bluuebunny/crossref_metadata_2025 huggingface dataset:
Human bone marrow endothelial cells elaborate non‐stromal‐cell‐derived factor‐1 (SDF‐1)‐dependent chemoattraction and SDF‐1‐dependent transmigration of haematopoietic progenitors
Authors: Jo Deog‐Yeon , Hwang Jin‐Hee , Kim Jin‐Man , Yun Hwan‐Jung , Kim Samyong
Published: May 2003

Summary. This study investigated human bone marrow endothelial cells (BMEC) chemoattractive activity in relation to haematopoietic cell trafficking. BMEC‐conditioned medium induced chemoattraction of haematopoietic progenitor cells. Migration was not inhibited by pretreating the cells with pertussis toxin (PTX) or 12G5, indicating that the chemoattractive activity was not dependent on stromal‐cell‐derived factor‐1 (SDF‐1). Spontaneous migration, but not SDF‐1‐mediated chemotaxis of haematopoietic progenitors, was better supported by BMEC as compared with umbilical vein endothelial cells. The superior migration was abolished by pretreating the cells with PTX, indicating that BMEC‐derived SDF‐1 favours bone marrow endothelium, with better transmigration of haematopoietic progenitors.
Progenitor cells divide symmetrically to generate new colony‐forming cells and clonal heterogeneity
Authors: Marley Stephen B. , Lewis John L. , Gordon Myrtle Y.
Published: May 2003

Summary. Self‐renewal is the most fundamental property of haemopoietic stem and progenitor cells. However, because of the need to produce differentiated cells, not all cell divisions involve self‐renewal. We have used a colony replating assay to follow the fates of individual haemopoietic progenitor cell clones. For this, human myeloid colony‐forming cells (CFCs) were cultured by standard methodology. Onset of proliferation and growth rates were established by a video recording method. Individual colonies were replated several times to document the rate of clonal extinction, and the numbers of secondary, tertiary and quaternary CFCs. The clonogenic population exhibited similar kinetics in terms of onset of proliferation and growth rate. Clonal extinction was progressive so that only 30 ± 7% (mean ± standard error of the mean; n = 4) of the original primary colonies formed quaternary colonies after the third replating step. However, individual primary CFCs that produced colonies throughout the experiment generated, on average, 40 ± 8 secondary and tertiary CFCs overall. The values obtained in standard culture conditions were modified when granulocyte colony‐stimulating factor (G‐CSF) or G‐CSF plus interleukin 3 were used to stimulate colony growth, showing that the kinetics of colony formation respond to extrinsic regulation. Examination of the replating potential of individual secondary colonies in the clones demonstrated that they generated different numbers of tertiary colonies. The data best fit a stochastic model of haemopoietic cell development where event probabilities can be modified by extracellular factors.
Asymptomatic carriership of factor V Leiden and genotypes of the fibrinogen gene cluster
Authors: Marchetti Giovanna , Ferraresi Paolo , Legnani Cristina , Pinotti Mirko , Lunghi Barbara , Scapoli Chiara , Gemmati Donato , Coccheri Sergio , Palareti Gualtiero , Bernardi Francesco
Published: May 2003

Summary.We investigated the role of frequent fibrinogen polymorphisms in venous thromboembolic disease in conjunction with inherited thrombophilia. Two hundred unrelated subjects, all carriers of the factor V R506Q mutation (FV Leiden), were genotyped at the fibrinogen gene cluster. Among these subjects, 100 had experienced previous venous thromboembolism (VTE) and 100 were still asymptomatic for VTE. Significant differences were observed between the groups for the BclI polymorphism (P = 0·004). Scanning, by sequencing the DNA regions flanking the BclI marker, revealed new polymorphisms, a C to T transition and a G to T transversion at 1520 and 3369 base pairs 3′ to the β gene stop codon respectively. These markers showed less association with the clinical phenotype than BclI itself. A combined genotype including 10 markers was more frequent among the asymptomatic subjects (17%) than among patients (3%), and was associated with a reduction in fibrinogen antigen level (2·42 ± 0·35vs2·69 ± 0·41 g/l,P = 0·028) among the asymptomatic subjects. Our data suggest that, in the presence of inherited thrombophilia, frequent fibrinogen polymorphisms may interact to modulate the risk of venous thromboembolism.
The molecular basis for the thalassaemias in Sri Lanka
Authors: Fisher Christopher A. , Premawardhena Anuja , De Silva Shanthimala , Perera Giathra , Rajapaksa Shabna , Olivieri Nancy A. , Old John M. , Weatherall David J. ,   the Sri Lanka Thalassaemia Study Group
Published: May 2003

