Kinetic Process of β-Amyloid Formation via Membrane Binding

Recently we have studied thermodynamics of membrane-mediated β-amyloid formation in equilibrium experiments using penetratin-lipid mixtures. The results showed that penetratin bound to the membrane interface in the α-helical conformation when the peptide/lipid (P/L) ratios were below a lipid-dependent critical value P/L^∗. When P/L reached P/L^∗, small β-aggregates emerged, which served as the nuclei for large β-aggregates. Here we studied the corresponding kinetic process to understand the potential barriers for the membrane-mediated β-amyloid formation. We performed kinetic experiments using giant unilamellar vesicles made of 7:3 DOPC/DOPG. The observed time behavior of individual giant unilamellar vesicles, although complex, exhibited the physical effects seen in equilibrium experiments. Most interestingly, a potential barrier appeared to block penetratin from translocating across the bilayer. As a result, the kinetic value for the critical threshold P/L^∗ is roughly one-half of the value measured in equilibrium where peptides bind symmetrically on both sides of lipid bilayers. We also investigated the similarity and differences between the charged and neutral lipids in their interactions with penetratin. We reached an important conclusion that the bound states of peptides in lipid bilayers are largely independent of the charge on the lipid headgroups.     

Pattern analysis of stem cell differentiation during <Emphasis Type="Italic">in vitro Arabidopsis</Emphasis> organogenesis

Plant somatic cells have the capability to switch their cell fates from differentiated to undifferentiated status under proper culture conditions, which is designated as totipotency. As a result, plant cells can easily regenerate new tissues or organs from a wide variety of explants. However, the mechanism by which plant cells have such remarkable regeneration ability is still largely unknown. In this study, we used a set of meristem-specific marker genes to analyze the patterns of stem cell differentiation in the processes of somatic embryogenesis as well as shoot or root organogenesis in vitro. Our studies furnish preliminary and important information on the patterns of the de novo stem cell differentiation during various types of in vitro organogenesis.     

MV-mimicking micelles loaded with PEG-serine-ACP nanoparticles to achieve biomimetic intra/extra fibrillar mineralization of collagen in vitro

Since their discovery, matrix vesicles (MVs) containing minerals have received considerable attention for their role in the mineralization of bone, dentin and calcified cartilage. Additionally, MVs' association with collagen fibrils, which serve as the scaffold for calcification in the organic matrix, has been repeatedly highlighted. The primary purpose of the present study was to establish a MVs–mimicking model (PEG-S-ACP/micelle) in vitro for studying the exact mechanism of MVs-mediated extra/intra fibrillar mineralization of collagen in vivo. In this study, high-concentration serine was used to stabilize the amorphous calcium phosphate (S-ACP), which was subsequently mixed with polyethylene glycol (PEG) to form PEG-S-ACP nanoparticles. The nanoparticles were loaded in the polysorbate 80 micelle through a micelle self-assembly process in an aqueous environment. This MVs–mimicking model is referred to as the PEG-S-ACP/micelle model. By adjusting the pH and surface tension of the PEG-S-ACP/micelle, two forms of minerals (crystalline mineral nodules and ACP nanoparticles) were released to achieve the extrafibrillar and intrafibrillar mineralization, respectively. This in vitro mineralization process reproduced the mineral nodules mediating in vivo extrafibrillar mineralization and provided key insights into a possible mechanism of biomineralization by which in vivo intrafibrillar mineralization could be induced by ACP nanoparticles released from MVs. Also, the PEG-S-ACP/micelle model provides a promising methodology to prepare mineralized collagen scaffolds for repairing bone defects in bone tissue engineering.     

Non‐pollinating cheater wasps benefit from seasonally poor performance of the mutualistic pollinating wasps at the northern limit of the range of Ficus microcarpa

1. Species interactions in tightly bound ecological mutualisms often feature highly specialised species' roles in which competitive exclusion may preclude multi‐species coexistence. Among the 800 fig (Ficus) species, it was originally considered that each was pollinated by their own wasp (Agaonidae). However, recent investigations show that this ‘one‐to‐one’ rule often breaks down, as fig species regularly host multiple agaonids but in ways suggesting that competitive processes still mediate biodiversity outcomes. 2. A phenological survey was conducted of the fig–fig wasp pair, Ficus microcarpa and its associated pollinating wasp, alongside its sister species, the cheating wasp, in Xishuangbanna, China. 3. Reproductive output underwent extreme seasonal variation. Seed and pollinator production fell markedly during cooler, drier months, although high levels of fig production continued. However, this resource was predominantly utilised by the cheater species, which offers no pollination services. Pollinators and cheaters rarely co‐occur, suggesting that temporal coexistence is constrained by competition for access to figs. 4. The overall findings indicate periodic rearrangements of mutualism dynamics, probably resulting from a strongly seasonal environment. Sympatric co‐occurrence may result from a window of opportunity for a functionally divergent agaonid, potentially due to constraints on the main pollinator in adapting to variable year‐round conditions that prevent competitive exclusion.     

