RESUMEN
PURPOSE: The assessment of biological effects caused by radiation exposure has been currently carried out with the linear-quadratic (LQ) model as an extension of the linear non-threshold (LNT) model. In this study, we suggest a new mathematical model named as SeaSaw (SS) model, which describes proliferation and cell death effects by taking account of Bergonie-Tribondeau's law in terms of a differential equation in time. We show how this model overcomes the long-standing difficulties of the LQ model. MATERIALS AND METHODS: We construct the SS model as an extended Wack-A-Mole (WAM) model by using a differential equation with respect to time in order to express the dynamics of the proliferation effect. A large number of accumulated data of such parameters as α and ß in the LQ based models provide us with valuable pieces of information on the corresponding parameter b1 and the maximum volume Vm of the SS model. The dose rate b1 and the notion of active cell can explain the present data without introduction of ß, which is obtained by comparing the SS model with not only the cancer therapy data but also with in vitro experimental data. Numerical calculations are presented to grasp the global features of the SS model. RESULTS: The SS model predicts the time dependence of the number of active- and inactive-cells. The SS model clarifies how the effect of radiation depends on the cancer stage at the starting time in the treatment. Further, the time dependence of the tumor volume is calculated by changing individual dose strength, which results in the change of the irradiation duration for the same effect. We can consider continuous irradiation in the SS model with interesting outcome on the time dependence of the tumor volume for various dose rates. Especially by choosing the value of the dose rate to be balanced with the total growth rate, the tumor volume is kept constant. CONCLUSIONS: The SS model gives a simple equation to study the situation of clinical radiation therapy and risk estimation of radiation. The radiation parameter extracted from the cancer therapy is close to the value obtained from animal experiment in vitro and in vivo. We expect the SS model leads us to a unified description of radiation therapy and protection and provides a great development in cancer-therapy clinical-planning.
Asunto(s)
Neoplasias/radioterapia , Proliferación Celular/efectos de la radiación , Supervivencia Celular/efectos de la radiación , Humanos , Modelos Lineales , Modelos Teóricos , Estadificación de Neoplasias , Neoplasias/patología , Dosificación RadioterapéuticaRESUMEN
BACKGROUND: Plastid-encoded eubacterial-type RNA polymerase (PEP) plays a critical role in the transcription of photosynthesis genes in chloroplasts. Notably, some of the reaction center genes, including psaA, psaB, psbA, and psbD genes, are differentially transcribed by PEP in mature chloroplasts. However, the molecular mechanism of promoter selection in the reaction center gene transcription by PEP is not well understood. OBJECTIVE: Sigma factor proteins direct promoter selection by a core PEP in chloroplasts as well as bacteria. AtSIG5 is a unique chloroplast sigma factor essential for psbD light-responsive promoter (psbD LRP) activity. To analyze the role of AtSIG5 in chloroplast transcription in more detail, we assessed the effect of AtSIG5 hyper-expression on the transcription of plastid-encoded genes in chloroplast transgenic plants. RESULTS: The chloroplast transgenic tobacco (CpOX-AtSIG5) accumulates AtSIG5 protein at extremely high levels in chloroplasts. Due to the extremely high-level expression of recombinant AtSIG5, most PEP holoenzymes are most likely to include the recombinant AtSIG5 in the CpOXAtSIG5 chloroplasts. Thus, we can assess the promoter preference of AtSIG5 in vivo. The overexpression of AtSIG5 significantly increased the expression of psbD LRP transcripts encoding PSII reaction center D2 protein and psaA/B operon transcripts encoding PSI core proteins. Furthermore, run-on transcription analyses revealed that AtSIG5 preferentially recognizes the psaA/B promoter, as well as the psbD LRP. Moreover, we found that psbD LRP is constitutively active in CpOX-AtSIG5 plants irrespective of light and dark. CONCLUSION: AtSIG5 probably plays a significant role in differential transcription of reaction center genes in mature chloroplasts.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/metabolismo , Cloroplastos/genética , Nicotiana/genética , Proteínas del Complejo del Centro de Reacción Fotosintética/genética , Factor sigma/genética , Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , ARN Polimerasas Dirigidas por ADN/metabolismo , Regulación de la Expresión Génica de las Plantas , Operón , Complejo de Proteína del Fotosistema I/genética , Complejo de Proteína del Fotosistema II/genética , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente/crecimiento & desarrollo , Plantas Modificadas Genéticamente/metabolismo , Regiones Promotoras Genéticas , Proteínas Recombinantes/metabolismo , Factor sigma/metabolismo , Nicotiana/crecimiento & desarrollo , Nicotiana/metabolismoRESUMEN