Summary. The β‐globin gene mutations and the α‐globin genes of 620 patients with the phenotype of severe to moderate thalassaemia from seven centres in Sri Lanka were analysed. Twenty‐four β‐globin gene mutations were identified, three accounting for 84·5% of the 1240 alleles studied: IVSI‐5 (G→C) 56·2%; IVSI‐1 (G→A) 15·2%; and haemoglobin E (codon (CD)26 GAG→GAA) 13·1%. Three new mutations were found; a 13‐bp deletion removing the last nucleotide in CD6 to CD10 inclusively, IVSI‐129 (A→C) in the consensus splice site, and a frame shift, CD55 (–A). The allele frequency of α+ thalassaemia was 6·5% and 1·1% for ‐α3·7 and ‐α4·2 deletions respectively. Non‐deletion α‐thalassaemia was not observed. Triplicate or quadruplicate α‐globin genes were unusually common. In 1·5% of cases it was impossible to identify β‐thalassaemia alleles, but in Kurunegala detailed family studies led to an explanation for the severe thalassaemia phenotype in every case, including a previously unreported instance of homozygosity for a quadruplicated α‐globin gene together with β‐thalassaemia trait. These findings have implications for the control of thalassaemia in high‐frequency populations with complex ethnic histories.
Cytogenetic abnormalities in childhood acute myeloid leukaemia: a Nordic series comprising all children enrolled in the NOPHO‐93‐AML trial between 1993 and 2001
Authors: Forestier Erik , Heim Sverre , Blennow Elisabeth , Borgström Georg , Holmgren Gösta , Heinonen Kristiina , Johannsson Johann , Kerndrup Gitte , Andersen Mette Klarskov , Lundin Catarina , Nordgren Ann , Rosenquist Richard , Swolin Birgitta , Johansson Bertil ,   on behalf of the Nordic Society of Paediatric Haematology and Oncology (NOPHO),   the Swedish Cytogenetic Leukaemia Study Group (SCLSG),   the NOPHO Leukaemia Cytogenetic Study Group (NLCSG)
Published: May 2003

Summary. Between 1993 and 2001, 318 children were diagnosed with acute myeloid leukaemia (AML) in the Nordic countries. The patient group comprised 237 children < 15 years of age with de novo AML, 42 children < 15 years with Down syndrome (DS) and de novo AML, 18 adolescents 15–18 years of age with de novo AML, and 21 children < 15 years with treatment‐related AML (t‐AML). The first group was all‐inclusive, yielding an annual childhood de novo AML incidence of 0·7/100 000. Cytogenetic analyses were successful in 288 cases (91%), and clonal chromosomal abnormalities were detected in 211 (73%). The distribution of ploidy levels were pseudodiploidy (55%), hyperdiploidy (34%) and hypodiploidy (11%). The most common aberrations (> 2%) were + 8 (23%) (as a sole change in 6·2%), 11q23‐translocations, including cryptic MLL rearrangements (22%) [t(9;11)(p21–22;q23) in 11%], t(8;21)(q22;q22) (9·0%), inv(16)(p13q22) (6·2%), −7/7q– (5·2%), and t(15;17)(q22;q12) (3·8%). Except for +8, these abnormalities were rare in group 2; only one DS patient had a t(8;21) and none had 11q23‐translocations, t(15;17) or inv(16). In the t‐AML group, three cases displayed 11q23‐rearrangements, all t(9;11); and there were no t(8;21), t(15;17) or inv(16). Overall, the observed frequencies of t(8;21) and t(15;17) were lower, and frequencies of trisomy 8 and 11q23‐translocations higher, than in previous studies. Furthermore, seven abnormalities that were previously reported as only single AML cases were also seen, meaning that der(4)t(4;11)(q26–27;q23), der(6)t(1;6)(q24–25;q27), der(7)t(7;11)(p22;q13), inv(8)(p23q11–12), t(11;17)(p15;q21), der(16)t(10;16)(q22;p13) and der(22)t(1;22)(q21;q13) are now classified as recurrent abnormalities in AML. In addition, 37 novel aberrations were observed, 11 of which were sole anomalies.
Endotoxaemia modulates Toll‐like receptors on leucocytes in humans
Authors: Marsik Claudia , Mayr Florian , Cardona Francesco , Derhaschnig Ulla , Wagner Oswald F. , Jilma Bernd
Published: May 2003

Summary. The modulation of Toll‐like receptors (TLR) 1, 2 and 4 was studied during experimental human endotoxaemia. Healthy volunteers received 2 ng/kg of lipopolysaccharide (LPS) endotoxin (n = 10). TLR1, 2 and 4 expression occurred on monocytes and neutrophils, with monocytes expressing higher baseline levels of TLR2. LPS infusion downmodulated TLR4 expression on neutrophils, with maximal downregulation occurring at 24 h (−62% from baseline; P < 0·03 versus baseline). Monocyte TLRs were upregulated in vivo (TLR1 and 2), and in vitro (TLR1, 2 and 4) 8 h after LPS bolus (P < 0·05 versus baseline). Therefore, neutrophils and monocytes differentially express surface TLRs, and endotoxaemia differentially regulates TLR expression.
Testing the resource concentration hypothesis with tarnished plant bug on strawberry: density of hosts and patch size influence the interaction between abundance of nymphs and incidence of damage
Authors: Rhainds Marc , English‐Loeb Greg
Published: May 2003

Abstract. 1. Attributes of patches with strawberry plants were manipulated experimentally to assess the impact of patch size and host density on the abundance of tarnished plant bug (Hemiptera: Miridae) and incidence of fruit damage.

2. The density of nymphs per inflorescence increased with patch size and host density for some but not all generations of plant bug, providing partial support for the resource concentration hypothesis, while emphasising the importance of replicating experiments across several generations of herbivore.

3. Increasing density of nymphs with increasing patch size and host density did not translate into a high incidence of damage, which may be due to the relatively low feeding impact of nymphs in patches with numerous fruits and to the relatively high perimeter‐to‐area ratio in small patches resulting in a relatively high proportion of damaged fruits.