Enhancement of cell growth by intracellularly expressed herpes simplex virus thymidine kinase

A recombinant cell line (NIH3T3:pLtkSN) was made by infecting parental cells (NIH3T3) with a recombinant retrovirus (pLtkSN) encoding herpes simplex virus thymidine kinase (HSVtk) gene. The cells expressing HSVtk (NIH3T3:pLtkSN) grew 2.3 times more than the parental cells (NIH3T3) in Dulbecco's Modified Eagles Media containing 10% (v/v) horse serum. The NIH3T3:pLtkSN cells also showed a significant enhancement in the maximal cell concentration and the specific growth rate even at 2.5% serum concentration. The specific O2 uptake rate of NIH3T3 was 2.1 times greater than that of NIH3T3:pLtkSN. Under both O2-limited and O2-unlimited conditions, it appears that HSVtk plays an important role in enhancing the growth characteristics of animal cells.     

Intra- and inter-specific effects of mast seeding on seed fates of two sympatric <Emphasis Type="Italic">Corylus</Emphasis> species

We released seeds of two sympatric tree species, Corylus mandshurica (seed with thinner seed hull, higher nutrition) and C. heterophylla (seeds with thicker seed hull, lower nutrition) in the masting year of C. mandshurica in 2008, and C. heterophylla in 2009, respectively, to investigate how seed masting of the two sympatric Corylus species affects seed removal and dispersal fitness of the two species differently at both intra- and inter-specific levels. At intra-specific level, the authors found mast seeding of both C. mandshurica and C. heterophylla significantly reduced seed removal, seed consumption, but increased seed dispersal distance and seed dispersal fitness of the released seeds. Mast seeding of C. mandshurica increased seed caching of C. mandshurica. At inter-specific level, the authors found mast seeding of C. mandshurica reduced seed removal of C. heterophylla, but mast seeding of C. heterophylla did not significantly reduce seed removal of C. mandshurica. Mast seeding of C. mandshurica reduced seed consumption of C. heterophylla, while mast seeding of C. heterophylla reduced seed consumption of C. mandshurica. We found mast seeding of C. mandshurica significantly reduced seed dispersal distance of C. heterophylla, while mast seeding of C. heterophylla significantly increased seed dispersal distance of C. mandshurica. We found that mast seeding of C. mandshurica significantly increased seed dispersal fitness of C. heterophylla, while mast seeding of C. heterophylla did not significantly increase seed dispersal fitness of C. mandshurica. More studies are needed to reveal the ecological consequences of mast seeding at inter-specific or community-level. Seed traits may attribute the differences of mast seeding at inter-specific level. Because seeds with thinner seed hull and higher nutrition were more harvested and eaten by rodents, mast seeding of C. mandshurica might have reduced seed removal and seed consumption, but increased dispersal fitness of C. heterophylla (seeds with thicker seed hull, lower nutrition). Therefore, synchrony among species is, or is not, selectively beneficial to the focus species depends on seed traits which determine gains from mast seeding at inter-specific level.     

Assessment of uncoupling activity of uncoupling protein 3 using a yeast heterologous expression system.

Uncoupling protein 3L, uncoupling protein 1 and the mitochondrial oxoglutarate carrier were expressed in Saccharomyces cerevisae. Effects on different parameters related to the energy expenditure were studied. Both uncoupling protein 3L and uncoupling protein 1 reduced the growth rate by 49% and 32% and increased the whole yeast O2 consumption by 31% and 19%, respectively. In isolated mitochondria, uncoupling protein 1 increased the state 4 respiration by 1.8-fold, while uncoupling protein 3L increased the state 4 respiration by 1.2-fold. Interestingly, mutant uncoupling protein 1 carrying the H145Q and H147N mutations, previously shown to markedly decrease the H+ transport activity of uncoupling protein 1 when assessed using a proteoliposome system (Bienengraeber et al. (1998) Biochem. 37, 3-8), uncoupled the mitochondrial respiration to almost the same degree as wild-type uncoupling protein 1. Thus, absence of this histidine pair in uncoupling protein 2 and uncoupling protein 3 does not by itself rule out the possibility that these carriers have an uncoupling function. The oxoglutarate carrier had no effect on any of the studied parameters. In summary, a discordance exists between the magnitude of effects of uncoupling protein 3L and uncoupling protein 1 in whole yeast versus isolated mitochondria, with uncoupling protein 3L having greater effects in whole yeast and a smaller effect on the state 4 respiration in isolated mitochondria. These findings suggest that uncoupling protein 3L, like uncoupling protein 1, has an uncoupling activity. However, the mechanism of action and/or regulation of the activity of uncoupling protein 3L is likely to be different.