Purpose: This is a paper based on a talk given in the BER2018 conference by M. Bando. We first emphasize the importance of collaborations among scientists in various fields for the low dose/dose-rate effects on biological body. We make comparisons of quantitative estimations of mutation caused by the radiation exposure on various animals and plants using one mathematical model. We derive the importance of the spontaneous mutation at the DNA level, which provides the key to understand the biological evolution. We try to make a guide map to solve this problem and find that the mutation is an important stage of the pathway from the DNA damage to the macroscopic biological evolution. Materials and methods: We construct a mathematical model for the mutation, named as 'WAM' model, which takes into account the recovery effect. The model setting is regarded as an extension of the survival and the hazard functions. The WAM model is used to reproduce accumulated data of mutation frequency of animals and plants. Especially the model analysis shows that the dose-rate dependence is important to understand various mutation data. Results and conclusions: The WAM model is successful in reproducing various mutation data of animals and plants. We find that the inclusion of the dose rate is important to understand all the mutation data. Hence, we are able to develop the 'scaling law' to make the cross-species comparison of mutation frequency data. With this finding, we can extract the dominant effect on the mutation to be caused by the spontaneous mutation, and quantify this amount. We are able to write then the artificial radiation frequency by subtracting the spontaneous mutation. With this success, we estimate the origin of the spontaneous mutation as due to ROS, the order of which agrees to the spontaneous mutation.
Asunto(s)
Evolución Biológica , Análisis Mutacional de ADN , Neoplasias/genética , Algoritmos , Animales , Daño del ADN , Relación Dosis-Respuesta en la Radiación , Drosophila melanogaster , Humanos , Ratones , Modelos Teóricos , Mutagénesis , Mutación , Radiobiología , Especies Reactivas de Oxígeno , Proyectos de Investigación , RiesgoRESUMEN
Purpose: We have proposed a mathematical model (WAM model) expressing increment of the dose-rate dependent mutation frequency caused by artificial radiations. In this model, it is defined that the pool of mutant cells in dynamic equilibrium in organisms. We verified the accuracy of the WAM prediction of mutation frequency in mice. Materials and methods: The theoretical values calculated by the WAM model were compared with the experimental values obtained from the large mouse genetics program at the Oak Ridge National Laboratory (ORNL). Results: Most of all the theoretical values in acute and chronic irradiation conditions nearly coincided with the experimental values. However, the theoretical value of the chronic conditions at the dose-rate of 0.8 R/min was significantly higher than its experimental value. This discordance was able to be minimized in the WAM assumption, when the period from the end of exposure to start mating was two weeks longer. Conclusions: As a result of comparison between experimental and theoretical data, the certainty of the WAM model was confirmed in mice and it was shown that the genetic influence varies depending on the dose-rate.
Asunto(s)
Relación Dosis-Respuesta en la Radiación , Tasa de Mutación , Dosis de Radiación , Animales , Muerte Celular , Proliferación Celular/efectos de la radiación , Análisis Mutacional de ADN , Masculino , Ratones , Modelos Genéticos , Protección Radiológica , Radiobiología/métodos , Reproducibilidad de los Resultados , Espermatogonias/efectos de la radiaciónRESUMEN
The cyanobacterium Synechocystis PCC 6803 possesses three Rieske isoforms: PetC1, PetC2 and PetC3. While PetC1 and PetC2 have been identified as alternative subunits of the cytochrome b6f complex (b6f), PetC3 was localized exclusively within the plasma membrane. The spatial separation of PetC3 from the photosynthetic and respiratory protein complexes raises doubt in its involvement in bioenergetic electron transfer. Here we report a detailed structural and functional characterization of the cyanobacterial PetC3 protein family indicating that PetC3 is not a component of the b6f and the photosynthetic electron transport as implied by gene annotation. Instead PetC3 has a distinct function in cell envelope homeostasis. Especially proteomic analysis shows that deletion of petC3 in Synechocystis PCC 6803 primarily affects cell envelope proteins including many nutrient transport systems. Therefore, the observed downregulation in the photosynthetic electron transport - mainly caused by photosystem 2 inactivation - might constitute a stress adaptation. Comprehensive in silico sequence analyses revealed that PetC3 proteins are periplasmic lipoproteins tethered to the plasma membrane with a subclass consisting of soluble periplasmic proteins, i.e. their N-terminal domain is inconsistent with their integration into the b6f. For the first time, the structure of PetC3 was determined by X-ray crystallography at an atomic resolution revealing significant high similarities to non-b6f Rieske subunits in contrast to PetC1. These results suggest that PetC3 affects processes in the periplasmic compartment that only indirectly influence photosynthetic electron transport. For this reason, we suggest to rename "Photosynthetic electron transport Chain 3" (PetC3) proteins as "periplasmic Rieske proteins" (Prp).