4. The decreasing proportion of damaged fruits with increasing density of fruits per patch suggests that nymphs exhibit a saturating functional response to density of strawberry fruits. Functional responses of herbivores may be a critical yet overlooked component that influences interactions between insects and their host plant. In particular, concentrated plant resources may result in increased numbers of herbivores yet sill have a negligible influence on plant damage and/or fitness.
Canopy herbivore community structure: large‐scale geographical variation and relation to forest composition
Authors: Franklin Anne J. , Liebhold Andrew M. , Murray Kathleen , Donahue Charlene
Published: May 2003

Abstract.  1. Geographical distributions of individual foliage‐feeding forest herbivore species have been found to be aligned closely with the distribution of their host trees, however little is known about the extent to which broad herbivore communities are geographically associated with distinct host communities.

2. Large‐scale geographic variation in canopy herbivore communities in a 80 000 km2 area (the state of Maine, U.S.A.) was characterised using historical insect survey data. Variation in insect communities was compared with corresponding variation in forest over‐storey composition, which was quantified using data from a regional forest inventory survey.

3. Principal components analysis was used to characterise associations among herbivore and tree species. Analysis of the herbivore data identified three main insect groups: group A corresponded to a single species (Choristoneura fumiferana), group B corresponded to pine‐feeding species including Semiothisa sp., and group C corresponded to the spruce‐feeding species Gilpinia hercyniae and Pikonema alaskensis. Analysis of the forest inventory data characterised three important forest types: northern hardwoods, eastern white pine, and northern spruce‐fir forest types.

4. Spatial analyses were carried out on the first two components of each of the principal components analyses. Factor 1 of the insect data showed a trend of decreasing values from south to north, while factor 2 of the forest inventory data showed an opposite trend. These inverse trends reflected the distribution of the main contributing species to the principal components analysis, C. fumiferana and Pinus strobus respectively. These distributions were highlighted further by the significant negative cross‐correlations that were found between the two factors up to distances of 120 km.

5. Analyses indicated a parallel between the geographic variation in the insect guilds associated with conifers and the geographic pattern of their conifer hosts. Hardwood‐feeding caterpillars, on the other hand, did not form well‐defined guilds and showed varying geographical distributions. The survey data showed varying quality in defining large‐scale associations in the structures of herbivore and host communities.

6. Implications for biodiversity management are discussed.
Clutch size in frugivorous insects as a function of host firmness: the case of the tephritid fly Anastrepha ludens
Authors: Díaz‐Fleischer Francisco , Aluja Martín
Published: May 2003

Abstract. 1. Optimal clutch size theory predicts that individuals will oviposit the number of eggs that increases their fitness. In Anastrepha ludens Loew (Diptera: Tephritidae), females oviposit larger clutches in unripe (firm) fruits than in ripe (soft) fruits. The following hypotheses were tested: (1) Using fruit firmness as an indicator of fruit quality, A. ludens females vary the number of eggs per clutch every time they reach an oviposition decision. (2) Maximising offspring survival with respect to either unripe or ripe fruit requires placing large clutches in firm fruit and smaller clutches in soft fruit.

2. Agar spheres were used as artificial hosts. Three agar concentrations resulted in three degrees of firmness. Mango fruits Mangifera indica L. served as natural hosts. Ripe and unripe fruits were used to test soft and firm host conditions respectively. Females laid significantly larger clutches in the firmer artificial hosts than in the softer hosts. They also laid significantly more eggs in artificial hosts without sugar than in hosts with sugar. Firm (unripe) mangoes also received significantly larger clutches than soft (ripe) mangoes.

3. When an individual female was first presented with a firm artificial host, it laid a large clutch. If subsequently offered a soft host, the female laid a significantly smaller clutch. Finally, if again offered a firm host, clutch size was increased significantly.

4. Possible trade‐offs in offspring fitness were explored in ripe and unripe mangoes by measuring offspring egg‐to‐adult survival, pupal weight, mean adult longevity, and fecundity. Despite the fact that larval survival was greater in soft fruit than in firm fruit, parameters such as pupal weight, mean longevity, and fecundity of adults stemming from both fruit types did not differ significantly.

5. A probable trade‐off between high offspring mortality caused by host unsuitability and low offspring and adult mortality caused by parasitism and predation is discussed as the reason for the exploitation of sub‐optimal hosts.
The effect of prey species and environmental complexity on the functional response of Franklinothrips orizabensis: a test of the fractal foraging model
Authors: Hoddle Mark S.
Published: May 2003

Abstract. 1. The hypothesis proposed by the fractal foraging model, that prey procurement by predators declines as habitat complexity increases, was tested. To evaluate this hypothesis, the effect of two prey species, second‐instar larvae of Scirtothrips perseae Nakahara and Heliothrips haemorrhoidalis (Bouché) (both Thysanoptera: Thripidae), and environmental complexity on the functional response of the predatory thrips Franklinothrips orizabensis Johansen (Thysanoptera: Aeolothripidae) was examined.

2. The Koch curve, a well‐studied fractal, was used to generate the shapes of experimental arenas to test the effect of environmental complexity on the functional response of F. orizabensis. Complexity was defined in terms of the number of acute vertices in which prey thrips could seek refuge and the length of the perimeter that had to be searched by the predator. Four shapes were tested: a circle (zero acute vertices, circumference = 186.61 mm), equilateral triangle (three acute vertices, perimeter = 240 mm), star (six acute vertices, perimeter = 277.13 mm), and snowflake (18 acute vertices, perimeter = 333.65 mm). All shapes were scaled so that the area of each arena was 2771 mm2.

