MONITTR enables real-time imaging of the transcriptional dynamics of the endogenous hsp-16.41 upon heat shock in adult epidermal cells. (A) Representative images to show the response of hsp-16.41p::GFP under different heat shock durations. 1-day-old worms were imaged immediately after heat shock at 30°C with various durations. All images are maximum intensity projections from z-stacks. Scale bars: 200 μm. (B) Measurements of mean fluorescence intensity of each animal under different conditions as shown in A. n represents the number of animals. (C) Confocal images showing hsp-16.41 nascent mRNA levels and HSP-16.41::mCherry protein level upon heat shock at 30°C. Animals were initially cultured at 20°C to 1 day adult and imaged immediately after heat shock. z-stacks were captured and proper single-focal-plane images were shown. Scale bars: 20 μm. Arrowheads: nascent RNAs. (D) Quantification of the percentage of nuclei with RNA spots as shown in C. n = 25 animals were analyzed for each group. (E) Quantification of transcriptional output of single alleles under different conditions as shown in C. n represents the number of alleles. N/A: not available as no RNA spot was observed for these time points. (F) Quantification of the number of active alleles in each nucleus as shown in C. n represents the number of nuclei. (G) Quantification of total nascent transcripts of hsp-16.41 produced per epidermal nucleus under different conditions as shown in C. n represents the number of nuclei. (H) Quantification of HSP-16.41::mCherry expression level by measuring the fluorescence intensity for each condition in C. n represents the number of animals. (I) Line chart illustrating the percentage of nucleus with RNA spots of hsp-16.41. Animals were initially cultured at 15°C (dotted line) or 20°C (solid line) to 1-day-old adult, and then subjected to heat shock at 30°C (blue), 32°C (pink), and 34°C (green) for different durations. n ≥ 17 animals for each group were quantified. (J) Line chart showing the percentage of nucleus with RNA spots of hsp-16.41. Wild type or hsf-1 mutant animals were initially cultured at 15°C or 20°C to 1-day-old- adult, and then heat-shocked at various temperatures for 30 min n ≥ 12 animals for each group were quantified. All data are presented as mean ± SEM. ns: not significant. ****P < 0.0001 (one-way ANOVA with the Tukey correction).