Dinoflagellate luciferases: purification of luciferases from Gonyaulax polyedra, Pyrocystis lunula, and Pyrocystis fusiformis

The isolation and purification of three luciferases from Pyrocystis lunula, Pyrocystis fusiformis, and Gonyaulax polyedra are described in this paper. The three luciferases have low molecular weights, 30,000 for G. polyedra and 40,000 for P. lunala and P. fusiformis, and each is composed of a single polypeptidic chain. The molecular weight of these luciferases is independent of both the period of the circadian rhythm and the pH of the extraction medium between pH 5.4 and pH 8. These enzymes are probably metalloproteins. Indeed, chelating agents such as EDTA, EGTA, and chlorotetracycline and also sodium azide and potassium cyanide inhibit the light emission. Three cations (Mn²⁺, Mg²⁺, and Ca²⁺) increase the flash height and the total light emitted, whereas other cations (Fe²⁺, Fe³⁺, Cu²⁺, Ni²⁺, and Zn²⁺) inhibit the light emission. The three luciferases cannot be replaced by peridoxases or oxidases as in the Balanoglossus and the Pholas systems. The pH dependence of the luciferase activities is represented by a symmetrical function with optimum near pH 7. Thus, the flashing mechanism cannot be explained by means of a switch mechanism controlled by the pH. The presence of a specific luciferin-binding protein has not been observed in the three extracts of dinoflagellates. The difference between our observations and those described in the literature may be explained by the difference of the degree of purification of these enzymes.     

Circadian Clock Regulation of the Cell Cycle in the Zebrafish Intestine

The circadian clock controls cell proliferation in a number of healthy tissues where cell renewal and regeneration are critical for normal physiological function. The intestine is an organ that typically undergoes regular cycles of cell division, differentiation and apoptosis as part of its role in digestion and nutrient absorption. The aim of this study was to explore circadian clock regulation of cell proliferation and cell cycle gene expression in the zebrafish intestine. Here we show that the zebrafish gut contains a directly light-entrainable circadian pacemaker, which regulates the daily timing of mitosis. Furthermore, this intestinal clock controls the expression of key cell cycle regulators, such as cdc2, wee1, p21, PCNA and cdk2, but only weakly influences cyclin B1, cyclin B2 and cyclin E1 expression. Interestingly, food deprivation has little impact on circadian clock function in the gut, but dramatically reduces cell proliferation, as well as cell cycle gene expression in this tissue. Timed feeding under constant dark conditions is able to drive rhythmic expression not only of circadian clock genes, but also of several cell cycle genes, suggesting that food can entrain the clock, as well as the cell cycle in the intestine. Rather surprisingly, we found that timed feeding is critical for high amplitude rhythms in cell cycle gene expression, even when zebrafish are maintained on a light-dark cycle. Together these results suggest that the intestinal clock integrates multiple rhythmic cues, including light and food, to function optimally.     

ORP8与SPAG5相互作用并影响细胞周期

目的：筛选与氧化固醇结合蛋白相关蛋白8（Oyxterol binding protein related protein 8,ORP8）相互作用的蛋白质,为揭示ORP8在细胞中的功能及其机制提供线索,并根据相互作用蛋白质初步探索ORP8的功能。方法：构建重组诱饵质粒pGBKT7-ORP8m,利用GAL4酵母双杂交系统筛选人Universal cDNA文库,筛选出与ORP8相互作用的蛋白质,通过GSTPull-down以及免疫共沉淀（Co-immunoprecipitation,Co-IP）验证蛋白质相互作用,并通过流式细胞仪检测过表达ORP8对HepG2细胞周期的影响。结果：酵母双杂交筛选得到了精子相关抗原5（Homo sapiens sperm associated antigen 5,SPAG5）,体外GSTpull-down和Co-IP实验确证了ORP8-SPAG5的相互作用,流式细胞术显示ORP8过表达后与空载体相比,人肝癌细胞系HepG2的S期细胞数增加,G1期细胞数减少。结论：SPAG5是与ORP8相互作用的蛋白质,ORP8过表达影响人肝癌细胞系HepG2的细胞周期,可能通过SPAG5起作用。ORP8-SPAG5的相互作用为进一步研究ORP8在肝细胞中的功能及其机制提供了有用的线索     

Circadian Clock Genes Modulate Human Bone Marrow Mesenchymal Stem Cell Differentiation,Migration and Cell Cycle

Many of the components that regulate the circadian clock have been identified in organisms and humans. The influence of circadian rhythm (CR) on the regulation of stem cells biology began to be evaluated. However, little is known on the role of CR on human mesenchymal stem cell (hMSCs) properties. The objective of this study was to investigate the influence of CR on the differentiation capacities of bone marrow hMSCs, as well as the regulation of cell cycle and migration capabilities. To that, we used both a chemical approach with a GSK-3β specific inhibitor (2’E,3’Z-6-bromoindirubin-3’-oxime, BIO) and a knockdown of CLOCK and PER2, two of the main genes involved in CR regulation. In these experimental conditions, a dramatic inhibition of adipocyte differentiation was observed, while osteoblastic differentiation capacities were not modified. In addition, cell migration was decreased in PER2^-/- cells. Lastly, downregulation of circadian clock genes induced a modification of the hMSCs cell cycle phase distribution, which was shown to be related to a change of the cyclin expression profile. Taken together, these data showed that CR plays a role in the regulation of hMSCs differentiation and division, and likely represent key factor in maintaining hMSCs properties.     