3. Franklinothrips orizabensis exhibited a Type II functional response for both prey species and all four experimental arenas tested. Significantly fewer S. perseae larvae were killed in the most complex arena (i.e. the snowflake) when prey densities exceeded 16. For H. haemorrhoidalis, significant differences in mortality were observed only when prey densities equalled four. These results demonstrated that the fractal foraging model was supported when certain prey densities coincided with particular levels of environmental complexity.

4. Subtle changes in environmental complexity and different prey species of varying density can affect prey–predator interactions significantly.
Use of low frequencies for sub‐basalt imaging
Authors: Ziolkowski Anton , Hanssen Peter , Gatliff Robert , Jakubowicz Helmut , Dobson Andrew , Hampson Gary , Li Xiang‐Yang , Liu Enru
Published: May 2003

Many prospective passive ocean margins are covered by large areas of basalts. These basalts are often extremely heterogeneous and scatter the seismic energy of the conventional seismic reflection system so that it becomes difficult to obtain information on deeper reflectors. Since high frequencies are scattered more than low frequencies, we argue that the acquisition system for sub‐basalt targets should be modified to emphasize the low frequencies, using much larger airguns, and towing the source and receivers at about 20 m depth. In the summer of 2001 we obtained seismic reflection data over basalt in the northeast Atlantic using a system modified to enhance the low‐frequency energy. These new data show deep reflections that are not visible on lines shot in the same places with a conventional system.
Imaging and regional distribution of basalt flows in the Faeroe‐Shetland Basin
Authors: White Robert S. , Smallwood John R. , Fliedner Moritz M. , Boslaugh Brian , Maresh Jenny , Fruehn Juergen
Published: May 2003

We demonstrate that the use of long‐offset seismic data allows wide‐angle reflections and diving waves to be recorded, and that these can be used in conjunction with prestack depth migrations to constrain and to image the base of the basalt flows and the underlying structure in the Faeroe‐Shetland Basin. Crustal velocity models are built first by inverting the traveltimes of the recorded reflections and diving waves using ray‐tracing methods. Finer details of the velocity structure can then be refined by analysis of the amplitudes and waveforms of the arrivals. We show that prestack depth migration of selected wide‐angle arrivals of known origin, such as the base‐basalt reflection, using the crustal velocity model, allows us to build a composite image of the structure down to the pre‐rift basement. This has the advantage that the wide‐angle first‐arriving energy must be primary, and not from one of the many multiples or mode‐converted phases that plague near‐offset seismic data. This allows us to ‘tag’ these primary arrivals with confidence and then to identify the same arrivals on higher‐resolution prestack migrations that include data from all offsets. Examples are drawn from the Faeroe‐Shetland Basin, with a series of regional maps of the entire area showing the basalt depths and the thickness of the basalt flows and underlying sediment down to the top of the pre‐rift basement. The maps show how the basalts thin to the southeast away from their presumed source west of the present Faeroe Islands, and also show the extent to which the structure of the pre‐rift basement controls the considerable variations in sediment thickness between the basement and the cap formed by the overlying basalt flows.
Velocity imaging by tau–p transformation of refracted seismic traveltimes
Authors: Barton P. , Barker N.
Published: May 2003

We present a new method for producing a ‘brute’ velocity image rapidly and automatically from traveltimes picked from densely sampled refraction data. The procedure involves imaging by data transformation from the time–offset domain into the tau–p (intercept–slope) domain, and does not include conventional modelling steps. Differences in apparent velocity and tau along reciprocal paths in the up‐ and downdip directions allow the estimation of the true velocity and geometrical position of the ray turning points. The tau–velocity–turningpoint (τ–ν–x) map distributes phases automatically on the basis of geometry and velocity to give a two‐dimensional representation of subsurface structure. This map may be converted simply to depth and two‐way‐time images. Such images have potential for direct geological interpretation, for use as a starting model for seismic inversion, for superimposition on to conventional reflection images, or for input into prestack depth migration and other processing routines.
Combined structure and velocity stacks via the tau–p transform
Authors: Jones G.D. , Barton P.J. , Singh S.C.
Published: May 2003

Reflection and refraction data are normally processed with tools designed to deal specifically with either near‐ or far‐offset data. Furthermore, the refraction data normally require the picking of traveltimes prior to analysis. Here, an automatic processing algorithm has been developed to analyse wide‐angle multichannel streamer data without resorting to manual picking or traveltime tomography. Time–offset gathers are transformed to the tau–p domain and the resulting wavefield is downward continued to the depth–p domain from which a velocity model and stacked section are obtained. The algorithm inputs common‐depth‐point (CDP) gathers and produces a depth‐converted stacked section that includes velocity information. The inclusion of long‐offset multichannel streamer data within the tau–p transformation enhances the signal from high‐velocity refracted basalt arrivals. Downward continuation of the tau–p transformed wavefield to the depth–p domain allows the reflection and refraction components of the wavefield to be treated simultaneously. The high‐slowness depth–p wavefield provides the velocity model and the low‐slowness depth–p wavefield may be stacked to give structural information. The method is applied to data from the Faeroe Basin from which sub‐basalt velocity images are obtained that correlate with an independently derived P‐wave model from the line.
A quantitative study on the use of converted waves for sub‐basalt imaging
Authors: Hanssen Peter , Ziolkowski Anton , Li Xiang‐Yang
Published: May 2003

