Project description:The circadian clock in mammalian cells is cell-autonomously generated during the cellular differentiation process, but the underlying mechanisms are not understood. Here we show that perturbation of transcriptional program by constitutive expression of c-Myc and Dnmt1 ablation disrupts the differentiation-coupled emergence of the clock from mouse embryonic stem cells (ESCs). Using these model ESCs, 484 genes are identified by global gene expression analysis as correlating factors with differentiation-coupled circadian clock development. Among them, we find the misregulation of Kpna2 (Importin-alpha2) during the differentiation of the c-Myc over-expressed and Dnmt1-/- ESCs, in which sustaining cytoplasmic accumulation of PER proteins is observed. Moreover, constitutive expression of Kpna2 during the differentiation culture of ESCs significantly impairs clock development and KPNA2 facilitates cytoplasmic localization of PER1/2. These results suggest that the programmed gene expression network regulates the differentiation-coupled circadian clock development in mammalian cells, at least in part via post-transcriptional regulation of clock proteins.
Project description:Transcriptional Program of Kpna2 (Importin-α2) Regulates Cellular Differentiation-Coupled Circadian Clock Development in Mammalian Cells
Project description:The circadian clock in mammalian cells is cell-autonomously generated during the cellular differentiation process, but the underlying mechanisms are not understood. Here we show that perturbation of transcriptional program by constitutive expression of c-Myc and Dnmt1 ablation disrupts the differentiation-coupled emergence of the clock from mouse embryonic stem cells (ESCs). Using these model ESCs, 484 genes are identified by global gene expression analysis as factors correlated with differentiation-coupled circadian clock development. Among them, we find the misregulation of Kpna2 (Importin-α2) during the differentiation of the c-Myc over-expressed and Dnmt1-/- ESCs, in which sustained cytoplasmic accumulation of PER proteins is observed. Moreover, constitutive expression of Kpna2 during the differentiation culture of ESCs significantly impairs clock development and KPNA2 facilitates cytoplasmic localization of PER1/2. These results suggest that the programmed gene expression network regulates the differentiation-coupled circadian clock development in mammalian cells, at least in part via post-transcriptional regulation of clock proteins.
Project description:To test whether nuclear importin alpha2 can regulate transcription, we sought to examine gene expression changes in cells with nuclear accumulation of importin alpha2 by performing microarray analysis. We designed an experiment in which EGFP-fused full-length importin alpha2 was transfected into HeLa cells. To exclude the possibility that exogenous, full-length importin alpha2 protein enhances nuclear transport of karyophilic proteins such as transcription factors and thereby directly influences gene expression, a mutant of importin alpha2 which is mutated in the C-terminal CAS-binding domain was also transfected, so that it is never recycled to the cytoplasm and shows complete nuclear localization. We undertook to investigate whether there were changes in gene expression common to cells expressing the full-length importin alpha2 and the C-terminal mutant (C-mutant) isoform. EGFP vs. EGFP-importin alpha2 full length, or EGFP vs EGFP-importin alpha2 CAS-binding mutant. One replicate each. EGFP-expressing cells are used as a control.
Project description:To test whether nuclear importin alpha2 can regulate transcription, we sought to examine gene expression changes in cells with nuclear accumulation of importin alpha2 by performing microarray analysis. We designed an experiment in which EGFP-fused full-length importin alpha2 was transfected into HeLa cells. To exclude the possibility that exogenous, full-length importin alpha2 protein enhances nuclear transport of karyophilic proteins such as transcription factors and thereby directly influences gene expression, a mutant of importin alpha2 which is mutated in the C-terminal CAS-binding domain was also transfected, so that it is never recycled to the cytoplasm and shows complete nuclear localization. We undertook to investigate whether there were changes in gene expression common to cells expressing the full-length importin alpha2 and the C-terminal mutant (C-mutant) isoform.
Project description:The circadian clock, which regulates cellular physiology, such as energy metabolism, resides in each cell level throughout the body. Recently, it has been elucidated that the cellular circadian clock is closely linked with cellular differentiation. Moreover, the misregulation of cellular differentiation in mouse embryonic stem cells (ESCs) induced abnormally differentiated cells with impaired circadian clock oscillation, concomitant with the post-transcriptional suppression of CLOCK proteins. Here, we show that the circadian molecular oscillation is disrupted in dysdifferentiation-mediated mouse kidney tumors induced by partial in vivo reprogramming, resembling Wilms tumors. The expression of CLOCK protein was dramatically reduced in the tumor cells despite the Clock mRNA expression. We also showed that a similar loss of CLOCK was observed in human Wilms tumors, suggesting that the circadian molecular clockwork may be disrupted in dysdifferentiation-mediated embryonal tumors such as Wilms tumors, similar to the in vivo reprogramming induced mouse kidney tumors. These results support our previous reports and may provide a novel viewpoint for understanding the pathophysiological nature of cancers through the correlation between cellular differentiation and circadian clock.
Project description:Mammalian circadian rhythms are based on coupled transcriptional-translational feedback loops driven by the transcription factors CLOCK and BMAL1. Chromatin remodeling mechanisms are essential for the proper timing and extent of circadian gene expression. We report that the S-adenosylhomocysteine (SAH) hydrolysing enzyme AHCY binds to CLOCK-BMAL1 at chromatin and drives circadian transcription by promoting cyclic H3K4 trimethylation and recruitment of BMAL1 to chromatin.
Project description:Mammalian circadian rhythms are based on coupled transcriptional-translational feedback loops driven by the transcription factors CLOCK and BMAL1. Chromatin remodeling mechanisms are essential for the proper timing and extent of circadian gene expression. We report that the S-adenosylhomocysteine (SAH) hydrolysing enzyme AHCY binds to CLOCK-BMAL1 at chromatin and drives circadian transcription by promoting cyclic H3K4 trimethylation and recruitment of BMAL1 to chromatin.
Project description:We show that the cyclin-dependent kinase 5 (CDK5) regulates the mammalian circadian clock via phosphorylation of PER2. CDK5 phosphorylated PER2 at serine residue 394 (S394) as shown by an in vitro kinase assay.
Project description:The circadian clock in murine articular cartilage is a critical temporal regulatory mechanism for tissue homeostasis and osteoarthritis. However, translation of these findings into humans has been hampered by the difficulty in obtaining circadian time series human cartilage tissues. As such, a suitable model is needed to understand the initiation and regulation of circadian rhythms in human cartilage. We used a chondrogenic differentiation protocol on human embryonic stem cells (hESCs) as a proxy for early human chondrocyte development. Chondrogenesis was validated using histology and expression of pluripotency and differentiation markers. The molecular circadian clock was tracked in real time by lentiviral transduction of human clock gene luciferase reporters. Differentiation-coupled gene expression was assessed by RNAseq and differential expression analysis.