CDK inhibitor p21 is degraded by a proliferating cell nuclear antigen-coupled Cul4-DDB1Cdt2 pathway during S phase and after UV irradiation

Previous reports showed that chromatin-associated PCNA couples DNA replication with Cul4-DDB1(Cdt2)-dependent proteolysis of the licensing factor Cdt1. The CDK inhibitor p21, another PCNA-binding protein, is also degraded both in S phase and after UV irradiation. Here we show that p21 is degraded by the same ubiquitin-proteasome pathway as Cdt1 in HeLa cells. When PCNA or components of Cul4-DDB1(Cdt2) were silenced or when the PCNA binding site on p21 was mutated, degradation of p21 was prevented both in S phase and after UV irradiation. p21 was co-immunoprecipitated with Cul4A and DDB1 proteins when expressed in cells. The purified Cul4A-DDB1(Cdt2) complex ubiquitinated p21 in vitro. Consistently, p21 protein levels are low during S phase and increase around G(2) phase. Mutational analysis suggested that in addition to the PCNA binding domain, its flanking regions are also important for recognition by Cul4-DDB1(Cdt2). Our findings provide a new aspect of proteolytic control of p21 during the cell cycle.     

Characteristics of specific bindings of nitrendipine and PN200-110 to various crude membranes: induction of irreversible bindings by UV irradiation

The characteristics of the specific bindings of [3H]nitrendipine (Nit) and [3H](+)PN200-110 (PN) to crude membranes from rat skeletal, cardiac, and uterine muscle and whole brain were investigated, with special interest in the effect of UV irradiation on these bindings. The specific bindings of [3H]Nit and [3H](+)PN to these crude membranes were saturable and reversible. The specific bindings of [3H]Nit to all these membranes except crude skeletal membranes was maximum in the presence of 0.15 M NaCl plus 1 mM CaCl2 and minimal in the absence of these ions, but the specific bindings of [3H](+)PN to these crude membranes was not affected significantly by these ions. A calcium agonist and antagonists inhibited the specific bindings of [3H]Nit and [3H](+)PN to these crude membranes, the order of their inhibitory effects on specific [3H]Nit bindings being roughly Nit greater than or equal to (+)PN greater than or equal to (-)PN much greater than Bay K 8644 (Bay) greater than verapamil (Ver) greater than diltiazem (Dil). In crude skeletal membranes only, PN caused significant stereospecific inhibition. The order of inhibitions of specific [3H](+)PN bindings to these crude membranes was generally (+)PN greater than Nit greater than or equal to (-)PN greater than Bay much greater than Ver greater than or equal to Dil. In all these crude membranes, UV irradiation completely prevented decrease in the amount of specific binding of [3H](+)PN binding on addition of excess unlabeled (+)PN. These findings suggested that [3H]Nit and [3H](+)PN bind to voltage-sensitive calcium channels in crude membranes from rat skeletal, cardiac, and uterine muscle and whole brain, and that UV irradiation changes the specific bindings of [3H]Nit and [3H](+)PN from reversible to irreversible bindings.     

Chemical and genetic study of Ligularia duciformis and related species in Sichuan and Yunnan Provinces of China

The chemical constituents of the root extracts and the evolutionarily neutral DNA base sequences were studied for 28 samples of Ligularia duciformis, L. kongkalingensis, and L. nelumbifolia collected in Sichuan and Yunnan Provinces of China. The samples could be classified into four chemotypes (1-4). Sesquiterpenoids having eremophilane and oplopane skeletons were isolated from two (Chemotype?1) and three (Chemotype?2) samples, respectively. Two new oplopane derivatives were isolated and their structures were determined. In 18 samples, phenylpropenoids were the major components (Chemotype?3). In five samples, neither phenylpropenoids nor sesquiterpenoids were found (Chemotype?4). Despite this large chemical variety, no correlation was found between the chemotype and the morphological criteria of species identification. The analysis of the evolutionarily neutral DNA regions also indicated that the samples were not separated into distinct clades and that introgression was extensive.     

MAIR‐II deficiency ameliorates cardiac remodelling post‐myocardial infarction by suppressing TLR9‐mediated macrophage activation

Macrophages are fundamental components of inflammation in post‐myocardial infarction (MI) and contribute to adverse cardiac remodelling and heart failure. However, the regulatory mechanisms in macrophage activation have not been fully elucidated. Previous studies showed that myeloid‐associated immunoglobulin–like receptor II (MAIR‐II) is involved in inflammatory responses in macrophages. However, its role in MI is unknown. Thus, this study aimed to determine a novel role and mechanism of MAIR‐II in MI. We first identified that MAIR‐II–positive myeloid cells were abundant from post‐MI days 3 to 5 in infarcted hearts of C57BL/6J (WT) mice induced by permanent left coronary artery ligation. Compared to WT, MAIR‐II–deficient (Cd300c2 ^−/−) mice had longer survival, ameliorated cardiac remodelling, improved cardiac function and smaller infarct sizes. Moreover, we detected lower pro‐inflammatory cytokine and fibrotic gene expressions in Cd300c2 ^−/−‐infarcted hearts. These mice also had less infiltrating pro‐inflammatory macrophages following MI. To elucidate a novel molecular mechanism of MAIR‐II, we considered macrophage activation by Toll‐like receptor (TLR) 9–mediated inflammation. In vitro, we observed that Cd300c2 ^−/− bone marrow–derived macrophages stimulated by a TLR9 agonist expressed less pro‐inflammatory cytokines compared to WT. In conclusion, MAIR‐II may enhance inflammation via TLR9‐mediated macrophage activation in MI, leading to adverse cardiac remodelling and poor prognosis.     