The idea of imaging beneath a high‐velocity layer using converted waves has been popular since 1990. Because these wave types have their maximum amplitudes at mid‐ to far‐offsets, the search for pure P‐waves at the highly multiple‐contaminated near‐offsets can be avoided. For the Atlantic Margin, with buried thin‐layered basalts, our quantitative study shows that the initial single‐layered approach is not viable. Even in an unrealistic ideal geological setting, the amplitude of the symmetrical PSP‐mode is far too weak to be recognized on towed streamer data. Furthermore, in the far‐offset window, where locally converted waves have their strongest amplitudes, there is a multitude of other reflections, refractions and interbedded multiples, which have similar moveouts and, often, higher amplitudes. Without the removal of these events, a reliable image of the subsurface cannot be produced. We show that even if this problem were solved, it would be far easier to use the P‐wave reflection from beneath the basalt at near‐offsets. Our study shows that this wave type is by far the strongest response. A borehole‐derived model using a thin‐layered basalt sequence reveals that the strongest locally converted wave has an asymmetrical path and is 10 times weaker. All our results indicate that the pure P‐modes provide the best chance of imaging sub‐basalt sedimentary interfaces.
A case study of sub‐basalt imaging in land region covered with basalt flows
Authors: Reshef Moshe , Shulman Haim , Ben‐Avraham Zvi
Published: May 2003

In this study, a set of 20 2D seismic lines, acquired over the Golan Heights basaltic plateau, was processed and analysed. Although the data were acquired and processed by standard techniques, in some cases good‐quality seismic images were obtained under several hundred metres of basalts. We describe how the seismic characteristics of the top basalt layer were defined and show the effect of the numerous widespread volcanic sources on the quality of the final images. The new data reveal the first images of the sedimentary sequence under the basalt flows, and indicate that strands of the Dead Sea Transform extend into this area. The entire region was found to be very deformed. Several attractive traps for hydrocarbon exploration were also identified on the output sections.
Separation of P‐ and S‐wavefields from wide‐angle multicomponent OBC data for a basalt model
Authors: Wang Yanbin , Singh Satish C.
Published: May 2003

Wide‐angle multicomponent ocean‐bottom cable (OBC) data should further enhance sub‐basalt imaging by using both compressional and converted shear wavefields. The first step in analysing multicomponent OBC data is to decompose the recorded wavefields into pure P‐ and pure S‐wavefields, and extract the upgoing P‐ and S‐waves. This paper presents a new scheme to separate P‐ and S‐wavefields from wide‐angle multicomponent OBC data in the τ–p domain. By considering plane‐wave components with a known horizontal slowness, the P‐ and S‐wavefields are separated into the directions of observed P‐ and S‐wave oscillations using the horizontal and vertical components of the data. The upgoing P‐ and S‐waves are then extracted from the separated P‐ and S‐wavefields. The parameters used in the separation are the seismic wave velocities and the density at the receiver location, which can be estimated from the first reflection phase observed on the horizontal and vertical components. Numerical tests on synthetic data for a plane‐layered model show good performance and demonstrate the accuracy of the scheme. Separation of wavefields from a basalt model is performed using synthetic wide‐angle multicomponent OBC data. The results show that both near‐offset and wide‐angle reflections and conversions from within and below basalt layers are enhanced and clearly identified on the separated wavefields.
Expression of mCLOCK and Other Circadian Clock‐Relevant Proteins in the Mouse Suprachiasmatic Nuclei
Authors: Maywood E. S. , O'Brien J. A. , Hastings M. H.
Published: May 2003

Circadian timing in mammals is based upon the cell‐autonomous clockwork located in the suprachiasmatic nuclei (SCN) of the hypothalamus. It is thought to involve interlocked feedback loops in which periodic transcriptional drive to core clock genes is mediated by CLOCK/BMAL1 heterodimers. Negative‐feedback actions of the encoded proteins PER and CRY terminate this phase of the cycle. In lower species, rhythmic abundance of the mCLOCK homologue initiates the subsequent cycle. By contrast, it is proposed that the new circadian cycle in mammals is triggered by indirect, positive transcriptional actions leading to a subsequent surge in BMAL1. The aim of this study was to test predictions made by this model concerning the behaviour of the native clock factor mCLOCK in the mouse SCN. Using in situ hybridization, immunocytochemistry, Western blotting and immunoprecipitation, we demonstrate constitutive expression of mCLOCK as a nuclear antigen in the SCN. mCLOCK forms alternating, periodic associations with either mBMAL1 or the negative regulators mPER and mCRY. The results confirm predictions made by the ‘two‐loop’ model of the mouse clock, and further highlight the role of interlocked cycles of positive and negative transcriptional regulatory complexes at the heart of the circadian clockwork.
Melatonin Action in the Pituitary: Neuroendocrine Synchronizer and Developmental Modulator?
Authors: . Johnston J. D , Messager S. , Barrett P. , Hazlerigg D. G.
Published: May 2003

