Generation of a split mNeonGreen human iPS cell line.

A) A schematic representation of the split tagging strategy used in this study. An expression cassette carrying the mNG21-10 fragment was integrated at the AAVS1 locus in 201B7 iPSCs to generate the parental split mNeonGreen2 cell line (smNG2-P). Proteins of interest were tagged endogenously with the mNG211 fragment to visualize their expression and localization. The structure of mNeonGreen was generated from PDB (Protein Data Bank, structure identifier 5LTP; Clavel et al., 2016). B) A schematic of the mNG21-10 expression cassette is shown with the CAG promoter (blue) and sequences for stable expression (dark grey), Puromycin resistance marker (pink), and homology arms (light grey) for integration at the AAVS1 locus. Abbreviations: SA = splicing acceptor, T2A = Thosea asigna virus 2A peptide, bGH = bovine growth hormone poly-adenylation signal, β-glo = rabbit β-globin poly-adenylation signal. C) Sequencing chromatograms show the edited AAVS1 allele junctions in the smNG2-P cell line (bottom) compared to the WT allele (top). D) Representative G-banding karyotype of the smNG2-P cell line shows that the edited cells have a normal karyotype (46, XX). E) Flow cytometry plots show smNG2-P cells stained for pluripotency markers TRA-1-60 (left, green), OCT3/4 (center, yellow) and NANOG (right, red) or a secondary antibody control (blue). F) Flow cytometry plots show differentiated smNG2-P cells stained for PAX6 (ectoderm; left, green), NCAM (mesoderm; center, yellow) and FOXA2 (endoderm; right, red) compared to undifferentiated cells (blue) and unstained controls (dark colors). G) Fluorescent and brightfield images show fluorescence complementation after transfecting smNG2-P cells with a plasmid expressing H2B fused to mNG211. The scale bar is 10 microns.

Efficient endogenous tagging with mNG211 in smNG2-P cells.

A) A schematic shows the workflow used to tag proteins of interest with the mNG211 fragment. smNG2-P cells were transfected with Cas9/sgRNA RNPs and a ssODN repair template to integrate mNG211 at a target locus. After recovery, the edited populations were frozen, then assessed by Nanopore sequencing and flow cytometry. B) A bar graph shows the distribution of alleles (WT, indels or mNG211 tagged) in edited populations. The percentage of mNG211 alleles is indicated in white for each gene. C) Fluorescent and brightfield images show populations of tagged cells after enrichment by FACS as indicated. The scale bar is 50 microns.

Efficient clonal isolation and screening of tagged iPS cell lines.

A) The protocol used for single-cell isolation and the recovery of tagged iPSC clones is shown. Tagged cell populations were pre-treated with ROCK inhibitor Y-27632 for 2 hours before sorting individual cells into 96-well plates by FACS. Cells were kept in recovery media for 6 days, then colonies were screened on day 10 to select those for further passaging into 96-well plates on day 11. Fully-grown clones were frozen on day 15, and cells were genotyped by barcoding PCR followed by Nanopore sequencing. B) A stacked bar graph shows the distribution of genotypes inferred from multiplexed Nanopore sequencing for isolated clones of tagged H2BC11, ACTB, TUBA1B, ANLN and RHOA (sample size is indicated above each bar). C-G) The genotypes of the final tagged cell lines are shown: H2BC11-smNG2 (C), smNG2-ACTB (D), smNG2-TUBA1B (E), smNG2-ANLN (F) and smNG2-RHOA (G). The target gene coding sequence is in blue, indel mutations are in red and mNG11 tag in green. H) Fluorescent images show the localization of smNG2 (green) and DNA (stained with Hoechst; magenta) in the final tagged cell lines. The scale bar is 10 microns.

Image restoration for live imaging and quantitative measurements in iPSCs.

A) A graph shows the signal-to-noise ratio measured from low-(pink) and high-exposure (blue) images of the tagged iPS cell lines as indicated. B) A schematic shows the training and application of the CARE neural network for image restoration. The neural network developed by Weigert et al. (2018) was trained on sets of low- and high-exposure images for each tagged cell line and used to restore timelapse movies. C-G) Comparisons of raw (Input; top panel) and restored timelapse images (Network; bottom panel) by the CARE neural network are shown for iPSCs expressing smNG2-anillin (C), smNG2-RhoA (D), H2B-smNG2 (E), smNG2-Tubulin (F) and smNG2-actin (G) undergoing cytokinesis (smNG2 in green; DNA stained with Hoechst in magenta). The scale bars are 10 microns, and time is relative to anaphase onset (00:00).

Cytokinesis is uniquely regulated in iPSCs.

A) Schematics show the core pathways regulating contractile ring assembly and ingression (left) and their localization inside a late anaphase cell (right). B) A schematic (left) shows how the duration of ingression was measured in anillin-tagged iPSCs (right; n = 39). C) A schematic (left) shows how the ratio of cortical to cytosolic protein was measured in metaphase cells for smNG2-anillin, smNG2-RhoA and smNG2-actin (right; n = 10 for each line). D) A schematic (left) shows the location and timing of the linescans used to plot the fluorescence intensity along the cortex in single iPSCs for smNG2-anillin (center) and smNG2-RhoA (right). Timepoints are shown in different colors as indicated in the scale. E) A schematic (left) shows the location of the linescans used to plot the intensity of fluorescence along the cortex at the onset of furrowing for smNG2-anillin (center) and smNG2-RhoA (right; n = 10 for each). F) A schematic (left) shows how the breadth of protein localization at the equatorial cortex at furrow initiation was calculated for smNG2-anillin and smNG2-RhoA (n = 10 for each). G) Fluorescent images show the location of DNA (left; stained with Hoechst) and smNG2-Tubulin (grayscale) in a cell. For tubulin, a lower focal plane (center) is shown to highlight astral microtubules (indicated by pink arrows), and a higher focal plane (right) is shown to highlight the central spindle. The scale bar is 10 microns. H) A schematic (top) shows the location of the linescan used to plot the fluorescence intensity along the midzone of a cell expressing smNG2-tubulin in anaphase (bottom). I) A schematic shows a comparison of conventional view of cytokinesis (HeLa cell; left) and an iPS cell (iPSCs; right). HeLa cells have a strongly enriched central spindle, which keeps the equatorial of active RhoA narrow, and astral microtubules that extend all the way to the cortex and restrict the localization of anillin to the same zone as RhoA. iPSCs have a weakly enriched central spindle, resulting in a broader zone of active RhoA, and prominent astral microtubules that keep anillin in a narrow equatorial zone. Box plots in B, C and F show the median line, quartile box edges and minimum and maximum value whiskers. Statistical significance was determined by Brown-Forsythe and Welch’s ANOVA for C and Welch’s t test for F (ns, not significant; * p≤0.05; ** p≤0.01; *** p≤0.001; **** p≤0.0001).