Project description:In the model organism Caulobacter crescentus, a network of two-component systems involving the response regulators CtrA, DivK and PleD coordinate cell cycle progression with differentiation. Active phosphorylated CtrA prevents chromosome replication in G1 cells while simultaneously regulating expression of genes required for morphogenesis and development. At the G1-S transition, phosphorylated DivK (DivK~P) and PleD (PleD~P) accumulate to indirectly inactivate CtrA, which triggers DNA replication initiation and concomitant cellular differentiation. The phosphatase PleC plays a pivotal role in this developmental program by keeping DivK and PleD phosphorylation levels low during G1, thereby preventing premature CtrA inactivation. Here, we describe CckN as a second phosphatase akin to PleC that dephosphorylates DivK~P and PleD~P in G1 cells. However, in contrast to PleC, we do not detect kinase activity with CckN. The effects of CckN inactivation are largely masked when PleC is present, but become evident when PleC and DivJ, the major kinase for DivK and PleD, are absent. Accordingly, mild overexpression of cckN restores most phenotypic defects of a pleC null mutant. We also show that CckN and PleC are proteolytically degraded in a ClpXP-dependent way well before the onset of the S phase. Surprisingly, known ClpX adaptors are dispensable for PleC and CckN proteolysis, suggesting the existence of adaptors specifically involved in proteolytic removal of cell cycle regulators. Since cckN expression is induced in stationary phase, depending on the stress alarmone (p)ppGpp, we propose that CckN acts as an auxiliary factor responding to environmental stimuli to modulate CtrA activity under suboptimal conditions.
Project description:In the model organism Caulobacter crescentus, a network of two-component systems involving the response regulators CtrA, DivK, and PleD coordinates cell cycle progression with differentiation. Active phosphorylated CtrA prevents chromosome replication in G1 cells while simultaneously regulating expression of genes required for morphogenesis and development. At the G1-S transition, phosphorylated DivK (DivK∼P) and PleD (PleD∼P) accumulate to indirectly inactivate CtrA, which triggers DNA replication initiation and concomitant cellular differentiation. The phosphatase PleC plays a pivotal role in this developmental program by keeping DivK and PleD phosphorylation levels low during G1, thereby preventing premature CtrA inactivation. Here, we describe CckN as a second phosphatase akin to PleC that dephosphorylates DivK∼P and PleD∼P in G1 cells. However, in contrast to PleC, no kinase activity was detected with CckN. The effects of CckN inactivation are largely masked by PleC but become evident when PleC and DivJ, the major kinase for DivK and PleD, are absent. Accordingly, mild overexpression of cckN restores most phenotypic defects of a pleC null mutant. We also show that CckN and PleC are proteolytically degraded in a ClpXP-dependent way before the onset of the S phase. Surprisingly, known ClpX adaptors are dispensable for PleC and CckN proteolysis, raising the possibility that as yet unidentified proteolytic adaptors are required for the degradation of both phosphatases. Since cckN expression is induced in stationary phase, depending on the stress alarmone (p)ppGpp, we propose that CckN acts as an auxiliary factor responding to environmental stimuli to modulate CtrA activity under suboptimal conditions.IMPORTANCE Two-component signal transduction systems are widely used by bacteria to adequately respond to environmental changes by adjusting cellular parameters, including the cell cycle. In Caulobacter crescentus, PleC acts as a phosphatase that indirectly protects the response regulator CtrA from premature inactivation during the G1 phase of the cell cycle. Here, we provide genetic and biochemical evidence that PleC is seconded by another phosphatase, CckN. The activity of PleC and CckN phosphatases is restricted to the G1 phase since both proteins are degraded by ClpXP protease before the G1-S transition. Degradation is independent of any known proteolytic adaptors and relies, in the case of CckN, on an unsuspected N-terminal degron. Our work illustrates a typical example of redundant functions between two-component proteins.
Project description:Protein phosphorylation is a well-established post-translational mechanism that regulates protein functions and metabolic pathways. It has been shown that several plant mitochondrial proteins are phosphorylated in a reversible manner. However, the identity of the phosphatases/kinases involved in this mechanism and their role in the regulation of the TCA cycle remains unclear. Here, we isolated and characterized plants lacking two mitochondrially targeted phosphatases (Sal2 and PP2c63) alongside pyruvate dehydrogenase kinase (PDK). Protein-protein interaction, quantitative phosphoproteomics and enzymatic analyses revealed that PDK specifically regulates pyruvate dehydrogenase (PDH), whilst Sal2 and PP2c63 regulate PDHand fumarase. Alongside with the recombinant protein complemented the purified mitochondria, the PP2c63 directly regulate the PDH and fumarase while the Sal2 indirectly regulated. Characterization of steady-state metabolite levels and fluxes in the corresponding mutants revealed that these phosphatases regulate the fluxes through the TCA cycle, with altered metabolism compromising growth of the sal2/pp2c63 double. The combined data are collectively discussed in the context of current models of the control of respiration in plants.