Melatonin inhibits the gonadotropin‐releasing hormone (GnRH)‐stimulated secretion of luteinizing hormone and follicle‐stimulating hormone from the pars distalis region of the neonatal rat pituitary gland. Over the initial weeks of postnatal life, this response to melatonin declines in parallel with a loss of iodo‐melatonin binding sites. Although neonatal gonadotrophs have since been extensively used to study melatonin receptor signalling pathways, the mechanisms driving this phenomenon, together with its physiological significance, remain unknown. Melatonin receptors are expressed in the foetal pars distalis before activation of the GnRH system. Furthermore, the MT1 melatonin receptor promoter contains response elements for transcription factors involved in both pituitary differentiation and gonadotroph regulation. These data, coupled with the known ability of melatonin to regulate rhythmical gene expression in adult pars tuberalis cells, leads us to propose that melatonin acts in the developing animal as a regulator of internal synchrony between tissues.
Photic and Circadian Regulation of Retinal Melatonin in Mammals
Authors: Tosini G. , Fukuhara C.
Published: May 2003

Several studies have established that melatonin synthesis occurs in the retina of vertebrates, including mammals. In mammals, a subpopulation of photoreceptors (probably the cones) synthesize melatonin. Melatonin synthesis in the retina is elevated at night and reduced during the day in a fashion similar to events in the pineal gland. Both the MT1 and MT2 melatonin receptors are present in the retina and retinal melatonin does not contribute to circulating levels, suggesting that retinal melatonin acts locally as a neurohormone and/or neuromodulator. Melatonin synthesis in the retina of mammals is under the control of a circadian oscillator, and circadian rhythms in melatonin synthesis and/or release have been described for several species of mammals. These rhythms are present in vivo, persist in vitro, are entrained by light and are temperature compensated. The cloning of the gene responsible for the synthesis of the enzyme arylalkylamine N‐acetyltransferase (the key enzyme in the melatonin biosynthetic pathway) has allowed studies of the molecular mechanisms responsible for the generation of retinal melatonin rhythmicity. The present review focuses on the cellular and molecular mechanisms that regulate melatonin synthesis. In particular, we discuss how the photic environment and the circadian clock interact in determining melatonin levels, in addition to the role that melatonin plays in retinal physiology.
Flies and Fish: Birds of a Feather
Authors: Katherine Tamai T. , Vardhanabhuti V. , Arthur S. , Foulkes N. S. , Whitmore D.
Published: May 2003

The identification of specific clock‐containing structures has been a major endeavour of the circadian field for many years. This has lead to the identification of many key components of the circadian system, including the suprachiasmatic nucleus in mammals, and the eyes and pineal glands in lower vertebrates. However, the idea that these structures represent the only clocks in animals has been challenged by the discovery of peripheral pacemakers in most organs and tissues, and even a number of cell lines. In Drosophila, and vertebrates such as the zebrafish, these peripheral clocks appear to be highly autonomous, being set directly by the environmental light/dark cycle. However, a hierarchy of clocks may still exist in mammals. In this review, we examine some of the current views regarding peripheral clocks, their organization and how they are entrained.
Importance and Relevance of Melatonin to Human Biological Rhythms
Authors: Arendt J.
Published: May 2003

The pineal hormone melatonin is a remarkable molecule, with a conserved time‐keeping function across species. It is extensively used as a self‐administered remedy for sleep disturbance in countries where it is freely available, and to some extent when it is available on prescription, as in the UK. In some circumstances, notably free‐running sleep disorder of the blind, it is the treatment of choice. It is also the marker rhythm of choice for the determination of circadian phase and period. This review outlines the current state of knowledge within a physiological perspective with emphasis on human biological rhythms.
Sensitization: A Mechanism for Melatonin Action in the Pars Tuberalis
Authors: Barrett P. , Schuster C. , Mercer J. , Morgan P. J.
Published: May 2003

Sensitization of adenylate cyclase is a recently discovered phenomenon. Melatonin can induce a sensitized response of adenylate cyclase in ovine pars tuberalis cells where the receptor for melatonin is endogenously expressed. Although the mechanism is not fully understood, sensitization of adenylate cyclase may be an important part of the mechanism by which melatonin encodes daylength in the pars tuberalis of sheep and other animals. We used this as a hypothesis to search for a natural ligand that would activate adenylate cyclase in ovine pars tuberalis cells. The approach revealed pituitary adenylate cyclase activating polypeptide to be an indirect activator of adenylate cyclase in the ovine pars tuberalis. We discuss this in relation to the mechanism and importance of sensitization to the function to the pars tuberalis.
Role of Melatonin in the Regulation of Human Circadian Rhythms and Sleep
Authors: Cajochen C. , Kräuchi K. , Wirz‐Justice A.
Published: May 2003

The circadian rhythm of pineal melatonin is the best marker of internal time under low ambient light levels. The endogenous melatonin rhythm exhibits a close association with the endogenous circadian component of the sleep propensity rhythm. This has led to the idea that melatonin is an internal sleep ‘facilitator’ in humans, and therefore useful in the treatment of insomnia and the readjustment of circadian rhythms. There is evidence that administration of melatonin is able: (i) to induce sleep when the homeostatic drive to sleep is insufficient; (ii) to inhibit the drive for wakefulness emanating from the circadian pacemaker; and (iii) induce phase shifts in the circadian clock such that the circadian phase of increased sleep propensity occurs at a new, desired time. Therefore, exogenous melatonin can act as soporific agent, a chronohypnotic, and/or a chronobiotic. We describe the role of melatonin in the regulation of sleep, and the use of exogenous melatonin to treat sleep or circadian rhythm disorders.
Clock Genes and the Long‐Term Regulation of Prolactin Secretion: Evidence for a Photoperiod/Circannual Timer in the Pars Tuberalis
Authors: Lincoln G. A. , Andersson H. , Hazlerigg D.
Published: May 2003

