Ontogeny of the antigen-reactive lymph follicle-forming capacity of the popliteal lymph node in neonatal mice

The ontogenetic development of the reactive lymph follicle-forming capacity of the popliteal lymph node was investigated immunohistochemically in young mice which had received a single injection of hemocyanin (KLH) in a rear footpad at a predetermined age (between 1 and 21 days). The mice were sacrificed at various intervals after injection. In non-stimulated young mice, primary lymph follicles first appeared in the popliteal node at 11 days of age. When KLH was given to 7-day-old or older mice, each draining popliteal node showed a marked increase in B lymphocytes in the extrafollicular zone 3 days after injection and produced a number of "new" lymph follicles outside the pre-existing follicles over the next few days. In mice injected at 2-4 days of age, these nodes showed an increase in B lymphocytes in the outer cortex and had produced several lymph follicles by 8 days of age. The number of lymph follicles produced by each node tended to increase in line with age at injection. These results indicate that neonatal popliteal nodes become able to produce lymph follicles in response to exogenous antigens some time before ontogenetically developing follicles appear. The formation of new lymph follicles observed in draining popliteal nodes after KLH injection at an early postnatal age is discussed in relation to the ontogenetic development of stromal cells (precursors of follicular dendritic cells) that are capable of interacting with B lymphocytes and the extent of B lymphocyte influx into the node induced by KLH stimulation.     

Molecular dissection of a medicinal herb with anti-tumor activity by oligonucleotide microarray

It is difficult to understand precisely the physiological actions of herbs because they contain a complex array of constituent molecules. In the present study we used DNA microarray data for 12600 genes to examine the anti-proliferative activity of the herb Coptidis rhizoma and eight constituent molecules against eight human pancreatic cancer cell lines. We identified 27 genes showing strong correlation with the 50% inhibitory dose (ID50) of C. rhizoma after 72-h exposure. Hierarchical cluster analysis with correlation coefficients between expression levels of these 27 C. rhizoma-related genes and the ID50 of each constituent molecule classified these test molecules into two clusters, one consisting of C. rhizoma and berberine and the other consisting of the remaining seven molecules. Our results suggest that one molecule, berberine, can account for the majority of the anti-proliferative activity of C. rhizoma and that DNA microarray analyses can be used to improve our understanding of the actions of an intact herb.     

The N-terminal domain of chlorophyllide a oxygenase confers protein instability in response to chlorophyll B accumulation in Arabidopsis

Plants acclimate to variations in light intensity by changing the antenna size of photosystems. This acclimation allows them to undergo efficient photosynthesis and creates a protective strategy to minimize photodamage. Chlorophyll b synthesis by chlorophyllide a oxygenase (CAO) is a key regulatory step in the control of antenna size. Recently, we found that higher plant CAOs consist of three domains (A, B, and C domains) and confirmed that the C domain possesses catalytic function. To investigate the function of the A domain, we fused various combinations of these three domains with green fluorescent protein (GFP) and introduced them into Arabidopsis thaliana. When a full-length CAO-GFP fusion protein was introduced into a chlorophyll b-less chlorina1-1 mutant, chlorophyll b accumulated to almost the same levels as in the chlorophyll b-containing Columbia wild type, but the CAO-GFP could not be detected by immunoblotting. By contrast, when a GFP-C domain fusion was introduced into chlorina1-1 or Columbia wild type, a large amount of GFP-C domain protein accumulated and the chlorophyll a/b ratio decreased drastically from 3.6 to 2.2 in Columbia wild type. When an A domain-GFP was introduced into Columbia wild type, A domain-GFP levels were very low. Conversely, a large amount of the protein accumulated when it was introduced into the chlorina1-1 mutant. These results indicate that the A domain may sense the presence of chlorophyll b and regulate the accumulation of CAO protein in the chloroplasts.     

Time-related mapping of quantitative trait loci controlling grain-filling in rice (Oryza sativa L.)

Grain-filling is a crucial process that determines final grain yield in rice (Oryza sativa L.). To understand the genetic basis of dynamics of grain-filling, quantitative trait locus (QTL) analysis was conducted using time-related phenotypic data on grain-filling collected from a population of 155 recombinant inbred lines (F12), derived from a cross between Milyang 23 and Akihikari. Two QTLs detected on chromosomes 8 and 12 were strongly associated with increased filling percentage per panicle. These QTLs were not linked with those controlling spikelet numbers per panicle. This result confers the possibility of improving grain-filling together with an enlargement of sink size. The QTL for filling percentage per panicle on chromosome 8 exactly overlapped that for non-structural carbohydrate (NSC) content in the culm and leaf sheaths during grain-filling, and the Milyang 23 allele associated with increased grain-filling percentage per panicle was associated with decreased NSC content. Therefore, this QTL may be directly involved in NSC translocation from the culm and leaf sheaths to panicle. In addition, the Milyang 23 alleles of QTLs associated with greater spikelet number per panicle on chromosomes 1 and 6 were also related with a reduction in NSC content in the culm and leaf sheaths during grain-filling. These results indicate that NSC dynamics during grain-filling is partly dependent on sink size. NSC accumulation in the culm and leaf sheaths at the heading stage was mainly controlled by different genetic regulations from NSC dynamics during grain-filling. Nitrogen dynamics during grain-filling may also be involved in carbohydrate dynamics.     

