Dual specificity phosphatase 7 drives the formation of cardiac mesoderm in mouse embryonic stem cells

Dual specificity phosphatase 7 (DUSP7) is a protein belonging to a broad group of phosphatases that can dephosphorylate phosphoserine/phosphothreonine as well as phosphotyrosine residues within the same substrate. DUSP7 has been linked to the negative regulation of mitogen activated protein kinases (MAPK), and in particular to the regulation of extracellular signal-regulated kinases 1 and 2 (ERK1/2). MAPKs play an important role in embryonic development, where their duration, magnitude, and spatiotemporal activity must be strictly controlled by other proteins, among others by DUSPs. In this study, we focused on the effect of DUSP7 depletion on the in vitro differentiation of mouse embryonic stem (ES) cells. We showed that even though DUSP7 knock-out ES cells do retain some of their basic characteristics, when it comes to differentiation, they preferentially differentiate towards neural cells, while the formation of early cardiac mesoderm is repressed. Therefore, our data indicate that DUSP7 is necessary for the correct formation of neuroectoderm and cardiac mesoderm during the in vitro differentiation of ES cells.

Roles of individual human Dishevelled paralogs in the Wnt signalling pathways

Dishevelled (DVL) proteins are key mediators of most Wnt pathways. In all vertebrates, three DVL paralogs are present (DVL1, DVL2 and DVL3) but it is poorly defined to what extent they are functionally redundant. Here, we generated T-REx HEK 293 cells with only one DVL paralog (i.e., DVL1-only, DVL2-only, and DVL3-only) and compared their response to Wnt-3a and Wnt-5a ligands with wild type and DVL triple knockout cells. We show that DVL is essential, in addition to the previously shown Wnt-3a-induced phosphorylation of LRP6 and transcriptional activation of TCF/LEF-dependent reporter, also for Wnt-3a-induced degradation of AXIN1 and Wnt-5a-induced phosphorylation of ROR1. We have quantified the molar ratios of DVL1:DVL2:DVL3 in our model to be approximately 4:80:16. Interestingly, DVL-only cells do not compensate for the lack of other paralogs and are still fully functional in all analyzed readouts with the exception of Wnt-3a-induced transcription assessed by TopFlash assay. In this assay, the DVL1-only cell line was the most potent; on the contrary, the DVL3-only cell line exhibited only the negligible capacity to mediate Wnt signals. Using a novel model system - complementation assays in T-REx HEK 293 with amplified Wnt signal response (RNF43/ZNRF3/DVL1/DVL2/DVL3 penta KO cells) we demonstrate that it is not the total amount of DVL but ratio of individual paralogs what decides the signal strength. In sum, this study contributes to our better understanding of the role of individual human DVL paralogs in the Wnt pathway.

12-O-Tetradecanoylphorbol-13-acetate increases cardiomyogenesis through PKC/ERK signaling

12-O-Tetradecanoylphorbol-13-acetate (TPA) is the most widely used diacylglycerol (DAG) mimetic agent and inducer of protein kinase C (PKC)-mediated cellular response in biomedical studies. TPA has been proposed as a pluripotent cell differentiation factor, but results obtained have been inconsistent. In the present study we show that TPA can be applied as a cardiomyogenesis-promoting factor for the differentiation of mouse embryonic stem (mES) cells in vitro. The mechanism of TPA action is mediated by the induction of extracellular signal-regulated kinase (ERK) activity and the subsequent phosphorylation of GATA4 transcription factor. Interestingly, general mitogens (FGF, EGF, VEGF and serum) or canonical WNT signalling did not mimic the effect of TPA. Moreover, on the basis of our results, we postulate that a TPA-sensitive population of cardiac progenitor cells exists at a certain time point (after days 6–8 of the differentiation protocol) and that the proposed treatment can be used to increase the multiplication of ES cell-derived cardiomyocytes.

Dishevelled-3 conformation dynamics analyzed by FRET-based biosensors reveals a key role of casein kinase 1

Dishevelled (DVL) is the key component of the Wnt signaling pathway. Currently, DVL conformational dynamics under native conditions is unknown. To overcome this limitation, we develop the Fluorescein Arsenical Hairpin Binder- (FlAsH-) based FRET in vivo approach to study DVL conformation in living cells. Using this single-cell FRET approach, we demonstrate that (i) Wnt ligands induce open DVL conformation, (ii) DVL variants that are predominantly open, show more even subcellular localization and more efficient membrane recruitment by Frizzled (FZD) and (iii) Casein kinase 1 ɛ (CK1ɛ) has a key regulatory function in DVL conformational dynamics. In silico modeling and in vitro biophysical methods explain how CK1ɛ-specific phosphorylation events control DVL conformations via modulation of the PDZ domain and its interaction with DVL C-terminus. In summary, our study describes an experimental tool for DVL conformational sampling in living cells and elucidates the essential regulatory role of CK1ɛ in DVL conformational dynamics.