Prolactin secretion is regulated by photoperiod through changes in the 24‐h melatonin profile and displays circannual rhythmicity under constant photoperiod. These two processes appear to occur principally within the pituitary gland, controlled by the pars tuberalis. This is evident because: (i) hypothalamic‐pituitary disconnected (HPD) sheep show marked changes in prolactin secretion in response to switches in photoperiod and manipulations of melatonin, similar to brain‐intact controls; (ii) HPD sheep also show photoperiod‐specific, long‐term cycles in prolactin secretion under constant long or short days, with the timing maintained even when prolactin secretion is blocked for 2–3 months; and (iii) pars tuberalis cells, but not lactotrophs, express high concentrations of melatonin (MT1) receptor, and exhibit a duration‐sensitive, cAMP‐dependant, inhibitory response to physiological concentrations of melatonin. This suggests the existence of an intrinsic, reversible photoperiod‐circannual timer in pars tuberalis cells. A full complement of clock genes (Bmal1, Clock, Per1, Per2, Cry1 and Cry2) are expressed in the ovine pars tuberalis, and undergo 24‐h cyclical expression as observed in a cell autonomous, circadian clock. Activation of Per genes occurs in the early day (melatonin off‐set), while activation of Cry genes occurs in the early night (melatonin on‐set). This temporal association is evident under both long and short days, thus the Per–Cry interval varies directly with photoperiod. Because, PER : CRY, protein : protein interactions affect stability, nuclear entry and gene transcription based on rodent data, the change in phasing of Per/Cry expression provides a potential mechanism for decoding the long day/short day melatonin signal. A speculative, but testable, extension of this hypothesis is that intrinsically regulated changes in the phase of Per/Cry rhythms, regulates both photorefractoriness and the generation of circannual rhythms in prolactin secretion.
The Circadian Clock: A Manager of Biochemical Processes Within the Organism
Authors: Holzberg D. , Albrecht U.
Published: May 2003

The periodic succession of night and day has influenced life on earth for millions of years. Many organisms have ‘internalized’ this periodic change in the form of the circadian clock. Its main function is to organize the time course of biochemical, physiological and behavioural processes thereby optimizing an organism's performance in anticipating changing environmental conditions. Therefore, it is important to understand the underlying mechanisms that connect the core pacemaker, which is located in the suprachiasmatic nuclei (SCN) of the hypothalamus, with peripheral organs. Several laboratories set out to identify genes that are under the influence of the circadian clock. It appears that the circadian clock coordinates transcription of key metabolic pathways thereby orchestrating the time course of physiological and behavioural processes. We review these investigations and put our experiments, the comparison of gene expression in SCN tissue of Per2 mutant and wild‐type mice, in the context of these findings.
Genetic, Temporal and Developmental Differences Between Melatonin Rhythm Generating Systems in the Teleost Fish Pineal Organ and Retina
Authors: Falcón J. , Gothilf Y. , Coon S. L. , Boeuf G. , Klein D. C.
Published: May 2003

Complete melatonin rhythm generating systems, including photodetector, circadian clock and melatonin synthesis machinery, are located within individual photoreceptor cells in two sites in Teleost fish: the pineal organ and retina. In both, light regulates daily variations in melatonin secretion by controlling the activity of arylalkylamine N‐acetyltransferase (AANAT). However, in each species examined to date, marked differences exist between the two organs which may involve the genes encoding the photopigments, genes encoding AANAT, the times of day at which AANAT activity and melatonin production peak and the developmental schedule. We review the fish pineal and retinal melatonin rhythm generating systems and consider the evolutional pressures and other factors which led to these differences.
Molecular Control of Xenopus Retinal Circadian Rhythms
Authors: Green C. B.
Published: May 2003

Vertebrate retinas contain endogenous circadian clocks that control many aspects of retinal physiology. Our work has focused on studying the molecular mechanism of this clock and the way in which it controls the many cellular rhythms within the retina. These studies focus on the retina of Xenopus laevis, a well‐established model system extensively used for the study of both retinal physiology and circadian function. We have cloned Xenopus homologues of the genes thought to be critical for vertebrate clock function, including Clock, Bmal1, cryptochromes and period, as well as other rhythmic genes such as nocturnin. We have used these genes to manipulate the clock within different subsets of retinal photoreceptors via cell‐specific promoters, in order to study the location of the clock within the retina. These in vivo experiments have shown that photoreceptor cells contain clocks that are necessary for the rhythmic production of melatonin. We have also used biochemical approaches to further investigate the molecular events that drive specific rhythmic outputs, such as circadian regulation of nocturnin gene transcription and control of post‐transcriptional events within these clock‐containing cells.
14‐3‐3 Proteins in Pineal Photoneuroendocrine Transduction: How Many Roles?
Authors: Klein D. C. , Ganguly S. , Coon S. L. , Shi Q. , Gaildrat P. , Morin F. , Weller J. L. , Obsil T. , Hickman A. , Dyda F.
Published: May 2003