Aspects of Interaction of Putative Anchorosomal Protein p68 with the Nuclear Envelope during the Cell Cycle

In the interphase nucleus, the chromatin associated with the nuclear envelope is represented by a layer of anchorosomes, granules with a diameter of 20–25 nm. Biochemically, the fraction of chromatin directly associated with the nuclear envelope is characterized by resistance against decondensing influences, a low level of DNA methylation, and presence of specific acid-soluble proteins. However, the mechanisms lying at the base of chromatin-nuclear envelope interaction have been insufficiently studied. Specifically, it is unknown whether anchorosomes are constant structures or subject to reversible disassembly, when the contacts between chromatin and nuclear envelope are destroyed. We obtained immune serum recognizing a 68 kDa protein from the nuclear envelopes fraction and studied the localization of this protein in interphase and mitotic cells. We show that this protein, present in the NE/anchorosomal fraction, does not remain bound with chromosomes during mitosis. It dissociates from chromosomes at the beginning of the prophase and then can be identified again at the periphery of the newly forming nuclei in the telophase.     

Estimation of Circadian Variations In Cell Cycle Phase Durations In Murine Epidermal Basal Cells

Circadian variations in the proliferative activity of squamous epithelia are well known. However, circadian variations in the duration of the various cell cycle phases (S, G₂ and mitosis) have been disputed. the percent labelled mitoses method, which is traditionally used to obtain duration of cell cycle phases, is poorly suited for identification of circadian variations. Therefore methods combining changes in compartment size (cell cycle phase) and cellular flux through the compartments have been used. Three different methods using such data are presented. These incorporate various simplifying assumptions that cause methodological errors. Limits for use of the different methods are indicated. the use of all three methods gives comparable and pronounced circadian variations in the duration of S and G₂ phase. These results are also compatible with circadian variations in the mitotic duration, but they may also represent artefacts due to sensitivity to model errors.     

Molecular Interaction Map of the Mammalian Cell Cycle Control and DNA Repair Systems

Eventually to understand the integrated function of the cell cycle regulatory network, we must organize the known interactions in the form of a diagram, map, and/or database. A diagram convention was designed capable of unambiguous representation of networks containing multiprotein complexes, protein modifications, and enzymes that are substrates of other enzymes. To facilitate linkage to a database, each molecular species is symbolically represented only once in each diagram. Molecular species can be located on the map by means of indexed grid coordinates. Each interaction is referenced to an annotation list where pertinent information and references can be found. Parts of the network are grouped into functional subsystems. The map shows how multiprotein complexes could assemble and function at gene promoter sites and at sites of DNA damage. It also portrays the richness of connections between the p53-Mdm2 subsystem and other parts of the network.     

Identification of Cell Cycle Dependent Interaction Partners of the Septins by Quantitative Mass Spectrometry

The septins are a conserved family of GTP-binding proteins that, in the baker''s yeast, assemble into a highly ordered array of filaments at the mother bud neck. These filaments undergo significant structural rearrangements during the cell cycle. We aimed at identifying key components that are involved in or regulate the transitions of the septins. By combining cell synchronization and quantitative affinity-purification mass-spectrometry, we performed a screen for specific interaction partners of the septins at three distinct stages of the cell cycle. A total of 83 interaction partners of the septins were assigned. Surprisingly, we detected DNA-interacting/nuclear proteins and proteins involved in ribosome biogenesis and protein synthesis predominantly present in alpha-factor arrested that do not display an assembled septin structure. Furthermore, two distinct sets of regulatory proteins that are specific for cells at S-phase with a stable septin collar or at mitosis with split septin rings were identified.Complementary methods like SPLIFF and immunoprecipitation allowed us to more exactly define the spatial and temporal characteristics of selected hits of the AP-MS screen.     

A Conserved DNA Damage Response Pathway Responsible for Coupling the Cell Division Cycle to the Circadian and Metabolic Cycles

The circadian clock drives endogenous oscillations of cellular and physiological processes with a periodicity of approximately 24 h. Progression of the cell division cycle (CDC) has been found to be coupled to the circadian clock, and it has been postulated that gating of the CDC by the circadian cycle may have evolved to protect DNA from the mutagenic effects of ultraviolet light. When grown under nutrient-limiting conditions in a chemostat, prototrophic strains of budding yeast, Saccharomyces cerevisiae, adopt a robust metabolic cycle of ultradian dimensions that temporally compartmentalizes essential cellular events. The CDC is gated by this yeast metabolic cycle (YMC), with DNA replication strictly segregated away from the oxidative phase when cells are actively respiring. Mutants impaired in such gating allow DNA replication to take place during the respiratory phase of the YMC and have been found to suffer significantly elevated rates of spontaneous mutation. Analogous to the circadian cycle, the YMC also employs the conserved DNA checkpoint kinase Rad53/Chk2 to facilitate coupling with the CDC. These studies highlight an evolutionarily conserved mechanism that seems to confine cell division to particular temporal windows to prevent DNA damage. We hypothesize that DNA damage itself might constitute a “zeitgeber”, or time giver, for both the circadian cycle and the metabolic cycle. We discuss these findings in the context of a unifying theme underlying the circadian and metabolic cycles, and explore the relevance of cell cycle gating to human diseases including cancer.