Fig. 2. Dietary serine enhances FUdR toxicity but not FUdR-to-FUMP conversion.

Throughout this figure: % hatchlings and LC–MS data were analyzed as described in Fig. 1. Statistical significance was assessed via two-tailed unpaired nonparametric t-test for % hatchlings quantification. LC–MS data were analyzed using one-tailed ratio t-test after ROUT outlier treatment. Data are presented as mean values ± SEM, scale bars = 200 µm, n = # independent biological replicates. Source data are provided as a Source Data file. a Screen setup to search for dietary amino acids (AAs) that enhance FUdR toxicity (cause developmental delay). Worms cultured on E. coli HB101 were treated with 12.5 µg/mL FUdR from the L1 stage ± serial dilutions of AAs (0.05–6 mg/mL). AA-only wells were included to detect AA toxicity. Wells were scored after 60 h at 20 °C, when FUdR-only wells show 100% embryonic lethality but no developmental delay. b Heat map representing degree of developmental delay caused by supplemented AAs. Color and symbol key depicted below. Thymidine is a positive control. c Representative images of targeted validation of developmental delay induced by co-administration of 12.5 µg/mL FUdR with 1.5 mg/mL of serine. Images taken after 60 h of incubation at 20 °C. n > 3. d Representative images of progeny viability of C. elegans cultured on HB101 and treated from L1 with mock, subLth-FUdR (1 μg/mL FUdR, which is sublethal because using HB101), 1.5 mg/mL serine, or subLth-FUdR plus serine. n > 10. e Quantification of % hatchlings relative to mock of treatments represented in d. n = 5. f Quantification of % hatchlings in worms exposed to lawns of E. coli pretreated “in tube” with ±subLth-FUdR ±serine. In this setup, worms are not directly exposed to FUdR or serine (Supplementary Fig. 4). n = 3. g LC–MS measurement of intracellular 5-FU relative to internal standard (IS) [1,3-¹⁵N2]Uracil in E. coli treated with subLth-FUdR plus serine compared to subLth-FUdR. n = 4. h LC–MS measurement of intracellular FUMP relative to internal standard (IS) [¹³C9,¹⁵N2]UMP in E. coli treated with subLth-FUdR plus serine compared to subLth-FUdR. n = 4. i Representative images of progeny viability of C. elegans cultured on WT (BW25113) or upp;udk KO E. coli lawns treated from L1 with subLth-FUdR (0.25 μg/mL) ± serine. j Quantification of % hatchlings relative to mock of treatments represented in i and the triple E. coli KO upp;udp;udk. n = 3.