Biliverdin reductase from the liver of Atlantic salmon (Salmo salar)

Biliverdin reductase was characterized and purified from the liver of Atlantic salmon (Salmo salar) using a novel enzymatic staining method. The properties of the enzyme are quite different from those of mammals. The purified enzyme is a monomeric protein with a molecular weight of approximately 68 kD and an isoelectric point of around 3.8. The enzyme can utilize both NADH and NADPH as coenzyme, but the kinetic properties of the NADH-dependent and the NADPH-dependent enzyme activities are different: K _m value for biliverdin IX is 0.6 M in the NADPH system, while it is 6.8 M in the NADH system. Both enzyme activities are inhibited by excess biliverdin IX, but the NADPH-dependent enzyme activity is far more susceptible. The optimum pH for activity is 5.5 with NADPH and 6.0 with NADH. The optimum reaction temperature is 35°C.     

The direct regeneration hypothesis in northern forests

Question: Can the direct regeneration hypothesis (DRH) be used to predict post‐disturbance regeneration after fire, wind disturbance, and clearcutting in northern forests? Do life‐history traits such as regeneration strategy and shade tolerance influence post‐disturbance regeneration success of tree species? Location: Northern forests in North America. Methods: A meta‐analysis was conducted by collecting published data on pre‐ and post‐disturbance stand compositional characteristics in the northern forests. For each tree species, compositional difference (CD) was calculated as the difference between basal area proportions of the post‐ and pre‐disturbance stands, but for post‐disturbance stands <25 years of age, post‐disturbance proportions were calculated based on relative stem density. Results: Species response to disturbances was best explained by regeneration strategy, while disturbance type had no effect on CD. The proportion of broadleaf trees with either strong or weak vegetative reproduction ability increased after all disturbances. Serotinous species had CD values not significantly different from zero after fire, while CD for semi‐serotinous species was negative. The post‐disturbance proportions of non‐serotinous conifers decreased after all forms of disturbance. Conclusions: All disturbances promote broadleaf trees, regardless of regeneration strategy (suckering, sprouting, or seeding). The DRH is supported for conifers with serotinous cones after fire. Fire causes local extinction of non‐serotinous conifers, while wind and clearcutting only decrease the proportion of non‐serotinous conifers because of partial survival of seed sources and advanced regeneration. This study suggests that increasing stand‐replacing disturbances associated with global climate change will promote broadleaf trees in northern forests.     

RNA-induced inflammation and migration of precursor neurons initiates neuronal circuit regeneration in zebrafish

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Coordinated activation of Wnt in epithelial and melanocyte stem cells initiates pigmented hair regeneration

Melanocyte stem cells (McSCs) intimately interact with epithelial stem cells (EpSCs) in the hair follicle bulge and secondary hair germ (sHG). Together, they undergo activation and differentiation to regenerate pigmented hair. However, the mechanisms behind this coordinated stem cell behavior have not been elucidated. Here, we identified Wnt signaling as a key pathway that couples the behavior of the two stem cells. EpSCs and McSCs coordinately activate Wnt signaling at the onset of hair follicle regeneration within the sHG. Using genetic mouse models that specifically target either EpSCs or McSCs, we show that Wnt activation in McSCs drives their differentiation into pigment-producing melanocytes, while EpSC Wnt signaling not only dictates hair follicle formation but also regulates McSC proliferation during hair regeneration. Our data define a role for Wnt signaling in the regulation of McSCs and also illustrate a mechanism for regeneration of complex organs through collaboration between heterotypic stem cell populations.     

Mevalonate-derived proteins in liver regeneration

Sixteen hours after partial hepatectomy in the rat, the synthesis of mevalonate (MVA) is not committed to produce cholesterol and only partially utilized for dolichol formation. In order to investigate the fate of MVA in this replicative system, slices of the remaining liver were incubated with 5-³H-MVA. Labeled proteins from whole liver and purified nuclei were analyzed after extensive delipidation and separation by SDS-PAGE. Many MVA-derived proteins were identified at 16 hours, while only two labelled peptides were detectable at 24 hours. The radioactivity was localized in covalently bound lipid moieties. A highly labeled 26 kD peptide was detectable in the nucleus at 16 hours, suggesting its involvement in the cell cycle progression.     

