Fig 2: PB Mutagenesis in OCT4 Reporter Human ES Cells(A) Splicing consequences of PB[Insertional Mutagenesis,NANOG] (PB[IM,N]) insertion either in front of or within the intron of a gene. PB[IM,N] insertion into any reading frame is capable of inducing both overexpression of the downstream transcript with the β actin promoter and triple reading frame start cassette (not shown) as well as simultaneous expression of Katushka fluorescent marker by the splicing of Katushka/IRES into the native transcript with the splice donor (SD). This construct is also able to create N-terminally truncated transcripts with the splice acceptor, triple reading frame stop cassette, and poly A tail (SA-stop-pA). PB[IM,N] can also constitutively overexpress NANOG transcript from the independent NANOG overexpression cassette.(B) (Top) FACS analysis of Katushka expression from PB[IM,N] in human ES cells 48 hr after transfection in single-cell suspension using the RFP channel. Mean of triplicate independent experiments is shown. Error bars represent SD. (Bottom) PB copy number within ten individual PB[IM,N] transfected human ES cell clones as assessed by real time PCR. There is a mean of five PB[IM,N] insertions per clone.(C) Protocol of screen performed in H1 OCT4-EGFP cells for resistance to RA-induced differentiation using PB[IM,N]. Cells in six-well plates were transfected with PB[IM]N, puromycin selected, and subsequently treated with RA and G418. Cells were then split from the six-well plates into 10-cm plates at a 2:1 ratio and maintained on G418 alone.(D) Brightfield and fluorescent images of the six unique clones recovered from the screen. All clones are positive for EGFP and Katushka fluorescent reporters for OCT4 expression and PB[IM,N] insertion within an actively expressed gene.

Fig 3: PB Mutagenesis of DENND2C Causes Morphological Changes and Resistance to RA(A) (Top) Screenshot from the UCSC Genome Browser detailing the position and orientation of the PB[IM,N] insertion in DENND2C mapped in clone 2 (red arrow). (Bottom right) PB[IM,N] insertion results in overexpression of the C-terminal half of DENND2C, made up primarily of its DENN domain. (Bottom left) The C terminus of DENND2C is significantly upregulated in clone 2 by real-time PCR. Graph shows mean of triplicate technical replicates, and error bars represent SD. ∗∗p < 0.001 in Student’s t test.(B) Brightfield and OCT4-EGFP reporter images of clone 2 and DENND2C expressing human ES cells. Clone 2 aggregates into either balls of cells or flat, extremely dense colonies that resist spontaneous differentiation. Cells stably transfected with full-length (FL) or truncated (TR) DENND2C also display this behavior. Scale bar represents 50 μm.(C) RT-PCR showing maintenance of stemness in DENND2C expressing human ES cells, which do not display markers of differentiation.(D) Western blot demonstrating that DENND2C overexpressing cells produce NANOG and OCT4 proteins at levels comparable to the parental WT and NANOG overexpressing cell lines. Overexpressed DENND2C-FL runs as a doublet, while only DENND2C-TR lysate exhibits a band running at the predicted 50 kDa of truncated DENND2C.(E) Alkaline phosphatase-stained plates after RA/G418 treatment. Experiments were performed in triplicate. A representative plate for each set of experiments is shown.See Figure S1 for additional information.

Fig 4: NANOG Expression from PB Constructs Induces Resistance to RA-Induced Differentiation(A) OCT4 immunostaining in WT and NANOG expressing human ES cells. NANOG expressing cells resist spontaneous differentiation and maintain OCT4 signal in colony centers at larger diameters than WT cells. Scale bar represents 100 μm.(B) (Top) Morphology of RA differentiated cells. The red square highlights a cluster of morphologically undifferentiated NANOG expressing cells after RA treatment, magnified in inset. Scale bar represents 200 μm. (Bottom) RT-PCR analysis of RA-differentiated cells.(C) Immunostaining of RA-differentiated cells co-stained for NANOG and GATA6. RA induces differentiation of human ES cells as assessed by GATA6 endoderm marker. Scale bar represents 150 μm.(D) Real-time PCR (top) and western blot (bottom) analysis of stemness marker expression in RA-treated cells. The addition of a NANOG overexpression cassette to PB[IM] induces protein overexpression of both NANOG and the NANOG target OCT4 and induces weak persistence of NANOG and OCT4 after RA treatment. Graph shows mean of triplicate independent experiments. Error bars represent SD. ∗∗p < 0.001 in Student’s t test.(E) Alkaline phosphatase staining of combined RA/G418-treated cells after 16 days. Experiments are performed in duplicate. A representative plate is shown.

Fig 5: DENND2C Phenotype Is Induced by Loss of Active RHOA and RAC1(A) DAPI and F-actin immunostaining of WT and DENND2C expressing human ES cells. Scale bar represents 30 μm.(B) Brightfield and OCT4-EGFP reporter images of cells stably expressing dominant-negative RHOA T19N (RHOA DN) and dominant-negative RAC1 T17N (RAC1 DN). Scale bar represents 50 μm.(C) DAPI and F-actin immunostaining of WT and RHOA DN and RAC1 DN mutant human ES cells. Scale bar represents 30 μm.(D) Plates stained for alkaline phosphatase after RA/G418 treatment. Experiments were performed in triplicate. A representative plate for each set of experiments is shown.(E) The induction of lineage markers with RA assessed by real-time PCR. RA treatment induces differentiation as reflected by the induction of the endoderm marker GATA6. NANOG expression from PB induces some repression of GATA6 and no upregulation of endogenous NANOG. NANOG/DENND2C and NANOG/RHOA DN cells display enhanced repression of GATA6 and upregulation of endogenous NANOG at the RNA level. Graph shows mean of triplicate independent experiments. Error bars represent SD. ∗∗p < 0.001, ∗p < 0.05 in Student’s t test.(F) Immunoprecipitation of active RHOA and RAC1 in DENND2C expressing cells. DENND2C expressing cells have decreased active RHOA and RAC1 relative to WT cells.See Figure S2 for additional information.