Asunto(s)
Proteínas Bacterianas/metabolismo , Membrana Celular/metabolismo , Proteínas del Complejo de Cadena de Transporte de Electrón/metabolismo , Proteínas de Transporte de Membrana/metabolismo , Fotosíntesis , Synechocystis/metabolismo , Proteínas Bacterianas/química , Proteínas Bacterianas/genética , Cristalografía por Rayos X , Transporte de Electrón , Proteínas del Complejo de Cadena de Transporte de Electrón/química , Proteínas del Complejo de Cadena de Transporte de Electrón/genética , Transferencia de Energía , Homeostasis , Proteínas de Transporte de Membrana/química , Proteínas de Transporte de Membrana/genética , Modelos Moleculares , Periplasma/metabolismo , Filogenia , Dominios y Motivos de Interacción de Proteínas , Proteómica , Espectrometría de Fluorescencia , Relación Estructura-Actividad , Synechocystis/genética , Synechocystis/crecimiento & desarrolloRESUMEN
The `Rieske protein' PetC is one of the key subunits of the cytochrome b(6)f complex. Its Rieske-type [2Fe-2S] cluster participates in the photosynthetic electron-transport chain. Overexpression and careful structure analysis at 2.0 Å resolution of the extrinsic soluble domain of PetC from the thermophilic cyanobacterium Thermosynechococcus elongatus BP-1 enabled in-depth spectroscopic and structural characterization and suggested novel structural features. In particular, both the protein structure and the positions of the internal water molecules unexpectedly showed a higher similarity to eukaryotic PetCs than to other prokaryotic PetCs. The structure also revealed a deep pocket on the PetC surface which is oriented towards the membrane surface in the whole complex. Its surface properties suggest a binding site for a hydrophobic compound and the complete conservation of the pocket-forming residues in all known PetC sequences indicates the functional importance of this pocket in the cytochrome b(6)f complex.
Asunto(s)
Complejo de Citocromo b6f/química , Complejo III de Transporte de Electrones/química , Synechococcus/química , Secuencia Conservada , Cristalografía por Rayos X , Complejo de Citocromo b6f/genética , Complejo III de Transporte de Electrones/genética , Ligandos , Oxidación-Reducción , Synechococcus/genéticaRESUMEN
In contrast to eukaryotes, most cyanobacteria contain several isoforms of the Rieske iron-sulfur protein, PetC, resulting in heterogeneity in the composition of the cytochrome b(6)f complexes. Of three isoforms in the mesophilic cyanobacterium Synechocystis PCC 6803, PetC1 is the major Rieske protein in the cytochrome b(6)f complex, whereas the physiological function of PetC2 and PetC3 is still uncertain. Comparison of wild type and various petC-deficient strains under selected light conditions revealed distinct functional differences: high-light exposure of wild type cells resulted in a significantly enhanced petC2 transcript level, whereas a Delta petC1 mutant showed a low cytochrome b(6)f content, low electron flux, and a considerably increased accumulation of cytochrome-bd oxidase. In contrast to wild type and Delta petC1, Delta petC2 and Delta petC3 strains still grew fast under high-light conditions although all three Rieske proteins are required for maximal electron transport rates. Although the presence of PetC3 appears to be required for activation of the cyclic electron transport, state transitions were more effective in the absence of PetC2 and/or PetC3. In summary, our data suggest defined roles of the various PetC proteins in short- and long-term light adaptation.
