RESUMO
The mammalian circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus controls many physiological and behavioral rhythms. The SCN is compartmentalized in two functionally distinct subregions: a dorsomedial subregion that rhythmically expresses clock genes, and a ventrolateral subregion which, in contrast, mainly expresses clock genes at a constant level. In the golden hamster, this ventrolateral part of the SCN contains a subpopulation of neurons expressing calbindin D28k. This subpopulation has recently been implicated in the control of locomotor rhythmicity. Because both the pattern and level of locomotor activity are affected by day-length, we investigated whether photoperiod also affects calbindin expression. We show that calbindin expression is negatively correlated to the day-length. The number of calbindin immunopositive neurons and calbindin mRNA levels were markedly increased in hamsters exposed to short photoperiods (light/dark cycle [LD] 6:18 and LD10:14) when compared with hamster exposed to long photoperiods (LD18:6 and LD14:10). This suggests that calbindin neurons are involved in the encoding of seasonal information by the SCN.
Assuntos
Ritmo Circadiano , Expressão Gênica/efeitos da radiação , Fotoperíodo , Proteína G de Ligação ao Cálcio S100/metabolismo , Núcleo Supraquiasmático/efeitos da radiação , Animais , Comportamento Animal , Calbindinas , Contagem de Células/métodos , Cricetinae , Imuno-Histoquímica/métodos , Hibridização In Situ/métodos , Masculino , RNA Mensageiro/metabolismo , Reação em Cadeia da Polimerase Via Transcriptase Reversa/métodos , Núcleo Supraquiasmático/metabolismoRESUMO
The suprachiasmatic nuclei (SCN) contain the master circadian pacemaker in mammals. Generation and maintenance of circadian oscillations involve clock genes which interact to form transcriptional/translational loops and constitute the molecular basis of the clock. There is some evidence that the SCN clock can integrate variations in day length, i.e. photoperiod. However, the effects of photoperiod on clock-gene expression remain largely unknown. We here report the expression pattern of Period (Per) 1, Per2, Per3, Cryptochrome (Cry) 1, Cry2, Bmal1 and Clock genes in the SCN of Syrian hamsters when kept under long (LP) and short (SP) photoperiods. Our data show that photoperiod differentially affects the expression of all clock genes studied. Among the components of the negative limb of the feedback loop, Per1, Per2, Per3, Cry2 but not Cry1 genes show a shortened duration of their peak expression under SP compared with LP. Moreover, mRNA expression of Per1, Per3 and Cry1 are phase advanced in SP compared with LP. Per3 shows an mRNA peak of higher amplitude under SP conditions whereas Per1 and Per2 peak amplitudes are unaffected by photoperiod changes. Bmal1 expression is phase advanced without a change of duration in SP compared with LP. Furthermore, the expression of Clock is rhythmic under SP whereas no rhythm is observed under LP. These results, which provide further evidence that the core clock mechanisms of the SCN integrate photoperiod, are discussed in the context of the existing molecular model.
Assuntos
Ritmo Circadiano/genética , Proteínas de Drosophila , Proteínas do Olho , Expressão Gênica , Fotoperíodo , Células Fotorreceptoras de Invertebrados , Núcleo Supraquiasmático/metabolismo , Fatores de Transcrição ARNTL , Animais , Fatores de Transcrição Hélice-Alça-Hélice Básicos , Proteínas CLOCK , Proteínas de Ciclo Celular , Cricetinae , Criptocromos , Flavoproteínas/genética , Flavoproteínas/metabolismo , Hibridização In Situ/métodos , Masculino , Dados de Sequência Molecular , Proteínas Nucleares/genética , Proteínas Nucleares/metabolismo , Proteínas Circadianas Period , RNA Mensageiro/biossíntese , Receptores Acoplados a Proteínas G , Fatores de Tempo , Transativadores/genética , Transativadores/metabolismo , Fatores de Transcrição/genética , Fatores de Transcrição/metabolismoRESUMO
The duration of the photosensitive phase of the suprachiasmatic nuclei (SCN), as revealed by light-induced Fos protein expression, depends on the photoperiod and is tied to the length of the night. We show here in Syrian hamsters that after a transfer from long to short photoperiod, lengthening of the photosensitive phase of the SCN is significantly delayed but not abolished when the intergeniculate leaflets (IGL) are lesioned. Thus IGL modulate the integration by the SCN of a photoperiodic change.