Mathematical analysis of the honeybee waggle dance

A honeybee informs her nestmates of the location of a flower by doing a waggle dance. The waggle dance encodes both the direction of and distance to the flower from the hive. To reveal how the waggle dance benefits the colony, we created a Markov model of bee foraging behavior and performed simulation experiments by incorporating the biological parameters that we obtained from our own observations of real bees as well as from the literature. When two feeders were each placed 400 m away from the hive in different directions, a virtual colony in which honeybees danced and correctly transferred information (a normal, real bee colony) made significantly greater numbers of successful visits to the feeders compared to a colony with inaccurate information transfer. Howerer, when five feeders were each located 400 m from the hive, the inaccurate information transfer colony performed better than the normal colony. These results suggest that dancing's ability to communicate accurate information depends on the number of feeders. Furthermore, because non-dancing colonies always made significantly fewer visits than those two colonies, we concluded that dancing behavior is beneficial for hives' ability to visit food sources.     

Reproductive activity in the checkered snapper, Lutjanus decussatus, off Ishigaki Island, Okinawa

The checkered snapper, Lutjanus decussatus, is an important species for fisheries in the Okinawan region. This study estimated the reproduction of this lutjanid species in the waters around Ishigaki Island. The main spawning season was estimated to be between June and October, since oocytes at the maturation stage and/or postovulatory follicles were found during the study period. In the main spawning season, high gonadosomatic index values were found around the time of the last quarter moon for each month from June to September. It is suggested that L. decussatus is a lunar-synchronized spawner off Ishigaki Island.     

Arabidopsis AtRRP44A Is the Functional Homolog of Rrp44/Dis3, an Exosome Component,Is Essential for Viability and Is Required for RNA Processing and Degradation

The RNA exosome is a multi-subunit complex that is responsible for 3ʹ to 5ʹ degradation and processing of cellular RNA. Rrp44/Dis3 is the catalytic center of the exosome in yeast and humans. However, the role of Rrp44/Dis3 homologs in plants is still unidentified. Here, we show that Arabidopsis AtRRP44A is the functional homolog of Rrp44/Dis3, is essential for plant viability and is required for RNA processing and degradation. We characterized AtRRP44A and AtRRP44B/SOV, two predicted Arabidopsis Rrp44/Dis3 homologs. AtRRP44A could functionally replace S. cerevisiae Rrp44/Dis3, but AtRRP44B/SOV could not. rrp44a knock-down mutants showed typical phenotypes of exosome function deficiency, 5.8S rRNA 3ʹ extension and rRNA maturation by-product over-accumulation, but rrp44b mutants did not. Conversely, AtRRP44B/SOV mutants showed elevated levels of a selected mRNA, on which rrp44a did not have detectable effects. Although T-DNA insertion mutants of AtRRP44B/SOV had no obvious phenotype, those of AtRRP44A showed defects in female gametophyte development and early embryogenesis. These results indicate that AtRRP44A and AtRRP44B/SOV have independent roles for RNA turnover in plants.     

Dynamic nature of disulphide bond formation catalysts revealed by crystal structures of DsbB

In the Escherichia coli system catalysing oxidative protein folding, disulphide bonds are generated by the cooperation of DsbB and ubiquinone and transferred to substrate proteins through DsbA. The structures solved so far for different forms of DsbB lack the Cys104–Cys130 initial‐state disulphide that is directly donated to DsbA. Here, we report the 3.4 Å crystal structure of a DsbB–Fab complex, in which DsbB has this principal disulphide. Its comparison with the updated structure of the DsbB–DsbA complex as well as with the recently reported NMR structure of a DsbB variant having the rearranged Cys41–Cys130 disulphide illuminated conformational transitions of DsbB induced by the binding and release of DsbA. Mutational studies revealed that the membrane‐parallel short α‐helix of DsbB has a key function in physiological electron flow, presumably by controlling the positioning of the Cys130‐containing loop. These findings demonstrate that DsbB has developed the elaborate conformational dynamism to oxidize DsbA for continuous protein disulphide bond formation in the cell.     

Evolution of mitochondrial cell death pathway: Proapoptotic role of HtrA2/Omi in Drosophila

Despite the essential role of mitochondria in a variety of mammalian cell death processes, the involvement of mitochondrial pathway in Drosophila cell death has remained unclear. To address this, we cloned and characterized DmHtrA2, a Drosophila homolog of a mitochondrial serine protease HtrA2/Omi. We show that DmHtrA2 normally resides in mitochondria and is up-regulated by UV-irradiation. Upon receipt of apoptotic stimuli, DmHtrA2 is translocated to extramitochondrial compartment; however, unlike its mammalian counterpart, the extramitochondrial DmHtrA2 does not diffuse throughout the cytosol but stays near the mitochondria. RNAi-mediated knock-down of DmHtrA2 in larvae or adult flies results in a resistance to stress stimuli. DmHtrA2 specifically cleaves Drosophila inhibitor-of-apoptosis protein 1 (DIAP1), a cellular caspase inhibitor, and induces cell death both in vitro and in vivo as potent as other fly cell death proteins. Our observations suggest that DmHtrA2 promotes cell death through a cleavage of DIAP1 in the vicinity of mitochondria, which may represent a prototype of mitochondrial cell death pathway in evolution.