Physiological and regulatory characterization of KatA and KatY in Yersinia pestis

The catalase or catalase-peroxidase activity commonly exists in many pathogens and plays an important role in resisting the oxidative burst of phagocytes helping the pathogen persistently colonize in the host. Yersinia pestis is a facultative pathogen and the causative agent of plague. KatY has been identified as a thermosensing antigen with modest catalase activity in this pathogen. Here Y. pestis KatA and KatY were experimentally confirmed as a monofunctional catalase and bifunctional catalase-peroxidase, respectively. Their expression induced by H2O2 was proven to be mediated by the oxidative regulator, OxyR. Expression of KatA changed with growth phases and was crucial to its traditional physiological role in protecting Y. pestis cells against toxicity of exogenous H2O2. KatY was regulated by temperature and H2O2, two major elements of phagolysosomal microenvironments. Consistent with the above results, gene expression of katY increased significantly during intracellular growth of Y. pestis compared with that in vitro growth. However, a DeltakatY mutant was fully virulent to mice, suggesting that KatY is not required for Y. pestis virulence.     

Reproductive biology of female blue shark <Emphasis Type="Italic">Prionace glauca</Emphasis> in the southeastern Pacific Ocean

Polyandry is extremely common across a wide range of organisms. In promiscuous mating systems, females are often sexually harassed by males, but at the same time obtain benefits from multiple mating. It remains unclear whether polyandry is exclusively imposed by males or is also promoted by females. Here, we investigated this question by recording the time spent by female guppies near a single male or a group of males with similar size and colour patterns over three consecutive days. We accounted for the effect of shoaling by using a control treatment where a group of females was used instead of a group of males. Results showed that females spent significantly more time near the group of males, but not with the group of females. In the presence of a group of males, total female mating preference time did not change over the course of the study, but rather shifted from spending more time near the single male at the beginning of the experiment to spending more time near the group of males. The consequence of this female preference for associating with a group of males in a non-experimental setup would be to promote multiple mating. Our result indicates that polyandry in guppies is at least partially encouraged by females, and not entirely a consequence of male sexual behaviour.     

Thf1 interacts with PS I and stabilizes the PS I complex in Synechococcus sp. PCC7942

Thylakoid formation1 protein (Thf1) is a multifunctional protein that is conserved in all photosynthetic organisms. In this study, we used the model cyanobacterium Synechococcus sp. PCC7942 (hereafter Synechococcus) to show that the level of Thf1 is altered in response to various stress conditions. Although this protein has been reported to be involved in thylakoid formation, the thylakoid membrane in the thf1 deletion strain (ΔThf1) was not affected. Compared with the WT, ΔThf1 showed reduced PS II activity, with increased levels of D1 under high light (HL) conditions, which was resulted from blocked D1 degradation by the FtsH protease and thus inhibits PS II repair. PS I was found to be more seriously affected than PS II in ΔThf1, even under low light conditions, suggesting that PS I damage could be the primary effect of thf1 deletion in Synechococcus. Further analysis revealed that the ΔThf1 mutant had a lower PS I subunit content and lower PS I stability under HL conditions. Further sucrose gradient fractionation of the membrane protein complexes and crosslinking and immunoblot analysis indicated that Thf1 interacts with PS I. Together, our results reveal that Thf1 interacts with PS I and thereby stabilizes PS I in Synechococcus.     

Effects of Apolipoprotein E Genotype on the Off-Line Memory Consolidation

Spontaneous brain activity or off-line activity after memory encoding is associated with memory consolidation. A few recent resting-state functional magnetic resonance imaging (RS-fMRI) studies indicate that the RS-fMRI could map off-line memory consolidation effects. However, the gene effects on memory consolidation process remain largely unknown. Here we collected two RS-fMRI sessions, one before and another after an episodic memory encoding task, from two groups of healthy young adults, one with apolipoprotein E (APOE) ε2/ε3 and the other with APOE ε3/ε4. The ratio of regional homogeneity (ReHo), a measure of local synchronization of spontaneous RS-fMRI signal, of the two sessions was used as an index of memory-consolidation. APOE ε3/ε4 group showed greater ReHo ratio within the medial temporal lobe (MTL). The ReHo ratio in MTL was significantly correlated with the recognition memory performance in the APOE ε3/ε4 group but not in ε2/ε3 group. Additionally, APOE ε3/ε4 group showed lower ReHo ratio in the occipital and parietal picture-encoding areas. Our results indicate that APOE ε3/ε4 group may have a different off-line memory consolidation process compared to ε2/ε3 group. These results may help generate future hypotheses that the off-line memory consolidation might be impaired in Alzheimer’s disease.     

Chimeric contribution of human extended pluripotent stem cells to monkey embryos ex vivo

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Catch bonds: physical models, structural bases, biological function and rheological relevance

Force can shorten the lifetimes of macromolecular complexes (e.g., receptor-ligand bonds) by accelerating their dissociation. Perhaps paradoxical at first glance, bond lifetimes can also be prolonged by force. This counterintuitive behavior was named catch bonds, which is in contrast to the ordinary slip bonds that describe the intuitive behavior of lifetimes being shortened by force. Fifteen years after their theoretical proposal, catch bonds have finally been observed. In this article we review recently published data that have demonstrated catch bonds in the selectin system and suggested catch bonds in other systems, the theoretical models for their explanations, possible structural bases, their relation to flow-enhanced adhesion, and the potential biorheological relevance.     

黑曲霉发酵过程中菌体形态的分析方法建立及应用

丝状真菌(Filamentous fungi)的发酵生产通常具有较高的工业应用价值,但其菌体形态是一个区别于其他非丝状菌的一个重要发酵指标。针对目前形态分析的瓶颈,本研究使用琼脂糖凝胶对黑曲霉菌形进行固定,利用平板实现菌球样本的大量制备,并结合图形处理软件自建自动化处理程序,实现了大量准确可靠的菌体形态参数的获得,大大增加了形态数据处理通量及准确度。应用该方法于黑曲霉发酵生产糖化酶过程中不同供氧水平及剪切水平下菌体形态的研究,通过大量形态数据定量阐明了黑曲霉在不同剪切水平下的分区域形态分布特性,为进一步工业过程的形态优化提供了重要的研究方法。