Asunto(s)
Adaptación Fisiológica , Proteínas Bacterianas/metabolismo , Complejo III de Transporte de Electrones/metabolismo , Luz , Fotosíntesis/fisiología , Isoformas de Proteínas/metabolismo , Synechocystis/metabolismo , Proteínas Bacterianas/genética , Clorofila/metabolismo , Complejo de Citocromo b6f/metabolismo , Transporte de Electrón/fisiología , Complejo III de Transporte de Electrones/genética , Regulación Bacteriana de la Expresión Génica , Oxidación-Reducción , Ficocianina/metabolismo , Isoformas de Proteínas/genética , Subunidades de Proteína/genética , Subunidades de Proteína/metabolismo , Synechocystis/genéticaRESUMEN
Two novel nuclear genes, OsSIG5 and OsSIG6, encoding potential plastid sigma factors of RNA polymerase (RNAP) were identified in Oryza sativa. The deduced amino acid sequences contain conserved regions, regions 1.2-4.2, and a novel region A/B at the N-terminus. Tissue-specific and light-responsive transcripts of OsSIG5 and OsSIG6 were observed. The N-terminal region of OsSig5 conferred import of green fluorescent protein into the chloroplast. Specific transcripts of rice psbA were synthesized in vitro by reconstituted OsSig5-RNAP holoenzymes. These results indicated that OsSig5 is a plastid sigma factor. This is the first report of the Sig5-type sigma factor in crops.
Asunto(s)
ARN Polimerasas Dirigidas por ADN/genética , Oryza/genética , Proteínas de Plantas/genética , Plastidios/genética , Factor sigma/genética , Secuencia de Aminoácidos , Secuencia Conservada , ARN Polimerasas Dirigidas por ADN/química , Datos de Secuencia Molecular , Filogenia , Hojas de la Planta/genética , Proteínas de Plantas/química , Raíces de Plantas/genética , Tallos de la Planta/genética , Factor sigma/químicaRESUMEN
Plastids are semiautonomous plant organelles exhibiting their own transcription-translation systems that originated from a cyanobacteria-related endosymbiotic prokaryote. As a consequence of massive gene transfer to nuclei and gene disappearance during evolution, the extant plastid genome is a small circular DNA encoding only ca. 120 genes (less than 5% of cyanobacterial genes). Therefore, it was assumed that plastids have a simple transcription-regulatory system. Later, however, it was revealed that plastid transcription is a multistep gene regulation system and plays a crucial role in developmental and environmental regulation of plastid gene expression. Recent molecular and genetic approaches have identified several new players involved in transcriptional regulation in plastids, such as multiple RNA polymerases, plastid sigma factors, transcription regulators, nucleoid proteins, and various signaling factors. They have provided novel insights into the molecular basis of plastid transcription in higher plants. This review summarizes state-of-the-art knowledge of molecular mechanisms that regulate plastid transcription in higher plants.
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ARN Polimerasas Dirigidas por ADN/genética , Regulación de la Expresión Génica de las Plantas , Plastidios/genética , Regiones Promotoras Genéticas , Factores de Transcripción/genética , Transcripción Genética , ARN Polimerasas Dirigidas por ADN/metabolismo , Filogenia , Estructuras de las Plantas/genética , Estructuras de las Plantas/metabolismo , Plastidios/metabolismo , Factores de Transcripción/metabolismoRESUMEN
Eubacterial-type multi-subunit plastid RNA polymerase (PEP) is responsible for the principal transcription activity in chloroplasts. PEP is composed of plastid-encoded core subunits and one of multiple nuclear-encoded sigma factors that confer promoter specificity on PEP. Thus, the replacement of sigma factors associated with PEP has been assumed to be a major mechanism for the switching of transcription patterns during chloroplast development. The null mutant (sig6-1) of plastid sigma factor gene AtSIG6 exhibited a cotyledon-specific pale green phenotype. Light-dependent chloroplast development was significantly delayed in the sig6-1 mutant. Genetic complementation of the mutant phenotype by the AtSIG6 cDNA demonstrated that AtSIG6 plays a key role in light-dependent chloroplast development. Northern and array-based global analyses for plastid transcripts revealed that the transcript levels of most PEP-dependent genes were greatly reduced in the sig6-1 mutant, but that the accumulation of nuclear-encoded RNA polymerase (NEP)-dependent transcripts generally increased. As the PEP alpha subunit and PEP-dependent trnV accumulated at normal levels in the sig6-1 mutant, the AtSIG6 knockout mutant probably retained functional PEP, and the transcriptional defects are likely to have been directly caused by AtSIG6 deficiency. Most of the AtSIG6-dependent genes are preceded by sigma70-type promoters comprised of conserved -35/-10 elements. Thus, AtSIG6 may act as a major general sigma factor in chloroplasts during early plant development. On the other hand, the mutant phenotype was restored in older seedlings. Arabidopsis probably contains another late general sigma factor, the promoter specificity of which widely overlaps with that of AtSIG6.