Project description:CDC14 phosphatases are critical components of the cell cycle machinery that drives exit from mitosis in yeast. However, the two mammalian paralogs, CDC14A and CDC14B, are dispensable for cell cycle progression or exit, and their function remains unclear. By generating a double Cdc14a; Cdc14b -null mouse model, we report here that CDC14 phosphatases control cell differentiation in pluripotent cells, and their absence results in deficient development of the neural system. Lack of CDC14 impairs neural differentiation from embryonic stem cells (ESCs) accompanied by deficient induction of genes controlled by bivalent promoters. CDC14 directly dephosphorylates and destabilizes Undifferentiated embryonic Transcription Factor 1 (UTF1) during the exit from stemness. Multiomic single-cell analysis of differentiating ESCs suggest that increased UTF1 levels in the absence of CDC14 prevent the firing of bivalent promoters required for differentiation. These results, along recent data suggesting a critical role for cell cycle kinases in pluripotency, suggest that cell cycle kinase-phosphatase modules such as CDK-CDC14 are critical for linking cell cycle regulation and self-renewal, with a specific function for CDC14 phosphatases modulating key epigenetic regulators during the terminal exit from pluripotency.
Project description:CDC14 phosphatases are critical components of the cell cycle machinery that drives exit from mitosis in yeast. However, the two mammalian paralogs, CDC14A and CDC14B, are dispensable for cell cycle progression or exit, and their function remains unclear. By generating a double Cdc14a; Cdc14b -null mouse model, we report here that CDC14 phosphatases control cell differentiation in pluripotent cells, and their absence results in deficient development of the neural system. Lack of CDC14 impairs neural differentiation from embryonic stem cells (ESCs) accompanied by deficient induction of genes controlled by bivalent promoters. CDC14 directly dephosphorylates and destabilizes Undifferentiated embryonic Transcription Factor 1 (UTF1) during the exit from stemness. Multiomic single-cell analysis of differentiating ESCs suggest that increased UTF1 levels in the absence of CDC14 prevent the firing of bivalent promoters required for differentiation. These results, along recent data suggesting a critical role for cell cycle kinases in pluripotency, suggest that cell cycle kinase-phosphatase modules such as CDK-CDC14 are critical for linking cell cycle regulation and self-renewal, with a specific function for CDC14 phosphatases modulating key epigenetic regulators during the terminal exit from pluripotency.
Project description:Cell cycle progression requires the coordination of cell growth, chromosome replication, and division. Consequently, a functional cell cycle must be coupled with metabolism. However, direct measurements of metabolome dynamics remained scarce, in particular in bacteria. Here, we describe an untargeted metabolomics approach with synchronized Caulobacter crescentus cells to monitor the relative abundance changes of ~400 putative metabolites as a function of the cell cycle. While the majority of metabolite pools remains homeostatic, ~14% respond to cell cycle progression. In particular, sulfur metabolism is redirected during the G1-S transition, and glutathione levels periodically change over the cell cycle with a peak in late S phase. A lack of glutathione perturbs cell size by uncoupling cell growth and division through dysregulation of KefB, a K+/H+ antiporter. Overall, we here describe the impact of the C. crescentus cell cycle progression on metabolism, and in turn relate glutathione and potassium homeostasis to timely cell division.
Project description:H2A.Z is a H2A-type histone variant essential for many aspects of cell biology, ranging from gene expression to genome stability. From deuterostomes, H2A.Z evolved into two paralogues, H2A.Z.1 and H2A.Z.2, that differ by only three amino acids and are encoded by different genes (H2AFZ and H2AFV, respectively). Despite the importance of this histone variant in development and cellular homeostasis, very little is known about the individual functions of each paralogue in mammals. Here, we have investigated the distinct roles of the two paralogues in cell cycle regulation and unveiled non-redundant functions for H2A.Z.1 and H2A.Z.2 in cell division. Our findings show that H2A.Z.1 regulates the expression of cell cycle genes such as Myc and Ki-67 and its depletion leads to a G1 arrest and cellular senescence. On the contrary, H2A.Z.2, in a transcription independent manner, is essential for centromere integrity and sister chromatid cohesion regulation, thus playing a key role in chromosome segregation.