Recent studies suggest that a common theme links the diverse elements of pineal photoneuroendocrine transduction –regulation via binding to 14‐3‐3 proteins. The elements include photoreception, neurotransmission, signal transduction and the synthesis of melatonin from tryptophan. We review general aspects of 14‐3‐3 proteins and their biological function as binding partners, and also focus on their roles in pineal photoneuroendocrine transduction.
Melatonin: A Clock‐Output, A Clock‐Input
Authors: Stehle J. H. , Von Gall C. , Korf H.‐W.
Published: May 2003

In mammals, the circadian system is comprised of three major components: the lateral eyes, the hypothalamic suprachiasmatic nucleus (SCN) and the pineal gland. The SCN harbours the endogenous oscillator that is entrained every day to the ambient lighting conditions via retinal input. Among the many circadian rhythms in the body that are driven by SCN output, the synthesis of melatonin in the pineal gland functions as a hormonal message encoding for the duration of darkness. Dissemination of this circadian information relies on the activation of melatonin receptors, which are most prominently expressed in the SCN, and the hypophyseal pars tuberalis (PT), but also in many other tissues. A deficiency in melatonin, or a lack in melatonin receptors should therefore have effects on circadian biology. However, our investigations of mice that are melatonin‐proficient with mice that do not make melatonin, or alternatively cannot interpret the melatonin message, revealed that melatonin has only minor effects on signal transduction processes within the SCN and sets, at most, the gain for clock error signals mediated via the retino‐hypothalamic tract. Melatonin deficiency has no effect on the rhythm generation, or on the maintenance of the oscillation. By contrast, melatonin is essential for rhythmic signalling in the PT. Here, melatonin acts in concert with adenosine to elicit rhythms in clock gene expression. By sensitizing adenylyl cyclase, melatonin opens a temporally‐restricted gate and thus lowers the threshold for adenosine to induce cAMP‐sensitive genes. This interaction, which determines a temporally precise regulation of gene expression, and by endocrine–endocrine interactions possibly also pituitary output, may reflect a general mechanism by which the master clock in the brain synchronizes clock cells in peripheral tissues that require unique phasing of output signals.
Encoding Time of Day and Time of Year by the Avian Circadian System
Authors: Brandstätter R.
Published: May 2003

The most important zeitgeber for seasonal rhythmicity of physiology and behaviour in birds is the annual cycle of photoperiod. Regulatory mechanisms are less well understood in birds than in mammals since photic information can be perceived by photoreceptors in the retina and the pineal gland, as well as in the brain, and photoperiodic time measurement might be performed with reference to at least three autonomous circadian systems, the retina, the pineal gland and a hypothalamic oscillator. In many bird species, the pineal melatonin rhythm plays a central role in circadian organization. Durations of elevated melatonin in the blood reflect night length when animals are kept under natural photoperiodic conditions, as well as under different light/dark schedules in the laboratory. In the house sparrow, time of year is encoded in a particular melatonin signal, being short in duration and high in amplitude in long photoperiods and being long in duration and low in amplitude in short photoperiods, independent of whether the light zeitgeber is natural or artificial or varies in strength. Specific features of the melatonin signal are retained in vivo as well as in vitro when birds or isolated pineal glands are transferred to constant conditions. To regulate daily and seasonal changes of behaviour and physiology, melatonin may act at various target sites, including a complex hypothalamic oscillator that, unlike that in mammals, is not confined to a single cell group in the house sparrow. There is increasing evidence that interactions between two or more components of the songbird circadian pacemaking system are essential to encode and store biologically meaningful information about time, and thus provide the basis for photoperiodic time measurements and after effects in birds.
The Photoreceptive Capacity of the Developing Pineal Gland and Eye of the Golden Hamster (Mesocricetus auratus)
Authors: Foster R. G. , Provencio I. , Bovee‐Geurts P. H. M. , DeGrip W. J.
Published: May 2003

Anatomical and physiological studies have suggested that the pineal gland of neonatal mammals has a photoreceptive capacity. Using the golden hamster (Mesocricetus auratus) as our model, we applied biochemical approaches to look for a functional photopigment within the pineal during early development. Immunocytochemistry and enzyme‐linked immunosorbent assay (ELISA) were used to localize and quantify opsin, and high‐performance liquid chromatography (HPLC) to identify photopigment chromophore (11‐cis and all‐trans retinaldehyde) in the developing eye and pineal. For HPLC analysis, retinaldehydes were converted to their corresponding retinoid oximes. Eluted retinoids were identified by comparison with standard vitamin A1 retinoid oxime isomers on the basis of relative elution sequence and characteristic absorbance spectra. Both immunocytochemistry and ELISA suggested an increase in the opsin content of the pineal during the first week of life. In the eye, 11‐cis retinaldehyde was first detected between days 3 and 5 after birth. In three separate extractions, and using a considerable excess of pineal tissue, we failed to identify chromophore within the pineal during the first week of postnatal development. The appearance of 11‐cis retinaldehyde within the eye between postnatal days 3–5 is consistent with the hypothesis that retinol isomerase activity is coordinated with outer segment development. The failure to identify chromophore within the neonatal pineal suggests that this gland lacks a functional opsin‐based photopigment. These data contradict physiological evidence suggesting that the neonatal pineal of mammals contains photoreceptors.