Antinociceptive effect of 7-hydroxymitragynine in mice: Discovery of an orally active opioid analgesic from the Thai medicinal herb Mitragyna speciosa

Mitragynine is an indole alkaloid isolated from the Thai medicinal plant Mitragyna speciosa. We previously reported the morphine-like action of mitragynine and its related compounds in the in vitro assays. In the present study, we investigated the opioid effects of 7-hydroxymitragynine, which is isolated as its novel constituent, on contraction of isolated ileum, binding of the specific ligands to opioid receptors and nociceptive stimuli in mice. In guinea-pig ileum, 7-hydroxymitragynine inhibited electrically induced contraction through the opioid receptors. Receptor-binding assays revealed that 7-hydroxymitragynine has a higher affinity for micro-opioid receptors relative to the other opioid receptors. Administration of 7-hydroxymitragynine (2.5-10 mg/kg, s.c.) induced dose-dependent antinociceptive effects in tail-flick and hot-plate tests in mice. Its effect was more potent than that of morphine in both tests. When orally administered, 7-hydroxymitragynine (5-10 mg/kg) showed potent antinociceptive activities in tail-flick and hot-plate tests. In contrast, only weak antinociception was observed in the case of oral administration of morphine at a dose of 20 mg/kg. It was found that 7-hydroxymitragynine is a novel opioid agonist that is structurally different from the other opioid agonists, and has potent analgesic activity when orally administered.     

Chlorophyll metabolism

Since the 1970s, researchers have proposed several regulatory pathways governing chlorophyll metabolism, but only recently have the underlying molecular mechanisms been elucidated. The recent data indicate that such regulatory systems are more complex than originally anticipated. For instance, the pathways involve a series of protein-protein interactions, including complex formation, the dual localization of enzymes within chloroplasts, and a novel protein degradation mechanism that is triggered by pigments. Furthermore, several lines of evidence suggest that chlorophyll metabolism might not only significantly impact the assembly of photosynthetic machineries but also influence processes such as programmed cell death, the 'stay-green' phenomenon, and chloroplast-nucleus communication.     

Species cohesion of an extremophyte (Carex angustisquama,Cyperaceae) in solfatara fields maintained under interspecific natural hybridization

Background and AimsHybridization is the main driver of plant diversification, and gene flow via hybridization has multifaceted effects on plant evolution. Carex angustisquama is an extremophyte that grows on soils heavily acidified by volcanism. Despite its habitat distinct from that of other species, this species is known to form interspecific hybrids, implying interspecific gene flow. It is crucial to verify the extent and direction of interspecific gene flow between C. angustisquama and closely related species to understand the evolutionary process of an extremophyte in solfatara fields.MethodsIn this study, expressed sequence tag–simple sequence repeat markers were utilized to infer the extent and direction of interspecific gene flow between C. angustisquama and closely related species.Key ResultsBayesian clustering and simulation analyses revealed that all individuals of the three hybrid species were classified into the first hybrid generation or first backcross to C. angustisquama; therefore, current interspecific gene flow is limited. Moreover, in the Bayesian inference of historical gene flow based on multispecies samples, the model that assumed no interspecific gene flow was the most strongly supported across all species pairs, including phylogenetically close but ecologically distinctive species pairs.ConclusionsOur results revealed that interspecific gene flow between C. angustisquama and its related species has been limited both currently and historically. Moreover, our results of Bayesian inference of historical gene flow indicated that extrinsic, rather than intrinsic, factors probably act as isolating barriers between Carex species, with hybrid breakdown via microhabitat segregation being the probable potential barrier. Overall, our findings provide insights into the evolutionary process of an extremophyte in solfatara fields and offer an important example of the mechanisms of diversification of the speciose genus Carex.     

Principles of branch dynamics governing shape characteristics of cerebellar Purkinje cell dendrites

Neurons develop dendritic arbors in cell type-specific patterns. Using growing Purkinje cells in culture as a model, we performed a long-term time-lapse observation of dendrite branch dynamics to understand the rules that govern the characteristic space-filling dendrites. We found that dendrite architecture was sculpted by a combination of reproducible dynamic processes, including constant tip elongation, stochastic terminal branching, and retraction triggered by contacts between growing dendrites. Inhibition of protein kinase C/protein kinase D signaling prevented branch retraction and significantly altered the characteristic morphology of long proximal segments. A computer simulation of dendrite branch dynamics using simple parameters from experimental measurements reproduced the time-dependent changes in the dendrite configuration in live Purkinje cells. Furthermore, perturbation analysis to parameters in silico validated the important contribution of dendritic retraction in the formation of the characteristic morphology. We present an approach using live imaging and computer simulations to clarify the fundamental mechanisms of dendrite patterning in the developing brain.