Asunto(s)
Proteínas de Arabidopsis/fisiología , Arabidopsis/fisiología , Cloroplastos/fisiología , Cotiledón/fisiología , ARN Polimerasas Dirigidas por ADN/fisiología , Regulación del Desarrollo de la Expresión Génica/fisiología , Factor sigma/fisiología , Arabidopsis/genética , Arabidopsis/crecimiento & desarrollo , Secuencia de Bases , Cotiledón/crecimiento & desarrollo , Cotiledón/ultraestructura , Regulación de la Expresión Génica de las Plantas/fisiología , Datos de Secuencia Molecular , Mutagénesis Insercional , Fenotipo , Regiones Promotoras Genéticas/fisiología , Transcripción GenéticaRESUMEN
Light is one of the most important environmental factors regulating expression of photosynthesis genes. The plastid psbD gene encoding the photosystem II reaction center protein D2 is under the control of a unique blue light responsive promoter (BLRP) that is transcribed by a bacterial-type plastid RNA polymerase (PEP). Promoter recognition of PEP is mediated by one of the six nuclear-encoded sigma factors in Arabidopsis. The replacement of the plastid sigma factor associated with PEP may be the major mechanism for switching of plastid transcription pattern in response to environmental and developmental signals. This study demonstrates that AtSig5 is a unique sigma factor that is essential for psbD BLRP activity. A T-DNA insertional mutant with reduced AtSIG5 expression resulted in loss of primary transcripts from the psbD BLRP. Furthermore, transient overexpression of AtSig5 in dark-adapted protoplasts specifically elevated psbD and psbA transcription activities. On the other hand, overproduction of AtSig2 enhanced the transcription of psbA gene and trnE operon, but not psbD transcription. The AtSIG5 gene is phylogenetically distinct from other plastid sigma factors, and its expression is induced exclusively by blue light. We propose that AtSig5 acts as a mediator of blue light signaling that specifically activates the psbD BLRP in response to blue light in Arabidopsis.
Asunto(s)
Proteínas de Arabidopsis/genética , Arabidopsis/genética , Complejo de Proteína del Fotosistema II/genética , Plastidios/genética , Factor sigma/genética , Factores de Transcripción/genética , Transcripción Genética , Arabidopsis/efectos de la radiación , Proteínas de Arabidopsis/metabolismo , Secuencia de Bases , Cartilla de ADN , ADN Bacteriano/genética , Escherichia coli/genética , Luz , Filogenia , Plantas Modificadas Genéticamente/genética , Plastidios/efectos de la radiación , Subunidades de Proteína/genética , Factor sigma/metabolismo , Factores de Transcripción/metabolismo , Transcripción Genética/efectos de la radiaciónRESUMEN
The transcription of plastid gene psbD is under the control of the BLRP (blue-light-responsive promoter) recognized by plastid-encoded RNA polymerase, in which nuclear-encoded sigma factors play a crucial role in the promoter recognition. We examined the effects of light on mRNA levels of six different SIG genes in Arabidopsis and found that blue light extensively induced the accumulation of SIG5 transcripts, but red light did not. The blue light specificity was not observed in the accumulations of remaining five SIG genes. The blue light dependency of the SIG5 expression well explains the light-dependent behavior of the psbD BLRP.