Figure 1

(A) Schematic of the CDK sensor fused to GFP (top) or 2xmKate2 (bottom) and a nuclear mask (H2B::FP) separated by a self-cleaving peptide (P2A). Inset: nuclear localization signal (NLS), nuclear export signal (NES), and consensus CDK phosphorylation sites on serine (S) residues. (B) Schematic of CDK sensor translocation during the cell cycle. (C) Representative fluorescence overlay (bottom), H2B (top), and DHB::2xmKate2 (middle) time series images during embryo cell divisions (see Figure 1—video 1). Orange arrowheads follow the division of a single blastomere. (D) Confocal micrograph montage of CDK sensor expression in a C. elegans L3 stage larva. (D’) Three somatic tissues are highlighted (inset, dashed orange box) shown at higher magnification with pseudo-colored nuclei (magenta) depicting cells of interest. (E) Schematic of quantification and equation used to obtain the cytoplasmic:nuclear ratio of DHB. (F) Representative images of sensor expression in vulval precursor cells (VPCs) at peak G2 and 20 min after anaphase during G1 in DHB::GFP (gray) and DHB::2xmKate2 (magenta). Orange arrowheads indicate the VPCs. (G) Dot plot depicting G2 and G1 DHB ratios of the two CDK sensor variants in the VPCs (n ≥ 15 cells per phase). (H) Plot of DHB ratios in VPCs during one round of cell division, measured every 5 min (n ≥ 11 mother cells per strain). Dotted line indicates time of anaphase. Error bars and shaded error bands depict mean ± SD. (I) Representative images of sensor and PCNA expression in VPCs during G1 and S phase. Orange arrowheads indicate the VPCs. Blue arrowheads indicate S phase PCNA puncta. (J) Dot plot depicting G1 and S phase DHB::2xmKate2 ratios based on absence or presence of PCNA puncta (n ≥ 10 cells per phase). **p≤0.01, ****p≤0.0001. Significance determined by statistical simulation; p-values in Supplementary file 1. Scale bar = 10 µm (except in D: 20 µm and F, I: 5 µm).