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. 2020 Dec 9;9:e64007. doi: 10.7554/eLife.64007

Figure 5. Nonsense-mediated decay (NMD) negatively regulates casein kinase I (CKI) levels via UPF1PRD-6, establishing a basis for the upf1prd-6 prd-2 genetic epistasis on circadian period length.

96-well plate luciferase assays were used to measure the circadian period length in triplicate wells per three biological replicate experiments for: ras-1bd controls (black, τ = 21.5 ± 0.3 hr), ras-1bd Δprd-2 (blue, τ = 25.5 ± 0.4 hr); ras-1bd Δupf1prd-6 (purple, τ = 18.1 ± 0.2 hr), ras-1bd Δupf1prd-6Δprd-2 double mutants (yellow, τ = 19.4 ± 0.7 hr); ras-1bd Δupf2 (purple, τ = 18.5 ± 0.5 hr), ras-1bd Δupf2 Δprd-2 double mutants (yellow, τ = 18.1 ± 0.3 hr); ras-1bd Δupf3 (purple, τ = 19.8 ± 0.3 hr), ras-1bd Δupf3 Δprd-2 double mutants (yellow, τ = 20.1 ± 0.2 hr). Each individual NMD subunit knockout is epistatic to the Δprd-2 long period phenotype (A). Raw RNA-seq data from a previous study (Wu et al., 2017) were analyzed using the same pipeline as data from Figure 3A (see Materials and methods). Control and Δupf1prd-6 gene expression levels (log2-transformed) are shown for core clock genes. The ck-1a transcript is >2× more abundant in Δupf1prd-6 (B). 3’-UTR lengths from 7793 genes were mined from the N. crassa OR74A genome annotation (FungiDB version 45, accessed on 10/25/2019), and plotted as a histogram. The arrow marks the 3’-UTR of ck-1a, which is 1739 bp and within the top 100 longest annotated UTRs in the entire genome (C). Representative race tubes (RTs) from ras-1bd Pqa-2-ck-1a single (pink) and ras-1bd Pqa-2-ck-1a Δupf1prd-6 double (yellow) mutants are shown at the indicated concentrations of quinic acid to drive expression of ck-1a. All results are shown in a scatterplot, where each dot represents one RT’s free running period length. ras-1bd controls (black) had an average period of 22.4 ± 0.4 hr (N = 20), and period length was not significantly affected by QA concentration (ANOVA p=0.605). ras-1bd Δupf1prd-6 controls (purple) had an average period of 17.5 ± 0.6 hr (N = 16), and period length was not significantly affected by QA concentration (ANOVA p=0.362). Period length of ras-1bd Pqa-2-ck-1a single mutants (pink) was significantly altered across QA levels (ANOVA p=2.9×10−8), and the average period at 10−5 M QA was 27.6 ± 0.8 hr (N = 8). Period length of ras-1bd Pqa-2-ck-1a Δupf1prd-6 double mutants (yellow) was also significantly affected by QA levels (ANOVA p=9.4×10−12), and the average period at 10−5 M QA was 24.7 ± 0.9 hr (N = 8). Thus, the double mutant period length was not genetically additive at low levels of QA induction, and the short period phenotype of Δupf1prd-6 is rescued (D). CKI protein levels were measured from the indicated genotypes grown in 0.1% glucose liquid culture medium (LCM) with QA supplemented at the indicated concentrations for 48 hr in constant light. A representative immunoblot of three biological replicates is shown, and replicates are quantified in the bar graph relative to ras-1bd control CKI levels from a 2% glucose LCM culture (E). CKI protein levels were measured from the indicated genotypes grown in 2% glucose LCM for 48 hr in constant light. A representative immunoblot of three biological replicates is shown, and replicates are quantified in the bar graph relative to ras-1bd control CKI levels (F). CKI protein levels are increased in Δupf1prd-6, decreased in the Δprd-2 mutant, and Δupf1prd-6 is epistatic to Δprd-2 with respect to CKI levels and circadian period length.

Figure 5.

Figure 5—figure supplement 1. The cap-binding protein CBP80 (NCU04187) is not required for a normal clock, and does not alter the Δprd-2 long period phenotype, suggesting that ck-1a degradation is controlled by NMD machinery without the Exon Junction Complex and nuclear cap-binding complex.

Figure 5—figure supplement 1.

96-well plate luciferase assays were used to measure the circadian period length. Traces represent the average of three technical replicates across two biological replicate experiments for: ras-1bd controls (black, τ = 21.6 ± 0.4 hr), ras-1bd Δcbp80 (purple, FGSC22441, τ = 21.5 ± 0.3 hr), ras-1bd Δprd-2 (blue, τ = 25.7 ± 0.2 hr), and ras-1bd Δcbp80 Δprd-2 (yellow, τ = 24.9 ± 0.2 hr). ΔNCU04187 has a wild-type circadian period length and does not genetically interact with Δprd-2, suggesting that ck-1a regulation does not require CBP80.
Figure 5—figure supplement 2. Long untranslated regions (UTRs) are characteristic of casein kinase I gene orthologs across species.

Figure 5—figure supplement 2.

Neurospora 3’-UTR lengths were mined from 7793 annotated genes (as described in Figure 5C) and plotted as a histogram. The black arrow marks the 3’-UTR of ck-1a (NCU00685) at 1739 bp in length (A). UTR lengths from Drosophila melanogaster were mined from 13,552 uniquely annotated genes (Ensembl GTF version BDGP6, accessed on 8/5/2020 from Illumina iGenomes) and plotted as a histogram. The black arrow marks the UTR of dbt (FBgn0002413) at 2443 bp in length (B). UTR lengths from Mus musculus were mined from 20,477 uniquely annotated genes (Ensembl GTF version GRCm38, accessed on 8/5/2020 from Illumina iGenomes) and plotted as a histogram. The black arrow marks the UTR of CSNK1D (ENSMUSG00000025162) at 2157 bp in length, and the blue arrow corresponds to CSNK1E (ENSMUSG00000022433) at 1456 bp (C). UTR lengths from Homo sapiens were mined from 22,401 uniquely annotated genes (Ensembl GTF version GRCh37, accessed on 8/5/2020 from Illumina iGenomes) and plotted as a histogram. The black arrow marks the UTR of CSNK1D (ENSG00000141551) at 2113 bp in length, and the blue arrow corresponds to CSNK1E (ENSG00000213923) at 1247 bp (D).