Assuntos
Ritmo Circadiano/fisiologia , Corpos Geniculados/fisiologia , Fotoperíodo , Núcleo Supraquiasmático/fisiologia , Vias Visuais/fisiologia , Animais , Axotomia , Contagem de Células , Cricetinae , Regulação para Baixo/fisiologia , Corpos Geniculados/citologia , Corpos Geniculados/cirurgia , Imuno-Histoquímica , Masculino , Neurônios/citologia , Neurônios/metabolismo , Neuropeptídeo Y/metabolismo , Tamanho do Órgão , Estimulação Luminosa , Proteínas Proto-Oncogênicas c-fos/metabolismo , Estações do Ano , Núcleo Supraquiasmático/citologia , Testículo/metabolismo , Vias Visuais/citologiaRESUMO
The modern era of Drosophila circadian rhythms began with the landmark Benzer and Konopka paper and its definition of the period gene. The recombinant DNA revolution then led to the cloning and sequencing of this gene. This work did not result in a coherent view of circadian rhythm biochemistry, but experiments eventually gave rise to a transcription-centric view of circadian rhythm generation. Although these circadian transcription-translation feedback loops are still important, their contribution to core timekeeping is under challenge. Indeed, kinases and posttranslational regulation may be more important, based in part on recent in vitro work from cyanobacteria. In addition, kinase mutants or suspected kinase substrate mutants have unusually large period effects in Drosophila. This chapter discusses our recent experiments, which indicate that circadian transcription does indeed contribute to period determination in this system. We propose that cyanobacteria and animal clocks reflect two independent origins of circadian rhythms.
Assuntos
Ritmo Circadiano/genética , Ritmo Circadiano/fisiologia , Drosophila/genética , Drosophila/fisiologia , Animais , Proteínas de Drosophila , Retroalimentação Fisiológica , Genes de Insetos , Modelos Biológicos , Proteínas Nucleares/genética , Proteínas Nucleares/fisiologia , Proteínas Circadianas Period , Transcrição GênicaRESUMO
A comprehensive approach is introduced using parametric equations to describe the motion induced by type J and cross-axis type coil planet centrifuges. The plots of a line parallel to the coil axis are given. The centrifugal forces are then analyzed in two ways. Three-dimensional graphs show their geometry and the relative intensity of the lateral component is compared to that of the perpendicular component. This allowed a better understanding of the differences in paths and acceleration fields induced by the two types of counter-current chromatography devices.
Assuntos
Centrifugação/instrumentação , Cromatografia/instrumentação , AceleraçãoRESUMO
Retention of the stationary phases of one organic-aqueous solvent system and three aqueous-aqueous polymer solvent systems was investigated on a cross-axis coil planet centrifuge. A graphic statistical treatment of all the data highlighted the prevailing effect of the inward-outward elution mode. A simplified model was proposed and studies on the paths and accelerations of cross-axis devices described in the previous paper provided explanations about the observed hydrodynamic behaviors.
Assuntos
Centrifugação/instrumentação , Cromatografia/instrumentação , Modelos Teóricos , Polímeros , SolventesRESUMO
An improved model of the cross-axis synchronous flow-through coil planet centrifuge has been designed in light of previous studies. The apparatus has a versatile feature in that both analytical and preparative columns can be accommodated in both off-center and central positions. Each has merit in separations. Retention of stationary phase was examined with various two-phase solvent systems used for the separation of biopolymers. Both analytical and preparative columns showed satisfactory retention of the stationary phase under optimum conditions. The apparatus was evaluated in separation of a set of protein samples using a polyethylene glycol-potassium phosphate biphasic system. In both types of columns all proteins were resolved with partition efficiencies of 260 to 670 theoretical plates. Further studies indicated that the relatively low partition efficiency of proteins is mainly attributed to their high molecular mass or molecular heterogeneity within each species rather than due to the high viscosity of the polymer phase system.
Assuntos
Centrifugação/instrumentação , Cromatografia/instrumentação , Proteínas/análise , Indicadores e Reagentes , Polietilenoglicóis , Proteínas/isolamento & purificação , SolventesRESUMO
Direct measurements of total reaction cross sections (sigma R) have been performed in the energy range of 10-300 MeV/nucleon for heavy ion collisions. A decrease of sigma R with increasing energy was observed for a wide range of masses of the colliding systems. The data suggest that sigma R reaches a minimum located around 300 MeV/nucleon independently of the projectile target combination. A dependence of sigma R on mass asymmetry of the svstem is also demonstrated. Trends of sigma R in this energy range are well reproduced by the predictions of a simple microscopic model based on individual nucleon-nucleon collisions. Our data have been employed in this framework to derive a new semi-empirical parametrization of sigma R. Most of the experimental results in the intermediate and high energy range have been reproduced by this parametrization using a single energy-dependent parameter.