补体系统及其在肝损伤再生中的作用

补体系统是机体免疫防御机制的重要组成部分,参与免疫识别和防御。近年来,系统研究发现补体除免疫调节外,还具有参与生殖发育、成骨、组织和器官再生等重要生理机能的作用。多项研究报道了补体活化和各种肝损伤／再生的关系,对此进行综述,以期促进对补体多样性功能的了解。     

Human augmenter of liver regeneration: molecular cloning, biological activity and roles in liver regeneration

The complete amino acid sequence of human augmenter of liver regeneration (hALR) was reported by deduction from nucleotide sequence of its complementary DNA . The cDNA for hALR was isolated by screening a human fetal liver cDNA library and the sequencing of this insert revealed an open reading frame encoding a protein with 125aa and highly homologous (87% ) with rat ALR encoding sequence. The recombinant hALR expressed from its cDNA in transient expression experiments in cos-7 cells could stimulate DNA synthesis of HTC hepatoma cell in the dose-dependent and heat-resistant way. Northern blot analysis with rat ALR cDNA as probe confirmed that ALR mRNA was expressed in the normal rat liver at low level and that dramatically increased in the regenerating liver after partial hepatectomied rat. This size of hALR mRNA is 1.4 kb long and expressed in human fetal liver, kidney and testis. These findings indicated that liver itself may be the resource of ALR and suggested that ALR seems to be an im-portant parac     

A quantitative model of liver regeneration in the rat

The ability of various theories to generate the kinetics of rat-liver regeneration is considered. Wound hormone and functional demand theories are shown to be either inadequate or overly complex. A simple model based on a liver-produced mitotic inhibitor is, however, able to match the experimental results on the mitotic rate and thymidine uptake of parenchymal cells in the liver as a function of time following various degrees of partial hepatectomy. The inhibitor itself would belong to the class of molecules known as chalones and differential equations describing the mechanism of its action are derived and solved numerically. The only arbitrary parameters required for the solution are those giving the halflife and dose-response curve of the inhibitor. Optimal matching of theory to data is obtained when the half-life is about 3 h and the dose-response curve is given by a negative exponential function. Experimental procedures for measuring these parameters are discussed and an explanation of the uneven distribution of mitoses in regenerating liver is given.     

Conformational changes in rat liver chromatin after liver regeneration.

N-Pyrenemaleimide, a fluorescent probe that specifically labels histone H3 of rat liver chromatin in situ, was used to monitor the accessibility of histone H3 in chromatin isolated from rat liver at different times during degeneration. At times of maximum DNA synthesis (18--24 h after hepatectomy), the accessibility of the probe was found to be markedly (40--50%) increased. This increase is abolished, however, by treatment of the chromatin fibres with high salt (2 M-NaCl) or detergent. Tryptophan fluorescence was also enhanced at points of maximum DNA synthesis, suggesting that some non-histone tryptophan-containing protein was being synthesized. The polarization of the labelled histone H3 is not markedly altered, suggesting that fibre aggregation or dissociation does not occur. Mononucleosomes extracted from sham-operated and hepatectomized animals did not exhibit any difference in binding to the probe. Also, analysis of the chromatin protein by electrophoresis on detergent- and acid/urea/ Triton-X-100-containing polyacrylamide gels showed no detectable difference in histone H3 : 1, H3 : 2 or H3 : 3 subclasses.     

Fibrinolysis and liver regeneration.

The plasmin and plasminogen activator proteases of the plasma fibrinolytic system were investigated as potential blood-borne mediators of the proliferative activation of hepatocytes by partial hepatectomy. Partial (68%) liver resection, as well as proliferatively activating the remaining hepatocytes, rapidly (by 30 minutes) doubled the level (or activity) of circulating plasminogen activator but later (2 hours) greatly depressed this level. This later depression of the activity of circulating plasminogen activator lasted for eight to ten hours before returning to the normal level two to four hours before the hepatocytes in the liver remnant began to synthesize DNA. This sequence of changes in the fibrinolytic potential was not abolished by prior thyroparathyroidectomy which is known to inhibit the initiation of hepatocyte DNA synthesis and to prevent the secretion of the calcium homeostatic hormones, another early systemic consequence of partial liver resection. Since the early rise in plasminogen activator activity did not cause the appearance of active (free) circulating plasmin, and since the injection of large doses of the fibrinolytic and protease inhibitors, EACA and Trasylol®, during this early, post-operative period of hyperfibrinolytic potential did not prevent hepatocytes from initiating DNA synthesis, it is unlikely that either plasmin or its activator protease are blood-borne initiators of hepatocyte proliferative development.     

Molecular biology of liver regeneration

Liver regeneration is a good system for studying cell proliferation in an in vivo, physiologically controlled situation. Various hepatotrophic factors, neuromediators, hormones and growth factors, presumably acting in synergy, seem necessary to induce the switch from quiescence to proliferation. As a consequence of this activation, a number of changes occurs in the hepatocyte: modifications of the plasma membrane proteins; metabolic changes such as variations in albumin and fibrinogen concentrations, and induction of the acute phase proteins; induction of several specific mRNAs; variations in cAMP concentrations, and consequently in the activity of protein kinases and several other enzymes; modifications in chromosomal proteins; induction of proteins involved in DNA replication. A model has been constructed which is more a basis for reflexion than a theoretical model. It takes into account the possible connections between the different molecular events cited above. It is hypothesized that DNA replication is at least partly uncoupled from mitosis, and that the initial events of the proliferative response may be triggered by nutritional elements.