3) null mutants exposed to oxidation induced by b, Fe²⁺SO₄ (1 h, 15 mM) and c, H₂O₂ (3 h, 5 mM). Bars represent the mean ± SEM. The number of independent experiments (n) is shown in the figure. 60–80 animals per condition per experiment were used. One-way ANOVA followed by Holm-Sidak post-hoc test for multiple comparisons versus wild-type was used. d, Survival to heat (4h at 35°C) of wild-type, tdc-1, tbh-1, tdc-1; zfIs29[Ptbh-1::TDC-1] (tyramine but not octopamine deficient) and the quadruple tyramine-receptor mutant QW833 (lgc-55; ser-2; tyra-2; tyra-3). Bars represent the mean ± SEM. The number of independent experiments (n) is shown in the figure. 60–80 animals were used per condition per experiment. One-way ANOVA followed by Holm-Sidak post-hoc test for multiple comparisons was used. tdc-1 mutants have an improved survival to thermal stress. Octopamine-deficient mutants (tbh-1) were slightly more heat resistant than wild-type animals, albeit not at the level of tyramine/octopamine deficient tdc-1 mutants. Moreover, rescue of tdc-1 expression in only the octopaminergic neurons (tdc-1; Ptbh-1::TDC −1) failed to reduce thermoresistance of tdc-1 mutants. In addition, the quadruple mutants of all tyramine receptors show heat resistance levels similar to that of tdc-1. These results indicate that the lack of tyramine underlies the oxidative and thermal resistant phenotype of tdc-1 mutants. e, Scatter dot plot (line at the mean) showing pharyngeal pumping rates (pumps per minute) of wild-type, tdc-1, tbh-1 and tph-1 null mutants. tph-1 (tryptophan hydroxylase) mutant animals, which lack serotonin, have a reduced pharyngeal pumping and were used as a control. Since tdc-1 mutants have no obvious defects in pharyngeal pumping, dietary restriction is not likely to be the cause of the enhanced stress resistance and increased longevity. n=30 animals per condition. One-way ANOVA followed by Holm-Sidak post-hoc test versus wild type was used.